United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/600/2-90/061
January 1991
&EPA
State-of-the-Art
Procedures and
Equipment for Internal
Inspection of Underground
Storage Tanks
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EPA/600/2-90/061
January 1991
STATE-OF-THE-ART PROCEDURES AND EQUIPMENT FOR
INTERNAL INSPECTION OF UNDERGROUND STORAGE TANKS
By
S. E. Boone, P. J. Mraz and
J. M. Miller
PEI Associates, Inc.
Washington, DC 20036
and
J. J. Mazza and M. Borst
CDM Federal Programs Corporation
Edison, NJ 08837
Contract Number 68-03-3409
Project Officer
Robert W. Hillger
Releases Control Branch
Risk Reduction Engineering Laboratory
Edison, NJ 08837
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
For sale by the Superintendent of Document's, U.S. Government
Printing Office, Washington, D.C. 20402
Printed on Recycled Paper
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NOTICE
The information in this document has been funded entirely by the United States
Environmental Protection Agency under Contract No. 68-03-3409 to COM Federal
Proqrams Corporation. This document has been subject to the Agency s peer and
administrative review and has been approved for publication as an EPA document.
This report is intended to present information on procedures and equipment
used to conduct internal inspections of underground storage tanks. The study from
which this report was developed characterized the state-of-the-art in internal
inspections. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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FOREWORD
As industrial products and practices continue to rapidly develop and change,
the generation of solid and hazardous wastes is frequently increased. If improperly
dealt with, these materials can threaten both public health and the environment.
Underground storage tank (UST) systems have been identified by the U.S.
Environmental Protection Agency (EPA) as a significant source of contamination to
surrounding soils and groundwater. Failure to monitor UST systems and control and
mitigate releases may result in health and safety problems affecting surrounding
populations. Consequently, EPA has promulgated regulations that prescribe
performance standards and financial responsibility requirements for owners and
operators to remediate sites where contamination from existing USTs has been
detected. These regulations implement technical requirements designed to reduce
the possibility of leaks from developing in new or existing tank systems.
The Risk Reduction Engineering Laboratory plays a critical role in further
defining the technical standards set forth in the Federal regulations and in the
development of information to facilitate the implementation of state and localUST
programs. One aspect of UST management for which little information is available
pertains to tank inspections and their potential in fostering an overall reduction of
contamination. Clearly, early detection by regular inspection is a key step in the
prevention of releases to the environment. The objective of internal inspection is to
identify weakness of tank walls, presence of corrosion, quality of lining material, and
suitability of cleaning techniques prior to closure. The study focused on inspection
methods that evaluate the structural integrity of the tank interior. This report presents
the results of a review of state-of-the-art internal inspection procedures and equipment
for underground storage tanks.
For further information, please contact the Releases Control Branch of the Risk
Reduction Engineering Laboratory.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
in
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ABSTRACT
Preventing leaks from underground storage tanks is of paramount importance in
this decade as environmental resources are seriously threatened by the release of
toxic substances and costs of reparation are exorbitant. Inspecting underground
storage tanks is one action that helps prevent and correct potential tank failures that
could result in such release. This study identifies and characterizes the types of
internal practices (current, emerging, and outmoded) to conduct internal inspections of
underground storage tanks.
Professional and trade associations have developed some standards,
guidelines, and recommended practices for conducting internal inspections of USTs
for wall thickness, structural integrity and lining integrity. Industry is developing
additional instruments and methods to conduct UST internal inspections,, However,
many of these procedures have overlapping or contradictory requirements. There are
no data currently available to indicate how widely these procedures are understood or
followed in the field.
EPA sponsored this survey of state-of-the-art internal inspection methods as an
initial compilation of this important information, for dissemination to the regulated
community. This document addresses those methods pertaining to tanks; description
of the inspections performed on ancillary equipment (pipes, vents, etc.) of UST
systems is not within the scope of this report. The report is the result of an effort to
examine the various tools and techniques used for conducting internal inspections.
This study documents the significant factors evaluated during an inspection. It
examines the application of each inspection method by identifying the objectives of the
technique, its'procedural steps, the necessary equipment and instrumentation, the
circumstances under which the method is performed, and any important
considerations for use in the field.
Seventeen internal inspection methods were identified during this study. These
methods fall into one of four categories: tank wall thickness, tank deflection, lining
integrity, or tank integrity. Most methods are non-destructive, and while all evaluate
components of the tank interior, not all methods require tank entry. The selection of a
particular method is dependent upon the type of activity being performed (e.g.,
installation, upgrading, repair). The findings of this study have raised several key
questions and clearly support further research.
This report was submitted in partial fulfillment of Contract No. 68-03-3409 by
COM Federal Programs Corporation under the sponsorship of the U.S. Eilnvironmental
Protection Agency. The research was conducted in the period from December 1989 to
April 1990, and work was completed May 30,1990
IV
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TABLE OF CONTENTS
Page
Foreword y
Abstract "I!"!"""""""'"!"""""" vi
Figures .."!!!."!!!!!!!!!!."!.'.'.'.'."."."!!.'.".'."!!." ix
Tables I.':!!!!!.".".'."'!!."!.'.".'!."."."."."."!!! x
Abbreviations ............................".."!"!!..! xi
Acknowledgements .....!!!!!!!!!!!!!!"!!!!!!!!!!"."!."!.'.'"".'!.' xii
1.0 INTRODUCTION 1
1.1 Background ..........."" 1
1.2 Purpose "" 2
1.3 Approach ..:..'."""!Z." 3
• Literature Search 4
• Industry Contacts 4
• Trade Association Contacts 4
• Standards Investigated 5
• State Surveys 5
1.4 Definitions .. „. 5
• State-of-the-Art 5
• Internal Inspection 5
• Ancillary Equipment ., 6
• Destructive Testing 6
• Maintenance 6
• Non-Destructive Testing 7
• Operational Life 7
• Repair. 7
• Tank 7
• Underground Storage Tanks or USTs . 7
• Upgrade 7
1.5 Summary of Findings 7
• Tank Wall Thickness 8
• Deflection 8
• Lining Integrity 8
• Tank Discontinuity. 8
• Tank Integrity 8
1.6 Selecting Internal Inspection Methods 11
2.0 CONCLUSIONS 13
3.0 RECOMMENDATIONS 19
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TABLE OF CONTENTS (Continued)
4.0 INTERNAL INSPECTION METHODS 21
4.1 Tank Wall Thickness 25
• Ultrasonic Testing . 25
• Hammer Testing 34
4.2 Tank Deflection • 36
• Internal Tank Diameter.... 36
4.3 Tank Lining Integrity . • 39
• Holiday Tests •••• 41
• Dry Film Thickness Measurements 44
• Lining Hardness Tests • • 46
4.4 Tank Discontinuities , , • » 50
• Visual Examination 50
• Liquid Dye Penetrant 53
• Magnetic Particle Testing 59
4.5 Tank Integrity • • - 64
• Bubble Testing , 65
• Positive Pressure Testing 66
• Vacuum Tests • 70
5.0 OUTMODED METHODS . • 72
5.1 Radiography • • 72
5.2 Eddy Current 72
6.0 EMERGING TECHNOL9GIES • 74
6.1 Acoustic Emission 74
6.2 Boroscope • 75
6.3 Microwave 75
REFERENCES ; • 77
Appendices
A. Tank Emptying and Cleaning 80
B. Tank Isolation and Tank Surface Preparation 89
C. Standards Investigated •••• 91
D. Internal Inspections During Tank Remanufacture 93
E. Safety Precautions 96
F. Classification of Surface and Subsurface Discontinuities for
Translucent Visual Examination of FRP Tanks 111
G. Qualification Procedure for Non-Standard Temperatures for Liquid
Dye Penetrant Tests • 115
H. Control Tests Recommended by ASME SE-709 for Magnetic
Particle Tests • 117
I. Tank Integrity Test Method Summary 119
vi
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FIGURES
Number
1
3
4
5
6
7
8
9
10
11
12
E-1
Description .. ' " Page
Example of Wave Activity Through Tank Wall
Using Ultrasonic Test. 26
Relationship Between Transit Time and Thickness in
Ultrasonic Test 28
Dual Transducer Nonlinearity 29
Tank Head Diagram : 31
Tank Wall Grid Diagram 32
Two Drawings Showing Exaggerated Ellipitical
Deflection in Cross-Section.... 37
Three Step Procedure for Measuring Internal Diameter 40
Elcometer Coating Thickness Gauge 45
Diagram of Barcol Impressor 48
Flowcharts of Three Different Visible Dye Penetrant
Techniques 55
Localized Magnetization 60
Pressurization Setup of a Double Walled Manway Tank 66
Confined Space Entry Permit: Operating Tanks 101
VII
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TABLES
Number
1
2
3
4
7
8
9
10
11
Description
Internal Inspection Methods Used for Different Types of
Tanks and Inspections >
Internal Measurements Employed During Inspections ;
Summary of Internal Inspection Methods I
Internal Inspection Methods and Environmental
Considerations ............
Suggested Weights of the Oil Couplants for Surface
Roughness . •
Maximum Allowed Single-Walled Tank Deflection At
Installation •
Suggested Voltages For High Voltage Spark Testing
Recommended Samples Sizes to Equalize the Variance
Of the Average •••
Liquid Dye Penetrant Techniques and Equipment
Specifications of Magnetization Instruments....,
Remanufacturing Steel/FRP Composite Tanks '.
Page
9
TO
16
22
33
38
43
49
57
63
94
VIII
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LIST OF ABBREVIATIONS
AC -- Alternating current
ACT -- Association of Composite Tanks
API -- American Petroleum Institute
ASME •-- American Society of Mechanical Engineers
ASTM -- American Society for Testing and Materials
AWS ~ American Welders Society
CFR -- Code of Federal Regulations
CRT -- Cathode ray tube
DC -Direct current
DFT - Dry film thickness
DRI ~ Direct reading indicator or instrument
EPA -- U.S. Environmental Protection Agency
F -- Fahrenheit
fc -- foot-candles
FPTPI -- Fiberglass Petroleum Tank & Piping Institute
FR -- Federal Register
FRP -- Fiberglass-reinforced plastic
ft/s -- feet per second
HWDC - half-wave rectified direct current
kPa - kilo Pascals
mm -- millimeters
mm Hg/m « millimeters of mercury per meter
m/s ~ meters per second
NACE « National Association of Corrosion Engineers
NDTA -- Non-Destructive Testing Association
NFPA - National Fire Protection Association
NLPA ~ National Leak Prevention Association
NTIS -- National Technical Information Service
oz. -- ounces
PEI — Petroleum Equipment Institute
psi ~ pound per square inch
psig - pound per square inch, gauge
QA/QC ~ Quality assurance, Quality control
M.ITI - micrometer
RCRA ~ Resource Conservation and Recovery Act
SOTA « State-of-the-art
STI -- Steel. Tank Institute
UL ~ Underwriters Laboratories
UST -- Underground storage tank
V - Volts
ix
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ACKNOWLEDGEMENTS
The authors gratefully acknowledge the guidance received over the course of
this project from several monitors at the EPA Office of Research and Development.
The continuing contributions of Robert W. Hillger and Anthony N. Tafuri, Releases
Control Branch, Risk Reduction Engineering Laboratory, U.S. Environmental
Protection Agency, have been invaluable throughout this project. Mr. James Yezzi, Mr.
Thomas Schruben, and Mr. Richard Koustas served as peer reviewers for ORD.
In addition, the guidance from Joan O. Knapp, COM Federal Programs Corp.;
Warren Lyman, Camp, Dresser, & McKee, Inc.; and John P. Murphy and Roy Chaudet,
PEI Associates, Inc., is appreciated. Information obtained both formally and informally
from a number of tank manufacturing companies, lining contractors, and independent
consultants was instrumental for the development of the subject matter and the
completion of this report. In particular, the authors would like to thank the extra efforts
of George Crosby and Michael Messner from O/C Tanks Corporation and Craig
Peterson from Xerxes Corporation.
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SECTION 1.0
INTRODUCTION
1.1 BACKGROUND
Underground storage tank (UST) systems have been identified by the U.S.
Environmental Protection Agency (EPA) as a significant source of contamination to
surrounding soils and groundwater. Underground storage tanks (USTs) systems are
routinely used to store petroleum products and hazardous materials and are likely to
remain in common use for the foreseeable future. Failure to monitor UST systems
and control and mitigate releases represents a significant threat to human health and
the environment because of the millions of USTs in active use, and the potential for
each leaking UST to affect a large number of people through contaminated drinking
water supplies. Consequently, EPA has promulgated regulations that prescribe
performance standards and financial responsibility requirements for tank owners and
operators to remediate sites where contamination from existing USTs has been
detected. These performance standards implement technical requirements designed
to reduce the possibility of leaks from developing in new or existing tank systems. In
support of these regulations, EPA is working to identify or develop sound engineering
practices which can be implemented to minimize the probability of leaks from
developing, and the size and duration of leaks should they occur.
As methods to detect releases from underground storage tanks continue to be
developed, the number of releases being detected are rapidly increasing nationwide.
Internal inspection fulfills an important role in release prevention from tanks during
installation, repair, maintenance, and upgrading. Inspection methods range from the
simple (visual) to the complex (e.g., ultrasonic and magnetic testing). A common
inspection method (that is, one that is used most commonly), for example, involves
striking a ball peen hammer on the interior wall of a tank and making a determination
of its thickness based on the ringing sound produced.
Unless underground tanks are contained in an accessible vault, external visual
inspections are not possible without unearthing the tank. However, internal
inspections may be performed if the tank is equipped with a manhole. The techniques
that may be used in such instances include ultrasonic tests and radiation-type tests.
Spark tests may also be used in tanks that do not contain flammable or combustible
materials.
Internal tank inspection is inherently hazardous. The tank must be emptied of
liquid, freed of gases, washed and cleaned prior to entering. (Details on tank
emptying and cleaning procedures appear in Appendix A. A summary of tank isolation
and surface preparation activities appears in Appendix B.) As.an added precaution, a
breathing apparatus and fire-resistant clothing should be worn when entering a tank
1
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that contained flammable material. It should be noted here that it is sometimes a
clumsy and difficult task to enter a tank with a breathing apparatus. However, it is
more difficult to remove a body where such apparatus was not worn. All activities
should be conducted in such a fashion as to minimize the creation of static electricity.
Federal regulations raise the issue of inspections only as they pertain to the
operation and maintenance of corrosion protection equipment. During the rulemaking
process, EPA determined that general inspections were duplicative of leak detection
measures and that inaccessibility of USTs further made inspections impractical. The
resulting regulations refer tank owner/operators to standards developed by nationally-
recognized associations for activities pertaining to tank upgrade and repair. The
subject of internal LIST inspections has not yet been fully addressed by EPA.
However, many of the associations identified by EPA have developed procedures for
conducting examinations of tank interiors. The impetus for the study was to
characterize internal inspections.
EPA sponsored this project through the Risk Reduction Engineering Laboratory,
to identify, catalogue, and characterize the procedures and equipment used for
internal inspections. This report describes the procedures, equipment, and
techniques; it does not provide a comparison of methods. It is intended to serve as a
broad review of current practices and emerging technologies rather than an evaluation
of the specific approaches.
1.2 PURPOSE
This report is the result of an effort to examine the various tools and techniques
used for conducting internal inspections of underground storage tanks. It documents
the significant factors evaluated during an inspection, and examines the application of
each inspection method by identifying the objectives of the technique, its procedural
steps, the necessary equipment and instrumentation, the circumstances under which
the method is performed, and documents important considerations for use in the field.
This is a survey of all methods which could be identified; it is not an evaluation of the
performance of a given device. No conclusions about the performance of any
protection method (e.g., cathodic protection) should be inferred.
In order to develop this report, a number of specific task activities were
identified.
• Identify the state-of-the-art (SOTA) for internal inspection methods.
• Determine the impact, if any, of size of tank on the performance of the
method.
• Provide recommendations regarding the SOTA and the need for further
investigation of existing technology.
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Internal tank inspection is frequently used with other investigatory methods to
determine whether a tank is leaking or in need of upgrading or repair. There are
numerous ways to internally inspect a tank. The overall objective of this project is to
identify the methods and equipment used to conduct internal inspections of
underground storage tanks.
In order to accomplish this goal, a number of specific task activities were
identified.
• Identify the state-of-the-art for internal inspection methods.
• Determine the impact, if any, of size of tank on the performance of the
method.
• Provide recommendations regarding the state-of-the-art (SOTA) and the
need for further investigation of existing technology.
This study identifies and characterizes current techniques used for conducting
internal inspections of underground storage tanks. The study investigated the state-of-
the-art (SOTA) for internal inspection methods. The term "state-of-the-art" is defined as
the current level of development and capability in terms of procedure, process, and
technique. Generally, this refers to methods which are commercially available, but
technically advanced procedures and equipment have also been addressed. This
study includes a review of existing industry standards and practices and a review of
applicable non-destructive test methods.
Seventeen methods that apply to internal inspections have been identified
during the course of this study. Each method has been presented in detail in Sections
4.0, 5.0, and 6.0. Discussions with industry experts and practitioners indicate that only
a few of these methods (i.e., visual observation, hammer testing) are widely used.
Many others are applied infrequently throughout the country. In addition, the research
identified a few speculative technologies (e.g., acoustic emission) with potential for
internal tank inspections that are not in current practice.
1.3 APPROACH
The research effort involved consisted of a review of available literature, and
conversations with manufacturers and vendors, trade and professional associations,
and independent consultants. A description of these efforts follows.
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Literature Search
An extensive review of the current literature dealing with USTs was conducted.
This review included accessing the National Technical Information Service (NTIS) and
Applied Science and Technology computerized data bases. The libraries accessed
included:
• University of Cincinnati Engineering Library
• USEPA/Risk Reduction Engineering Laboratory Technical Library
• University of Maryland Engineering Library
• Rutgers University Library
industry Contacts
Representatives of the industries that manufacture tanks, apply linings, and
provide inspection services were contacted to obtain details on particular inspection
methods. The following companies were contacted:
Armor Shield
Bridgeport Chemical Company
Buffalo Tank Company
Certified Coating Inspection
Highland Tank and Manufacturing
M.W. Farmer and Company
Owens-Corning Fiberglass
Permaseal
Physical Acoustics Corporation
Tank Liners Inc.
Trade Association Contacts
Professional and trade associations were contacted to obtain information on state-
of-the-art inspection practices. The following organizations were contacted:
American Petroleum Institute
American Society for Testing & Materials
Association of Composite Tanks
Fiberglass Petroleum Tank & Piping Institute
National Association of Corrosion Engineers
National Leak Prevention Association
Non-Destructive Testing Association
Petroleum Equipment Institute
Steel Structures Painting & Coating
Steel Tank Institute
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Standards Investigated
Section 9005 of the Resource Conservation and Recovery Act (RCRA)
encourages the use of inspection methods developed by professional societies, trade
associations, and testing laboratories. Standards relevant to tank inspections were
identified and reviewed. Numerous standards were investigated and are presented in
Appendix C.
State Surveys
A few states were contacted as part of this study. Rather than conduct a
comprehensive survey, an attempt was made to broadly ascertain the level of state
involvement in requiring or supervising the performance of internal inspections.
Representatives from the states of New Jersey, New York, Massachusetts, Missouri,
Iowa, and California were contacted for information. Additional input was solicited
from EPA Regions I, III, and VII. The representatives were either LIST program
coordinators, Regional Project Monitors (RPMs), or On-Scene Coordinators (OSCs).
At this writing, all data suggest that state agencies are not actively involved in
the application of internal inspection methods. State or Regional EPA personnel
rarely enter or inspect tanks internally. This activity is generally left up to the
manufacturers or to firms that provide installation, cleaning, and lining services.
i.4 DEFINITIONS
This project, from the beginning, required definitions and careful selection and
use of nomenclature. This subsection presents definitions of all applicable
terminology. Where possible, regulatory definitions were used.
State-of-the-Art
The project reviewed the overall practice of internal inspections in current
practice. The project was not intended to only summarize technically advanced
methods. Advanced tools identified during the course of the study are included for
general information only in Section 6.0. The term "state of the art" therefore, has been
conceptualized to describe methods commercially available in current practice. This
study was restricted to tanks that routinely contain petroleum products. This restriction
was placed on the scope because the majority of USTs are used for this purpose.
Internal Inspection
40 CFR 280.11 of the technical standards and corrective action requirements for
UST owners and operators does not define the terms "internal inspection" or
"inspection". Therefore, for purposes of this study, the term "internal inspection" has
been defined as any non-volumetric determination of one or more internal attributes of
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a tank in an underground storage tank system by destructive or non-destructive
methods. Such internal measurements may be obtained by direct or indirect means.
This includes activities designed to:
1) verify the structural integrity of the tank prior to and after installation;
2) detect structural discontinuities, ascertain structural strength, arid determine
structural deflection prior to a change in service, tank reuse, or the
application of an internal lining material;
3) detect lining discontinuities, measure hardness, and determine lining
thickness; and
4) verify the cleanliness of the tank at closure or removal from service.
While volumetric tests evaluate the overall integrity of a tank as a means of leak
detection, they do not provide any kind of detail on the cause or location of the leak.
One can make an argument that non-volumetric methods, such as inventory
reconciliation, could be classified as internal inspections because they are designed
to detect leaks. However, this study addresses only those methods which meet the
four criteria described above. For a comprehensive discussion of the state-of-the-art of
leak detection methods, refer to ("Underground Tank Leak Detection Methods: A
State-of-the-Art Review. Prepared by S. Niaki and J. Broscius, IT Corporation.
Prepared for U.S. EPA, ORD, Cincinnati, Ohio. Contract No 68-03-3069. EPA/600/2-
86/001. January 1986.) Pipes, vents, valves, pumps, and other ancillary components
of the UST system are excluded by restricting the examination in this study to the tank
only. Site monitoring, site remediation, or site assessment activities are also excluded.
Internal inspection procedures generally require a man or machine to enter the
tank, in almost all cases, to conduct the inspection. This document addresses all
inspection scenarios identified to date. The definition is not restricted to inspections
requiring physical entry of the system. A few methods described here do not require
physical entry.
Ancillary Equipment
Any devices including, but not limited to, such devices as piping, fitting, flanges,
valves, and pumps used to distribute, meter, or control the flow of regulated
substances to and from an UST.
Destructive Testing
Destructive testing methods involve examination procedures that result in permanent
physical or structural damage to the object undergoing testing.
Maintenance
The normal operational upkeep to prevent an underground storage tank system from
releasing product.
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Nondestructive Testing
A nondestructive testing method does not require damaging or destroying the object
undergoing testing through microscopic or macroscopic examinations of the physical
structure, a nondestructive test will detect a potential structure failure or weaknesses.
Operational Life
The period beginning when installation of the tank system has commenced until the
time the tank system is properly closed under 40 CFR 280 Subpart G. The operational
life of the UST as defined here, is the period which has been defined to include all
internal inspections. Inspections that occur before and after the operational life of the
tank are not included.
Repair
To restore a tank or UST system component that has caused a release of product from
the UST system.
Tank
A stationary device designed to contain an accumulation of regulated substances and
constructed of non-earthen materials (e.g., concrete, steel, plastic) that provide
structural support. The inspection of USTs as described in this dpcument is specific to
the tank portion of the system. Pipes/vents, pumps, valves and other ancillary
equipment are not included in the scope of this report. Beyond this limitation, the
terms "UST and "tank" are used synonymously.
Underground Storage Tanks or USTs
Any one or combination of tanks (including underground pipes connected thereto) that
is used to contain an accumulation of regulated substances, and the volume of which
(including the volume of underground pipes connected thereto) is 10 percent or more
beneath the surface of the ground.
Upgrade
The addition or retrofit of some UST systems with features such as cathodic protection,
lining, or spill and overfill controls to improve the ability of an underground storage
tank system to prevent the release of product.
1.5 SUMMARY OF FINDINGS
A total of seventeen internal inspection methods were identified during this
study. Each method is designed to evaluate a particular characteristic of the tank.
There are five key categories of characteristics whereby the methods identified are
classified: tank wall thickness, deflection, lining integrity, tank discontinuities, and tank
tightness. Deterioration of the tank in any of these categories will result in risk of the
development of a leak or complete failure.
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Tank Wall Thickness i
This parameter refers to the thickness of a steel tank's shell. A minimum wall
thickness must be maintained at all times in order for any tank to remain operational.
Corrosion is the principal culprit in reducing wall thickness.
Deflection
All tanks (steel and FRP) change in shape as product is added or removed.
However, the ability to repeatedly accommodate a change in shape while supporting
the load of the surrounding backfill is crucial to preventing failure of the entire tank.
Measurements are obtained and calculations performed to evaluate whether
deflection is within normal limits.
i
Lining Integrity
Many tanks are lined with epoxy or fiberglass resin to further protect against the
development of leaks and cracks in the outer tank shell. It is therefore necessary to
monitor the lining itself both after application and at regular intervals during the tank's
life. Various methods exist to inspect the lining thickness, hardness, and integrity
(cracks, pinholes, air bubbles).
Tank Discontinuity
4
Inspections designed to identify discontinuities are checking for surface or
subsurface flaws which develop as a result of corrosion, stress, improper welding (of
steel) or improper lamination of lining material. A variety of methods exist to assess
the presence of any such discontinuities.
Tank integrity
Examination of tank integrity is generally required or recommended by UST
manufacturers, trade organizations, and Federal regulations. Test methods in active
practice indicate the presence of leaks or provide information about structural strength.
Table 1 presents the internal inspection methods that were identified during this
study which have been organized according to their use for different types of tanks and
inspections.
Internal inspections can be categorized into four critical phases during the
operational life of a tank: installation, upgrading and repair, maintenance, and closure.
Table 2 lists the internal inspection methods that are used during each type of
inspection for both steel and FRP tanks. Any of the internal inspections methods
discussed can be used for a multitude of inspections. These methods have been
categorized according to the four phases of tank life to assist inspection personnel in
identifying which method(s) might be most appropriate under the circumstances.
8
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Installation inspections are designed to identify structural damage immediately
before and after the tank is in place and to check tank tightness. Upgrade or repair
inspection activities are designed to evaluate a tank's lining/discontinuities, wall
thickness, tightness, and deflection. Routine maintenance activities provide an
excellent opportunity for determining the overall integrity of the tank. The final
regulations provide for internal inspection for upgrade or repair. The maintenance
aspect appears to have little interplay with inspection. All experts contacted agreed
that owners tend to ignore the installed UST until evidence of a leak is detected.
There is no preventive maintenance inspection procedure in common use. By
definition, the UST must leak for a repair to be initiated, inspections at closure assist in
ascertaining the level of cleanliness before removal or abandonment-in-place. A new
element in internal inspections is the remanufacture of tanks that have been taken out
of service. Information is still being collected on this very new and rapidly evolving
business area.
Procedures to empty and clean tanks, which are a necessity when performing
internal inspections, have been researched and documented. Appendix A has been
created for this report to present essential information pertaining to tank emptying and
cleaning activities.
Frequently a tank's surface must be prepared after cleaning and before the
internal inspection can be performed. A general discussion on procedures associated
with tank surface preparation is presented in Appendix B. Information relative to tank
isolation procedures is also addressed in Appendix B. The reader is encouraged to
obtain comprehensive information on both tank cleaning and surface preparation.
Many methods necessitate tank entry. Entry is an inherently hazardous activity.
There are risks posed by the inspection of confined spaces including chemical
exposure, fire, and explosion. Additionally, standard health and safety procedures call
for extra precautions when working in contaminated environments. While many health
and safety plans exist for internal inspection methods, their quality was found to vary
dramatically. Although the quality of health and safety procedures is beyond the
technical scope of the project, its importance cannot be overstated nor ignored.
Appendix E has been developed to introduce critical issues pertaining to safety
precautions, but is not intended to replace an in-house safety program. „
1.6 SELECTING INTERNAL INSPECTION METHODS
Information gathered throughout this study indicates that the selection of
inspection methods is dependent upon several factors. The selection process is a
tiered one, however, and is presented here only as a general guide. Further
investigation is needed to validate the parameters in this process. A brief summary of
the selection process is presented below.
11
-------
The primary consideration in the selection process is the type of activity
occurring at the tank (i.e., installation, upgrading/repair, maintenance, closure). With
the exception of visual inspection, internal inspection methods are categorized by the
particular activities associated with the unique phases of a tank's operational life as
shown in Table 2.
The second consideration in the selection process is the construction material
of the tank. Many methods that are designed for steel tanks would result in structural
damage if performed on FRP tanks: The application of a hammer test would be futile
on an FRP. A third consideration in choosing an appropriate inspection method is the
type of equipment used to perform the test. It is important to identify and evaluate the
potential for a particular instrument to compromise the integrity of the tank surface or
subsurface.
After the third phase of the method selection process has been completed, other
factors can narrow the choices. Six such factors include: 1) the cost associated with
the required downtime, 2) the availability of experienced inspectors/testers, 3) ease of
entry into the tank with equipment, 4) the effect of residues and product and test
results, 5) location of tank entry way, arid 6) whether the tank is surrounded by fill
material (or enclosed in a vault).
12
-------
SECTION 2.0
CONCLUSIONS
Literature reviewed in this study suggests that no compilation of internal
inspection methods has been prepared to date. The identification and description of
these methods in a single document serves to educate owner/operators in selecting
the most appropriate type of inspection under specific phases (e.g., installation,
closure) of the operational life of the tank. Several methods have also been identified
during the pre-installation and post-removal phases of the tank's life. However, since
the focus of the study is on the operational life of the tank, inspections associated with
manufacture and remanufacture are not emphasized in this study. Refer to
Appendix D for further discussion on inspections at remanufacture.
Little information is available on the impact of tank size on the performance of
the tests. Most methods require testing on a unit-surface-area basis. Tests are
repeated at regularly defined intervals over the entire internal surface of the tank.
Without the benefit of further investigation, this suggests that tank size has little
influence on the performance of tests or their results. One possible exception is that of
tank size versus size of the inspector and the impact it has on performing the test as
required. This information also indicates that tank size has little bearing on the
selection of the test method.
No information is currently available which provides an understanding of key
factors which affect the application and performance of each method. Only a
comprehensive study and comparison of the methods would provide this information.
Some standards contradict others, and, on occasion, there are conflicting
directions within individual standards. Vacuum tests and tank deformation tests, for
instance, are not explicitly required by EPA in the preamble to the regulations, but
referenced standards use these methods. Tanks that are repairable under API 1631
may not be repairable under NLPA 631. More common than outright contradictions
are instances where technical details are so subtle that they are probably beyond the
engineering expertise of the typical owner/operator. There is a clear need for a
cohesive, coordinated set of rules and standards that apply to UST inspections.
13
-------
Based on results of the study, the methods most often used were found to be:
Ultrasonic test
Hammer test
Internal tank diameter
Holiday test
Lining hardness test
Visual (human eye) examination
Bubble test
Positive pressure test
Two methods were practiced as internal inspection techniques for USTs in past
years, but their frequency of use. has been found to have dropped off significantly.
Radiography and eddy current technologies are no longer widely practiced for the
reasons described in Section 5.0. Among them are cost and the generation of wastes
which require special handling.
The remaining three methods have been used widely in applications otheir than UST
internal inspections which require further research, development, and demonstration
to adapt them for use as specific UST inspection methods. This work may involve
modifying the existing method to be less expensive and easier to conduct or may
require the development of performance standards for sensitivity, precision and
accuracy. These are acoustic emission, horoscope, and microwave technologies.
Further discussion of these technically advanced methods appears in Section 6.0.
In order to reduce the potential for tank failure and increase the life span of
tanks, EPA may need to develop performance standards, or guidelines for internal
inspection during two key stages of a tank's operational life: 1) at installation to ensure
proper seating and anchoring of tanks; and 2) at upgrade/repair to ensure that lining
materials are installed properly and are compatible with tank contents.
EPA recognizes that the majority of tank failures and petroleum releases occur
at these phases as a result of the absence or inappropriate use of internal inspections
or universal performance standards for a particular internal inspection method.
However, research does not reveal any mechanisms designed to enforce established
requirements which trigger inspections.
.Research conducted in this study has resulted in the consolidation of a body of
knowledge which raises questions about how this information can best be
disseminated. Clearly, additional investigation and evaluation would benefit the
regulated community by promoting the implementation of preventive programs
(proactive maintenance). Specific recommendations are provided in Section 3.0 of
this report.
14
-------
Internal inspections fall into four categories: installation, upgrading and repair,
maintenance, and closure. Table 3 is a compilation of the internal inspection methods
identified in this study and a summary of pertinent application and industry standards.
15
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SECTION 3.0
RECOMMENDATIONS
While the research conducted in this study has resulted in findings and
conclusions pertaining to the state-of-the-art in internal inspection methods, new
questions are raised relative to how this knowledge can best be used and what
additional information should be collected. In order to establish a full understanding of
the range of internal inspection applications and performance, several tasks have
been identified to undertake further research and evaluation.
• Obtain data concerning inspections applied by tank owner/operators as part
of a comprehensive maintenance program. Specifically, a determination
should be made from the information gathered in this study on the
identification of routinely-performed inspections as they may relate to a
comprehensive maintenance program.
• Develop protocol manuals to ensure that there is a standard application of
each internal inspection method for determining tank integrity. These
manuals should include both a protocol for conducting each method as well
as a decision tree for the selection of a method with respect to the phase of
operational life of the tank (e.g., installation, upgrading).
• Design and execute a bench-scale program to evaluate the key factors
affecting the application and performance of each test method. Such a
program would investigate variable parameters such as temperature,
pressure, and lining material and their impact on various standards and
methods employed by tank lining contractors.
• Develop procedures to improve the performance of several SOTA internal
inspection methods and validate more reliable protocols for those methods.
19
-------
Contact state regulatory agencies to ascertain which internal inspection
methods are used or permitted. A determination should then be made as to
the following:
- Frequency of inspections.
- Selection criteria for a particular inspection method.
- Effectiveness of the chosen method.
Because disposal of tanks that are taken out of service is costly, there is
increasing interest in the reuse and remanufacture of tanks. The Association
for Composite Tanks (ACT) is currently developing standards for Fiberglass-
reinforced plastics (FRP)/steel clad tanks and is currently lobbying
Underwriters' Laboratory (UL) for an appropriate standard. Further research
and development of performance standards for remanufactured tanks may
support this new market.
20
-------
SECTION 4.0
INTERNAL INSPECTION METHODS
Of the seventeen internal inspections identified, twelve are used regularly by
tank owners and operators and constitute the "state of the art." Table, 4 presents a
summary of internal inspection methods in light of various environmental
considerations.
This section contains detailed descriptions of those methods commonly used to
inspect tanks internally. These methods have been organized into groups based on
the primary objective of the inspection.
• Tank'Wall Thickness
- Ultrasonic testing
- Hammer testing
• Tank Deflection
Internal tank diameter measurements
• Tank Lining
- Holiday testing
- Barcol testing
- Dry film thickness testing
• Tank Discontinuities
- Visual examination
- Liquid dye penetrant testing
- Magnetic particle testing
• Tank Tightness
- Bubble testing
- Positive pressure testing
- Vacuum testing
For each of these methods, the fundamental operating principles, procedural
description, method performance and field considerations are discussed.
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Two methods which are no longer in active practice are described in
Section 5.0 and a discussion of three technically-advanced methods appears in
Section 6.0.
4.1 TANK WALL THICKNESS
The thickness of the steel tank shell is a critical parameter in deciding if it is to
be taken out of service. Both AP11631 and NLPA 631 require inspectors to identify
areas where corrosion has reduced tank wall thickness to 3.2mm (1/8-inch) or less.
The number, concentration, and size of these thin areas determine if a tank can be
lined and/or repaired.
Periodic wall thickness measurements potentially enable the owner to project
the remaining lifetime of an UST. This standard specifies that USTs must be taken out
of service when the mean wall thickness compiled using spot and/or area-weighted
averages reach specific values. Knowing that UL58 specifications control
manufacturing, the procedures in API 510 can be used as input to a present value
analysis of the alternatives. The owner/operator can make economic choices using
one of two methods for wall thickness determination: the ultrasonic test, and the
hammer test.
Ultrasonic Testing
Ultrasonic testing can determine the wall thickness or locate surface or
subsurface discontinuities of a steel or FRP UST. However, the use of ultrasonic
testing to detect discontinuities is time consuming and expensive. Therefore, wall
thickness determination is the primary use of ultrasonic testing for UST internal
inspections.
Fundamental Operating Principle--
There are several ultrasonic techniques used for thickness determination. The
most portable and widely used technique is the pulse-echo. This technique sends an
ultrasonic pulse (wave) propagating from the surface of the tank through the tank wall
at a constant velocity. The velocity of the pulse is dependent upon the physical
properties of the tank (e.g., material, surface finish). The ultrasonic pulse is reflected
back (echoed) to the instrument when it encounters a discontinuity or wall boundary.
Figure 1 provides an example of the pulse-echo activity of an ultrasonic instrument.
The transit time is the total time for the ultrasonic pulse to travel through the tank wall
and reflect back. The tank thickness is determined by multiplying the transit time by
the velocity of the pulse and dividing by two.1
A pulse-echo ultrasonic instrument measures the transit time of the ultrasonic
pulse and calculates the wall thickness. This instrument uses a transducer to convert
25
-------
Ultrasonic Transducer
Ultrasonic Wave
v (velocity)
Tank Wall
Figure 1. Example of Wave Activity Through Tank Wall
Using Ultrasonic Test
26
-------
electrical energy to high-frequency mechanical vibrations (ultrasonic pulses). The
echo or reflected vibration strikes the transducer which converts the vibration to a
measurable electrical signal. The time between transmission and the echo return
indicates the thickness of the medium or the depth of any discontinuities encountered.
The amplitude of the echo allows the user to discern what caused the echo. The
instrument can display the readings by digital readout or an analog meter. The
velocity of wave is determined on site with calibration blocks. Figure 2 is
taken from ASME SE-797 and graphically presents the relationship between the
transit time and thickness for steel.2
Other instruments used to measure thickness incorporate a dual transducer that
generates an inclined beam as seen in Figure 3 (Dual transducer nonlinearity). As
compared to Figure 2, the angled-beam is less accurate as the thickness of steel
becomes less than 2.5mm (0.10 in.). However, the angled-beam focuses the
ultrasonic energy onto a smaller area of the back surface. This allows the instrument
to measure the depth of corrosion pitting. Ultrasonic instruments that use the angled-
beam technique automatically correct the longer ultrasonic path length to calculate the
true wall thickness.3
Procedure Description-
Before the thickness determination inspection begins, the instrument should be
calibrated. Having a known velocity of the wave as it travels through the medium, the
instrument is calibrated by using reference blocks of known thickness, in the range of
the thickness to be measured. ASME SE-797 recommends that one block has a
thickness near the maximum and the other block near the minimum range of thickness.
Calibration and surface examination temperatures should be within 14C to avoid wave
velocity differences.4
A couplant, a thin liquid film that is placed between the transducer and the tank
wall, improves the transmittance of the ultrasonic waves. Examples of couplant liquids
are water, oil, grease or corrosion inhibitors. It is important to use the same couplant
that was used for the calibration process. Couplant variations in type and amount will
reduce the examination sensitivity. The most common couplant liquid is medium-
viscosity oil. Petroleum jelly is effective on vertical surfaces.3
The surface of the tank walls are to be free of loose rust, scale, paint, dirt or
other deposits that may interfere with the ultrasonic examination. Surfaces may
undergo sandblasting, grinding or other machining operations that produce a
smoother surface. Paint, epoxy, or organic coatings that exhibit strong adherence to
the tank walls will not interfere with results if these coatings are uniform.4
As outlined in NLPA 631, the thickness determination Of an UST requires the
establishment of the original wall thickness followed by a gauging procedure. The
original wall thickness is determined by obtaining measurements at the tank manway.
27
-------
en
1
8. —
6. -
4. -
2. ~
LOWER
VELOCITIES
HIGHER
VELOCITIES
I
5
.2
I I T
10 15 20
.4 .6 .8
THICKNESS
25
1.0
I
30
1.2
mm
in.
NOTE - Slope of velocity conversion line Is approximately that of steel.
Source: American Society Mechanical Engineers. Boiler and Pressure Vessel Code,, 1989 Edition.
Section V, Non-Destructive Testing: Standard Practice for Thickness Measurement by Manual
Contact Ultrasonic Method. ASME SE-797. New York, New York, July 1989. Reprinted with
permission.
Figure 2. Relationship Between Transit Time and Thickness
in Ultrasonic Test
28
-------
Transducers
(a) Proportional sound path increases with
decrease in thickness.
in. mm
.12 3.0 ~
O
| .08 2.0 ~
DC
%
UI
.04 1.0 ~
1 1 1
1.0 2.0 3.0
.04 .08 .12
ACTUAL THICKNESS
(b) Typical reading error values
mm
in.
Source: American Society Mechanical Engineers. Boiler and Pressure Vessel Code, 1989 Edition.
Section V, Non-Destructive Testing: Standard Practice for Thickness Measurement by Manual
Contact Ultrasonic Method. ASME SE-797. New York, New York, July 1989. Reprinted with
permission.
Figure 3. Dual Transducer Nonlinearity
29
-------
The gauging procedure is performed on each head of the tank and the circumference
of the walls for the length of the tank.
The heads of the tanks are divided into a minimum of 4 equal quadrants. The
maximum size of these quadrants is 1 m x 1 m square (3 ft x 3 ft) (see Figure 4). The
walls of the tank are divided into equal 1 m x 1 m square quadrants for the entire length
of the tank (see Figure 5). For each quadrant along the walls and heads of the tank, a
minimum of one thickness measurement is collected. As defined by NLPA 631,
thickness measurements less than 75% of the original wall thickness require further
subdivisions and measurements for that quadrant. Measurements greater than 75% of
the actual wall thickness may be used as an average measurement for the quadrant.5
UL58 states that the minimum thickness allowable for a LIST is'3.2mm (1/8 in.).
AP11631 indicates that ultrasonic measurements are used for UST inspection for wall
thickness determinations, but provides no guidelines for inspection. NLPA requires
the inspector to report any pits or discontinuities greater than 20% of the original wall
thickness. For example, an inspector will report discontinuities that measure 0.64cm
(1/4 inch) or more in depth of an UST that was originally 3.2mm (1/8 inch) thick. In
accordance with NLPA 631, a tank is acceptable for cathodic protection without interior
lining if: 1) there is no'internal or external pitting greater than 50% of the original tank
wall thickness, and 2) the average metal wall thickness of each 1 m x 1 m square is
greater than 85% of the original wall thickness.6
Equipment--
The instruments used to conduct an ultrasonic thickness examination vary in
size and complexity. To perform an ultrasonic test on an UST, the instrument needs to
be portable and versatile to accommodate the tank geometries. Considering these
factors, the instruments commonly used to examine a tank are simple hand-held direct
reading instruments (an example is shown in Figure 6). Such ultrasonic instruments
employ the time-of-travel between the pulse and echo using a quartz clock. Built-in
microprocessors allow the velocity value to be keyed in after being predetermined
during the calibration exercise.3
Ultrasonic instruments that measure the thickness of steel in the presence of
other materials are available. These instruments are useful for examining FRP-lined
tanks. Equipment needed to perform ultrasonic thickness examinations include: 1)
field notebook with a grid pattern; 2) a couplant (e.g., motor oil, petroleum jelly); 3)
calibration blocks (see Figure 7); and 4) a qualified inspector.
Method Performance-
The instruments in current use have a measuring thickness from 1.0 to
300.0mm with an accuracy or ±0.1 mm. Other factors that may affect the accuracy of an
examination include the couplant used, the surface condition, and the inspector's
ability to interpret the information.3
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The couplant helps transmit the ultrasonic waves through amplification and
minimizes the influence of surface roughness by providing a smoother contact surface
for the instrument. Table 5 lists the suggested weights of the oil couplants best suited
for approximate surface roughnesses.4
TABLE 5. SUGGESTED WEIGHTS OF THE OIL COUPLANTS FOR SURFACE
ROUGHNESS
Approximate Surface Roughness
Average (Ra),
Equivalent Couplant Viscosity,
Weight Motor Oil
5-100
; 50-200
100-400
250-700
Over 700
0.1-2.5
1.3-5.1
2.5-10.2
6.4-17.8
18-
SAE 10
SAE20
SAE30
SAE 40
Cup Grease
Source: ASTM Specification E 114-85. Recommended Practice for Ultrasonic Pulse-
Echo Straight-Beam Testing By the Contact Method.
The contact area of the search unit or transducer are important test parameters.
Large transducers allow the inspector to examine large surface areas at a faster rate,
but they sacrifice sensitivity. Smaller transducers have higher sensitivity and greater
accuracy, but require longer inspection durations.7
qThe accuracy of an ultrasonic examination depends heavily upon the inspector. The
inspector must properly prepare the surface, calibrate the instrument, and interpret the
readings and signals received during the examination. The accuracy of his or her
interpretations develop over time and the amount of examinations performed.
Professional societies and manufacturers require inspector certification for ultrasonic
examinations. NLPA requires personnel to be certified in accordance with NLPA 632
or Level I Competence, Limited to Ultrasonic Testing, with the( American Society for
Non-Destructive Testing (SNT-TC-1A, Personnel Qualification and Certification In
Non-Destructive Testing).
33
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Reid Considerations--
Ultrasonic equipment should not be subjected to extreme temperatures, high
humidity, or corrosive environmental conditions. Manufacturers provide operating
instructions and parameters for these instruments.7 Other field conditions such as
backfill material and groundwater depth were not addressed during the course of this
study. \
The pulse-echo ultrasonic thickness examination equipment is portable,
accurate, and less expensive than other types of ultrasonic equipment. The
instruments available for these examinations are simple to use, but a certified
instructor is needed for proper examination and interpretation of results. Ultrasonic
examinations may be used for discontinuity detection, but may prove to be time
consuming and expensive. There are other highly developed ultrasonic examination
methods that provide better accuracy. However, these methods are useful only for
smaller tank geometries and are not portable.
The cost of an ultrasonic examination is based on the duration of the inspection.
A certified ultrasonic examination technician costs about $28 per hour including
materials. The overall cost of an ultrasonic examination is dependent upon the type of
ultrasonic equipment used, the frequency of measurements, and the size of the tank
being investigated. For example, a technician examining a 10,000-gallon tank with a
large transducer at 1-by 1-meter increments is cheaper than the same investigation at
0.5 by-0.5 meter increments. Ultrasonic examinations may be used for discontinuity
detection, but have proven to be time consuming and therefore more expensive.
Hammer Testing
Fundamental Operating Principle-
This test is analogous to the inspection procedures developed to detect the
onset of rot or insect damage in telephone poles. For USTs, hammer testing is used to
estimate the wall thickness and identify areas of severe corrosion. The sound
produced, hammer rebound, and indentations generated after the wall is struck, are
indicative of the tank's current condition. Hammer testing is a non-destructive
examination that may only be used on steel tanks. Hammer testing may evolve into a
destructive test. Depending upon the condition of the tank, the hammer blows may
result in the creation of minimal or severe structural damage.
The hammer test is performed more frequently than any other wall thickness
method and is heavily relied upon by the tank lining and remanufacturing industry.
Ultrasonic .testing (described earlier) provides more accurate results but is more time
consuming and expensive. The experience and ability of the inspector are crucial
elements in affecting the accuracy of the results of the hammer test inspection.
34
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Procedure Description--
Hammer testing is performed after the interior surface of the tank has been
cleaned and sandblasted. The inspector strikes the tank wall over the surface with a
16 to 18 oz. (454-510 gram) non-sparking hammer. The vibration, or rebound of the
hammer and the sound produced are dependent upon the tank wall thickness. If the
inspector feels no vibration from the 'normal1 blows of the hammer, the inspector
strikes the suspect area with a hard blow to assess the tank thickness. Indentations of
6.4mm (1/4 in.) or more by the hard blow indicate the wall has corroded to 1.5mm
(1/16 in.) or less. Slight vibrations and shallow indentations indicate 3.2mm (1/8 in.)
wall thickness. If a series of radial fracture lines develop from the hard blows; severe
corrosion is present. A steel tank that is 6.4mm (1/4") thick will cause the hammer to
rebound and create a "ringing" sound. Thinner steel walls will have a "ringing" sound,
but the sound will not be as loud or as sustained.5 Figures 4 and 5 (shown earlier)
portray the grid patterns of the tank over which the hammer test is to be performed.
A complete description of hammer testing is provided in NLPA 631. While API
Recommended Practice (RP) 1631. Internal Lining of Underground Storage Tanks.
does not provide descriptive detail it suggests follow up testing in questionable areas.
The suspect area can be drilled to physically measure the thickness, or ultrasonic
measurements can be taken to provide precise data. Drilling a hole in the tank is a
destructive method and inhibits the tank's future use. Drilling the tank wall to measure
wall thickness should only be done as a last resort. All steps to avoid this action
should be considered. Drilling the tank wall is destructive and will compromise the
tank's integrity.
Equipment-
Instruments needed to perform hammer testing examinations include: 1) a 16 to
18 oz. brass hammer (454 to 510 grams), 2) a drill (for destructive determination of
wall thickness); and 3) a field notebook.
Method Performance-
A hammer testing examination is entirely dependent upon the senses of the
individual performing the test. The inspector uses a combination of sight, sound, and
"feel" to identify thin areas of the tank. Data is available to evaluate the effectiveness
of hammer testing. EPA concluded (Federal Register. Friday, September 23,1989,
vol. 58, no. 185, p. 37082-37247) that hammer testing in conjunction with lining has
been proven an effective method.
Field Considerations-
Hammer testing is inexpensive and portable; a ball-peen hammer and an
experienced field inspector are all that are required to perform this test. The
experience of the inspector is the critical parameter of this examination. The time and
35
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labor effort is minimal but if tests are inconclusive, additional thickness measurements
(e.g., ultrasonic, wall drilling) are needed. Hammer testing is applicable only for
unlined steel tanks and is usually performed during tank lining procedures or
remanufacturing.
Parameters such as backfill material and depth to groundwater may affect the
ability of inspector to interpret hammer ringing or rebound. Non-homogenous backfill
will produce variable responses and vibrations. These factors were not addressed
during the course of this study. It is recommended that future studies consider the
affect these factors may impose on inspection results.
Results of this study show that the hammer test is performed more frequently
than any other and is relied upon heavily by industry. Like an ultrasonic examination ,
the cost of a hammer test is dependent upon the duration of the examination. Since
hammer testing is faster, the overall cost is cheaper. A certified hammer test
technician costs approximately $28 per hour. However, if the hammer test proves
inconclusive and requires further testing (i.e., ultrasonic, drilling tank wall) the hammer
test may become more expensive.
4.2 TANK DEFLECTION
The cross-sectional geometric shape of FRP tanks is subject to change while
undergoing structural loading (e.g., backfill during installation). To a lesser degree,
steel tanks also change shape during loading. Measurements of the geometry provide
an Indication of the tank's ability to support and distribute the necessary loads with the
given backfill. Any inability to support this load will manifest itself as a change from an
elliptical to an elliptical enhanced cross-section as the tank compresses (see
Figure 6). Generally, this condition is found after a tank is filled with product.
However, the possibility exists that an exaggerated elliptical cross-section may occur
in empty tanks. This signals significant stress resulting from improper backfill or
installation. Deflection measurements are required at installation and recommended
before repair. Extreme deflection of UST tanks can allow the fill pipes to impact and
potentially rupture the tank bottom. Deflections of this magnitude can also break welds
and buckle tanks.
Internal Tank Diameter
NLPA 631 requires internal diameter measurements before repair or
lining of FRP USTs. The measurements are recommended after 1 year of service and
at 10-year intervals thereafter. The same standard also recommends structural
assessment within 20 years and at 10-year intervals after the initial inspection. O/C
Tanks and other manufacturers perform an internal deflection measurement as a
required step during their installation procedure. Neglecting to perform this inspection
could lead to violation of structural warranty.
36
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Total Length
1m
Figure 6. Two Drawings Showing Exaggerated Elliptical Deflection in Cross-Section
37
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Fundamental Operating Principle-
During tank installation, the deformation measurements of the empty tank
provide an immediate indication of the adequacy of the backfill to support the UST.
Measurement of the vertical internal diameter indicators will determine if excessive
deviations from the original tank structure exist.
Procedure Description--
The allowable deformation during installation is set by the manufacturer.
Measurements are made through the top openings and recorded at three points
during the fill process, when there is: 1) no fill on top of the tank; 2) partial fill material
has been placed; and 3) all fill has been placed. Measurements are made with an
everyday tank sounding dip-stick across defined datum planes. Table 6 lists
representative values of maximum deflection at installation. If these values are
exceeded, it'is assumed that the backfill is not compacted properly, and the tanks must
be reinstalled.
TABLE 6. MAXIMUM ALLOWED SINGLE-WALLED TANK DEFLECTION
AT INSTALLATION
Maximum Allowable
Nominal Tank Diameter Change in Diameter
(Ft) (M) (In) (mm)
10
8
6
4
3.05
2.44
1.83
1.23
1 1/2
1 1/4
5/8
1/2 "
38.1
31.8
15.9
12.5
Source: O/C Tanks Corporation, Publication 3-PE-7097- Reprinted with permission.
Tank deflection measurements are also made after the inspector enters the
tank. Measurements of the vertical and horizontal "diameters" are made at one-meter
(3 foot) intervals along the length of the UST and are used to determine the deflection,
or the "out of roundness" of the UST. Tanks with less than 1% deflection are
considered structurally sound. Tanks having a measured deflection of 1% are
considered structurally sound but also require reinforcement. Tanks varying by more
than 2% deflection are not considered structurally sound and cannot be repaired.
NLPA 631 does not define the precise meaning of "1% out-of-round." Assuming the
38
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intuitive definition applies, (in which the difference between the two measure
diameters must be less than 1% of the average), then a 2.4-m (96-in.) diameter tank
will have roughly a 25mm (1-in.) deflection limit before reinforcement is required and a
50mm (2-in.) deflection limit before the tank is closed. These allowable deflection
levels are not universally recbgnized values. The disparity between this value and
Table 6 emphasizes this. State regulators can have more stringent values. New York
State, for example, published recommendations applied within its jurisdiction.
Figure 7 shows the three-step procedure for measuring internal diameter.
Equipment--
Instruments needed to measure tank deflection include: 1) a dipstick (measures
internal diameter of the tank); 2) a nail (to act as a "pointer"); and 3) a calculator (to
calculate the amount of structural deflection or tabulated values).
Method Performance-
The performance of this method is solely dependent upon the accuracy of the
measurements taken and the experience of the individual performing the test.
Field Considerations-
An UST structure is not always symmetrical. For example, some FRP tanks are
25 to 50mm (1 to 2 in.) larger in diameter at the center of the tank than at the ends. It is
important to refer to the original tank parameters prior to and during an internal
deflection measurement.
This test is relatively inexpensive; a dipstick and an experienced field inspector
are all that are required. The time and experience requirements are minimal.
4.3 TANK LINING INTEGRITY
The application of tank linings (generally an epoxy compound) and coatings
has become a major component of tank reconditioning and/or tank repair. Lining is an
upgrade tool that allows tanks to meet the performance standards as required by the
Federal regulations. For lining to be considered a permanent upgrade, cathodic
protection should also be applied to the tank. Under Federal regulations, unless
cathodic protection is applied, lined tanks must be inspected ten years after the lining
was installed and every five years thereafter.8
Linings applied to steel and FRP tanks achieve a number of objectives
including:
• To protect from product release due to internal or external corrosion
• To repair existing perforations in otherwise structurally sound tanks
39
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Measurement Instructions
All measurements for vertical deflections are made from the bottom of the tank to the bottom of the
NPT fitting. All measurements should be made in inches using a standard gauging stick.
Measurement 1 may be above ground or in hole prior to backfilling. Measurements 2 and 3 must
. be made in an unencumbered access fitting (no fill tube insert).
Read Indies
Measurement 1
Measurement 2
Measurement 3
Measurement 1 is the inside diameter of the tank at a fitting
opening. Measure from the bottom of the tank to the bottom of
the fitting. This measurement should be taken prior to placing
any backfill.
Measurement 2 is the distance from the bottom of the tank
to the top of the riser pipe. Backfill should be to subgrade at
this time.
Measurement 3 is the distance from the bottom of the fitting
to the the top of the riser pipe. This measurement is taken by
using a tape measure or by driving a nail into the 1" point at a
right angle to the dipstick.
Lower the dipstick (or tape measure) down the riser pipe far
enough to extend below the bottom of the fitting. Lift the
dipstick until the nail catches on the lip of the fitting. Plead
measurement at the top of the riser pipe. If the dipstick method
is used, subtract 1" to allow for the point where the nail is in the
dipstick.
Source: O/C Tanks Corporation. Reprinted with permission.
Rgure 7. Three Step Procedure for Measuring Internal Diameter
40
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• To protect the internal surface of the tank (steel or fiberglass) from
degradation by the stored product
• To perform long-term preventive maintenance
• To extend the short-term life of a tank (as long as necessary) before closure
or temporary shutdown.5-9
• Tank linings are also being utilized to remanufacture steel tanks by creating
a steel/FRP cladded tank (see Appendix D for further discussion).
A variety of materials may be used for the lining of tanks including epoxy-based
resins, isophthalic polyester-based resins, neoprene, rubber, or urethane. Care
should be taken to ensure that the lining material and storage product are compatible.
If done properly, internal lining can extend the life of a steel tank at about one-third to
one-half the cost of installing a new tank.8
Tank lining application involves three separate inspection procedures that
ensure a proper lining cure and detection of lining discontinuities (holidays). A high
voltage electrical inspection (i.e., Holiday test) detects void space between the lining
and the original tank wall. A dry film thickness test measures the thickness of the lining
applied, and a lining hardness inspection measures the hardness of the lining to
ensure that the tank lining has cured properly. These three inspections are required
by NLPA 631 during the application of a tank lining. The following subsections
discuss these inspection methods in further detail.
Holiday Tests
Fundamental Operating Principle-
Holiday detectors locate discontinuities in protective coatings when applied to a
conductive surface. Discontinuities or holidays in the lining of an UST provide specific
sites for accelerated local corrosion. A discontinuity is defined as "a void, crack, thin
spot, foreign inclusion, or contamination in the coating film that significantly lowers the
dielectric strength of the coating. May also be identified as a holiday or pinhole."10
The recommended practice for detecting discontinuities includes two types of
test equipment: 1) low voltage wet sponge testers, and 2) high voltage spark testers.11
The low voltage holiday detector operates with voltages ranging from 5 to 90 V DC,
and is powered by a self-contained battery. This instrument is used to determine the
presence of discontinuities in protective linings that have a total thickness of less than
or equal to 0.5mm (20 mils). High voltage detectors operate at voltages greater than
8800 V DC and are used to determine the presence of discontinuities in protective
coating films of all thicknesses. Linings of less than 0.5mm may be damaged if tested
41
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with high voltage spark equipment (voltages of 10,000 to 70,000 V DC are commonly
used to find flaws and deficiencies).
Procedure Description-- ;
Low Voltage Wet Sponge Testing-Low voltage holiday detectors are used to
locate discontinuities in a nonconductive lining applied to a conductive substrate. The
device is self-powered, and, depending upon the equipment manufacturers' circuit
design, has voltages ranging from 5 to 90 V DC.
The detector uses an open-cell sponge electrode saturated with a solution to
probe the lining surface. A discontinuity is signaled by an audible and/or visual
indicator. A ground wire from the instrument ground output terminal attached to the
conductive substrate ensures electrical continuity. The sponge is saturated with a
solution of tap water and a low sudsing agent. The sponge is moved over the surface
of the lining at a rate of approximately 0.3 m/s (1 ft/s). Each area is inspected twice to
minimize the possibility of error.
High Voltage Spark Testing-Trie high voltage spark tester (>800 V) consists of
an electrical energy source, an exploring electrode, and a connection from the
indicator to the conductive substrate. Change in current flow through a lining indicates
a discontinuity. Because of the voltages involved, high voltage detectors require an
external power source.
Operation of this instrument is similar to that of the low voltage tester. The
maximum voltage applied to the coating should be determined from the lining
manufacturer to avoid excessive voltage that may result in holidays being produced in
the lining. Table 7 contains voltages that can be used as a guideline. Dielectric
strength of the lining film is another consideration in voltage selection.
42
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TABLE 7. SUGGESTED VOLTAGES FOR HIGH VOLTAGE SPARK TESTING
, Total Dry Film Thickness
(mils) (mm)
8-11
2-15
16-20
21-40
41-55
56-80
81 -125
126-135
0.20 -
0.30 -
0.40-
0.53-
1.01 -
1 .42 -
2.06-
3.20-
0.28
0.38
0.50
1.00
1.39
2.00
3.18
3.43
Suggested
Inspection
(V)
1,500
2,000
2,500
3,000
4,000
6,000
10,000
15,000
Source: NACE Standard RP0188-88
Description of Instrument--
Two wet sponge instrument designs are commonly used. One design uses
either an electromagnetic sensitive relay or a solid-state electronic relay circuit. The
circuit energizes when the sponge is in contact with a holiday and activates an audible
or visual alarm. The second wet sponge design is based on the principle of an
electronic relaxation oscillator circuit. This circuit reacts to an abrupt drop in electrical
resistance between the high dielectric value of the lining and the conductive substrate
at the point of a discontinuity.
High voltage electrical detectors may be either pulse or direct current types.
The direct current instrument discharges continuous voltage, while the pulse type
discharges a cycling, high voltage pulse.12
43
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Method Performance-
The sensitivity of both the low voltage wet sponge and high voltage holiday
detectors is very high providing the following conditions are met:
• The lining should be allowed sufficient drying or curing time prior to
conducting the test. (Solvents retained in the coating film can produce
erroneous results if the test is applied prematurely.)
• Sodium chloride should not be added to the wetting solution because drying
salt may form a continuous conductive path, producing a false positive
result.
• The wetting solution should be wiped dry from a previously detected
discontinuity to prevent telegraphing (current traveling through surface
moisture path to a discontinuity, resulting in a false positive reading).
• The low voltage wet sponge test is inaccurate for film thickness over 0.5mm
(20 mils). Most tanks are lined with film thickness which exceeds 0.5mm.
• The high voltage detectors should not be used for linings of less than 0.5mm
(20 mils) due to the possibility of producing a holiday from excess voltage.
Both the low voltage and the high voltage detectors require an electronically
conductive substrate. The test can only be applied to lining on steel USTs.
Field Considerations--
This method is fully portable and does not generate hazardous waste or require
any additional safety considerations beyond those associated with normal tank entry.
Care should be taken, however, to prevent electrical shock during holiday testing.
Manufacturers' safety instructions should be carefully followed in order to prevent
electrical shock (particularly when the test is powered by line voltage).
The cost of holiday detection using either of the described methods varies from
between $1100 to $1400 depending upon conditions of tank (i.e., empty or filled),
contents, and the accessibility, and the contractor's is labor.13
Dry Film Thlfftpass Measurements
Fundamental Operating Procedure- ,
The Elcometer inspector coating thickness gauge measures non-ferromagnetic
coating films, including paint, electroplating, galvanizing, powder, plastic, and rubber
applied to a ferromagnetic base. This instrument can be used to measure the lining or
coating thickness on steel tanks (see Figure 8). Branso® also manufactures dry film
thickness measuring instruments, however, a physical description or other information
i
44
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2
I
T3
(U
"
ex
O
O)
.9
5
•if
03
LLJ
I
O
CO
8)
i
CD
en
(/}
1
O
&
CD
I
01
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45
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was not available. Lining thickness tests should be performed in order to comply with
the requirements set forth in 40 CFR 280.33(a). NLPA Standard 631, which may be
used to comply with this regulation, requires that linings should be a minimum of
2.5mm(100 mils) with an average of 3.125mm (125 mils) or greater.5 A lining
thickness test should be performed at 1 position for every 3.35m2 (36 ft2) of surface
area.15 At this time there is no standard for this inspection method.
E -
Procedure Description--
The Elcometer uses magnetic principles to measure lining thickness. The
instrument is placed so that the rubber housing makes contact with the lining surface.
A knurled thumbwheel is depressed until the magnet makes contact with the surface.
The thumbwheel is then rotated until the magnet breaks from the surface of the lining.
A black indicator will appear and the gauge is read. The magnet arm is operated by
frictlonal drive to reduce the risk of damage to the lining surface.16
Description of Equipment--
The Elcometer consists of a magnetic arm contained in a rubber housing and a
calibrated indicator (Figure 8).
Method Performance--
The Elcometer has achieved wide use throughout the industry. Errors may
arise from the inconsistencies in the surface profile or the substrate material.
Recalibration of the instrument (by taking readings on a foil of known thickness) will
compensate for errors associated with inconsistencies in the lining. Manual
recalibration is possible for surfaces of different magnetic permeabilities.
Field Considerations-
The Elcometer is fully portable and will not generate hazardous waste. Tank
entry is required to perform the method and no additional safety considerations
beyond those associated with normal tank entry are required.
The cost of dry film thickness measurement using an Elcometer varies from
between $1100 to $1400 depending upon the condition of the tank (i.e., empty or
filled), contents, accessibility, and the cost of the contractor. 13
Lining Hardness
Lining hardness tests are performed to determine that the protective coating film
(lining) has cured to a hardness that meets the manufacturer's specifications.
Improper or inadequate curing of the lining will result in a softening of the lining.
Linings that have not achieved their specified hardness will be more susceptible to the
formation of discontinuities, voids or bare spots (holidays).
46
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Fundamental Operating Principle--
ASTM Standard D2583-87 covers the test method for the determination of
indentation hardness of both reinforced and non-reinforced rigid plastics using a
Barcol impressor (Model No. 934-1). This device utilizes manually-induced force
using a hardened-steel truncated cone to determine the lining hardness in a steel or
FRP tank. The barcol impressor does not completely penetrate the lining, but creates
a small (less than 0.76mm) indentation.
Procedure Description-
The following operational procedure has been outlined in ASTM 02583-87 to
measure lining hardness.
• The testing area must be smooth and free from mechanical damage.
• The impressor must be calibrated (using calibration disks) on a solid, flat,
firm surface.
• The point sleeve shown in the diagram of a Barcol impressor (Figure 9)
should be set on the surface to be tested. The point sleeve of the instrument
should be grasped between the operator's legs and force should be applied
by hand until the dial indicator reaches a maximum.
• The scale value is then read and recorded.14
Description of Equipment--
This device has a hardened-steel indentor shaped like a truncated cone. The
tip of the cone is flat and is 0.157mm (0.0062 in) in diameter. The tip is mechanically
connected to an indicator. The indicator has 100 divisions each
representing a cone penetration depth of 0.0076mm (0.00030 in). The maximum
lining indentation created by this instrument is 0.76mm.
Calibration standards, consisting of hard and soft aluminum alloy disks, are
supplied by the manufacturer. These disks have a known hardness that is correlated
to the measured penetration. The lining hardness is interpolated based on these
readings and the known hardness.
Method Performance--
This test method for gauging lining hardness has achieved widespread use. A
distinction should be made, however, between reinforced (non-homogeneous) and
non-reinforced (homogeneous) lining materials. A greater variation in hardness
readings will be obtained for the reinforced materials. This variation may be caused
47
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FRAME
SCREW
PLUNGER UPPER GUIDE NUT P|N
INDICATOR
COVER
SCREW
LEVER
LOCK NUT
SPRING
POINT SLEEVE
STOP RING
CASE & F-"RAME
ASSEMBLY
LEG
LOWER PLUNGER GUIDE
7 POINT L SPRING
Source: Standards Test Method for Identation Hardness of Rigid Plastics By Means Of A Barcol
Impressor. ASTM D2583-87. Reprinted with permission.
Figure 9. Diagram of Barcol Impressor
48
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by the difference in hardness between resin and filler materials in contact with the
indentor. Table 8 gives sample sizes necessary to equalize the variance-of-average
for homogeneous and nonhomogeneous materials.
TABLE 8. RECOMMENDED SAMPLE SIZES TO EQUALIZE THE
VARIANCE OF THE AVERAGE
Homogeneous Material
Hardness
M-934 Scale
20
30
40
50
60
70
80
Reading
Variance
2.47
2.20
1.93
1.66
1.39
1.12
0.65
Coefficient of
Variation, %
2.6
1.7
1.3
1.1
0.9
0.8
0.7
Variance of
Average
0.27
0.28
0.27
0.28
0.28
0.28
0.28
Minimum No.
of Readings
9
8
7
6
5
4
3
Non-homogeneous Materials
(Reinforced Plastics)
30
40
50
60
70
22.4
17.2
12.0
7.6
3.6
2.9
2.2
1.7
1.5
1.2
0.77
0.76
0.75
0.76
0.76
29
22
16
10
5
Source: ASTM D2583-87
Field Considerations-
This method is fully portable and will not generate a hazardous waste or require
any additional safety considerations beyond those associated with normal tank entry.
Environmental conditions such as temperature, moisture, or lining material were
not addressed during the course of this study. It is recommended that future field
studies of this inspection method address these environmental conditions.
The cost of hardness testing using the Barcol impressor varies between $1100
and $1400 depending upon condition of tank (empty or filled), contents, accessibility,
and contractor.13
49
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4.4 TANK DISCONTINUITIES
A discontinuity is a surface or subsurface flaw created by corrosion, stress,
improper welding of steels, or improper FRP laminations (i.e., delaminations). A
discontinuity may appear in the form of a crack, hole, pit, delamination, blister or other
imperfection that may directly impact the structural integrity of the tank. Surface
discontinuities (open flaws that exist on the surface of the tank) are the most
detrimental to the service life of the tank. Localized weak spots promote cracking,
corrosion and trap corroding materials which may eventually create holes and cause
tanks to leak. Criteria for discontinuities set by professional societies and standards,
are based on size, location and frequency of occurrence. ;
A visual examination inspection is the most popular internal inspection for steel
and FRP UST discontinuities. This inspection method is inexpensive, quick, and does
not require extensive equipment. A visual inspection is limited to surface
discontinuities both in size and in location. A liquid dye penetrant inspection requires
solvent-based "penetrants and developers" for flaw detection and may be used to
detect the surface and subsurface discontinuities of steel and FRP tanks. The method
is a little more time consuming than a simple visual inspection, but can detect smaller
surface discontinuities and estimate their depths. Depending on the technique used, a
liquid dye penetrant test may be performed without the use of supporting utilities. The
magnetic particle method, the most accurate of the three inspection methods for
discontinuities, detects surface and subsurface discontinuities in steel tanks.
However, this inspection method is less portable and more expensive than the visual
and liquid dye penetrant inspection methods.
The cost of these inspection methods is based on time and materials. The cost
of a certified technician to conduct a visual, liquid dye penetrant, or magnetic particle
examination ranges from $28 to $30 per hour. Since the technician rates are relatively
equal, the cost comparison of these examinations will be based on the time to perform
the examination and any support equipment needed to conduct the inspection.
The internal inspection methods for tank discontinuities in steel and FRP tanks
are discussed in the following subsections. There are several other non-destructive
methods for detecting surface and subsurface discontinuities in steel and FRP USTs
(i.e., acoustic emission, eddy current, radiography) which are not in widespread use.
Refer to Section 5.0 and 6.0 for further information about these methods. The methods
discussed in this section are the primary internal inspection methods in common use
for the inspection of USTs.
I
Visual Examination !
Fundamental Operating Principle--
Visual inspection is often used for interpretation of results from specific testing
methods for steel and FRP tanks. Visual examination is used to detect surface
discontinuities such as cracks, holes, and other porosities in steel and FRP tanks. A
50
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visual examination may be used to determine the subsurface conditions of a FRP tank
with the assistance of other instruments (e.g., artificial light) and tank placement (e.g.,
out-of-ground). The types of visual examinations discussed in this section do not
involve the assistance of other inspection methods.
Manufacturers prepare written procedures for the inspector that list the
components of the tank (e.g., surface, weld) to be examined and the acceptable
environmental conditions (e.g., light intensity). These procedures list necessary
equipment and arrangements for qualification. Personnel performing the inspection
must have certifications documenting their ability to perform the inspection and make
value judgements. Substitution of equipment or changes in test arrangement will not
require requalification. The manufacturers may require a visual examination to keep
the UST in compliance with valid structural or service warrantees.
The three types of visual examination recognized by the ASTM and ASME are:
1) direct visual examination, 2) remote visual examination, and 3) translucent visual
examination. Direct visual examination incorporates the use of a magnifying glass,
graphite mirrors, or other instruments to enhance visible flaws. Remote visual
examination include not only mirrors, but also other visual aids such as horoscopes,
telescopes, and microscopes. Translucent visual inspection entails the use of artificial
directional light on the inside of the tank.
Of the three types of visual inspection, direct visual examination is the most
frequently used for internal inspections of steel and FRP tanks because it is
inexpensive and requires no equipment. Remote visual examination (e.g.,
boroscopes) is occasionally used for USTs systems that contain interstitial areas (i.e.,
double-walled tanks). Translucent examinations are limited to FRP tanks that have
been removed from the ground.
NLPA 631 describes a direct visual examination method in which a graphite
cloth is used to wipe the internal surface of an FRP to enhance the detection of any
surface discontinuities. The graphite acts as a visual aid allowing easier and more
precise flaw detection. Direct visual examination is a recognized test by professional
organizations and is a current practice of several tank manufacturers and trade
associations, but is currently in practice.
Procedure Description-
The procedure for a visual internal inspection of an UST is to be done in
accordance to a written procedure provided by the tank manufacturer. Section V
Article 9 of the ASME Boiler and Pressure Vessel Code which applies to the conduct
of visual inspections of USTs among others. These procedures require that the written
procedure address the following:
(a) how the visual examination is performed,
(b) surface condition (type),
(c) method for surface preparation (e.g., cleaning, sandblasting),
51
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(d) type of viewing (i.e., direct, remote, translucent),
(e) equipment used,
(f) sequence of procedural steps,
(g) data required, and
(h) inspection reports.17
The procedural steps taken to perform a visual inspection are straightforward. The
precision is limited by the level of experience and the training of the inspector(s).
However, there are specific conditions necessary to perform a visual inspection. The
conditions (e.g., lighting, viewing distance) are dependent upon the type of visual test
performed. ,
For a direct visual examination, the area examined must be within 61cm (24 in.)
of the human eye. The angle of the surface may not be less than 30 degrees. Visual
aids such as mirrors and magnifying glasses may be used to detect discontinuities.
The minimal level of lighting for a visual examination is 161 lumen/m2 (15 fc); 537
lumen/m2 (50 fc) is required for detection of small surface discontinuities. All sources
of lighting must be intrinsically safe and effectively eliminate the risk of ignition. A
visual inspector is required to have an annual visual checkup. Deficiencies must be
corrected by prescription eyeglasses.17
Remote visual examinations substitute for direct visual examinations when the
area of interest is inaccessible. Section V, Article 9 of the ASME Boiler and Pressure
Vessel Code requires that the instrument have an equivalent resolution to a direct
examination. Section 6.0 discusses the use of boroscopes for remote visual
examinations. Use of other visual aids, such as telescopes and microscopes are not
applicable to USTs.
A translucent visual examination is primarily used for classifying surface and
subsurface defects in FRP tanks. The examination is performed inside the tank with an
artificial directional light that provides enough illumination for classification of visual
discontinuities. The artificial light must be intrinsically safe and be able to diffuse the
light evenly over the surface area. Ambient lighting must be oriented in a fashion to
eliminate any surface glare or reflections. The intensity of the ambient light must be
less than the translucent light used to inspect the area of interest. A translucent visual
examination may only be performed when a tank is out of the ground.
t
Before the visual inspection of a tank, the internal surface of the tank must be
free of dirt, oil, grease, rust, or other matter that may inhibit flaw detection. The tank
may be washed with soap and water following surface preparation (e.g., sludge
removal, sandblasting). Refer to Appendix A for a discussion of tank cleaning
procedures.
For FRP tanks, the classification of any internal discontinuities is designated by
type and by level. Appendix F lists types of discontinuities and defines them in
accordance to ASME SD-2563. If the type of flaw exceeds that of the level listed, it is
rejected for that category. If the flaw exceeds all three categories it is then assigned to
52
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Level IV. Level IV defects are to be described by a drawing stating size and location.
No list of acceptable flaws specific to steel or FRP USTs has been identified.
Equipment- -
Equipment varies for translucent and remote inspections, but generally the
following are needed for visual inspections: 1) fluorescent lighting; 2) a graphite cloth;
3) a magnifying glass; and 4) mirrors. Translucent and remote visual inspections will
require more specialized equipment (i.e., horoscope).
Method Performance--
The performance and accuracy of a visual inspection is dependent upon the
expertise of the individual inspector. Insufficient lighting conditions may inhibit correct
interpretation or detection of surface flaws. A direct visual inspection can only detect
surface discontinuities for steel and FRP tanks. But if the tank is out-of-ground, a
translucent visual examination may detect subsurface flaws for FRP tanks. Full face
safety equipment can affect the ability to see defects.
Field Considerations-- ,
Visual examination in the field is primarily affected by the lighting conditions
and the experience of the inspector. The inspection does not generate any waste
products nor does it require any extensive labor. It does, however, require safe health
conditions for entry into the tank. A visual inspection is the cheapest method of
discontinuity detection based on the fact that it is quick, intrinsically safe, and does not
require extensive support equipment. However, a visual inspection cannot readily
detect small surface or subsurface discontinuities. Remote and translucent visual
examinations requiring the use of additional materials and obviously will cost more.
How much more is dependent upon what is used to assist the examination or what is
required as a preliminary step (i.e., translucent examination requires the tank to be out
of the ground).
Liquid Dve Penetrant
Fundamental Operating Principle--
The liquid penetrant test is a simple non-destructive test used for detecting
surface discontinuities on steel and FRP tanks. This inspection is performed prior to
lining application or during tank remanufacture. The liquid penetrant is applied to a
clean surface and is drawn into surface discontinuities by a capillary action. The
capillary action continues for a period of time known as the "dwell time." After the
prescribed dwell time, excess penetrant is wiped from the surface and a developer is
applied. The developer draws the liquid dye penetrant out of the surface flaws. The
liquid dye penetrant produces indications that are visible by normal or ultraviolet light,
depending upon the class of dye penetrant used in the form of blotches at the
locations of flaws.
53
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A liquid penetrant test may be performed using one of two classes of liquid dye
penetrants. The dyes in the penetrants are either visible by color contrast in normal
light (visible dye penetrant), or in fluorescent light (florescent dye penetrant). There
are three penetrant techniques for the two classes of liquid dye penetrants. The
individual techniques are: 1) water washable, 2) post-emulsifiable, and 3) solvent-
removable. Figure 10 is a flow chart that plots the procedural steps for each technique
using a visible dye penetrant. The procedures are similar for each technique when
using a fluorescent dye penetrant. The visible dye penetrant and the solvent-
removable technique are conventionally used in the field due to their portability (dyes
are packaged in aerosol cans) and minimal labor.
Procedure Description--
Surface preparation is necessary since contaminants or deposits might mask
the indications of unacceptable discontinuities, or interfere with the effectiveness of the
examination. The accuracy of any dye penetrant inspection is influenced heavily by
surface contaminants. All areas of the tank to be inspected must be clean (e.g. free of
any rust, scale, welding flux, grease, oily films, dirt) and dry before application of the
penetrant. For welds, the adjacent area within 25-mm (1 inch) must be cleaned.18
Detergents, organic solvents, or chemical descaling solutions are used in the cleaninq
process. After cleaning, the area to be inspected is dried by applying induced hot air^
or by exposure to ambient conditions. Moisture or residue will obstruct the penetrant
process if the surface is not dry.
After surface preparation, the penetrant is applied by brush or spray method
Aerosol cans have proven to be highly portable and effective for application to UST
geometries. Care should be taken to avoid excess application and buildup (e g
pools) of penetrant. The time the penetrant needs for penetration is dependent upon
the manufacturer's specifications. Excess penetrant is removed as described for each
tyPe of technique (i.e., water-washable, post-emulsifiable, and solvent-removable)
After cleaning and penetrant application steps have been completed, there are various
procedures for performing dye penetrant tests. Different techniques are shown in
Figure 10.
Water-washable penetrants are removed directly from the inspection area usinq
water spray at a constant temperature, between 15 to 40C (60° to 104°F) and pressure
(less than 7 kPa or 1.0 psia), or by wiping the surface with a clean damp cloth. If post-
emulsifiable penetrants are used, the area is sprayed with an emulsifier that combines
with excess penetrant and forms a water-washable mixture. The dwell time of the
emulsifier is dependent upon the type of emulsifier applied (i.e., water-based or oil-
based) and the surface roughness. Rinsing the emulsifiable penetrant is done by a
water spray at a constant temperature (between 15 to 40C or 60° to 104°F) and
pressure (less than 50 kPa or 7.2 psia). The penetrant absorbed by the surface
discontinuities is not emulsified. Excess solvent-removable penetrants are removed
by using a clean, lint-free cloth until most traces of penetrant have been removed A
new, clean, lint-free, moistened cloth is used to remove any other excess penetrant
54
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Water-Washable
Technique
Post-Emulsifiable
Technique
Solvent-Removable
Technique
Source: Mix, Paul E., P.E., Introduction ot Non-destructive Testing A Training Guide.
John Wiley & Sons Inc., New York, New York. © 1987. Reprinted by permission of John Wiley &
Sons, Inc. Reprinted with permission. '
Figure 10. Flowcharts of Three Different Visible Dye Penetrant Techniques
55
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from the surface. Care should be taken to avoid the use of excess solvent. For each of
these techniques, failure to remove excess penetrant will hinder the inspection
performance.
For the water-washable and post-emulsifiable techniques, after the excess
penetrant has been removed, the surface area is again dried by induced hot air or
exposure to ambient conditions. Solvent-removable penetrant evaporates and does
not require extensive surface drying.
There are two types of developers to be used with a dye penetrant An aqueous
developer consists of a suspension of developer particles in water and may be applied
to either a wet or dry surface. The drying time of the aqueous developer may be
shortened by the use of induced warm air. A non-aqueous developer consists of a
suspension of particles in a solvent and is applied to only a dry surface. The non-
aqueous developer dries through evaporation.
Aqueous developer application is done immediately after the excess penetrant
has been removed. Application of developer (aqueous or non-aqueous) is done in
accordance with the manufacturer's instructions in an evenly distributed manner.
Excess aqueous developer is removed by spraying the surface with water. This action
prevents pooling that may inhibit flaw detection. After application is complete, the
surface area is dried using induced warm air or ambient air, not allowing the surface
temperature to exceed 40C (140°F).
Non-aqueous developers are applied after the surface area has been dried. A
thin film of developer is applied by using aerosol cans or dry powder spray guns in
accordance with manufacturer's instructions. Excess non-aqueous developer will
flush the penetrant from within the discontinuity and evaporate rapidly. The
development time for both of these developers (aqueous and non-aqueous) begins
immediately as soon as the surface area is dry. According to ASME, development
periods more than 30 minutes are acceptable.
The developers create a white background to expose the dye in the presence of
surface discontinuities. Large flaws will be visible immediately while smaller tighter
flaws will develop over time. The intensity of the color and the velocity of the bleedout
will help develop an indication of the flaw depth. Each of these visible dye penetrant
techniques may be inspected in natural or artificial light. Minimum light intensity is 351
iumen/m2 (33fc)
After the inspection is complete, cleaning the surface area is necessary in cases
where the residue may inhibit service or repair proceedings. Developers should be
removed immediately after inspection so that the residue does not fix onto the
discontinuities.
56
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Description of Instrument(s)--
Table 9 summarizes the techniques and equipment needed to perform the three
liquid dye penetrant inspection techniques with a visible or fluorescent dye penetrant.
TABLE 9. LIQUID DYE PENETRANT TECHNIQUES AND EQUIPMENT
Techniques
Water-
Washable
Post-
Emulsifiable
Solvent
Removable
Penetrant/
Developer
Visible Dye
Fluorescent
Dye
Visible Dye
Fluorescent
Dye
Visible Dye
Fluorescent
Dye
Application
Brush or
Spray
Brush or
Spray
Brush or
Spray
Brush or
Spray
Aerosol
Aerosol
Removal/
Rinsing
Water Hose
Water Hose
Water Hose
Water Hose
Lint Free Cloth
Lint Free Cloth
Drying
Fan
Ambient
Fan
Ambient
Fan
Ambient
Fan
Ambient
Evaporation
Evaporation
Lighting
Normal
Artificial
Normal
Artificial
Normal
Artificial
Utilities
Electric
Water
Electric
Water
Electric
Water
Electric
Water
None
Electric
Source: Mix, P.E. Introduction to Non-D_es.truciJve Testing. A Training Guide. John
Wiley & Sons, Inc., New York, New York. 1987
Method Performance--
A liquid dye penetrant performance is dependent on the ability of the penetrant
to enter the discontinuity, and the inspector to interpret the results. If performed
properly, the inspection will detect surface and subsurface flaws that may be
detrimental to the tank life span.
The penetrant performance is primarily affected by the existence of
contaminations or deposits in the surface flaws. For example, scale, rust, and
corrosion that usually occur within a tank not only blocks the penetrant from infiltrating
the surface flaws, but may also trap the penetrant and produce false readings. Steel
tanks, whose interior walls have an impermeable organic coating, can completely
obscure the detection of surface discontinuities. Surface preparation and cleaning will
influence the results of the liquid dye penetrant inspection. Effective removal of
contaminants from the surface flaws may be performed using detergents, organic
solvents, or pressurized water. The removal of coatings done by surface grinding
operations will smear the surfaces of steel tanks and cover the openings to the surface
flaws. It is imperative that these solutions are thoroughly removed after cleaning
57
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operations and that the surface is dried. Acidic or alkaline solutions that remain in
surface flaws will inhibit the penetrant performance. The reliability of the results
increases as surfaces are cleaner and drier.7
The characteristics of a good penetrant are related to surface tension, density,
and wetting properties. Visible dye penetrants, due to their properties, are less
vulnerable to contaminants than fluorescent dry penetrants. However, the fluorescent
dye penetrants provide higher sensitivity to surface flaw detection.7 Moisture or high
humidity conditions will affect the penetrant performance. Test temperatures for a
liquid dye penetrant inspection must be between 15 and 38C (60° to 100°F). For
temperatures below this range a qualification procedure is required (see Appendix G).
Liquid dye inspections are not recommended when the surface of the tank exceeds
38°C (100°F) due to a possible explosion or combustion hazard.18
The interpretation of the liquid dye penetrant inspection results is dependent
primarily upon the inspector performing the examination. Recognition of surface flaws
and eliminating the environmental interferences requires knowledge, experience, and
discipline. The inspector must understand the material he/she is testing and the
production process. Knowledge of the production process will help with interpretation
of results and reinforce a discipline so results are not biased.
Field Considerations--
Proper health and safety precautions should be taken when liquid dye
penetrant inspections are performed. Solvent-removable penetrants and developers
may generate fumes that are highly volatile and may be harmful if inhaled or if direct
eye contact occurs. Prolonged exposure to penetrants and developers nnay cause
headaches, nausea, and/or tightness or pain in the chest. Proper ventilation
throughout the tank is needed to maintain inspection safety. Prolonged hand contact
to penetrants and developers may cause chapped hands which may be avoided by
wearing rubber gloves.7
The technique and dye penetrant used most often in the field is the solvent-
removable technique with a visible dye penetrant. The aerosol spray cans are
portable, inexpensive, and can be readily disposed of in an industrial durnpster. The
aerosol sprays are effective for UST geometries and provide good test reproducibility
and sensitivity. A fluorescent dye penetrant may be used in the field with the solvent-
removable technique when electricity is available for the required lighting.7
A liquid dye examination is more expensive than a visual examination because
of the incurred material cost and longer inspection times. But, as discussed
previously, a liquid dye penetrant examination can detect both surface and subsurface
discontinuities. The solvent-removable technique is the cheapest method of
conducting a liquid dye penetrant examination. The aerosol cans are readily
disposable, requiring less process time, and are fully portable. The post-emulsifier
technique provides maximum sensitivity, but like the water-washable technique, is
58
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expensive and not portable. Both of these techniques generate a waste water stream
that may require proper disposal in accordance with local and state regulations.
Magnetic Particle Method
Fundamental Operating Principle--
Magnetic particle testing is a non-destructive test used for detecting surface and
subsurface discontinuities on a steel tank interior surface. After the surface has been
cleaned, a magnetic field is induced on a localized area of the tank surface while a
magnetic powder is applied (see Figure 11). The "flux leakage" created by a
discontinuity on the surface of the tank wall attracts the magnetic powder creating a
visual indication. This method is not applicable to materials which cannot be
magnetized (i.e., FRP tanks).
Magnetic particle inspections depend on four factors:
• the current used to induce magnetization (alternating current (AC), single
phase half-wave direct current (HWDC), or three phase full-wave direct
current (FWDC);
• the orientation of the magnetic field (i.e., circular, longitudinal);
• the selection of the magnetization method (e.g., coils, prods, yokes, or
cables); and
the type of magnetic particle used (wet or dry). These factors must be
considered in magnetic particle testing to maximize performance and
maintain portability.
The magnetic particles used for flaw detection must have high permeability to
allow magnetization and low retentivity to minimize their mutual attraction.* Dry
magnetic particles are cheaper and easier to use than the wet particles, but are not as
sensitive or accurate. The dry magnetic particles may be gray, red, black or yellow.
Fluorescent dry particles are more expensive and require specific artificial lighting
conditions. Wet magnetic particles are suspended in a water or oil solution for
application. These types of particles are used to detect localized discontinuities in
smaller types of equipment.
Because of their small size and versatility, flexible magnetic yokes and prods
are the most popular methods of conducting a magnetic particle internal inspection of
steel USTs. The yoke operates on a continuous 115V alternating current or a pulsed
300 V direct current for magnetization. The probe spacing is adjustable from 0 to
*(Retentivity is the residual flux density that corresponds to the saturation induction of the magnetic
particle).
59
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Powder Dispenser
Flux Leakage
'
Poles
\^V*"*^
t^
"'*~-^>
.Magnetic Powder
Poles
Localized Magnetization
\
Tank Wall
Figure 11. Localized Magnetization
60
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305mm (0 to 12 in) and produces a longitudinal magnetic field. The yoke has the
ability to contour itself to curved surfaces and difficult geometries. A second
instrument, similar in portability and size, is the prod. The prod utilizes a continuous
alternating current to induce a circular magnetic field. Both instruments utilize dry
magnetic particles.
Procedure Description--
A magnetic particle examination is done in accordance with ASME SE-709 and
ASTM E 709-80, "Standard Practice for Magnetic Particle Examination."
Prior to performing the actual instrument calibration, several control tests are
performed on the instruments to ensure accuracy. The following control tests are
recommended by ASME and ASTM:
1. ammeter accuracy check
2. timer control check
3. magnetic field quick break check
4. equipment current output check
5. internal short circuit check
6. electromagnetic yoke lifting force test19
In addition to these control tests (see Appendix H for description), the light intensity
level used for detection of dry magnetic particles is checked before the inspection.
The white light intensity at the surface of the tank is determined by the inspector. An
80 watt fluorescent light one meter from the surface is sufficient. It is imperative that
this light is intrinsically safe.
The surface of the tank must be clean of all oil, grease, dirt, sand, or other non-
ferromagnetic matter. Paint and weld spatter should also be removed because of its
potential ability to inhibit the mobility of the magnetic particles. Thin paint (0.02 to
0.05mm) will not inhibit magnetic particle formations, but must be removed from areas
where electrical contact is made. Surface cleaning is done with soap and water.
Sandblasting the tank and creating a rough surface will make visual interpretation of
the magnetic particles difficult. Rust, scale, and other tank debris will, if not removed,
hamper the interpretation of the flux. When testing a weld, the surrounding area must
also be cleaned. After cleaning, the surface area is dried by ambient conditions or
with induced air. Surface moisture will inhibit dry magnetic powder mobility.
The area to be inspected is magnetized by direct or indirect magnetization. A
prod is an instrument that magnetizes the surface area by inducting a circular
magnetic field (known as direct magnetization). The two electrodes of the prod are
pressed firmly against the inner wall of the tank which magnetizes the area between
the electrodes. Prod examinations require a second examination of the same surface
area with the electrodes rotated 90 degrees from the initial orientation. This technique
will reveal all existing flaws in the localized area. It is important that the prod tips
61
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remain clean to deter any arcing or overheating effects that may affect the properties of
the tank. Arcing is minimized by a remote switch that allows the inspector to induce
and remove the magnetic field once the prod is in place. (It is important to verify that
the tank has been properly inerted or degassed prior to performing this examination.
Check the lower explosion limit of the tank prior to entry (see Appendix Ei). The arcing
created by the magnetic instruments is an ignition source that poses an immediate
safety concern.
The yoke, like the prod, has two electrodes and must be rotated 90 degrees to
reveal all existing flaws. However, the yoke induces a longitudinal magnetic field
(indirect magnetization) that runs parallel with the instrument. Yokes generally have a
remote switch to eliminate arcing as the magnetic field is induced and removed. The
type of instruments used to perform a magnetic particle examination may differ in
magnetization and current, but they are similar to dry particle application.
For dry particle application, it is important that the area of interest remain
magnetized as the particles are applied to the localized area in a dust-like manner.
Hand-powered applicators or electric blowers are used to create the particle cloud.,.
The magnetization will maintain the particles' mobility and allow the migration to
surface discontinuities where flux leakage exists. After excess magnetic particles have
been blown off with dry air, the magnetization is stopped and the results are
interpreted with the assistance of light. The type of light is dependent upon the type
(i.e., fluorescent or non-fluorecent particles) of dry particles used.7
The indications of discontinuities are formed by the presence of magnetic flux
leakage. All magnetic particles held by ferromagnetic materials are a result of surface
and subsurface flaws, or conflicting material properties. Magnetic particles trapped in
weld depressions, scale, or rust must be recognized and disqualified as true
indications. Other irrelevant indications may also form at the edge of cold-worked
areas.
After an evaluation has been made, the localized area is demagnetized to
eliminate the possible source of ignition (i.e., static charge, arcing). This may be done
simply by magnetizing the area under the yoke or prod and slowly withdrawing the
instrument while it is still energized. It is important to demagnetize with the same
instrument that was used for magnetization (i.e., a yoke can be used to demagnetize if
a prod was used to perform the inspection). The effectiveness of the demagnetization
is measured by a magnetic field indicator or field strength measurement device.
After the magnetic particle inspection is complete, the surface area of the tank is
cleaned with compressed air to remove the dry particles only if the tank is subject to
further testing or processing actions.
62
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Description of Instrument--
Table 10 lists the operating specifications of typical magnetization instruments
used in the field.
TABLE 10. SPECIFICATIONS OF MAGNETIZATION INSTRUMENTS
weight
voltage
contacts (width)
cable (length)
Yoke
3.14kg
115 VAC or
300 VDC
0 to 305mm
N/A
Prod
(24 Ibs.) 10.91 kg
115 VAC
76 to 203mm
3.66m
Source: Mix> Paul E.( P.E. Introduction to Non-Destructive Testing. A Training
John Wiley & Sons, Inc. New York, New York, ©1987.
Equipment--
Instruments needed for magnetic particle examinations include: 1) ammeter
(checks level of magnetizing current); 2) a magnetic field indicator (for
demagnetization purposes); 3) a magnetic powder shaker or blower (for application of
magnetic powder); 4) a fan (to induce air for drying); and 5) an electric power source.
Method Performance--
Magnetic particle testing is most effective on surface discontinuities somewhat
less effective on discontinuities lying just below the surface, and ineffective on deep
subsurface defects (6.4mm below surface). Defects open to the surface are the most
detrimental to the service life of the tank because they are localized weak spots that
promote cracking and trap corroding materials.
By far, the most important consideration for obtaining reliable indications of
discontinuities and defects is the direction of the magnetic field. For greatest
sensitivity, a leakage field must be created at right angles to the surface and
subsurface discontinuities. If magnetic lines are parallel to the defect, there will be
little or no indication of the defect. 'For this reason, a versatile (yoke or prod)
instrument capable of rotating 90 degrees is used. Multidirectional magnetization is
the most effective method for testing surface flaws of steel USTs. A sufficient number
of lines of leakage flux must be produced for reliable defect indication, but the direction
of the magnetic field, not its strength, is much more important.
The yoke and the prod may be used with two types of current: AC instruments
are effective for surface discontinuities while HWDC instruments are effective for
surface and subsurface discontinuities. The HWDC has a pulsating characteristic that
63
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provides additional mobility to the magnetic particles, which increases the sensitivity
and level of detection. Magnetic yokes have the proven ability to detect a notch 1.5mm
wide x 5.0mm deep.7
Magnetic indications may be sharp or blurred depending on the depth of the
discontinuity. Subsurface flaws are only detectable when the tip of the crack is within
a few millimeters of the surface. The indications are, at best, broad and diffused.
False indications occur if magnetization is too high, or if the electrodes of the yoke or
prod are too close to each other. A "furring" effect is created as magnetic particles
build up around the electrodes or along edges and notches on the surfaces. Welds that
have undergone cold-working can produce false indications.
Field Considerations--
The most effective instrument in the field is the magnetic yoke, which utilizes a
HWDC current and dry magnetic particles. This system provides good results while •
minimizing waste and utility requirements. Dry magnetic particles are not affected by
temperature but moisture, tank residue, and sludge will inhibit performance by creating
particle agglomeration. This agglomeration will reduce particle mobility and directly
affect the accuracy of the inspection.
To maintain a proper health and safety level, it is imperative that the tank is
inerted or degassed prior to conducting a magnetic particle inspection, The
magnetization instruments have the tendency to arc and act as a source of ignition. An
explosimeter should be used to determine if the tank is safe for entry and operations
(see Appendix E).
Of the three discontinuity inspection methods discussed, a magnetic particle
examination is the most expensive. This inspection method is the most accurate and
is also the most labor intensive. The materials, utilities, and instruments required are
portable and may be commonly rented. The type of magnetic particles used also
influences the cost of the examination. When using dry magnetic particles, the amount
of waste generated is minimum. These particles are usually non-toxic, non-
hazardous and do not pose a potential disposal problem. The certified inspectors
required to perform these tests are readily available and usually require certification
from the American Welders Society (AWS).
4.5 TANK INTEGRITY
, I'
Several methods are used to determine tank integrity as part of the inspection
process required or recommended by LIST manufacturers and the various trade
organization standards for manufacturing and inspection of tanks. These include
bubble tests, pressure change tests, and vacuum tests. These methods are used to
indicate the presence of leaks or to demonstrate the structural strength of the tank as
specified by the manufacturer or referenced code. All of these tests can be used for
testing of both FRP and steel tanks to verify design criteria, as quality control checks at
manufacture, for integrity testing during installation, repair or upgrade, and at closure
64
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of the tank. Other methods to .determine tajik tightness are available, however, those
:methpd$ are generally used for precision leak"detection and are applied when the
tank is filled with product during its operational life^ ! ;.
Bubble Testing , ,. .,.,,,....,.,,.,,,,
Fundamental Operatrng Princjpl0--'":!u'; '1; 7l': ?:.,,...''
* '• '• * : -•--•.,•->*.. i -,..,-• \ v - i j, ,. -
• /Bubble testing focateis 'holes in tlie;tani<; using a^solution that will form bubbles
whefi; a pressurized gas passes through the;£oltjtiori: There are two bubble testing
rhethods: positive pressure and;vacuum bb£X:;F,or.the; positive pressure rnethqd,' the
tank is pressurized and the' bubble solution is applied'to the outer surf ace'of the tank.
The vacuum box method can be applied to either surface of the tank wall. The vacuum
is created to generate the pressure difference across the tank wall which'allows for
detection of the leak after the solution has been applied to the tank surface.
/•; -.'•**, .; ,•• '•'.-!' ;; •'•'?'< *;"';''.'.;•.;-,."•• ."• ;";•;• n.i?t? • ••; ~< f^>.?••-••. • ;;io: "•?-.;•"" ~- ;•;•.•;.'•" yi"
s- 'The vabuum box method'uses'a^ tank
geometry;- the box" ii'equipped with a transpare:ht yiewing window, gasketed sealing
surface, vacuum pump,' arid a vacuum gauge. The box sits'on the surface with'the "
bubble solution already 'applied and the gasket in' positibh: A vacuum1 is created^ within
the boxed volume using the vacuum pump. The surface is then observed through the
viewing window for the formation of Bubbles,20.7
The'positive'pressure bubble test is the mpre cpmrtionry'used of the two
methods; The direct pressure test can only be used when the exterior of the tank is
exposed.' As a result,:this test is predominantly performed during tank installation;
Bubble tests are also performed when there is a exposed exterior surface onto which a
soap solution can be applied, suqh as repair of a crack, a fitting, or checking, the seal of
the mariway. The Vacuum box method 'is5 seidbrn-us'ed for tank Irispectibns since it is
generally easier;tof perform ^positive' pressure bubble'test. However, a vacuum box
test!can be used to test the tank from the interior wHen access is provided.
Procedure E)escription^- ' ! ":"'•"" : "": '•''*':]':" '"'*'•'"' \ '"'^ •-•'' - '•'-' '-' --'^ '""'"-
I, '"• ," • iliJ/, ''•':" •:-^ !•; i't f-'" •-'Mil .,'lj'i" •"(;'< i :" C'-*i-'-'-'HV*.?.'.' *|V '--'.'' '•
;'• During ai direct p/essure bubble test, the'tank'"is pressurized with air or an inert
gas. The test pressure is' 21 to 34 kPa (3 to 5 psig) for FRP tanks, and 34 to 48 kPa (5
to 7 psig) for steel tanks. The actual test pressure may vary depending upon the
standard that is followed. Appendix I summarizes the test specifications required by
the various standards. Extreme caution must be used so the tank is not over-
pressurized which can.cause the tank to rupture or explode. Figure 12 shows a typical
setup for pressurizatibn of a double walled Mahway tank.
The tank walls must be free of oil, grease, paint, or other materials that might
mask a leak. Thelank is pressurized to the test pressure and is generally allowed to
"soak" at the test pressure for a minimum, of 15 minutes to allow the gas to work its way
through any tiny cracks that may be present.20 The pressure within the tank may drift
initially while the internai |ernperature equilibrates with the environment. The pressure
": 65
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TO COMPRESSOR
V
MANIFOLD VALVE
AIR SiUPPLY
VALVE
AIR SUPPLY
GAUGE
MANWAY
Source: Xerxes Corporation, Minneapolis, MN, 1990. Reprinted with permission.
Figure 12. Pressurization Setup of a Double Walled Manway Tank
66
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should be adjusted to maintain the required test pressure while the bubble test is
being conducted. Some standards do not specify a soak period.
The bubble solution is applied to the outer surface of the tank. If no continuous
bubble formation is observed, the tank is considered acceptable. Particular attention
should be focused on tank welds and tank openings.
The surface tension of the bubble solution controls the bubble formation
process. The surface tension must be low enough so that small leaks can be detected
but not so low that the bubbles are allowed to break rapidly. The bubble solution is
applied to form a film that does not break away from the area to be tested. The
solution is also applied so that a minimal number of bubbles is produced by the
application. The solution must be compatible with ambient conditions. Wind, rain,
subfreezing conditions, and ambient light conditions affect the test's effectiveness in
detecting leaks. The test can be repeated instantly on any area of the tank if there are
doubtful results.
The tank may be pressurized using an air compressor or a compressed gas
cylinder with an attached pressure regulator. The pressure gauges used generally
have full-scale readings 1 1/2 to 4 times the nominal test pressure. Gauge accuracy is
traditionally poor in the lower 10-20% of the full-scale value. All pressure gauges
used during the tests must be calibrated against a standard dead weight tester, a
calibrated master gauge, or mercury column and recalibrated annually unless
specified otherwise by the referencing code. All gauges must be recalibrated any time
that there is reason to believe they are in error.20
Method Performance--
The bubble test is the most commonly used tightness test due to its ability to
detect relatively small gas leaks and its ease of application. Common applications for
the bubble test to USTs include: design verification, manufacturer quality control
before installation, to check the seals of openings such as manways in partially buried
tanks, and following tank closure. A bubble test may also be performed in conjunction
with a pressure change test. One source estimates that bubble tests can reliably
detect leaks of air as small as 0.002 liter/hour.21
Field Considerations-
When performing a test that requires pressurization of a double-walled tank, the
annular space pressurization must follow the manufacturer's explicit instructions. In
some cases, not following the manufacturer's instructions will violate the
manufacturer's warranty. The annular space can very rapidly be over-pressurized due
to the much smaller volume of the annular space compared to the volume of the inner
tank. If the annular space alone requires pressurization, great care must be taken to
avoid rupture of the tank walls. When performing the test, adequate precautions
should be taken to protect people and property should an accident occur. Soaping the
67
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UST exterior wall and pressurizing the tank can only be completed as an integrity test
when the UST wall is viewable. The application to installed tanks requires excavation.
Bubble tests are very quick, typically requiring less than 1 hour for experienced
technicians.
Positive Pressure Testing
«•! iV i « 1 •!•* i • •» IMill • ir • iB-i»«»av*Baa««*Mma^ ^ _
Fundamental Operating Principle--
Two positive pressure integrity tests are performed as part of internal
inspections of USTs. A pressure change test consists of pressurizing the tank and
monitoring for change (i.e., decrease) in pressure that may be due to a hole. The
second positive pressure test is an extreme of the pressure change test. This test
consists of pressurizing the tank and looking for evidence of structural failure such as a
rupturing of the tank wall. This application of the pressure test differs from the pressure
change test only in that it is generally performed at a much higher pressure and failure
results in a rapid or nearly instantaneous reduction in pressure. A positive pressure
can be induced by pressurizing the tank with air or an inert gas, (usually Na) or by
filling it with water and topping off the tank with a water column. Tests using air or gas
as the pressurizing medium are sometimes referred to as aerostatic tests and those
using water are referred to as hydrostatic tests.
Procedure Description--
In most cases, a tank is tested by pressuring with air and monitoring for
decrease in pressure or structural failure (i.e., rupture). The test pressure and period
are determined by the specific code for which the tank is tested. When a water column
is used to pressurize the tank, a pressure change is monitored by measuring for a
decrease in the liquid column level. Appendix I lists the test requirements of the
various codes.
Before pressurizing, all tank openings must be blinded and fittings must b.e tight
and leak proof. The tank must be allowed to equilibrate (soak) for a set period of time
while under pressure, to compensate for initial temperature changes and tank
deformation. The soaking time will vary depending upon the size of the tank and the
referencing standard used for the test. The tank is considered to have a leak when a
certain percentage change in pressure has been observed as specified in the
referencing standard.20
The tank is pressurized using an air compressor or a compressed gas cylinder
with a pressure regulator. Pressure in the tank is monitored using a pressure gauge
that has full scale readings 1 1/2 to 4 times the nominal test pressure. Gauge accuracy
is traditionally poor in the lower 10-20% of the full-scale value. All pressure gauges
used during testing must be calibrated against a standard dead weight tester, a
calibrated master gauge, or a mercury column and recalibrated at least once a year,
unless specified otherwise by the referencing code. All gauges must be recalibrated
any time that there is reason to believe they are in error.20
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Method Performance--
Pressure tests are commonly performed as part of routine inspections during
the lifetime of a tank. They are easy to perform and can give a rapid indication of a
very problematic UST. In general, pressure tests are only capable of detecting
relatively large leaks (compared to bubble testing) and are seldom able to pinpoint the
location of a leak.21 Pressure tests are commonly applied during design verification,
manufacturer quality control, and before installation and following tank closure. Under
no circumstances should pressure tests be performed when product or residues are
present in the tank. . : '.'..'"". ',.'..
Several environmental factors can influence the accuracy of a pressure change
test. These include internal temperature changes, volume changes due to tank
deformation and changes in barometric pressure. Temperature and pressure of a
contained gas are directly proportional. Temperature decreases will induce,pressure
decreases. Tank deformation is a volumetric change that occurs when increased
pressure causes the tank to expand slightly. Changes in,barometric pressure will
cause a change in the measurement gauge pressure (versus absolute pressure).
Most tests will use pressure gauges that measure pressures above atmosphere
pressure (gauge pressure).20-7
For purposes of internal inspection, a high degree of test accuracy is not
normally required. Temperature, tank deformation and barometric pressure effects are
generally considered negligible or short-lived phenomenal However, the.effect of
these phenomena becomes increasingly important when testing for very small leaks or
very large tanks, due to the larger affected volume. In these cases, temperature and
barometric pressure changes may have to be monitored and their effects
compensated for in the determination of a pressure loss due to a leak.
Field Considerations-- ,
As described in the previous section (Bubble Testing), when pressurizing a
tank, particularly a double walled tank, the manufacturer's instructions should be
explicitly followed. ,..,; , :
The test conditions and environmental parameters can significantly affect the
test results and must be recorded. For example, when testing a backfilled tank, the
resistance to a leak is greater since the backfill material is in the leak path instead of
the air that would be in the leak path if the test were conducted above ground. A test
conducted after the tank has been backfilled requires greater sensitivity in the test
measurements.
When a hydrostatic test is performed, an effort must be made to completely
remove the water from the tank interior prior to filling with product. The effort required
to remove the water from the tank will depend on the quality of the product stored in
the tank and the incompatibility of the product with water.
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Vacuum Tests
Fundamental Operating Principle-- :
There are two types of vacuum tests: the pressure (vacuum) change test and the
structural integrity vacuum test. The vacuum change test is not normally performed as
part of internal inspection of tanks. In most applications the pressure change test is a
positive pressure test. The vacuum change test procedure is virtually the same as the
positive pressure change described earlier except that air is evacuated from the tank
which creates a negative pressure or vacuum. The structural integrity vacuum consists
of creating a vacuum within the tank and looking for evidence of structural failure such
as a rupturing or collapse of the tank wall.
Procedure Description--
A vacuum test is performed by creating negative pressure within the tank by
evacuating air from the tank using a vacuum pump. The test pressure and period are
determined by the specific standard for which the tank is tested. Appendix I provides a
list of test requirements as specified in various standards. Before testing, all tank
openings and fittings must be closed tightly and leak proof.
The vacuum gauges used should have scales that allow easy readings of the
vacuum change over the test range. All pressure gauges used during testing must be
calibrated against a master gauge or a mercury column and recalibrated annually,
unless specified otherwise by the referencing code. All gauges must be recalibrated
any time that there is reason to believe they are in error.20
Underwriters Laboratories Standard UL 1316 and NLPA 631 for fiberglass
tanks require that each tank should withstand, without rupture, a internal partial
vacuum according to the equation:
V = (1/2 D-i-h) x 73.33mm Hg/m
where:
V is the vacuum in mm Hg,
D is the tank diameter in meters, and
h is the maximum recommended burial depth in meters, but not less than 0.91m (3
feet).
Method Performance--
Common applications of the structural integrity vacuum test include design
verification, manufacture quality control, and testing before and following the operation
of the tank. Vacuum tests, in general, are not as accurate as bubble tests in
determining leak rate and location, however, they can provide a rapid indication of a
problematic tank.
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All of the environmental factors that influence the accuracy of positive pressure
tests also influence vacuum tests but in an inverse manner. These factors include
temperature changes, volume changes due to tanks deformation and changes in
barometric pressure. For tests requiring a high degree of accuracy and for tests on
large volume tanks, these environmental factors must be monitored and their effects
compensated for in the determination of a pressure loss due to a leak.
Field Considerations-- , .. ;
As described in the previous sections (Bubble Testing and Positive Pressure
Testing), the manufacturers instructions should be explicitly followed when
pressurizing a tank. Also as described in the previous sections, test conditions and
environmental parameters can significantly affect the test results and must be
recorded. ' " , ... • ,
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SECTION 5.0
OUTMODED METHODS
Radiography and eddy current tests are two methods of non-destructive testing
applicable to USTs. However, due to factors such as cost, waste generated, tank
geometry, and the availability of certified inspectors, these methods are no longer in
active practice for internal inspection of steel or FRP tanks. These methods do not
meet the definition of SOTA, but are discussed briefly as they are inclusive of the
current commercial practice by definition.
5.1 RADIOGRAPHY
Radiography is the practice of creating a photographic image by passing a
penetrating ionizing radiation beam (i.e., X-ray) through a specific object of interest.
The photographic image, or radiography, will allow the inspector to locate surface or
subsurface discontinuities, determine wall thickness, and identify localized corrosion
areas. After the tank has been backfilled, radiography is not feasible without
excavation.
To produce a radiograph, energy is projected through the film for an appropriate
time depending upon the x-ray intensity, object material, and the film itself. The film is
then processed (developed, fixed, washed and dried), so that the radiograph may be
illuminated and examined.3
The availability of radiography inspectors is minimal due to the intensive
training and education requirements for certification. The actual radiography
procedure is labor intensive. Radiography also generates radioactive wastes that
require proper regulated disposal and extensive permitting.22
5.2 EDDY CURRENT
Eddy current testing involves the use of alternating magnetic fields and can be
applied to any conductor (e.g., steel). The alternating magnetic fields create
circulating eddy currents in the test part. A crack in the test material obstructs the eddy
current, lengthens the eddy current path, reduces the secondary magnetic field, and
increases the coil impedance. The impedance increases with the severity of the
discontinuity.7 The eddy currents respond to surface dents, discontinuities, and
changes in wall thickness.
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Eddy current testing requires magnetization of the entire test part. This
requirement is cumbersome and, due to topology may not be feasible for larger USTs.
As with radiography, the testing procedure is labor intensive, slow, and expensive.
There is only minimal availability of certified inspectors to conduct eddy current testing.
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SECTION 6.0
EMERGING TECHNOLOGIES
Preliminary information on technically advanced methods which are emerging
in the area of UST internal inspections is being collected by RREL, EPA to assist states
and UST owner/operators in complying with future EPA regulations. Some emerging
technologies have been developed for use in other applications and are not yet
performed on underground storage tanks, for example a source of technologies that
could be adapted to internal tanks is the pressurized vessel industry. The emerging
technologies identified during the course of this project are acoustic emission,
horoscope, and microwave. Brief descriptions of these technologies are presented in
the following sections.
6.1 ACOUSTIC EMISSION
Acoustic emission testing is a non-destructive technique that is capable of
revealing the presence of latent structural cracks, lining failure, thinning, pitting,
blistering, deficient welds and corrosion by "listening" to the structure.2 The sounds
emitted by these flaws radiate throughout the structure and can be collected by
piezoelectric sensors placed on the surface of the tank. A computer then analyzes
signal severity and pinpoints the location of the leak.23 A structure can be monitored in
real-time to provide warning of impending failure. In general, this method relies on
standard acoustic emission time-signal processing, coupled with advanced random
signal correlation techniques.
Acoustic testing for leak detection is a common practice in the above ground
inspection of both steel and FRP petrochemical vessels. This same methodology has
been adapted for storage tanks as a cost-effective, in-service inspection tool.
Currently, acoustic emission technology is being applied to petroleum tank railway
cars and large aboveground tanks, by placing sensors on the outside of the vessel.
However, sensors can be applied to interior tank walls using suction cups, avoiding
the necessity to excavate the tank.
A minimum amount of training is required for the prospective technician to
perform the test. A number of vendors have developed and refined the technology for
performing acoustic emission tests on tanks and other vessels.
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Acoustic has many features indicating that it might be a promising candidate for
internal inspection. It is being used as a leak detection method for above ground
tanks. Vendors are familiar with many of the signals of stress which the
instrumentation will need to identify. Unlike all other methods currently in practice,
acoustic emission does not require the removal of product and cleaning of the tank.
This eliminates costly down time and labor charges. Additionally, acoustic emission
technology is that it is a non-destructive method. This method not only confirms the
presence of a discontinuity, but ascertains the location of the point(s) of stress.
6.2 BOROSCOPE
Boroscopes are optical instruments designed for remote visual examinations in
inaccessible areas (such as military equipment). For example, this instrument would
be used for inspecting the interstitial area of double-walled tanks and/or the structural
ribs of FRP tanks. Boroscopes are produced in several variations due to their multiple
applications. These instruments have either rigid or flexible components that are
microscopic in diameter or extendable in length. Manufacturers are now offering
boroscope instruments that may be incorporated with a high resolution video camera
and a closed circuit television system. Systems can be constructed that are
compatible with the needs of the object to be examined.
The performance of a boroscope is dependent upon the following optical
components: 1) the objective lens; 2) the relay lenses; and 3) the eye piece. The
objective lens transmits the primary image from the end of the boroscope to the relay
lens. The relay lens "relays" the primary image to the eye piece. The longer the
boroscope, the*more relay lenses required. The last relay lens generates a final
image for the human eye through the eye piece. The total magnification of the primary
image is the product of the magnification of each lens.
There are no nationally recognized standards for remote visual examinations
with a boroscope. All visual inspections are subjective, but the quality of interpretation
of results may be enhanced by the use of video recording equipment. The results of
visual examinations are dependent upon trained inspectors and the quality of their
instruments.7 The accuracy of the structural flaw measurements is dependent upon
instrument-to-object distance and the inspector's experience. Magnification is highest
at the closest viewing distances and decreases as the instrument-to-object distance
grows. Optimal surface or subsurface flaw detection in a tank would occur when the
instrument-to-object distance is minimal. This requirement creates a somewhat higher
level of effort in terms of both labor and equipment.
6.3 MICROWAVE
Microwave testing is a non-destructive testing method that involves
electromagnetic testing at frequencies in the microwave range. The microwaves are
directed to a test object and an antenna (i.e., transducer) receives response signals.
The interaction of microwaves with materials and test objects is described in terms of
75
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waves. The microwaves generated travel in straight lines, reflect, scatter and interfere
with materials and structures at a microscopic scale.25
Microwave testing is primarily applicable for internal inspections of FRP tanks.
This testing method may detect surface and subsurface flaws as well as determine
physical characteristics of the FRP material (e.g., thickness, moisture, state-of-cure).
Microwave testing may be used to detect surface discontinuities of steel tanks and,
under certain conditions, wall thickness as well. Thickness determination of steel
tanks is complicated and requires the use,of multiple microwave instruments. ,;
Microwaves and ultrasonic waves are similar in nature but not in ability. For
example, ultrasonic waves can penetrate steel; microwaves cannot. This ,
characteristic limits the use of microwave testing forsteei tanks. Microwave testing can
only be used to detect surface discontinuities of steel tanks. Ultrasonic transducers
require direct contact with the test object; microwave transducers dp not One major
distinction between ultrasonic waves and microwaves is the wave velocity. The slower
ultrasonic waves with smaller spatial extents allow the inspectors to discriminate;
interferences. However, the higher-velocity and non-contacting transducer permits
faster inspections.25
Microwaves are most effective with FRP materials due to phase measurements
and polarization of the reflected waves, information about internal flaws, material
orientation and structure, thickness, moisture content, and state-of-cure of the FRP
tank. The data generated can be displayed using holographic techniques or other
image reconstruction processes.25 . ,
Microwave testing is not commonly used, due to the low availability of non-
destructive testing engineers and technicians who are familiar with the technology.
However, with the current development of off-the-shelf instruments that incorporate ^
microprocessors, microwave testing is being improved and simplified.
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REFERENCES
1. Sattler, F. J. Finding Below Surface Defects With Non-Destructive Testing.
Chemical Engineering, September 1989, pp. 161-167.
2. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,
1989 Edition. Section V, Non-Destructive Testing: Standard Practice for
Thickness Measurement by Manual Contact Ultrasonic Method. ASME SE-797,
New York, New York July 1989.
3. Halmshaw, R. Non-destructive Testing. Edward Arnold Ltd., Baltimore, Maryland,
1987.
4. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,
1989 Edition. Section V, Nondestructive Testing: Recommended Practice For
Ultrasonic Pulse-Echo Straight-Beam Testing By the Contact Method. ASME SE-
114, New York, New York. July 1989.
5. National Leak Prevention Association. Internal Inspection, Repair and Lining of
Steel and Fiberglass Storage Tanks. NLPA 631, Second Edition, Cincinnati,
Ohio, September 1988.
6. National Leak Prevention Association. Internal Inspection of Steel Tanks for
Upgrading with Cathodic Protection Without Internal Lining. NLPA 632, Draft
Report, Cincinnati, Ohio, January 15,1988.
7. Mix, P. E. Introduction to Non-Destructive Testing, A Training Guide. John Wiley
& Sons Inc., New York, New York 1987.
8. Letter, J. L. Editor-in-Chief. Underground Storage Tank Guide. Thompson
Publishing Group, Washington, D.C., March 1990.
9. American Petroleum Institute. Interior Lining of Underground Storage Tanks. API
Recommended Practice 1631, Washington, D.C., December 1987.
10. National Association of Corrosion Engineers. Discontinuity (Holiday) Testing of
Protective Coatings. NACE Recommended Practice RP0188-88, Houston, Texas,
July 1988.
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11. National Association of Corrosion Engineers. High Voltage Electrical Inspection
of Pipeline Coatings Prior to Installation. NACE Recommended Practice RP0274,
Houston, Texas, August 1974.
12. Elcometer, Inc. Non-Destructive Coating Thickness Measurement Mechanical
Gauges. Rochester Hills, Michigan, 1989.
13. National Leak Prevention Association. Personal Communication with Tony
Reich. Cincinnati, Ohio, January 15 & 20,1990.
14. American Society for Testing and Materials. Standard Test Method for
Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor. ASTM
Standard 02583-87, Philadelphia, Pennsylvania, January 1989.
15. Tank Liners, Inc. Safety, Testihg and Application Standards. Hillsboro, Oregon,
Undated.
16. Elcometer, Inc. Non-Destructive Coating Thickness Measurement Mechanical
Gauges. Rochester Hills, Michigan, 1989. .
17. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,
1989 Edition. Section V, Non-Destructive Testing: Article 9, Visual [Examination.
New York, New York, July 1,1989.
18. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,
1989 Edition. Section V, Non-Destructive Testing: Standard Practice for Liquid
Penetrant Inspection Method, SE-165, New York, New York, July 1,1989.
19. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,
1989 Edition. Section V, Non-Destructive Testing, Standard Practice for
Magnetic Particle Examination, SE-709, New York, New York July 1,1989.
20. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,
1989 Edition. Section V, Non-Destructive Testing: Article 10, Leak Detection.
New York, New York, July 1,1989.
21. Dallum, B. J. Sensitivity of Leak Detection Methods: Vacuum and Soap Bubble
Testing Prior to Installation. O/C Tanks Corporation, Technical Report 643,
Conroe, Texas, April 3,1989.
22. Non-Destructive Testing Association. Personal Communication with Ron Sever,
Columbus, Ohio, January 17,1990.
23. Eleftherion, P. M. Tank Bottom Testing: The AE Approach Unpublished Paper.
Physical Acoustics Corporation, Princeton, New Jersey, undated.
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24. Wolske, B. K. Acoustic Emission Test Improves Tank Car Safety. Chemical
Processing, March 1988. Reprinted by Physical Acoustics Corporation,
Princeton, New Jersey.
25. Bahr, A. J. Microwave Nondestructive Testing Methods. Gordon and Breach
Science Publishers, New York, New York, 1982.
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APPENDIX A
TANK EMPTYING AND CLEANING
NOTE: The material in this appendix has been excerpted from Background Report
on Underground Storage Tank Closure: Current Practices
(Prepared for U.S. EPA by PEI Associates, Inc., and
Midwest Research Institute, 1988).
The regulations promulgated by EPA as well as the guidance documents
issued by industry require tanks to be "emptied" prior to tank entry or cleaning. The
term "empty" is not well defined and may represent from 1 to 7 inches of residual fuel,
water, and residues. The two methods used for removing petroleum products from
USTs are pumping and waterflooding; pumping is the most commonly-used method.
These methods are covered in AP11604 and API 2015. The salient features of the
guidelines are presented below.
Pumping
Pumping is used to remove liquid-phase petroleum products but can also be
used to remove some residual material (e.g., sludge or sediment.). Some information
indicates that pumps should be shut off when sludge is encountered while other
information indicates a substantial amount of sludge can be pumped out. It appears
that the amount of residual material removed depends at least in part on me type of
system used and the nature of the product being removed.
These products are usually pumped down to the lowest possible level in the
tank with explosion-proof or air-driven pumps. The suction line that extends from the
pump is manually placed through any opening, commonly the fill tube. In some
instances the suction line is routed along the tank bottom to remove remaining liquid,
as well as some residue. Pumping operations remove a large amount of petroleum
products, but due to suction line design limitations, not all of these products can be
removed by this method. Pumping systems that withdraw products through the fillpipe
are limited by the fillpipe length and may leave as much as 15-17.5 cm (6-7 inches) of
residual material in the tank.
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Water Flooding and Pumping
Pumping can be augmented by water-flooding. Water-flooding is a procedure
whereby water is added through the fill pipe to remove products less dense than
water. Water is introduced into the bottom of the tank to float liquid and residual
hydrocarbons to the pump-out connection. The pumpout line is located above the tank
bottom to remove the floating products. The rate that water is introduced into the tank
is less than the pump-out rate. By introduction of water at the bottom of the tank, the
risk of generating static electricity is decreased (due to a lower amount of friction) than
when introduced at some distance from the tank bottom. Residues denser than water
will not float and therefore are not removed by this process. Dense residues are
removed during tank cleaning.
A major disadvantage to this technique is that the water used during removal
operations may be considered to be hazardous waste. If it is treated as a hazardous
waste; the waste water must be managed in an approved RCRA Treatment, Storage,
or Disposal (TSD) facility. In order to limit the amount of water that must be hauled to a
TSD facility, many contractors minimize the volume of water used to flood the tanks or
reuse the same water in flooding other tanks. In some cases this may reduce the
effectiveness of product removal. However, not all states or municipalities consider
tank residues or waste water to be hazardous, and may be separated and treated as a
waste oil rather than a hazardous waste.
TANK CLEANING
After underground petroleum storage tanks have been emptied by a contractor,
they must be cleaned prior to inspection. A variety of methods may be used
depending upon the type of residuals remaining in the tank.
Types and Amounts of Residues
Following product removal and tank "emptying," a composite of residual
material remains in the tank. Based on phone interviews with tank lining contractors
and cleaning firms and a limited amount of published literature, the fundamental
components or types of residuals left in a tank appear to be: residual product or fuel;
residual water; sediment; tank rust and scale; tank sludge; and micro-organisms.
Residual product or fuel remains after product pumping and removal operations
have been completed. Water that remains in the tank will occur in a separate phase,
and may also be partly dissolved and suspended in the fuel. Tank sediment can
consist of fuel impurities introduced during tank filling, and rust particles and scale that
may settle over time. Tank scale consists primarily of corroded or rusted interior tank
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surfaces that probably oxidized when in contact with water. Tank sludge is semi-solid
material that may contain scale and sediment as well as water and by-products of the
interaction or reaction of these residues.
The quantity of material that remains after initial product removal generally
cannot be estimated because tank cleaners do not distinguish residue type. Tank
cleaners commonly measure the amount of residual material that is removed to the
drums that are filled during tank cleaning. Total residues may vary based on a number
of factors, discussed in following subsections. Tanks that originally contained
unoxygenated gasoline fuels but were changed to oxygenated fuels may have as
much as 170 gallons of residual material removed from a tank.
Location of Residues
Scale occurs in the upper portion of the tank while sludge and residual fuel and
water lie in the lower portion of the tank. Sludge has been observed in a number of
tanks not as residue on the bottom center of the tank but rather in positions of 5 and 7
o'clock. Corroded areas above the maximum level of sludge-covered areas are
referred to as "sludge-lines" or fingers and may possibly indicate the past location of
sludge as it settled during formation. Overall, less sludge or "sludge-lines" have been
noted in lined or FRP tanks than in steel tanks.
Scale and sediment are also more prevalent in steel tanks than fiberglass
tanks. Some sediment and scale are usually incorporated into the sludge during its
formation. Scale forms on the tank walls and can eventually accumulate in the
residual "bottoms." Sediment usually accumulates in the lower part of the tank.
Variables Affecting_Eroduct Removal and Amount of Residues
As noted above, a number of variables influence the nature and amount of
residues that remains in an LIST after tank emptying operations are complete. Initial
design constraints can limit the amount of product removed from the LIST system.
• Tank Tilt - Underground storage tanks are designed to be installed with a
slight tilt or slope in the direction of the fillpipe (the principal outlet by which
product is removed when emptying and cleaning). When a tank is
improperly sloped away from the fillpipe, residual product, water, and other
material collects at the opposite end of the tank. An improperly sloping tanl
may result from settling or incorrect installation and can make product
removal and cleaning operations less effective. In some cases the pump
suction line is fed in through the fillpipe or turbine pump hole and routed
along the tank bottom to remove product in the downslope portion of the
tank. It is not known which method is the most commonly used technique.
* Fuel Type - A general relationship exists between the amount of residual
material and fuel type. Higher molecular weight, more viscous fuels (e.g.,
diesel) tend to have more residual material than less viscous, lighter-
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molecular weight fuels (e.g., gasoline). The influence of additives in fuels is
not currently known. However, observations by owner/operators and firms
that clean tanks (e.g., tank lining contractors) have indicated that a change-
in-service from unoxygenated to oxygenated fuel (i.e., those with additives
such as ethanol) can remobilize existing sludge and residues.
• Tank Type and Age - Steel tanks tend to contain more residues than
fiberglass tanks, have been in use longer than fiberglass tanks, and tend to
internally corrode at a higher rate. Fiberglass tanks may be subject to
internal corrosion if sulfur is present in the residual aqueous phase.
• Proper Filling and Maintenance - Filling and maintenance procedures can
affect the total amount of foreign material or sediment that may be introduced
and the total water content in tank bottoms.
• System Through-Put/Dormancv - Tank systems that have low through-put
and remain relatively dormant (i.e., those infrequently pumping fuel in and
out) can allow time for residues to form, settle, and accumulate. Tank
systems with higher through-put keep solid particles suspended and
dispersed in the product and thus minimize settling and density segregation.
« Tank Location - Tank temperatures are generally lower for tanks located
below the water table and may promote water condensation in the tank,
oxidation of upper tank surfaces, as well as affecting microbial activity in the
tank.
The effect of these variables on residue formation has not been systematically
investigated and could provide valuable constraints that could be used to predict and
reduce residue generation.
Cleaning Methods
A wide range of methods and techniques are used in cleaning residues from
UST systems. The selection of a cleaning method apparently depends on the ultimate
fate of the tank. For example, contractors that line tanks for reuse indicate that a tank is
not "clean" (or ready for lining) until it has been sand blasted, while contractors
preparing tanks for disposal have indicated that a simple, single rinse with low-
pressure water is adequate.
At a minimum, state and local agencies require removal of combustible vapors
in the tank before transport for safety reasons. Residues remaining in a tank for a
period of a few hours after venting or purging may volatilize after a tank has been
"emptied." Vapors from the volatilized contamination in the residue can make the tank
hazardous for transport. Some contractors minimize the risk of later volatilization by
rapidly completing the cleaning, transport, and disposal operation rather than initially
removing more of the volatile residues in the tanks.
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There is also no consensus for determining when a tank is clean. Tanks may
be considered clean after a single rinse with low pressure water. Some jurisdictions
require multiple rinsing with high pressure water. Rinseate which is no longer
contaminated after multiple rinses is another criteria for measuring tank cleanliness.
Visual inspection may be adequate to confirm cleanliness in some cases, while an
analytical determination may be necessary in other cases. The remainder of this
section will discuss the methods of cleaning tanks, including:
• Entry and physical removal;
• High pressure water;
• High pressure steam; ;
• Cleaning agents; and
• Fuel cleaning.
Inerting--
To inert a tank, vapors from an UST are purged and an inert gas (e.g., COa and
N2) is introduced at low pressure through a single tank opening at a point near the
bottom of the tank at the end opposite the vent. Introducing compressed gas into the
tank may create a potential ignition hazard from the generation of static electricity.
Explosions have resulted from discharging CO2 fire extinguishers into tanks in the
flammable range. Solid dry ice is the^referred form of CO2-
Physical Removal of Residues
API publications 2015 and 2015A give general guidance on tank entry. API
publications 2201 and 631, and NLPA 631 provide guidance for cutting nnanways in
older tanks. Tanks are continually ventilated or purged during tank entry and physical
removal of residual material.
During tank entry, sludge, scale, sediment and residual petroleum products may
be physically removed by several techniques depending on tank design (e.g., number
and size of openings, size of tank). Physical removal of residues is usually
accomplished by:
• scraping of side scale to dislodge flakes;
• shoveling sludge, sediment, and scale into buckets and/or drums; or
• sandblasting.
Non-sparking scrapers and shovels are generally used (i.e., aluminum, brass, wood).
Once the tank has been scraped and shoveled, it is usually rinsed with water. Other
cleaning methods may include rinseates, such as detergents, solvents, high pressure
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water, or steam. Cleaning is complete once the tank has been washed or swept and
the remaining moisture in the tank has been removed by squeegees, rags, or sawdust.
Sandblasting is commonly used to abrasively remove scale or resistant sludge
deposits. The sandblasting process can produce a substantial amount of dust above
ground from the manway. A simple system used to control the dust consists of placing
alternating layers of perforated plastic sheet tubing across the manway. The tubing
directs the dust out of the perforations and is dampened by an adjacent waterline. A
sand slurry mixture is produced in this process and is usually allowed to runoff with the
excess water.
Removal of Residues by Low Pressure Water
Cleaning USTs with low pressure water is sometimes used rather than tank
entry and physical removal. Water is sprayed in from outside of the tank. The cleaning
process consists of rinsing with spray from a garden hose at low line pressure. The
rinseate and suspended residual material is then pumped out. The tank may or may
not be inclined in a direction to facilitate the removal of rinseate water and residual
material. There is no current objective information on the effectiveness of this method.
Many contractors do not confirm tank cleanliness and simply rinse once and call the
tank clean. , „ „
Removal of Residues bv High Pressure Water
Cleaning with high pressure water can be»used in lieu of physical removal
methods. The water is sprayed from outside of the tank using a hand-held nozzle or
agitating nozzle under enough pressure to physically dislodge resistant deposits of
sludge and scale (approximately 25,000-40,000 psi). Agitation with high pressure
water can generate static electricity which may act as a possible ignition source; thus
most tanks are purged or inerted with nitrogen or carbon dioxide (dry ice) prior to
cleaning. Water sprayed under high pressure (required to accomplish adequate
cleaning) can also cause serious injury. In some cases, for single-wall steel tanks,
high pressure water is used to dismantle the tank itself.
The volume of water that is required to clean the tank is generally less than that
required for simple low pressure rinsing. Thus, the total amount of rinseate water that
has to be disposed of is limited. Generally the volume of water generated is less than
1/3 of the total volume of the tank. In some jurisdictions tanks are rinsed three times
(i.e., triple-rinsed). Each wash water rinse is monitored for total petroleum
hydrocarbons (TPH) to determine if an acceptable level of cleanliness has been
achieved. The tank may have TPH levels less than the rinseate, and while the
rinseate may be considered unacceptable or corftaminated (e.g., <80 ppm TPH), the
tank will be considered clean. Monitoring of rinseate causes logistical problems and
increases both the time and cost of cleaning tanks. Other methods for determining
tank cleanliness involve visual inspection of rinse water as it is removed or visual
inspection of the tank surface. The particular method used to determine tank
cleanliness is dependent upon local or state regulatory requirements.
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Bemoval of Residues by High Pressure_Steam
Steam cleaning uses the abrasive action of pressure and combined with
temperature to dislodge sludge and scale from tank walls and to dissolve residual
hydrocarbon constituents that are soluble in water at elevated temperatures. High
pressure steam is sprayed into the tank from the outside and is generally done at
centralized facilities because of the need for specialized equipment and rinseate
runoff collection.
During cleaning, a hose is inserted through an anchor on a tank opening, which
discharges 200°C (400°F) steam at 300 psi. The hose agitates under pressure and
scours the tank interior with high velocity steam. Excess rinse water condensate and
dislodged sludge and scale are removed through tank openings. The rinse water may
or may not be separated from the tank residues and is treated according to RCRA
regulations. In some cases it is recycled or reused to clean other tanks.
Removal of Residues Using Special Cleaning Agents
Cleaning methods that involve the use of cleaning agents for dislodging and
partially dissolving some of the residual deposits may be performed from outside of the
tank. A solvent stream directed through open manways or rotating nozzles, agitators,
and other similar devices, has been used to dislodge sludge and scale for pumping
and removal. Two types of cleaning agents are commonly used:
• Caustic/acidic agents; and
• Biodegradable agents mcluding solvents, degreasers, and emulsifiers.
Caustic and acidic agents such as trisodium phosphate (TSP) are used as a rinse
(usually after the water rinses) to chemically leach lead from scale and rusit adhering to
the inside of the vessel walls. These agents lower the overall lead content of steel
tanks to enable the steel to go to a scrap dealer without further cleaning. TSP is a
strong cleaning agent and can be potentially hazardous. In some instances, it is used
instead of sandblasting for preparing a tank for lining. In general, these agents are
considered to be too harsh for tanks of marginal structural integrity.
Biodegradable solvent cleaners and degreasers are more common tank
cleaning agents. Some biodegradable agents are water soluble cleaner-degreasers
formulated with an organic nonpetroleum hydrocarbon solvent and multicomponent
surfactant-emulsifier. Rinse solutions that have been put into above ground
separation tanks or holding ponds after cleaning can undergo phase separation,
allowing residual hydrocarbons to rise to the surface. Other biodegradable agents or
emulsifiers containing no solvents. When applied with agitation, they break up oil
residues and form a nonflammable emulsion that can be washed easily away. Some
of these agents are combustible while others actually reduce the risk of combustion by
lowering the flashpoint of the mixture. These biodegradable cleaners have been
successfully used to clean tanks containing more viscous fuels, such as diesel fuels.
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Removal of Residues by Fuel Cleaning
An in SilU cleaning method involves recirculating fuel already in a tank through
a filtering system which then returns the fuel as a pressurized stream via a mobile
nozzle. The sprayed fuel hydraulically agitates tank sediments and cleans the tank.
Tank residues (sludge, scale, etc.) are pumped out along with recirculated fuel. Thus,
the end result is a clean tank containing clean fuel. The process is continuous and
requires multiple cycling of the entire tank contents. Tanks that contain a large amount
of sediment may require extended periods of recycling (e.g., as long as a week).
If a tank is tilted away from the fillpipe the fuel sprayer nozzle is not as effective
in cleaning the downslope portion of the tank. This cleaning method has been
observed to merely clean paths in tanks tilted away from the fillpipe and does hot
remove all of the residues. ;,
High temperatures in the surrounding environment can adversely affect the
development of the vacuum required to remove product and residues. The fuel heats
up and can volatilize during the recycling/filtration process. For fuels that have a high
vapor pressure, it is sometimes difficult to maintain the proper vacuum under these
higher temperatures. -.'•-, ..••*•
The amount of residues that are filtered from a particular fuel may vary
considerably depending on a number of factors noted earlier. Estimates for the
amount of residues removed from a tank containing gasoline during filtration are on
the order of 50 gallons of sediment per 50,000 gallons of fuel. However, some
residues are not cleaned out of the tank by this process. The quantity of material
remaining in a tank is a function of the design specifications of the pressurized stream
vacuum or pumpout line and the degree to which side scale, sludge and sediment are
mobilized from the tank walls.
On-Site Versus Off-Site Cleaning
Certain states or municipalities require cleaning of underground storage tanks
on-site prior to transport. Generally, the costs associated with off-site cleaning are
lower than those for on-site cleaning. Cleaning methods generally used on-site
include those used in situ prior to tank removal or used on tanks that have been
already removed. The fuel-cleaning method is strictly used for tanks in place.
Cleaning methods that are commonly used at off-site facilities include high pressure
water, high pressure steam and caustic/acidic solutions such as TSP. These methods
can also be conducted on-site if adequate runoff collection or pumping equipment is
used.
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REFERENCED DOCUMENTS
1. American Petroleum Institute. 1987. Recommended Practice for Removal and
Disposal of Used Underground Petroleum Storage Tanks. Publication 1604.
Washington, D.C.
2. American Petroleum Institute. 1985. Cleaning Petroleum Storage Tanks
Publication 2015. Washington, D.C. ,
3. American Petroleum Institute. 1985. Procedures for Welding or Hot Tapping on
Equipment Containing Flammables. Publication 2201. Washington, D.C.
4. American Petroleum Institute. 1983. Interior Lining of Underground Storage
Tanks. Publication 1631. Washington, D.C., - - , :-
5. American Petroleum Institute. 1982. A Guide for Controlling the Lead Hazard ,
Associated with Tank Entry and Cleaning. Publication 2015A. Washington, D.C.
6. Camp Dresser & McKee Inc. 1988. Evaluation of the Technical Aspects of UST
Closure. Boston, MA. Prepared for the U.S. Environmental Protection AgencyJrs
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APPENDIX B
TANK ISOLATION AND
TANK SURFACE PREPARATION
TANK ISOLATION
Before any work on the exterior or interior surfaces Of tanks begins, :tanks must
be isolated. An inspection is required to determine how the tanks can be separated
from other tanks and isolated from other fuel sources. If a tank is equipped with a vent
manifold, fill lines or syphon assembly, necessary measures must be taken to isolate
each tank. The vent for the tank being inspected must be isolated from vents for other
tanks which may still be in service. This separation may require a temporary separate
vent for the subject tank. All electrical switches supplying current to submerge pumps
and/or other equipment connected to the tank should be disconnected and locked.
Tank isolation prior to venting and entry is very important.
The following are procedures for tank isolation and preparation before tank lining or
repair of existing lining:
• Remove stored product from the tank to point less than one inch on the tank
bottom.
• Completely isolate and plug the product line at the pump to prevent product
from leaking into surrounding soils.
• If tanks are manifolded, the vent lines must be removed and plugged, the
ball check valve should be removed.
• Disconnect electricity to the pump. Lock-out the power supply. Remove the
pump.
• Remove the manway cover. If there is no manway, excavate an opening to
the tank dome. Shore the excavation to prevent any collapsing of the
excavation walls (cave-ins).
• Locate and open as many fittings in the tank as possible.
• Remove the drop and any siphon tubes.
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• Install the venting apparatus. The fumes must be vented at least 2 meters (6
feet) above grade.
• Before starting the venting process, take an initial tank reading (oxygen and
fumes) to establish a reference point.
• Vent the tank and monitor air quality within the tank every 15 minutes.
TANK SU RFACE PREPARATION
i
Tank walls must undergo surface preparation prior to any inspection activity.
This surface preparation consists of grinding away scale or loose glass fibers using
approved abrasive blasting materials and equipment. Safety precautions described
in Appendix A and API Publication 2077 (Ignition Hazards Involved in Abrasive
Blasting of Tanks in Service) should be followed during tank surface preparation.
Before and during abrasive blasting, the tank must be checked with a
combustible gas indicator to ensure that no flammable vapors have developed in the
tank. Abrasive blast operators should wear approved helmets connected to sources of
clean air. Bonding is recommended by FPTPI before internal inspection.
Personal safety and clothing requirements must comply with safety
requirements for sandblasting in a confined space. Separators and traps should be
used to remove oil and water from compressed air. Following completion of the
abrasive blasting operation, the surface shall be brushed with a clean hair, bristle or
fiber brush, and blown with compressed air.
The tank should be sandblasted to at least a near white (SSPC-SP10) metal,
removing all residues from plugged holes and sludge from all pits. Debris from the
sandblasting operations can be vacuum pumped. Cleaning should continue until the
tank Interior is free of all visible oil, grease, dirt, dust, mill scale, rust and paint.
REFERENCED DOCUMENTS
1. Midwest Research Institute and PEI Associates, Inc. "Background Report on
Underground Storage Tank Closure: Current Practices." Prepared for the U.S.
Environmental Protection Agency, Office of Underground Storage Tanks,
Washington, D.C. Draft 1988.
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APPENDIX C
STANDARDS INVESTIGATED
ACT-100
API 510
API 1631
API 2200
ASTM D 2563-70
ASTM D 2583-87
ASTM E 214-68
ASTM E 268-84a
ASTM E 269-84a
ASTM E 500-85
ASTM E 610-82
ASTM E 797
ASTM D 2563-70
Specifications for the Fabrication of FRP Clad Underground
Storage Tanks
(Association for Composite Tanks)
Pressure Vessel Inspection Code - Maintenance Inspection,
Rating, Repair, and Alteration
(American Petroleum Institute)
Interior Lining of Underground Storage Tanks
Repairing Crude Oil, Liquified Petroleum Gas, and Product
Pipelines
Recommended Practice for Classifying Visual Defects in Glass-
Reinforced Plastic Laminate Parts
(American Society for Testing and Materials)
Test Method for Indentation Hardness of Rigid Plastics by
means of a Barcol Impressor
Recommended Practice for Immersed Ultrasonic Testing by the
Reflection Method Using Pulsed Longitudinal Waves
Definitions of Terms Relating to Electromagnetic Testing
Definitions of Terms Relating to Magnetic Particle Examination
Terminology Relating to Ultrasonic Testing
Definitions of Terms Relating to Acoustic Emission
Practice for Measuring Thickness by Manual Ultrasonic
Recommended Practice for Classifying Visual Defects in Glass-
Reinforced Laminates and Parts Made Therefrom
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ASTM E165-80
ASTM E 270-84
NACE RP0184-84
NACE RP0188-88
NACE RP0274-74
NACE RP0287-87
NACE RP0288-88
NFPA 30
NLPA 631
NLPA 632
SSPC-SP 10
sti-Ps®
UL58
UL1316
Practice for Liquid Penetrant Inspection Method
Definition of Terms Relating to Liquid Penetrant Inspection
Repair of Lining Systems
(National Association of Corrosion Engineers)
Discontinuity (Holiday) Testing of Protective Coatings
High Voltage Electrical Inspection of Pipeline Cositings Prior to
Installation
Field Measurement of Surface Profile of Abrasive Blast
Cleaned Steel Surfaces Using a Replica Tape
Inspection of Linings on Steel and Concrete
Flammable and Combustible Liquids Code
(National Fire Protection Association)
Spill Prevention, Minimum 10-year Life Extension of Existing
Steel Underground Storage Tanks by Lining Without the
Addition of Cathodic Protection
(National Leak Prevention Association)
Internal Inspection of Steel Tanks for Upgrading with Cathodic
Protection without Internal Lining
Surface Preparation Specification No. 10 - Near-White Blast
Cleaning
(Steel Structures Painting Council)
Specification for Sti-Ps® System of External Corrosion
Protection of Underground Storage Tanks
(Steel Tank Institute)
Steel Underground Tanks for Flammable and Combustible
Liquids
(Underwriters Laboratories Inc.)
Glass-Fiber-Reinforced Plastic Underground Storage Tanks for
Petroleum Products
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APPENDIX D
INTERNAL INSPECTIONS DURING TANK REMANUFACTURE
A relatively recent development in tank overhauling is the practice of
"remanufacturing" tanks for reuse. The term "remanufacturing" specifically refers to
those activities designed to upgrade previously used tanks in accordance with Federal
regulations which prescribe performance standards. Some tank manufacturers view
remanufacturing as field service activities such as repairs or lining applications. These
activities "recondition" the tank to prolong its life span and involve similar procedures
as those done in tank manufacturing. However, the term "remanufacturing" as viewed
in this report is not reconditioning tanks on-site for continued use and regulatory
compliance, but rather reconditioning tanks that have been removed and would
otherwise be sent for disposal in a junkyard, scrapyard, or regulated landfill or
recycled.
Tank remanufacturing is primarily performed on steel tanks. In this process, the
interior and exterior surfaces of the steel tank are sandblasted and inspected. After the
internal and external inspection, the tank interior and exterior surfaces are laminated
or "cladded" using FRP material. The FRP application is performed within 12 hours of
the sandblasting process.
Table 11 provides a list of the inspections performed during the remanufacturing
process.
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TABLE 11. REMANUFACTURING STEEL/FRP COMPOSITE TANKS
Wall Thickness Determination
a. Ultrasonic Test, or
b. Hammer Testing
Tank Discontinuity Inspection
a. Visual Examination, or
b. Liquid Dye Penetrant, or
c. Magnetic Particle
Structural Integrity Inspection
a. Pressure Test
Tank Lining Integrity
a. Dry Film Thickness, and
b. Holiday Test
Structural Integrity
a. Bubble Test
===========
The Association for Composite Tanks (ACT) is primarily responsible for the
standards and specifications of tank remanufacturing for reuse. The organization has
developed a standard (ACT 100) for inspections and qualifications for
remanufacturing tanks and is currently lobbying with Underwriters Laboratories (UL)
for a new label for remanufacturing tanks that meet UL58 standards. ACT is
developing a standard for tank remanufacturing (ACT 200) that addresses inspection
requirements, remanufacturing procedures, and quality assurance. This standard is
essentially a revision of ACT 100, but it also incorporates the UL labelling procedure
and ACT tank certification.
At this writing, tank remanufacturing is a rapidly evolving business area,
preceding a comprehensive research effort in this study. Market growth is attributed to
the decreasing numbers of junkyards, scrap dealers and regulated landfills willing to
accept tanks for disposal. The disposal of tanks that do not meet current Federal
performance standards is costly to the owner/operator and poses a potential
environmental liability. Tank remanufacturing provides a cheaper alternative. Rather
than risk the liability of becoming an PRP at an improperly managed landfill or
junkyard, the owner/operator may have his tank remanufactured and experience the
following advantages:
1. A tank that is compatible with petroleum products, additives and alcohol
blends such as M-85,
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2. No complicated backfill procedures,
3. A tank with the structural strength of steel and the exterior corrosion
resistance of FRP, and
4. No post-installation requirements such as monitoring.
For further information on remanufacturing activities, contact:
Mr. Bob Holland
Executive Vice President
Association For Composite Tanks
Baltimore, MD 21211
301/235-6000
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APPENDIX E
SAFETY PRECAUTIONS
In this appendix, EPA and its contractors (COM, COM FPC, and PEI) are not
undertaking to meet the duties of employers, manufacturers, or suppliers to warn and
properly train and equip their employees, and others exposed, concerning health and
safety n'sks and precautions, or to fulfill their obligations under local, state or Federal
laws.
Information concerning safety and health risks and proper precautions with
respect to particular materials and conditions should be obtained from the employer,
the manufacturer or supplier of that material, or the applicable material safety data
sheet. In addition, the tank inspector needs to consult publications by API, NFPA,
NIOSH, and OSHA as well as Federal, state, or local regulations regarding flammable
and combustible liquids. Any safety and testing equipment used during internal
inspection should be operated by qualified people who understand how to use and
maintain the equipment.
HAZARDOUS ASSESSMENT
A variety of safety hazards exist when internally inspecting USTs. All personnel
working within the established exclusion zones should be familiar with the hazards
associated with chemical exposure, physical safety, an explosive atmosphere and an
oxygen-deficient atmosphere. This section outlines the chemical and physical
hazards, and the associated procedures and protective and monitoring equipment that
can reduce these hazards.
Chemical Hazards
Information concerning safety and health risks and proper precautions for
particular materials and conditions should be obtained from the employer, the
manufacturer or the supplier of that material, and the material safety data sheet.
Government agencies are additional sources of information. Toxicity considerations
for substances likely to be found in underground petroleum storage tanks are
described below. . • ,
Benzene - High occupational exposure to benzene has been associated
with various human blood disorders, including an increased risk of
leukemia. Very high levels have also been known to affect the central
nervous system. Benzene administered by mouth has induced cancer in
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laboratory animals in long-term tests. Benzene is rapidly absorbed through
the skin. The American Conference of Government industrial hygienists
(ACGIH) recommends a Threshold Limit Value (TLV) for benzene at 10 parts
per million time-weighted average, with a short-term exposure limit of 25
parts per million. The Occupational Safety and Health Administration
(OSHA) stipulates an 8-hour time-weighted average for benzene of 10 parts
per million with an acceptable ceiling concentration of 25 parts per million
and an acceptable peak of 50 parts per million for 10 minutes (29 CFR
1910.1000, Table Z-2), OSHA's Occupations Safety and Health Regulations
should be checked for the current TLV.t
• Tetraethyl Lead - Exposure to tetraethyl lead can cause diseases of the
central and peripheral nervous systems, the kidney, and the blood. Skin
absorption of this compound is a major route of entry into the body. The
ACGIH recommended time-weighted average is 0.1 milligrams per cubic
meter for general room air. Biological monitoring is essential for personnel
safety. The OSHA standard is 0.075 milligrams per cubic meter.
• Epoxv Compounds - The most commonly encountered toxic effects
associated with use of epoxy compounds are dermatitis, eye irritation, and
pulmonary irritation. Systemic effects in man are uncommon. Some of
these compounds have produced tumors in laboratory animals, generally by
dermal application.
Inhalation of Vapors. Accidental Ingestion. Dermal Absorption of Liquids and Solids
Symptoms
- Intoxication-like behavior
- Dizziness
- Excitement
- Unconsciousness
• Treatment
- Remove individual to fresh air
- Give oxygen, if necessary
- Give respiratory assistance if breathing has stopped
- Seek prompt medical attention
Health Precautions .
When working with petroleum substances:
1. Avoid skin contact.
2. Avoid inhaling vapors.
3. Keep petroleum liquids away from eyes, skin, and mouth; they can be
harmful or fatal if inhaled, absorbed through the skin, or ingested.
4. Use soap and water to remove any petroleum product that contacts skin.
5. Do not use gasoline or similar solvents to remove oil and grease from skin.
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6. Promptly wash petroleum-soaked clothes.
7. Properly dispose of rags.
8. Keep work areas clean and well ventilated.
9. Clean up spills promptly.
Physical Hazards
Physical hazards likely to occur during operations include the following:
• Fire Hazard
• Oxygen-Deficiency (Confined Space entry)
• Heat Stress
These physical hazards are described below along with safety precautions.
Rre Hazard--
Most UST removals will involve flammable vapors from products stored in the
tank and from accumulated residues left in the tank even after it has been pumped
dry. Be aware of the basic fire triangle: fuej, oxygen, ignition source. All three points
of the triangle are necessary to support combustion. These three elements need to
be recognized, evaluated, and controlled to make a safe work place and to avoid
disaster. Safe working operations require continuous attention to these potential
hazards to eliminate or reduce the risk of explosion.
Rre Prevention-
To reduce or eliminate fire hazards, one of the three elements must be removed
or controlled. Control methods are summarized for ignition sources, fuel, and oxygen.
If operations require the use of equipment that may become ignition sources
(e.g., abrasive blasting), the tank must be ventilated in order to reduce the flammable
(or combustible) vapors (the fuel in the fire triangle) below the lower flammable or
explosive limit or (L.F.L or LE.L). Ventilation equipment, such as venting eductors,
can be used to reduce the flammable (or combustible) vapors. In cases where tank
entry is not necessary, fire hazards can also be controlled by reducing the amount of
oxygen in the tank (e.g., flooding the tank with inert gases such as nitrogen).
Eliminate Sources of Ignition--
1. Flammable (or combustible) vapors are likely to be present in the work area.
The concentration of vapors in or around the tank may reach the flammable
(or explosive) range before venting is completed and a safe atmosphere is
reached. Precautions should be taken to:
a. eliminate all potential sources of ignition from the area.
• remove all smoking materials
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2.
3.
• remove nonexplosive-proof electrical and Internal combustion
equipment and internal combustion equipment.
• isolate tank from contaminated soils.
b. prevent the discharge of static electricity during venting of flammable
vapors.
c. prevent the accumulation of vapors at ground level
The process of introducing the compressed gases into the tank may create a
potential ignition hazard due to the development of static electrical charges.
The discharging device must therefore be grounded. Explosions have
resulted from the discharging of carbon dioxide fire extinguishers into tanks
containing a flammable vapor-air mixture.
Tanks or containers that have held high flash point liquids may become
hazardous during cutting or welding operations or when heated.
Ventilate-
1. Flammable (or combustible) vapors can be purged with an inert (non-
reactive) gas such as carbon dioxide or nitrogen. This method displaces
flammable (or combustible) vapors and reduces the oxygen levels. It,
therefore, should not be used if the tank is to be entered for any reason
unless an external oxygen supply is provided.
2. The vapors in the tank may be displaced by adding solid carbon dioxide (dry
ice) to the tank.
• Caution: Skin contact with dry ice may produce burns.
* Air pressure in the tank should not exceed 5 pounds per square inch.
3. Vapors can also be purged using explosion-proof eductors or other
ventilation equipment.
Notify Proper Authority-
1. Anyone who becomes aware of a hazardous condition should notify the
proper authority. However, every reasonable effort should be made first to
determine the degree of the problem.
99
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Oxygen-Deficiency (Confined Space Entry)--
Hazards associated with reduced oxygen environments are mainly from entering
confined spaces. The following discussion summarizes the hazards associated with
confined-space entry as defined in 29 CFR 1910.146. In addition, measures taken to
supply oxygen to the tank inspector are summarized below.
"Confined space" means any space not intended for continuous employee
occupancy, having a limited means of egress, and which is also subject to either the
accumulation of an actual or potentially hazardous atmosphere as defined in this
subsection or has a potential for engulfment as defined in this subsection. Open
spaces greater than 4 feet in depth, such as pits, tubs, vaults and vessels, may also
be categorized as confined spaces if the three criteria above are met.
All confined spaces shall be emptied, flushed, or otherwise purged of flammable,
injurious, or incapacitating substances to the extent feasible. To the extent feasible,
initial cleaning should be done from outside the confined space.
Where the existence of a hazardous atmosphere is demonstrated by tests
performed by a qualified person, the confined space shall be mechanically ventilated
until the concentration of the hazardous substance(s) is reduced to a safe level, and
ventilation shall be continued as long as the recurrence of the hazard(s) is possible.
In addition, appropriate personal protective equipment should be used. Confined
space entry must be performed by at least two people (i.e., the buddy system) and
comply with local, state and Federal codes. Figure E-1 gives an example of a
confined space entry checklist that is used in several states for permitting confined-
space entry.
The following guidelines have been dratted by FPTPI for classifying confined
space entry conditions and appropriate procedures:
• No Entry - Absolutely NO ENTRY is allowed if the oxygen levels are below
16% and/or the flammable (or explosion) levels are above 20% L.F.L. (or
L.E.L) regardless of the use an external air supply. Absolutely NO ENTRY
is allowed until the atmosphere inside the tank is improved using venting
procedures.
• Restricted Entry - The technician may enter the tank if the oxygon levels in
the tank are between 16..1% and 19.4% and flammable (or explosion) levels
are 10 to 20% L.F.L. (or L.E.L.). The technician can enter the tank only if
equipped with the proper breathing and safety gear. A stand-by must be
provided.
In this case, the proper safety equipment is either a self contained breathing
apparatus (SCBA) or a supplied air source.
100
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FIGURE E-1. CONFINED SPACE ENTRY PERMIT- OPERATING TANKS
PRE-ENTRY (Check if Yes)
1. Has tank been emptied?
2. Has the air mover been installed, properly grounded and is it
effectively exhausting air from the tank?
3. Have all internal openings into the tank been blanked, capped,
removed or disconnected?
4. Has the entry hole been adequately barricaded?
5. Has the stand-by been instructed on the use of safety harness and
self-contained breaking apparatus (SCBA)?
6. Has the stand-by been instructed as to his responsibilities?
Technician signature:.
Does he fully understand:
Stand-by signature:
7. Emergency Procedure reviewed?
Rescue/Life Squad Phone Number:
Police Phone Number:
Fire Department Phone Number:
8. Pre-entry readings:
Oxygen level:
Flammable Vapor level:
9. Air-supplied mask and air capsule in good working order?
10. Safety harness and lifelines secure?
11. Only air tools in the tank?
12. This entry checklist is posted near the entry hole?
POST-ENTRY
13. Have all tools, safety equipment and materials been moved?
Technician signature:
Date completed: -
101
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• Special Entry - For tanks that have stored flammable or combustible liquids
that are temporarily above ground during remanufacturing/recertification.
This tank may have oxygen levels between 19.5% and 21.4% and
flammable (or explosive) vapor levels of 3 to 10% L.F.L (or L.E.L)
With Special Entry tanks the technician must still wear a safety harness with
a rbpe, but can enter the tank wearing an approved organic cartridge
respirator. Several types of respirators are available for this purpose. A
stand-by must be provided.
• General Entry - The oxygen levels in this tank are between 19.5% and
21.4% and flammable (or explosive) vapor levels are below 3%. LF.L. (or
LE.L.) This tank is safe to enter, but, as always, a safety harness must be
worn. This level of tank must be maintained by continuous venting during
the remanufacturing or inspection process. A stand-by must be provided.
Thermal Stress--
One or more of the following control measures can be used to help control heat
stress:
• Provision of adequate liquids to replace lost body fluids. Employees must
replace water and electrolytes lost from sweating. Employees must be
encouraged to drink more than the amount required to satisfy thirst. Salt
tablets should be available. Thirst satisfaction is not an accurate indicator of
adequate salt and fluid replacement. Replacement fluids can be* a 0.1
percent salt water solution, commercial mixes such as Gatorade® or Quick
Kick®, or a combination of these with fresh water.
• Establishment of a work regimen that will provide adequate rest periods for
cooling down. This may require additional shifts or workers. All breaks are
to be taken in a cool rest area (77°F) is best.
• Cooling devices, such as vortex tubes or cooling vests, can be worn beneath
protective garments. ^
• Inform all employees of the importance of adequate rest, acclimation, and
proper diet in the prevention of heat stress.
During periods of intense activity, the site Health & Safety representative will
continually observe the workers for symptoms of heat stress, especially in areas where
protective clothing is being worn. If the body's physiological processes to maintain a
normal body temperature fail or are overburdened due to excessive heat exposure, a
102
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number of physical reactions can occur such as fatigue, irritability, anxiety, and
decreases in mental concentration. Heat-related problems are presented below:
• Heat Rash - This is caused by continual exposure to heat and humid air, and
aggravated by chaffing clothes. Heat rash decreases a person's ability to
tolerate heat as well as becoming an irritating nuisance.
• Heat Cramps - This is caused by profuse perspiration with inadequate water
intake and chemical electrolyte imbalance. This results in muscle spasm
and pain in the extremities and abdomen.
• Heat Exhaustion - Increased stress on various organs to meet increasing
demands to cool the body will result in signs and symptoms including
shallow breathing; pale, cool, moist skin; profuse sweating; dizziness and
lassitude.
• Heat Stroke - This is the most severe form of heat stress which must be
treated immediately by cooling the body or death may result. Signs and
symptoms include red, hot, dry skin; lack of perspiration; nausea; dizziness
and confusion; strong, rapid pulse; and coma.
The symptoms of heat stress may also include: fatigue; irritability; headache;
faintness; weak, rapid pulse; shallow breathing; cold, clammy skin; profuse
perspiration.
Treatment-
1. Instruct victim to lie down in a cool, shaded area or air-conditioned room.
Elevate feet.
2. Massage affected muscles.
3. Give cold salt water (1/2 teaspoon to 1/2 glass of water) or cool, sweetened
drink, especially iced tea and coffee, every 15 minutes until victim recovers.
4. DO NOT let victim sit up, even after feeling recovered.
5. Call for medical aid.
Protective Equipment
Specific levels of protection are used to safeguard employees on the job from
potential hazards. Three distinct levels of protection (i.e., levels B, C, or D) may be
required. The final determination of any required level of protection will be based
upon the hazards and current conditions of the work site. The only person who may
make this determination is the Health and Safety Representative. The situations
requiring specific levels of protection are described in the following sections.
103
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Level B Protection--
This level of personal protection will be utilized by individuals when: 1) the toxic
nature of the material or anticipated airborne concentration of known contaminants
may be greater than two times the OSHA permissible exposure limits (PEILs), 2) when
the total hydrocarbon reading on the HNu is greater than 10 ppm above background,
or 3) when the oxygen level on the MSA combustible gas indicator sustains a reading
of less than 19.5%.
The following equipment will be used for Level B Protection:
• Full-face self-contained breathing apparatus or supplied air respirator which
is NIOSH/MSHA approved.
• Hooded, chemical-resistant Saranex-coated Tyvek® (Outer)
• Unhooded, chemical-resistant white Tyvek® (Inner)
• Gloves - chemical-resistant nitrile or polyvinyl chloride (PVC) (Outer)
• Gloves - latex surgical or PVC (Inner)
• Boots - chemical-resistant neoprene with steel toes and shank (Outer).
Steel sole inserts will be used where materials could puncture boots.
Disposable PVC booties over steel-toed shoes for equipment operators.
• Hard hat
•
• Hearing protection (if necessary)
Level C Protection--
Level C protection will be required when the toxic nature of the material and
airborne concentration of contaminants are known to be at or above the TLV or the
PEL, or when the total hydrocarbon reading on the HNu is above background.
The following equipment will be used for Level C protection:
• Full-face, air purifying respirators with organic vapors which are
NIOSH/MSHA approved. Half-face respirators will be utilized if
accompanied by chemical splash goggles and specified by the Regional
Health and Safety Representative.
• Hooded, chemical-resistant white Tyvek®
• Gloves - chemical-resistant nitrile or PVC (Outer)
104
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• Gloves - latex surgical gloves (Inner)
• Boots - chemical-resistant neoprene with steel toes and steel-toed shoes
(Outer)
• Hard hat
• Hearing protection (if necessary)
Level D Protection-
The minimal level of protection that may be required of personnel at a site is
Level D. The following equipment is characteristic of Level D protection:
• Coveralls or Tyvek®
• Boots/Shoes - Safety shoes with steel toes
• Safety glasses or goggles
• Hard hat
• Chemical-resistant nitrile or PVC protective gloves with surgical latex
undergloves.
The levels of chemicals or oxygen that trigger the upgrade from Level D to Level
C or from Level C to Level B are determined by the Health and Safety Representative.
Fire and Other Safety Equipment-
The following equipment will also be used on site:
• An approved light source designed for an explosive atmosphere
• Fire extinguisher
• Safety harness
• An air-operated venting or tank de-fuming apparatus
• An extra compressed air cylinder or other air purifying system with
appropriate respirator and organic vapor cartridges
105
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• Approved safety goggles, safety glasses or face shield, ear plugs, rubber
gloves and rubber boots
• An appropriate first aid kit and fire blankets
Monitoring Equipment
In most tank work, two types of air monitoring equipment are generally
employed to warn workers of potential hazards (e.g..hazardous vapor concentrations,
flammable vapor levels, oxygen levels):
• Combustible Gas Indicator (CGI) - monitors the explosive levels of
flammable vapors and oxygen
• Organic vapor monitoring instrument (e.g., PID, FID, GC/MS, colorimetric
tubes) - monitors total organic vapor concentrations or individual constituent
levels in air around workers.
GENERAL WORK PRACTICES
All work being performed during the remedial action should be done using the
"buddy" system. Before beginning work each day, buddies should be assigned.
These team members will keep in visual contact with each other at all times. These
team members will be aware of: any slip or trip; all lifting hazards; any potential
exposure to chemical substances; all potential for heat or cold stress; and! any general
hazards within the work areas. All information regarding work to be performed,
emergency procedures, and health and safety hazards will be reviewed before the
work begins during a daily tailgate safety meeting. No work will be performed without.
completing these procedures. In addition, while work is being performed inside the
tank, a safety technician should monitor continuously the oxygen levels, flammable
vapors, and organic vapor levels inside the tank.
Transportation by any other means than those prescribed for movement of
personnel will be strictly prohibited. When trucks or other heavy equipment enter the
site, flagmen will direct traffic.
Several fire extinguishers will be on site. In the event of an emergency, these
extinguishers will be ready for the worker's safety and protection. Any deviation from
this site safety program must be discussed in advance with the Health and Safety
Representative. Smoking will not be permitted on the premises.
No unapproved electrical equipment for hazardous atmospheres v/ill be
permitted in areas where a flammable or combustible vapor atmosphere exists. All
static ignition sources will be identified and eliminated by the use of standard bonding
and grounding techniques.
106
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REFERENCES
The names of references and organizations that may be of value to those
responding to hazardous materials incidents are provided below. These names are
not all-inclusive, and can be expanded based on personal preferences and
requirements. References are listed according to title, author, publisher, and place of
publication. The year of publication is not always given because many of these
references are revised annually. The user should attempt to obtain the most recent
edition.
Sources of these references as well as other information that might be useful
are also listed. Usually, these agencies and associations will provide a catalogue on
request. Where available, phone numbers are also listed.
1. NIQSH/OSHA Pocket Guide to Chemical Hazards. DHHS No. 85-114, NIOSH,
Department of Health and Human Services, Cincinnati, OH.
2. Registry of Toxic Effects of Chemical Substances. DHHS No. 83-107. National
Institute for Occupational Safety and Health, Rockville, MD.
3. Respiratory Protective Devices Manual. American Industrial Hygiene Association,
Akron, OH.
4. TLVs Threshold Limit Values and Biological Exposure Indices (Threshold Limit
Values for Chemical Substances and Physical Agents in the Workroom
Environment). American Conference of Governmental Industrial Hygienists,
Cincinnati, OH.
5. Fire Protection Handbook. National Fire Protection Association, Quincy, MA.
6. Flammable Hazardous Substances Emergency Response Handbook: Control and
Safety Procedures. Prepared for U.S.EPA under Contract No. 68-03-3014.
7. Guidelines for the Selection of Chemical Protective Clothing. Volume 1: Field
Guide. A.D. Schwope, P.P. Costas, J.O. Jackson, D.J. Weitzman, Arthur D. Little,
Inc., Cambridge, MA (March 1983).
8. Guidelines for the Selection of Chemical Protective Clothing. Volume 2: Technical
and Reference Manual. A.D. Schwope, P.P. Costas, J.O. Jackson, D.J. Weitzman,
Arthur D. Little, Inc., Cambridge, MA (March 1983).
9. Hazardous Materials Injuries. A Handbook for Pre-Hospital Care. Douglas R. Stutz,
Robert C. Ricks, Michael F. Olsen, Bradford Communications Corp., Greenbelt, MD.
107
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10. National Safety Council Safety Sheets. National Safety Council, Chicago, I L.
1 1 . NIOSH Certified Equipment Lists. U.S. Dept. of Health and Human Services,
Washington, D.C.
12. Personal Protective Euiment for Hazardous Materials Incidents: A Selection
NIOSH, U.S. Department of Health and Human Services, Washington, D.C.
13. SCBA - A Fire Service Guide to the Selection. Use. Care, and Maintenance of Self-
Contained Breathing Apparatus. National Fire Protection Association, Batterymarch
Park, Quincy, MA.
1 4. Standard First Aid and Personal Safety. American Red Cross.
15. Underwriters Laboratories Testing for Public Safety. Annual Directory. Underwriters
Laboratories, Inc., Northbrook, IL.
Agencies and Associations
Agency for Toxic Substances Disease Registry
Shamlee 28 S., Room 9
Centers for Disease Control
Atlanta, GA 30333
404/452-4100
American Conference of Governmental Industrial Hygienists
6500 Glenway Avenue - Building D-5
Cincinnati, OH 45211
513/661-7881
American Industrial Hygiene Association
475 Wolf Ledges Parkway
Akron, OH 44311-1087
American National Standards Institute, Inc.
1430 Broadway
New York, NY 10018
212/354-3300
108
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American Petroleum Institute (API)
122QL St., NW, 9th Floor
Washington, DC 20005
202/639-2100 .......
•".-•:, ' i , ' .e / ...
Chemical Manufacturers Association
2501 M St., N.W.
Washington, DC 20037
202/887-1100
Compressed Gas Association
1235 Jefferson Davis Highway
Arlington, VA 22202
703/979-0900
CRC Press, Inc.
2000 Corporate Blvd. N.W.
Boca Raton, FL 33431
305/994-0555, Ext. 330
National Fire Protection Association
Batterymarch Park
Quincy, MA 02269
617/328-9290
U.S. Department of Transportation
Materials Transportation Bureau
Office of Hazardous Materials Operations
400 7th St. S.W.
Washington, DC 20590
202/336-4555
U.S. EPA, Office of Solid Waste (WH-562)
Superfund Hotline
401 M St, S.W.
Washington, DC 20460
800/424-9346
Superintendent of Documents
U.S. Government Printing Office
Washington, DC 20402
202/783-3238
109
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U.S. Mine Safety and Health Administration
Department of Labor
4015 Wilson Blvd. Room 600
Arlington, VA 22203
703/235-1452
U.S. National Oceanic and Atmospheric Administration
Hazardous Materials Response Branch
N/OMS 34
7600 Sand Point Way NEE
Seattle, WA 98115
206/527-6317
110
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APPENDIX F
CLASSIFICATION OF SURFACE AND SUBSURFACE DISCONTINUITIES
FOR TRANSLUCENT VISUAL EXAMINATION OF FRP TANKS
ASME SD-2563
111
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114
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APPENDIX G
QUALIFICATION PROCEDURE FOR NON-STANDARD TEMPERATURES
FOR LIQUID DYE PENETRANT TESTS
Approach --
This procedure is performed when the operating conditions of the liquid
dye penetrant test exceeds 125°F or are less than 60°F. Temperatures outside
the recommended range are referred to as "Non-Standard Temperatures," while
temperatures within the range are classified as "Standard Temperatures." Non-
standard test conditions require qualification by ASME standards. A quenched
aluminum block will be created in accordance to ASME specifications and be
designated as the liquid penetrant comparator block.
Liquid Penetrant Comparator --
The following parameters are required for Liquid Penetrants:
Material:
Dimensions:
Labeling:
Production:
ASTM B 209, Type 2024 or SB-211, Type
2024
2 in. x 3 in. x 3/8 in.
Center of each face shall be marked with a
950°F indicator crayon.
The aluminum block shall be heated to 950°F and
then immediately quenched in cold water. The
aluminum block is then dried by heating to 300°F.
This process generates fine cracks on both faces of
the block. After drying, the block is allowed to cool
and is cut into two equally sized blocks. These blocks
will be labelled block "A" and block "B".
Qualification ~
When using visible dye penetrants whose flaw detection is based on color
contrast, a single comparator block may be used for the standard and non-
standard temperatures. The block shall be thoroughly cleaned between the two
processing steps. Photographs are taken after testing at the non-standard
115
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temperature, and again after testing at the standard temperature. The flaw
indications of the block at the two temperatures are compared on the
photographs. If the flaw indications of the comparator block at the non-sstandard
temperature are essentially the same as the flaws at the standard temperature,
the penetrant procedure is then "qualified." If the non-standard temperature is
below 60°F and the procedure is "qualified," the penetrant procedure is qualified
from that specific non-standard temperature up to 60°F.
116
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APPENDIX H
CONTROL TESTS RECOMMENDED BY ASME SE-709
FOR MAGNETIC PARTICLE TESTS
Ammeter Accuracy Check ~
The equipment meter readings should be compared to a control test meter
reading, incorporating a shunt or current transformer to monitor the output current.
Comparative readings shall be taken at a minimum of three output levels
encompassing the usable range. The equipment meter reading shall not deviate by
more than +/-10% of full scale, relative to the actual current values as shown by the
test meter. When measuring half-wave current, the direct current test meter reading is
doubled.
Timer Control Check -
The timer should be checked and verified using a precision timer at routine
intervals or suspected malfunctions on equipment utilizing a timer to control the
duration of the current flow.
Magnetic Field Quick Break Check --
On equipment with magnetic field quick breaks, a test may be performed using
a suitable oscilloscope or a simple test device usually available from the manufacturer.
Equipment Current Output Check -
To assure the continued accuracy of the equipment, ammeter readings at each
transformer tap should be made with a calibrated ammeter-shunt combination. This
accessory is placed in series with the contacts. The equipment shunt should not be
used to check the machine of which it is an uncalibrated part. Variations exceeding
+/-10% from the equipment ammeter readings indicate the equipment needs service
or repair.
117
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Internal Short Circuit Check -
Magnetic particle equipment should be checked periodically for internal short-
circuiting. With the equipment set for maximum amperage output, any deflection of the
ammeter when the current is activated with no conductor between the contacts is an
indication of an internal short circuit.
Electromagnetic Lifting Force -
The magnetizing force of a yoke can be tested by determining its lining
power on a steel plate. The lifting force relates to the electromagnetic strength of the
yoke. Alternating current electromagnetic yokes should have a lifting force of at least
10 Ib, and direct current yokes of 40 Ib, at the maximum pole spacing.
118
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APPENDIX I
TANK INTEGRITY TEST METHOD SUMMARY
119
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