United States     Office ofj Solid Waste and
          Environmental Protection Emergency Response
          Agency       Washington DC 20460
                       I	
EPA/530/SW-89/069
September 1989
&EPA    Technical Guidance
          Document:

          The Fabrication of
          Polyethylene FML
          Field Seams

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                              EPA/530/SW-89/069
                              September 1989
     TECHNICAL GUIDANCE DOCUMENT
   THE FABRICATION
            FMLFffiL
OF POLYETHYLENE
,D SEAMS
   Office of Solid Waste
      U.S. Environmen
           Washington, DC 20460
             In cooperation with
RISK REDUCTION ENGINEERING LABORATORY
  OFFICE OF RESEARCH AND DEVELOPMENT
 u.s. ENVIRONMENTAL! PROTECTION AGENCY
         CINCINNATI, OHIO 45268

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                                   DISCLAIMER
     The  preparation of this  document  has  been funded wholly by the United States
Environmental Protection Agency. It has been subjected to the Agency's peer and administrative
review, and it has been approved for publication as an EPA document. Mention of trade names
or commercial products does not constitute endorsement or recommendation for use.


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                                     FOREWORD
     Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the injcreased generation of solid and hazardous wastes.
These materials, if improperly dealt with, can threaten both public health and the environment.
Abandoned waste sites and accidental releases of toxic and hazardous substances to the
environment also have important environmental and public health implications.  The Risk
Reduction Engineering  Laboratory assists in providing an  authoritative and defensible
engineering basis for assessing and solving these problems.  Its products support the policies,
programs, and regulations of the U.S. Environmental Protection Agency; the permitting and
other responsibilities of State and local governments; and the needs of both large and small
businesses in handling their wastes responsibility and economically.

     This document provides guidance for construction quality control and construction quality
assurance inspectors and related personnel ak to the proper techniques for making field seams on
polyethylene flexible membrane liners (FMlL's).  It focuses specifically on the three most widely
used techniques;  extrusion fillet, extrusion flat and hot wedge fabrication methods.  The
presentation of each of these methods details FML preparation in advance of seaming, equipment
preparation, the actual seaming process and finally the activities to be performed after the
seaming is completed. Rationale is provided for the various conditions and limitations that are
suggested. A glossary of terms relevant to fabrication of polyethylene FML field seams is given
at the end of the document.
                                             E. Timothy Oppelt, Director
                                             Risk Reduction Engineering Laboratory
                                           m

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                                     PREFACE

     Subtitle C of the Resource Conservation and Recovery Act (RCRA) requires the U.S.
Environmental Protection Agency (EPA) to establish a Federal hazardous waste management
program.  This program must ensure that hazardous wastes are handled safely from generation
until final disposition. EPA issued a series of hazardous waste regulations under Subtitle C of
RCRA that are published in Title 40 Code of Federal Regulations (40 CFR).  The principal 40
CFR Part 264 and 265 regulations  were issued on July 26, 1982 for treatment, storage, and
disposal (TSD) facilities and establish performance standards for hazardous waste landfills,
surface impoundments,  land treatment units, and waste piles.  The regulations have been
amended several times since then.

     In support of the regulations, EPA has been developing three types of documents to assist
preparers and reviewers of RCRA permit applications for hazardous waste TSD facilities. These
include RCRA Technical  Guidance Documents, Permit Guidance Manuals, and Technical
Resource Documents (TRDs).

     RCRA Technical Guidance Documents, such as this one, present design and operating
parameters or design evaluation techniques that generally comply  with, or demonstrate
compliance with, the Design and Operating Requirements and the Closure and Post-Closure
Requirements of 40 CFR Part 264.

     The  Permit Guidance Manuals are being developed to describe the permit application
information the Agency seeks, and to provide guidance to applicants and permit writers in
addressing information requirements.  These manuals will include a discussion of each set of
specifications that must be considered for inclusion in the permit.

     The Technical Resource Documents present summaries of state-of-the-art technologies and
evaluation techniques determined by the  Agency to constitute good engineering designs,
practices, and procedures. They support the RCRA Technical Guidance Documents and Permit
Guidance Manuals in certain areas (i.e., liners, leachate management, final covers, and water
balance) by describing  current technologies and methods for designing hazardous waste
facilities, or for evaluating the performance of a facility design. Although emphasis is given to
hazardous waste facilities, the information presented in these TRDs may be used for designing
and operating nonhazardous waste TSD facilities as well.  Whereas the RCRA Technical
Guidance Documents and Permit Guidance Manuals are directly related to the regulations, the
information in these TRDs covers a broader perspective and should not be used to interpret the
requirements of the regulations.

     This document is a Technical Guidance Document prepared by the  Risk Reduction
Engineering Laboratory of EPA's Office of Research and Development in cooperation with the
Office of Solid Waste and Emergency Response. The document has undergone extensive
technical review and has been revised accordingly. With the issuance of this  document, all
previous drafts are obsolete and should be discarded.
                                          iv

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     Comments are welcome at any time on the accuracy and usefulness of the information in
this document. Comments will be evaluated, and suggestions will be incorporated, wherever
feasible, before publication of any future revisions. Written comments should be addressed to
EPA RCRA Docket (OS-305), 401 M Street S.W., Washington, DC 20460. The document for
which comments are being provided should be identified by title and number.

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                                     ABSTRACT

     This technical guidance document is meant to augment the numerous construction quality
control and construction quality assurance (CQC and CQA) guidelines that are presently available
for high density polyethylene (HDPE) liner installation and inspection. In general, the tone of
these existing documents is to allow the installer almost complete freedom in making seams with
the only conditions being that they pass;

     (a) destructive shear and peel tests to a stipulated strength, and
     (b) selected nondestructive tests, e.g., vacuum box testing

Howeyer, there is a long-term concern regarding seam integrity which is not addressed by
following this course of action.  Simply expressed, it appears as though the long-term service life
of some HDPE liners is compromised when seams are  made improperly. This cornes about by
overgrinding, overheating, placing new welds directly over older welds, or simply by poor
workmanship.

     By developing a document somewhere between the typical CQC/CQA document and an
installer's training manual, i.e., a "standard-of-practice", it is hoped that the above negative
features of seam making can be avoided. It is hoped to provide deeper insight for an inspector as
to what the installer is trying to accomplish.  At the same time it might be also helpful to the
installer in recognizing that others have a vested interest in their specific activity.  After some
introductory material, the manual is focused toward three types of field seams used for
fabricating field seams in HDPE liners:

     • extrusion fillet seams
     • extrusion flat seams
     • hot wedge seams

Additional seam types will be added to future editions of this manual as considered desirable and
necessary.
                                          VI

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                                    CONTENTS
Disclaimer
Foreword
Preface
Abstract
Figures
Tables
Acknowledgement
 1.  Introduction    ;
 2.  Construction Quality Assurance Concepts
 3.  Polyethylene FML's
 4.  An Overview of Polyethylene Seaming Methods
 5.  Details of Extrusion Fillet Seams
     5.1 FML Preparation
     5.2 Equipment Preparation
     5.3 Actual Seaming Process
     5.4 After Seaming

 6.  Details of Extrusion Flat Seams

     6.1 FML Preparation
     6.2 Equipment Preparation
     6.3 Actual Seaming Process
     6.4 After Seaming

 7.  Details of Hot Wedge Seams

     7.1 FML Preparation
     7.2 Equipment Preparation
     7.3 Actual Seaming Process
     7.4 After Seaming

 8.  Concluding Statement
 9.  References
 10.  Glossary of Terms
  n
 iii
 iv
 vi
viii
  x
 xi

  1
  2
  6
  8
 11

 11
 13
 15
 20

 23

.23
 25
 27
 28

 30

 30
 32
 34
 35

 38
 39
 40

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                                     FIGURES
2

3

4
Number

  1     Fabrication of FML Seam Test Strip
        (a)  Two Sheets of Liner being Cleaned and 'Prepared for Trial Seaming
        (b)  The Two Sheets Being Seamed Together Thereby Forming the Test Strip
        (c)  The Completed Test Strip Being Cut into Individual Samples for
             Subsequent Inspection and Destructive Testing
        (d)  Marking the Test Strip Samples for Identification and Records

        Type of Hook Blade Used for the Cutting of Liner Materials

        Hand-Held Electric Rotary Grinder with Circular Disc Grit Grinding Paper

        Photographs of Various Types of Extrusion Fillet Welding Devices
        Upper: Automated Type
        Lower: Hand Held Type

        Preparing the Bevel of the Upper FML for Liner Thicknesses Greater Than
        50 Mil

        Proper Orientation and Grinding Preparation of Sheets Prior to Tacking and
        Extrudate Placement

        Photographs of Different Orientations of Grinding Patterns
        Upper: Grind Marks Perpendicular to Seam (Recommended Pattern)
        Lower: Grind Marks Parallel to Seam (Not Recommended Pattern)
        (Note, however, that both situations have grinding far in excess of what is
        required and are shown for illustration of the grinding patterns only, see
        Figure 8 following)

        Photographs of Different Extent of Grinding Patterns After Extrusion Fillet
        Seaming
        Upper:  Excessive and Irregular Grinding Beyond Extrudate
        Lower: Acceptable Grinding Pattern Just Showing Beyond Extrudate

 9      Smooth Propping Wedge Used When Tacking of Sheets is Done Before
        Surface Grinding of the FML Sheets

10      Schematic Diagrams of Various Cross Sections of Fillet Extrusion Seams
8
Page

  4

  4

  5
  5

 11

 13

 14
                                                                              15


                                                                              16

                                                                              17
                                                                              18
                                                                              19

                                                                              20
                                      vm

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11
12

13


14


15


16




17

18

19


20


21


22
                        FIGURES ^continued)

Photographs of Cross Sections of Various Types of Extrusion Fillet Seams
Upper: Machine Extrusion Seam without Squeeze-Out
Middle: Hand Held Extrusion Seam without Squeeze-Out (note thermal
         puckering at bottom of seam)
Lower: Hand Held Extrusion Seam with Squeeze-Out

Type of Hook Blade Used for the Cutting of Liner Materials
                                                                             22
Grinding Locations and Method Used in the Preparation of Hat Extrusion
Seams

Photograph and Schematic Diagram of flat Extrusion Seaming of FML
Sheets

Schematic Diagram of Cross Section of Extrusion Flat Seam with
Extrudate Out to the Edge of the Upper FML

Photographs of Cross Sections of Extrusion Rat Seams
Upper: Extrudate Short of the Edge of Overlapping Sheet
Middle: Extrudate Exactly at the Edge o'f Overlapping Sheet
Lower: Extrudate Squeeze-Out Beyond the Edge of Overlapping Sheet

Type of Hook Blade Used for the Cuttiijg of Liner Materials

Various Types  of Hot Wedge Seaming Devices

Diagrams of the Hot Wedge Elements (i.e., the Anvil) Upon Which the Two
Sheets to be Joined are Passed
                                  i    • • •
Details of the Hot Wedge System Showing Relative Positions of the Hot
Wedge, Rollers and Sheets to be Joinecl

Schematic Diagram of Cross Section ofiDual (Split) Hot Wedge Seam
Illustrating Squeeze-Out             j
                                  ]    .
Photographs of Cross Sections of Hot Ivedge Seams
Upper: Single Hot Wedge Seam with Acceptable Squeeze-Out
Middle: Dual Hot Wedge Seam with Excessive Squeeze-Out
Lower: Dual Hot Wedge Seam with Acceptable Squeeze-Out
23


25


26


27

29




30

32


33


34


36

37

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                                     TABLES
Number
   2
   3
Major Components in Various Types of Polymeric FML's, after
HaxoC?)
Classification of Polyethylenes, after Apse(g)
Various Seaming Methods for Polyethylene FMLs (modified from
reference #11)
'age

 6
 7

10

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                               ACKNOWLEDGMENT
     This technical guidance document grew ojut of a series of meetings of the various HDPE
manufacturers of FML's who are member organizations of the Geosynthetic Research Institute
(GRI) of Drexel University. Later drafts were reviewed by the various polyethylene resin
producers and the consulting engineering and testing firms within GRI. Still later drafts were
reviewed by several private owners of waste containment facilities. Robert M. Koerner was the
project coordinator who extends sincere appreciation for the excellent cooperation and openness
of this group  of organizations in sharing inforrnation and critiquing the various drafts of the
document.                                 I
                                          I                       "	''
     The EPA project manager of this technical [guidance document was Robert E. Landreth with
the assistance of David A. Carson.
                                          xi

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                                  1. INTRODUCTION

     The lining of hazardous and non-hazardous solid waste landfills, surface impoundments
and waste piles is a critical component in the prevention of contamination of subsurface soil and
groundwater.  When the contained solid or liquid is of a hazardous nature, every aspect of the
lining system must undergo the closest possible scrutiny. The need for both construction quality
control (CQC) and construction quality assurajice (CQA) becomes requisite at many facilities.
With an extremely large number of facilities currently planned and under construction there also
comes many organizations with a lack of experience in specialized topics. Certainly an area such
as flexible membrane liners (FMLs) made from'polyethylene (PE) falls into this category. Many
inspection firms entering into this area have ha|d little formal training or practical experience in
dealing with polyethylene FML's. This is not to say that experienced firms are not available;
they are indeed, and are very active in providing excellent inspection services. However, there
appears to be a need to have a primer on certain aspects of FML installation and this document
will hopefully fill part of this need.

     As will be seen, this manual is very narrowly focused, addressing only one part of the total
liner system, that is the seams. Furthermore, only field seams of polyethylene FMLs will be
addressed in this report. Still further, it is the iriaking (or fabrication) of the seams which will be
the focus,  not their destructive or nondestructive testing.  There are numerous excellent
documents on this  latter topic, see, for example, FroberC1), Lord, et al.(2), Overmann(3) and
Richardson(4X                             I

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                2. CONSTRUCTION QUALITY ASSURANCE CONCEPTS

      As written in EPA Report 600/2-88/052 entitled "Lining of Waste Containment and other
 Impoundment Facilities"(5) construction quality assurance (CQA) is a planned system of activities
 that provides assurance that the unit is constructed as specified in the design. Thus, CQA refers
 to those activities initiated by the owner of the facility that ensure that the construction of the
 entire facility, including manufacture, fabrication, and installation of the various components of
 the lining system, meets design specifications and performance requirements. The activities
 include inspections, verifications, audits, and evaluations  of materials and workmanship
 necessary to determine and document the quality of the constructed facility.  These activities are
 often performed by a third-party quality assurance team that is independent of the designer
 manufacturer, fabricator, installer, operator and owner to ensure impartiality.

      CQA activities should be differentiated from construction quality control (CQC) activities
 which include those activities and procedures initiated by the designer, manufacturer, fabricator
 installer, or  contractor(s) necessary to control the quality of the constructed or installed
 component and to ensure that specifications are being met. Even though the CQC activities will
 overlap with those performed in fulfillment of the CQA plan, the two activities are often
 performed by independent organizations.

      Regarding the elements of a CQA plan, EPA Report 530-SW-86-031 entitled "Construction
 Quality Assurance for Hazardous Waste and Land Disposal Facilities"^) presents the following
 key elements                                                                        6

      *  Responsibility and Authority -  The responsibility and authority of organizations and
        personnel involved in permitting, designing, and constructing the facility should be
        described in the CQA plan.

      *  .CQA Personnel Qualifications - The qualifications of the CQA officer and supporting
        CQA inspection personnel should be presented in the CQA plan.

      •  irnspeption Activities  - The observations and tests that will be used to ensure that the
        construction or installation meets or exceeds  all design criteria, plans, and specifications
        for each component should be described in the CQA plan.

      •  Sampling Strategies - The sampling activities, sample size, methods for determining
        sample locations, frequency of sampling, acceptance and rejection criteria, and methods
        for ensuring that corrective measures are implemented should be presented in the CQA
        plan.

     •  Documentation - Reporting requirements for CQA activities should be described in
        detail in the CQA plan.

This particular manual focuses on one specific aspect of CQA "inspection activities", namely the
inspection of field seams used in the joining of polyethylene FML's.

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     One item that is in many CQA documents
is the requirement of making "test welds" or "test
strips" on a periodic basis.  This procedure is often stipulated to be at least every four hours,
every time personnel are changed or at the request of the field inspector.  This practice is highly
recommended and must be a part of standard practice for the seaming of all FML's, including
those made from polyethylene.  The ultimate purpose of such tests is to establish proper seaming
temperatures, pressure and rates, along with the necessary FML preparation procedures and
subsequent seam evaluation.  Photographs of) the preparation of such  "test strips" follow in
Figure 1. Figure l(a) shows the two FML pieces to be seamed being cleaned and properly
aligned, l(b) shows the actual test strip being Beamed, l(c) shows the sampling of the test strip
for subsequent destructive testing, and l(d) shows the individual samples cut from the test strip
being identified.            ,     .

      Test strips of the type shown in Figure 1  are approximately 5 ft. long for extrusion seams,
to 10 ft. long for hot wedge seams.  The seam is centered lengthwise between the two sheets to
be joined. After fabrication of the seam, 1.0 in. jwide seam specimens  are cut from the completed
test strip and evaluated in the field  using a portable tensiometer.  Both shear and peel tests are
conducted. If a test seam fails to meet field seam specifications, the seaming apparatus and/or
seamer shall not be accepted and shall not be used for seaming until the deficiencies are corrected
and  two consecutive  successful full test seams are achieved.  As seen in Figure l(d), the
remainder of the test strip is cut into pieces fojr laboratory testing and retention by the various
parties involved, e.g., agency, owner, manufacturer, CQC and/or CQA organizations.

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   (a) Two Sheets of Liner Being Cleaned and Prepared for Trial Seaming
(b) The Two Sheets Being Seamed Together Thereby Forming the Test Strip





             Figure 1. Fabrication of FML Seam Test Strip

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(c) The Completed Test Strip Being Cut into Individual Samples for Subsequent Inspection and
                                  Destructive Testing
            (d) Marking the Test Strip Samples

                               Figure 1.
   for Identification and Records

(Continued)

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                            3. POLYETHYLENE FML's

     FML's can be made from a wide variety of polymeric materials.  Table 1 below illustrates
the three different classes of FML's along with the various additives  that are often used. It is
based on 100 parts by weight of the particular polymer resin or alloy with other materials being
added as would be practiced in the actual compounding of the final product.


   TABLE 1. MAJOR COMPONENTS IN VARIOUS TYPES OF POLYMERIC FML's,
                                 AFTER HAXO(7>
Component
Composition in Parts by Weight
                     Thermoset
         Thermoplastic
Semicrystalline
Polymer or Alloy
Oil, Plasticizer or
Processing Agent
Fillers
carbon black
inorganics
Antidegradants
Crosslinking
inorganic
sulfur
100
5-40


5-40
5-40
1-2

5-9
5-9
100
5-55


5-40
5-40
1-2

0-5
—
100
0-10


2-5
'
1


— —
Due in large part to the lack of ingredients other than the polymer or alloy itself, the
semicrystalline material "polyethylene" is often used for liners beneath hazardous solid and liquid
waste facilities.  It should be noted, however, that polyethylene is both thermoplastic and
semicrystalline but the latter property gives it its distinction. As seen below, polyethylene has a
very simple repeating molecular unit giving rise to a long chain, high molecular weight,
structure.

                     REPEATING POLYTHEYLENE MOLECULE
                                      H   H
                                       I    I
                                        	 /"• I	
                                           Vx"["

                                           I
                                           H

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     Note that the above repeating molecule is the general form for low-, medium-, and
high-density polyethylene. To .distinguish beiween the various types, the degree of crystallinity
and extent of branching must be known; see Table 2 for such a classification based on resin
density.^) For greater detail on polyethylene (classifications versus property values see reference
#9.                                     I

         TABLE 2.  CLASSIFICATION OF POLYETHYLENES, AFTER APSE(8)
Type of
Polyethylene ,','_•
[0
I
n
m
IV

Low Density (LDPE ;
Medium Density
High Density (Copob
"'.'••"
, Nominal Density . ..
.'.. ;.;. .' . . ; ' (g/cc) ; \ :

indLLDPE)
• • -: • • . ;.
'mer)
High Density (Homopolymer)
under 0.910] '' ;
: 0.910-0.925
0.926-0.940
0.941-0.959
' 0.960 and higher
                                     )art'<
The descriptions in parentheses are not part! of the ASTM standard and Type O is merely a
suggestion for a future class. Except for thejinclusion of LDPE with its long branches within
Type I, these polymers are all linear polyethylenes.

     Most of the polyethylene resins used fo|r the fabrication of FML's for waste containment
applications are in the density range of 0.932 - 0.940 g/cm3  which places the material in the
upper range of the medium density category!, not the customarily referenced high density, or
HOPE, category as defined by ASTM D-1248. The addition of carbon black, however, will
bring the final compound to a gross density range of 0.941 g/cm3, or greater, which the liner
industry then refers to as HDPE.  In this standard:of-practice we will also refer to the material as
HOPE thereby recognizing that the above stated industry position is the customarily accepted
situation.

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             4. AN OVERVIEW OF POLYETHYLENE SEAMING METHODS

     Due to the high chemical resistance of most polyethylenes, they cannot be solvent bonded
like other thermoplastic FMLs.  Furthermore, their surface hardness prevents taping as with
thermoset FMLs.  Thus polyethylenes are either extrusion welded or thermal fused (melt bonded)
for seam fabrication. Both categories have a number of specific techniques^10)

     Extrusion welding is used exclusively on FMLs made from polyethylene.  It is a direct
parallel of metallurgical welding in that a ribbon of molten polymer is extruded over the edge of,
or in between, the two surfaces to be joined. The hot extrudate causes the surfaces of the sheet
material to become molten and the entire mass then fuses together. One particular system has a
mixer in the molten zone which aids in homogenizing the extrudate and the molten surfaces.  The
technique is called extrusion fillet welding when the extrudate is placed over the leading edge of
the seam, and is called extrusion flat welding when the extrudate is placed between the two
sheets to be joined. It should be noted that extrusion fillet welding is essentially the only method
that can be used for patching and in poorly accessible areas like sump bottoms and around pipes.

     There are a number of thermal fusion or melt bonding, methods that can be used on
semicrystalline geomembrane materials like polyethylene.  In  all of them, portions of the
opposing  geomembrane surfaces are truly melted.  This being the case, temperature,  pressure
and seaming rate all play important roles in that too much melting weakens the geomembrane and
too little melting results in poor seam strength. Hot air makes use  of a device consisting of a
resistance heater, a blower, and temperature controls to blow air between two sheets to melt the
opposing  surfaces. Usually, temperatures of the "gun" greater than 480°F (250°C) are required.
Immediately following the melting of the surfaces, pressure is applied by counter-rotating
knurled rollers on  the top and  bottom of the seamed area.  The hot air technique is not
recommended to be used as a permanent seaming method for polyethylene FMLs and will not be
discussed as a major topic.  It is, however,  used to tack sheets together for subsequent
(permanent) seaming. In this case, a hand held  hot air heater is generally used. The hot wedge
or hot shoe method consists of an electrically heated resistance element in the shape of a wedge
that is passed between the two sheets to be sealed.  As it melts the surfaces, a shear flow occurs
across the upper and lower surfaces of the wedge and then roller pressure is applied. Hot wedge
units are  automated as far  as temperature, amount of pressure applied and travel rate is
concerned. A single hot wedge is  continuous in its width, while a dual hot wedge (or "split"
wedge) forms two parallel seams with an unbonded space between them.  This space is
subsequently pressurized with air for seam continuity testing. Dielectric bonding is used only for
factory seams and not for HOPE. It is regularly used for other FML materials including some
lower density polyethylenes.  An alternating current is used at a frequency of approximately 27
MHz, which excites the polymer molecules, generating heat by intermolecular friction.  This
melts the polymer and when followed by roller pressure  a seam results.  A variation of this
method has recently been introduced for the manufacture of field seams on some types of the
lower density polyethylene liners, but not HOPE. The  method will not be further described in
this manual.  Ultrasonic bonding utilizes a wedge shaped tool, or "horn", vibrating at
approximately 40 kHz which is passed between the overlapped FML sheets in a manner similar
to a hot wedge. The vibration of a knurled portion of the tip of the wedge creates heating of the
FML by friction into a molten state. Pressure is  then applied to squeeze the sheets together via a
set of opposing wheels which follows the melting process. The method is in the development

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stage and has only recently been used in the field for HOPE liners.  It will not be further
described in this manual.  Electric resistance  welding is  yet another new technique for
polyethylene seaming wherein a stainless  steel wire  is placed between overlapping
geomembranes and energized with approximately 36 volts and 10 to 25 amps current. The hot
wire radially melts the entire region within about 60 seconds to develop a bond. It is later used
with a high voltage and a low current in it arijd a questioning wire outside of the seamed region
thereby becoming a nondestructive testing method for locating pinholes. Since this method is
also in a development stage, it will not be further described in this manual.

     The above mentioned seaming techniques for polyethylene have recently been reviewed^11),
see Table 3, which illustrates the seam configuration and many relevant comments. It should be
fully recognized that the seaming of thick sheets of polyethylene is a formidable task which
requires considerable care and expertise. In the text to follow the three most common seaming
methods will be specifically addressed in as much detail as possible.  Such details are at the heart
of proper field seaming of polyethylene FM] _/s. The specific methods to be described are the
following:
     ° extrusion fillet seams
     • extrusion flat seams
       hot wedge (or hot shoe) seams
                                           9

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      TABLE 3. VARIOUS SEAMING METHODS FOR POLYETHYLENE FMLS (modified from reference #11)
Method
Extrusion Fillet*
Extrusion Flat*
Hot Air
Hot Wedge*
(a) Single Track
(b) Dual Track
Dielectric
Ultrasonic
Electric Resistance
Welding
Seam Confiauration
_^







_^~~ «cr" .Jj" ' ic^i
^5






Tvoical Rate
200 ft/hr.
300 ft/hr.
50 ft/hr.
300 ft/hr.
300 ft/hr.
unknown
unknown
unknown
Comments
Upper and lower sheets must be ground
Upper sheet must be beveled for 50 mil and greater
Height and location are hand controlled
Can be rod or pellet fed
Extrudate must use same polymer compound
Air heater can preheat sheet
Routinely used for difficult details
Upper and lower sheets must be ground
Good on long flat surfaces
Highly automated and patented machine
Cannot be used for close details
Extrudate must use same polymer compound
Air heater can preheat sheet
Controlled pressure and temperature
Good to tack sheets together
Hand held and automated devices
Air temperature fluctuates greatly
No extrudate added
Single and double tracks available
Double track may be patented
Built-in nondestructive test
Cannot be used for close details
Highly automated machine
No extrudate added
Controlled pressure for squeeze-out
Only for factory seams
Cannot be used for close details
No extrudate added
New technique for FMLs
Sparse experience in the field
Capable of full automation
No extrudate added
New technique for FMLs
Still in development stage
No extrudate added
Wire coating must use same polymer compound
Wires provide possibility of doing spark test
'Methods described in this manual

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5.1 FML Preparation
                     5. DETAILS OF EXTRUSION FILLET SEAMS
    (a)  Note, that this document assumes that the proper FML has been delivered to the site
        and has been brought to its exact plan position for final installation and -seaming,.'  "

    (b)  The two FMLs to be joined must be properly positioned such that a minimum of 4 in.
        of overlap exists.                  1

    (c),  If the overlap is insufficient, lift the FML up to allow air beneath it and "float" it into
        proper position. Avoid dragging FML sheets particularly when they are on rough soil
        subgrades since scratches in the material can create various stress points of different
        depths and orientations.             '
    (d)  If the overlap is excessive and is to
                                  be removed it should be done by trimming the
                         If this is not possi sle and the upper sheet must be trimmed do not
                         unshielded blade to cut off the excessive amount because; the blade
lower sheet only.
use a knife with an
facing downward can easily scratch the underlying FML in a very vulnerable location.
A shielded blade or a hook blade should be used to trim  off the excess FML.  A
photograph of such a device is shown in Figure 2.  Whenever possible it should be
used from beneath the liner in an upward cutting motion.         .  ,1 .*  .
             Figure 2. Type of Hook Blade Used for the Cutting of Liner Materials

                                          II

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(e)  All cutting and preparation of odd shaped sections or small fitted pieces must be
    completed at least 50 ft ahead of the seaming operation so that seaming may be
    continued with as few interruptions as possible.

(f)  Check the two opposing FMLs to be joined for acceptability as far as lack of scratches,
    blemishes, flaws, color, texture and other visual characteristics are concerned.

(g)  If the plans require overlaps to be shingled in a particular direction this should be
    checked.

(h)  Excessive undulations (waves) along the seams during the seaming operations should
    be avoided.  When this occurs due  to either the upper or lower sheet having more slack
    than the other, it often leads to the undesirable formation of "fishmouths" which must
    be trimmed, laid flat and reseamed via a patch.

(i)  There generally will be designed-in slack that may appear to be excessive in the FML's
    depending on the  ambient temperature, length of time  the FML will be exposed,
    location in the facility, etc.  This is a design consideration and the plans and
    specifications must be project specific on the amount and orientation of slack.

(j)  The sheets which are overlapped  for seaming must be clean. If dirty, they must be
    wiped clean with dry rags.

(k)  The sheets which are  overlapped for seaming must be completely free of moisture in the
    area of the seam. Air blowers are usually preferred over rags because sufficient dry
    rags are usually not available to keep the FML dry enough to be suitable for seaming.

(1)  Seaming is not allowed during rain or snow, unless proper precautions  are made to
    allow the seam to be made on dry FML materials, e.g., within an enclosure or shelter.

(m) The soil surface beneath the FMLs cannot be saturated, because the heat of seaming
    will attract water to the region to be joined. Ponded water on the soil's surface beneath
    the FML is never allowed.

(n)  If the soil beneath the FML is frozen, the heat of seaming can thaw the frost allowing
    water to be attracted to the region to be joined. This is  not acceptable and must be
    avoided.

(o)  Ambient temperatures for seaming should be above freezing, i.e. 32°F (0°C) unless it
    can be proven via test strips  that good  seams can be fabricated at lower temperatures.
    However, temperature (per se) is less a concern to good seam quality than is  moisture.

(p)  For cold weather seaming, it may be  advisable to preheat the sheets with a hot air
    blower, to use a tent of some sort  to prevent heat losses during seaming and to make
    numerous test  welds in order to determine appropriate seaming conditions, e.g.,
    equipment temperatures may have to  be set higher and seaming rates slowed down
    during cold weather seaming.

(q)  Ambient temperatures for seaming should be below 105°F (40.6°C) measured two feet
    above the liner at which point the FML is significantly warmer and working conditions
    become extremely difficult.
                                       12

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5.2: Equipment Preparation

    (a)
    (b)
A working and properly functioning small electric generator must be available within
close proximity of the seaming region and with adequate extension cords to complete
the entire seam. The generator must be rubber tired, or placed on a smooth plate such
that it is completely stable so that nojdamage can occur to the FML or to the .clay liner.
Fuel (gasoline or diesel) for the generator must be stored off of the FML.

A hand-held electric rotary grinder having a circular disk grinding plate approximately
4.0 in. in diameter and adequate #80Jgrit paper must be available. See the photograph
of Figure 3 following.  Also acceptable is #100 grit paper which is finer than #80.
Sandpaper coarser than #80, e.g. #6(1 is not acceptable.
       Figure 3. Hand-Held Electric Rotary Grinder with Circular Disc Grit Grinding Paper
    (c) " A hot air welder or hot wedge with temperature capability to 480°F (250°C) must be
        available to tack weld the FML sheets after they are properly positioned.
    (d) The extrusion fillet welding apparatus, may be of two types depending upon the location
        where the seams are to be made.  Either rubber wheeled, automated seam extruders or
        hand-held portable extruders are avaijlable.  Photographs of various systems are shown
        inFigure 4.
                                          13

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Figure 4. Photographs of Various Types of Extrusion Fillet Welding Devices
                      Upper:  Automated Type
                      Lower:  Hand Held Type         •


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    (e)  All extrusion fillet seaming devices must be equipped with properly functioning
         temperature controllers displaying the temperature in the extrusion barrel.            .
                                     s*  ^   I       '!,-' : ?}$?     -                  ' '.   .
    (f)  All types of extrusion fillet seaming (devices have teflon or metal dies of different
         shapes and sizes where the extrudate exits onto the FML. These dies must be inspected
         for wear, sharp notches or creases, and for correctness for the particular application.
         Commercially available extrusion die's are available for 30, 40, 60, 80 and 100 mil
         sheet thicknesses.  Many, however, are specifically made or modified by installers.
         Both the width and thickness of the extrudate are dependent upon the proper die.  It
         must be field verified for correctness, a detail which will be described later.
    (g)  Adequate extrudate welding rod or pel
        resin must be properly formulated with
                                    ets, of exactly the same type as the FML itself,
         must be available, dry, clean and ready for feeding through the extruder.  All extrudate
                                    the same compound as the FML sheet material.
        If in doubt, chemical fingerprinting methods must be performed.(6)  All extrudate
        material must be kept free of dirt, debris and foreign matter.

5.3 Actual Seaming Process
    (a)
Whenever the FMLs are 50 mils in thickness or greater, the leading edge of the upper
sheet must be ground to a 45° bevel. It is important that the sheet to be beveled is lifted
up off of the lower sheet so that no grind marks whatsoever occur in the lower sheet,
see Figure 5 following. Note that grinding must be done prior to tack welding in order
to exercise control against damage to the lower sheet.
                Grinding Wheel
                                                        Extreme care must be exercised
                                                        so that this surface is not
                                                        touched with grinding wheel
                                 3.0" Min.
  Figure 5. Preparing the Bevel of the Upper FML for Liner Thicknesses Greater Than 50 Mil


    (b) Following the preparation of the bevel, the upper sheet is lowered and laid flat on the
        lower sheet and the horizontal surfacb grinding of both upper and lower sheets is
        completed as shown in Figure 6. All ofjthe surface sheen in the area to be seamed must
        be totally removed. Heavy textured grit sand paper coarser than #80 size that leaves
        deep ridges that might become stress points or leak channels are unacceptable. All of
        the material that has been ground from
        from the actual seaming zone.
                                    the FML sheets must be wiped or blown away

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                                           Extrudate Width
                                                       ~
                                            To Be Covered
                                     1/2"  to  3/4"
                   Upper FML
1/2"  to  3/4"
                                                                   Lower FML
                                    3.0" Min.
             Surfaces To Be
          Prepared By Grinding
Figure 6. Proper Orientation and Grinding Preparation of Sheets Prior to Tacking and Extrudate
         Placement


    (c) The preferred orientation of grinding marks is perpendicular to the seam direction rather
        than parallel to it.  It should be mentioned  that this is  a  slower process for the
        installation contractor to perform.  The reason for parallel grinding is that deep, parallel
        grooves decrease parent material thickness and can lead to seam failure in the parent
        material.  Although the film tear bond criterion is usually satisfied it is often at a
        reduced stress due to the thinner material. Additionally, parallel grinding marks .can
        give rise to stress crack initiation. See Figure 7 following for the distinction between
        the two different patterns.  Please note that both grinding patterns are excessive in their
        extent beyond the extrudate and are shown for illustration purposes only.

    (d) The depth of the grinding marks (whatever the direction) is  of paramount interest.
        Grind marks should never be more than 10% of the sheet thickness and in general
        should only be approximately 5% of the sheet thickness.  The objective of grinding is
        to remove oxide layers and waxes from the surfaces and to roughen the sheets.

    (e) Regarding the extent of the grinding, the general rule should be that grinding marks
        should not appear beyond 1/4 inch of the extrudate after it is placed,'see Figure 8.
        Thus if the final extrudate bead width is 1.5 in. width, the total grinding pattern should
        be no more than 2.0 in., which is one inch on each side of the weld centerline.

    (f) Grinding shall be completed no more than 10 minutes before seaming takes place so
        that surface oxide layers are not recreated prior to placement of the extrudate.

    (g) The hand held grinder used for the grinding process must be turned off whenever it is
        not in  use. Never leave it running. If it contacts the liner while running it will cause
        serious damage.

    (h) A hot  air or hot wedge welder may be used to  "tack" the two sheets together thereby
        maintaining proper alignment and intimate contact between the two sheets.  The tacking
        should be just that, it is not meant to be the primary seam. There should be no heat
        distortion showing on the surface of the upper  sheet. Note that if the tacking is done
        before the beveling and grinding operations described in steps "a" through "g", then
        extreme caution  against  overgrjnding  and mistakes must be taken. It might  be
                                           16


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Figure 7.  Photographs of Different Orientations of Grinding Patterns
          Upper: Grind Marks Perpendicular to Seam (Recommended Pattern)
          Lower: Grind Marks Parallel to Seam (Not Recommended Pattern)
          (Note, however, that both situations have grinding far in excess of what is
          required and are shown for illustration of the grinding patterns only, see
          Figure 8 following)        '
                                     17

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Figure 8.  Photographs of Different Extent of Grinding Patterns After Extrusion Fillet Seaming
          Upper:  Excessive and Irregular Grinding Beyond Extrudate
          Lower:  Acceptable Grinding Pattern Just Showing Beyond Extrudate
                                         18

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         necessary to provide a wedge to lift up the overlying FML as shown in Figure 9 or to
         use a thin metal sheet with rounded corners and slide it along the grinding area on top
         of the bottom sheet. Double sided tape should not be used, as it includes trace levels of
         hydrocarbon solvents that may be released and affect environmental monitoring.
                       Hot Air Tacking
                           Zone
                          '
                          -1.0"
         Upper FML
                     -Temporary
                  s  Propping
                      Wedge
                                                            Lower FML
Figure 9. Smooth Propping Wedge Used When Tacking of Sheets is Done Before Surface
         Grinding of the FML Sheets


    (i)  The extrusion welder is to be pur.ge.d ^f all heat degraded extrudate in the barrel prior to
        beginning a seam.  This must be done' every time the extruder is restarted after a 2 min.,
        or longer, down time. The purged extrudate should not be discharged onto the surface
        of previously placed liner nor on the prepared subgrade where it would eventually form
        a hard lump under the liner.

    (j)  Extrudate in the form of a molten, vi scous bead is now deposited over the overlapped
        seam.  The center of the extrudate must be directly over the edge of the upper FML.
        The extrudate should cover the grind marks on each side of the upper FML to within
        1/4 in. Note the photographs following this section for proper extrudate placement.

    (k) The extrudate thickness should be approximately two times the specified sheet
        thickness measured from the top of the bottom sheet to the top or crown of the
        extrudate, see Figure  10. Excessive [squeeze-out (or flashing) as shown in the  lower
        sketch of Figure 10 is acceptable as'long as it is equal on both  sides and will not
        interfere with subsequent vacuum box testing. If, however, pulling up on the extrudate
        squeeze-out pulls the entire extrudare off of the sheet it is obviously unacceptable.
        Squeeze-out generally means that the extrusion die was not riding directly against the
        FML, the extrudate temperature was
        was too slow.
improper for adequate flow, or the seaming rate
                                          19

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                                             Extrudate
          nt"      Upper FML
             T
Lower FML
t
1
4
1
I
\
> i
r- I '
k
^ 1
                             Upper FML
                                                                    Squeeze-Out
                                                                    or Flashing
                                                                   Lower FML
        Figure 10. Schematic Diagrams of Various Cross Sections of Fillet Extrusion Seams


     (1)   Where possible, inspect the underside of the lower FML for heat distortion.  This can
         be done at the end of seams and where samples are cut out of the seam.  A slight
         amount of thermal "puckering" on relatively thin FMLs (for example, less than 50 mils)
         is acceptable. It signifies that heat was felt through the entire sheet. If the underside is
         greatly distorted, however, lower the temperature or increase the rate of seaming. For
         thick FMLs of 80 mils or greater there should never be any indication of this type of
         thermal "puckering".

     (m) Depending upon the records to be kept, one might record  a number of different
         temperatures. For example, the temperatures of the extruding apparatus' melt zone, the
         extrudate temperature at the nozzle, the FML surface temperature and the ambient
         temperature. This is a site specific decision.

5.4 After Seaming

    (a)   A smooth insulating plate or heat insulating fabric is always to be placed beneath the hot
         extrusion welding apparatus after usage. The tip die and barrel must not be placed on
         any FML or other geosynthetic surface ~ it is extremely hot and can cause severe
         damage.

    (b)   Visual inspection of the extrudate bead should be made particularly for straight line
         alignment, height, and uniformity of surface texture.  There should be no bubbles or
         pock marks in the extrudate.  Such surface details  on the extrudate indicates the
         presence of air, water or debris within the extrudate rod or pelletized polymer.

    (c)   Grind marks should only be visible for 1/4 in. beyond the extrudate.  They should be
         extremely faint and never appear as heavy gouge marks, recall the earlier photographs.
         Excessive grinding also has a depth consideration. As stated previously, excessive is
         considered to be  greater than 10% of the  FML thickness. If it is excessive, do not
         apply additional extrudate over the original  extrusion fillet seam.  It is necessary to
                                          20

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    place a cap strip over the entire seam where the excessive grinding is observed.

(d) If properly planned, each seam run shot Id terminate at a panel end, at a specific detail
    or on a long straight run where it can be easily resumed.

(e) If the seaming needs to be interrupted at mid-seam, the extrudate end should trail off
    gradually, rather than terminate with a large mass of solidified extrudate.

(f)  Where extrusion fillet welds are temporarily terminated long enough to cool, they must
    be  ground prior  to applying new extrudate over the existing seam.  This restart
    procedure must necessarily be followed! on patches, pipes, fittings, appurtenances and
    "T" or "Y" seams.                  1

(g) Photographs of various types of extrusion fillet seams follow in Figure 11.
                                        21

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Figure 11. Photographs of Cross Sections of Various Types of Extrusion Fillet Seams
          Upper:  Machine Extrusion Seam without Squeeze-Out
          Middle:  Hand Held Extrusion Seam without Squeeze-Out (note thermal puckering
                  at bottom at seam)
          Lower:  Hand-Held Extrusion Seam with Squeeze-Out
                                       22

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                      6. DETAILS OF EXTRUSION FLAT SEAMS
6.1 FML Preparation
    (a)  Note, that this document assumes that the proper FML has been delivered to the site
        and has been brought to its exact plai position for final installation and seaming.

    (b)  The two FMLs to be joined must be properly positioned such that a minimum of 4 in.
        of overlap exists.

    (c)  If the overlap is insufficient, lift the FML up to allow air beneath it and "float" it into
        proper position. Avoid dragging FML sheets particularly when they are on rough soil
        subgrades since scratches in the material can create various stress points of different
        depths and orientations.

    (d)  If the overlap  is excessive and is to be removed it should be done by trimming the
        lower sheet only.  If this is not possible and the upper sheet must be trimmed do not
        use a knife with an unshielded bladej to cut off the excessive amount because the blade
        facing downward can easily scratch the underlying FML in a very vulnerable location.
        A shielded blade  or a hook blade should be used to trim off the excess FML.  A
        photograph of such a device is shown in Figure 12. Whenever possible it should be
        used from beneath the liner in an upward cutting motion.
             Figure 12. Type of Hook Blade Used in the Cutting of Liner Materials

                                         23

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(e)  All cutting and preparation of odd shaped sections or small fitted pieces must be
    completed at least 50 ft ahead of the seaming operation so that seaming may be
    continued with as few interruptions as possible.

(f)  Check the two opposing FMLs to be joined for acceptability as far as lack of scratches,
    blemishes, flaws, color, texture and other visual characteristics are concerned.

(g)  If the plans require overlaps to be shingled in a particular direction this should be
    checked.

(h)  Excessive undulations (waves) along the seams during the seaming operation should be
    avoided. When this occurs due to either the upper or lower sheet having more slack
    than the other, it often leads to the undesirable formation of "fishmouths" which must
    be trimmed, laid flat and reseamed via a patch.

(i)  There  generally will be excessive slack in the FML's depending on the ambient
    temperature, length of time the FML will be exposed, location in the facility, etc. This
    is a design consideration and the plans and specifications must be project specific on the
    amount and orientation of slack.

(j)  The sheets which are overlapped for seaming must be clean.  If dirty, they must be
    wiped clean with dry rags.

(k)  The sheets which are overlapped for seaming must be completely free of moisture in the
    area of the seam. Air blowers are usually preferred over rags because sufficient dry
    rags are usually not available to keep the FML dry enough to be suitable for seaming.

(1)  Seaming is not allowed during rain or snow, unless proper precautions are made to
    allow the seam to be made on dry FML materials, e.g., within an enclosure or shelter.

(m) The soil surface beneath the FMLs cannot be saturated, because the heat of seaming
    will draw the water into the region to be joined. Ponded water on the soil's surface
    beneath the FML is never allowed.

(n)  If the soil beneath the FML is frozen, the heat of seaming can thaw the frost allowing
    water to be drawn into the region to be joined. This is not acceptable and must be
    avoided.

(o)  Ambient temperatures for seaming should be above freezing, i.e. 32°F (0°C) unless it
    can be proven via test strips that good searns can be fabricated at lower temperatures.
    However, temperature (per se) is less  a concern to good seam quality than is moisture.

(p)  For cold weather seaming, it may be advisable to preheat the sheets with a hot air
    blower, to use a tent of some sort to prevent heat losses during seaming and to make
    numerous  test  welds in  order to determine appropriate seaming conditions, e.g.,
    equipment temperatures may have to be set higher and seaming rates slowed down
    during cold weather seaming.

(q)  Ambient temperatures for seaming should be below 105°F (40.6°C) measured two feet
    above the liner at which point the FML is significantly warmer and working conditions
    become extremely difficult.
                                      24

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6.2 Equipment Preparation

    (a) A working and properly functionir
g small electric generator must be available within
        close proximity of the seaming region and with adequate extension cords to complete
        the entire seam. The generator must be rubber tired, or placed on a smooth plate such
        that it is completely stable so that rlo damage can occur to the FML or to the clay liner.
        Fuel (gasoline or diesel) for the generator must be stored off of the FML.

    (b) Grinding of the opposing FML surfaces to be joined is to be done with a hand held
        rotary grinder having #80 disk sandpaper. Finer paper's, e.g. #100, are allowable, but
        not coarser.

    (c) The grinding of the lower sheet is to be done first, with a suitable width (approximately
        2 to 3 inches) being prepared such that surface oxide is removed and the sheet is
        roughened. The depth of the grind marks must be no greater than 10% of the original
        thickness of the sheet.

    (d) The upper sheet is bent over  backwards so that its underside  can be ground at the
        location where it will meet the loWer sheet's prepared surface. It is important to note
        that all ground sheet must eventually be covered with extrudate to within 1/4 in.

    (e) Alternatively to the type of surface preparation just described in parts "b", "c", and "d",
        an automated wire brush technique can be used. With this instrument it is possible to
        prepare the bottom of the top shee|t and the top of the bottom sheet at the same time.
        See Figure 13.
                             Grinding Areas
                ROTARY GRINDER
                                                                           Grinding
                                                                           'Area
                                                         WIRE BRUSHING
                        i               ,-.--.,-..'.           ,•
  Figure 13. Grinding Locations and Method Used in the Preparation of Flat Extrusion Seams
    (f)  The extruder itself must be purge'd of old extrudate.  This extrudate should not be
        ejected on the previously placed FML nor on the soil subgrade where it will form a hard
        lump beneath title liner.            I

    (g)  Some extrudate should also be ejeqted to see if the nozzle is the appropriate width and
        thickness. Usually flat extrudate ribbons are 1.5 in. to 2.0 in. width and about 60 mils
        thick.  However, welding speed will affect this thickness, which ranges from about 20
        mils thick when fast, to 80 mils thiick when slow. Properly functioning temperature
        controllers must monitor the extrudate temperature.  A photograph and schematic
        diagram of a extrusion flat seaming device is given in Figure 14.
                                         25

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                                      Welding Direction
                                  ContactHOPEI
                                  Pressure   Extrudate Tube&Dle
                                            With Hot Air Jets
                           Principles of Extrusion Welding For Site Joining
Figure 14. Photograph and Schematic Diagram of Flat Extrusion Seaming of FML Sheets
                                                26


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    (h) Preheating of the opposing surfaces to be joined is done by air jet which must be full
        seam width at a constant temperature.  The nozzle should be inspected for obstructions
        on a daily basis. The actual temperature of the exjrudate varies with ambient conditions
        but is approximately 480°F (250°C).  This temperature causes surface softening.  Due
        to the rate of travel, however, the sheet interior is not fully melted.  .

    (i)  Pressure rollers should be inspected for sharp edges or irregular surfaces. On some
        systems these rollers are in tandem where the front set (nearest the extrudate) should be
        set at a lower pressure than the rear set.

6.3 Actual Seaming Process

    (a) The preheat system previously described serves the purpose of preparing the previously
        ground surfaces to accept the extrudate in the form of a ribbon.

    (b) The extrudate is placed at about 480°F (250°C) in a full width, full thickness ribbon,
        see Figure 15.  It cannot be visually inspected since it is occurring between the two
        sheets, directly following the hot air preparation and directly preceding the pressure
        rollers.

                                                  Extrudate

-.'."••'• Lower FML
                                                                             < t
                                                                         < 3t
Figure 15.  Schematic Diagram of Cross Section of Extrusion Flat Seam with Extrudate Out to
           the Edge of the Upper FML
    (c)
    (d)
    (e)
The outside edge of the seam should be visually observed to ensure that the extrudate is
embedded between the liner sheets. JAs will be seen in the photographs following this
section, three cases are possible.  These are the edge of the extrudate being somewhat
under the overlapping sheet, exactly even with  it, or beyond it  in  the form of
"squeeze-out".  Either one of the latter two situations are necessary if vacuum box
testing of the seam is subsequently required.

The rollers exert considerable pressure and are adjusted according to sheet thickness.
Indentations on the surface of the upper FML should be observable but should not
create a rut, e.g., the indentation should be barely capable of being felt.
                                surfa
Thermal "puckering" of the upper surface of the overlying FML should not appear.
Although the lower surface of the underlying FML is rarely, seen (except at sheet ends,
trial strips, or where samples are taken) it should not be puckered.  Thermal puckering
signifies excessive heat and/or insufficient seaming rate.
    (f)   Depending upon the records to be kept, one might record a number of different
         temperatures. For example, the temperatures of the extruding apparatus melt zone, the
         extrudate temperature at the nozzle the FML surface temperature, and the ambient
         temperature. This is a site specific decision.
                                           27

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6.4 After Seaming

    (a) Hand held grinders or mechanical wire brushes are always to be turned off when not in
        use. If placed on the FML while running they can cause considerable damage.

    (b) A smooth insulating plate or heat insulating fabric is to be placed beneath  any hot
        welding apparatus after usage.

    (c) Grinding marks on the lower sheet of the completed seam should be observable but
        only for a distance of 1/4 in. beyond the extrudate. Note, however, that only the lower
        sheet can be inspected in this regard.

    (d) Placement of the extrudate to the edge of the upper sheet or squeeze-out of the extrudate
        beyond the edge is necessary if vacuum box testing is required.

    (e) If properly planned, each seam run should terminate at a panel end, specific detail or on
        a long straight run where it can be easily resumed.

    (f)  Where extrusion flat welds are terminated long enough to cool, the start-up continuation
        seam must completely melt the leading edge of the cooled seam. Since this is occurring
        beneath the overlapped sheet and cannot be observed, the location must be marked for
        subsequent vacuum box testing. If it fails, a  cap strip must be placed over the general
        area.

    (g) The extrudate end should trail off gradually, rather than terminate with a large  mass of
        solidified extrudate.

    (h) Photographs of the various types of extrusion flat seams are shown in Figure 16.
                                          28

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Figure 16. Photographs of Cross Sections of Extrusion Flat Seams
          Upper:   Extrudate Short of the Edge of Overlapping Sheet
          Middle:  Extrudate Exactly at the Edge of Overlapping Sheet
          Lower:   Extrudate Squeeze-Otit Beyond the Edge of Overlapping Sheet
                                     29

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                        7. DETAILS OF HOT WEDGE SEAMS

7.1 FML Preparation

    (a)  Note, that this document assumes that the proper FML has been delivered to the site
         and has been brought to its exact plan position for final installation and seaming.

    (b)  The two FMLs to be joined must be properly positioned such that typically 3 to 5 in. of
         overlap exists. The actual value depends on the width of the wedge element to be used.

    (c)  If the overlap is insufficient and it does not fully cover the wedge, lift the FML up to
         allow air beneath it and "float" it into proper position. Avoid dragging FML sheets
         particularly when they are on rough soil subgrades since scratches in the material can
         create various stress points of different depths and orientations.

    (d)  If the overlap is excessive and is to be removed it should be done by trimming the
         lower sheet only.  If this is not possible and the upper sheet must be trimmed do not
         use a knife with an unshielded blade to cut off the excessive amount because the blade
         facing downward can easily scratch the underlying FML in a very vulnerable location.
         A shielded blade  or a hook blade should be used to trim off the excess FML. A
         photograph of such a device is shown in Figure 17. Whenever possible it should be
         used from beneath the liner in an upward cutting motion.
              Figure 17. Type of Hook Blade Used in the Cutting of Liner Materials

                                          30

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     completed at least 50 ft ahead of the
 (e)  All cutting and preparation of odd shaped sections or small fitted pieces must be
                                    seaming operation so that seaming may be
 (f)
continued with as few interruptions as possible.

Check the two opposing FMLs to be joined for acceptability as far as lack of scratches,
blemishes, flaws, color, texture and other visual characteristics are concerned.
 (g)  If the plans require overlaps to be shingled in a particular direction this should be
     checked.

 (h)  Excessive undulations (waves) along the seams during the seaming operation should be
     avoided.  When this occurs due to either the upper or lower sheet haying more slack
     than the other, it often leads to the undesirable formation of "fishmouths" which must
     be trimmed, laid flat and reseamed via a patch.                              .

 (i)   There generally will be excessive slack in the FML's depending on the'' ambient
     temperature, length of time the FML will be exposed, location in the facility, .etc. This
     is a design consideration and the plans and specifications must be project specific on the
     amount and orientation of slack.                  ,

 (j)   The sheets which are overlapped for seaming must be clean.  If dirty, they  must be
     wiped clean with dry rags.

 (k)  The sheets which are overlapped for seanjiing must be completely free of moisture in the
     area of the seam. Air blowers are usually preferred over rags  because sufficient  dry
     rags are usually not available to keep the JFML dry enough to be suitable for seaming.

 (1)   Seaming is not allowed during rain or snow, unless,proper precautions are made to
     allow the seam to be made on dry FML materials, e.g., within an enclosure or shelter.

 (m)  The soil surface beneath the FMLs cannot be saturated, because the heat of seaming
     will draw the  water into the region to be joined.  Ponded water on the soil's surface
     beneath the FML is never allowed.

 (n)  If the soil beneath the FML is frozen, thfe heat of seaming can thaw the frost allowing
     water to be drawn into the region to be joined. This is not acceptable and must be
     avoided.                         .     , ;;

(o)  Ambient temperatures for seaming should be above freezing, i.e. 32°F  (0°C) unless it
     can be proven via test strips that good seams can be fabricated at lower temperatures.
     However,  temperature (per se) is less a concern to good seam quality than is moisture.

(p)  For cold weather seaming, it may be advisable to preheat the sheets  with a hot air
     blower, to use a tent of some sort to prejyent heat losses during seaming and to make
     numerous test welds  in order  to determine appropriate  seaming conditions, e.g.,
     equipment temperatures may  have to be, set higher and seaming rates slowed down
     during cold weather seaming.          I

(q)  Ambient temperatures for seaming shoul i be below 105°F (40.6°C) measured two feet
     above the liner at which point the FML is1 significantly warmer and working conditions
     become extremely difficult.

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7.2 Equipment Preparation

    (a)  A working and properly functioning small electric generator must be available within
        close proximity of the seaming region and with adequate extension cords to complete
        the entire seam. The generator must be rubber tired, or placed on a smooth plate such
        that it is completely stable so that no damage can occur to the FML or to the clay liner.
        Fuel (gasoline or diesel) for the generator must be stored off of the FML.

    (b)  Hot wedge seaming devices are completely self contained systems sometimes referred
        to as a "mouse" or "hot shoe".  Photographs of different types of hot wedge seaming
        devices are shown in Figure 18.
                   Figure 18. Various Types of Hot Wedge Seaming Devices

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 (c)  As the hot wedge method is one of melting the opposing surfaces of the two FMLs to
     be joined, no grinding of sheets is necessary, nor allowed.
                                  i  *   I .,  , ••'-•?'*&  -*•
 (d)  Tacking of the FML sheets as done in extrusion fillet seaming is not possible since the
     wedge must travel between opposing parallel sheets which are to be joined.

 (e)  The hot wedge itself, or "anvil", should be inspected to see that it is uniform and
     reasonably tapered. Various types arej currently available. Some are smooth surfaced
     while other have patterned ridges in the direction of the seam. The taper dimensions
     vary according to different types of machines. The major point for inspection is that no
     sharp edges should exist wherever the FML sheet surfaces must pass.

 (f)  A single hot wedge has an anvil which is uniform over its entire surface.  A dual wedge
     has a split anvil forming two separate tracks.  See the sketches of Figure 10.  If a dual,
     or split, hot wedge seam is being mace, the recessed space for the central unseamed
     portion should be examined.
               Single  Hot Wedge
                                                                              -3'
                                                          3"
                                        tnei
                                                  Dual (Split)  Hot Wedge
Figure 19.  Diagrams of the Hot Wedge Elements (i.e., the Anvil) tfpon Which the Two
           Sheets to be Joined are Passed

(g) When knurled rollers are used for applying pressure on the sheets and driving the
    device they immediately follow the anvil.  They should be inspected for sharp surfaces
    and for wheels that are not smoothly beveled on the outside (both of which are not
    allowed).

(h) If a chain drive powers the device and abplies pressure to the nip/drive rollers it should
    be inspected for synchronization of travel and proper functioning.
(i)  As the FML sheet materials pass through the machine, they must come in contact with
    the full width of the wedge in order to heat the material properly.  Idler rollers or similar
                                       33

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        devices, on both sides of the wedge are adjustable and must make the material conform
        to,the wedge as it passes through the machine.  These roller heights are adjustable.
        Adjustment of these devices should be made while the wedge is cold. The procedure
        for doing this with some equipment is as follows: Insert the lower and upper layers of
        FML material in the nip/drive rollers, which will change the wedge height between the
        idler rollers.  Then, lock the wedge in position, and adjust the idlers so that one layer
        fits snugly between the wedge and the idlers.   The wedge has an adjustment that is
        actually a stopping device  to keep the wedge from being pulled into the nip/drive
        rollers.  Caution must be taken to ensure that the wedge is not adjusted too closely to
        the nip/drive rollers, especially when material is not going through the machine.  The
        drive, or wedge units, must be disengaged before the material runs completely out of
        the machine. Serious damage will occur to the FML sheets if the wedge gets pulled
        through the nip/drive rollers.

    (j)  The front part of the seaming device should be inspected for sharp corners and irregular
        details which may damage the FML's.

    (k) Temperature controllers on the wedge device should be set according to thickness,
        ambient temperature, and rate of seaming.  The "test strip" mentioned in the beginning
        of this manual is  essential in this regard.  Temperature gages should be checked for
        accuracy and repeatability.

    (1)  Force sensors at the nip rollers should be checked for accuracy and repeatability.

7.3 Actual Seaming Process

    (a) The hot wedge system  (i.e., the "mouse" or "hot shoe") should be properly positioned
        for the making of the desired single or dual (split) seam.

    (b) The principle of the hot wedge is that both surfaces to be joined come into intimate
        contact with the hot wedge, or anvil. The anvil slides between both layers of FMLs
        and fusion is brought about by compressing the two melted surfaces together, causing
        an  intermingling  of the polymers from both sheets. The hot anvil itself reduces the
        surface tension of the  viscous polymer sheets and acts as a scraper/mixer, followed
        closely by the nip rollers which squeeze the two FML's together, see Figure 20 for
        details.
                                                                               FMLs
                                     Direction of Travel
    Figure 20. Details of the Hot Wedge System Showing Relative Positions of the Hot
               Wedge, Rollers and Sheets to be Joined.
                                          34

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 (c)  Temperature settings will vary according to the FML thickness being installed, the
     ambient temperature and the rate of travel.  It is typically about 480°F (250°C) and is
     initially determined based on results of the test strip.
 (d)  Ambient factors such as clouds, wind,
                                            and hot sun will require the temperature setting
 (e)
(f)
         of the wedge to vary.  Depending upon the records to be kept, one might record a
         number of different temperatures. For example, the temperature of the hot anvil, the
        :temperature of the sheet after seaming, the temperature of the sheet away from the
         seaming area and the ambient temperature.  This is a site specific decision.
          •..-...••       -   '•-•-•.-•         , I ;     ' '  '  '   ..;••!',•    -••'.,-••
         Power for the drive motor should be off when positioning the machine to make a seam.
         Manually place the machine within the [overlapped sheet of material. The sheets shall be
         guided between the idlers and the wedge, and into the drive/nip rollers.  This procedure
         is only possible when starting with two new  sheets.  When starting a weld in the
         middle of two sheets, the material must be loaded from the sides. The machine is to be
         picked up  a few inches, loading the bottom sheet first, and then the top sheet. As soon
         as the nip rollers are engaged and the wedge is in position, the power to the drive motor
         should be turned on. Once the sheets are between the nip rollers, they shall be engaged
         immediately, otherwise a melt-through will occur within,a.few seconds.  The hot
         wedge should be moved into position abd locked.

         It is necessary that the operator keep constant visual contact with the temperature
         controls, as  well as the completed seam coming out of the machine.  Occasional
         adjustments of temperature or speed vjdll be necessary to maintain a consistent, weld,
     Visual inspection and constant hand
     recommended.
(g)
                                            testing by the peel method (or other) is also
         On some soils, the device tends to "bulldoze" into the ground as it travels.  This causes
         soil to enter the weld, making the seam weak and unacceptable. To overcome this, it is
         recommended that the operator take some of the weight off of the front of the machine
         by lifting it slightly. Alternatively, some type of base for the machine to travel on could
         be provided. Strips of geotextile or geomembrane have proven effective to prevent this
         bulldozing effect. It might be required jto change the size of the rollers in loose soils.  It
         is recommended that at least two people work together in making hot wedge seams; one
         operator and one helper.

7.4 After Seaming

    (a)   A smooth  insulating plate or heat insulating fabric is to be placed beneath the hot
         welding apparatus after usage.
(b)  A slight amount of "squeeze-out"  or
                                            "flashing" is a good indicator that the proper
    temperatures were achieved, see the sketch of Figure 21. It signifies aproper seam in
    that some of the melted polymer was [laterally extruded out of the seam zone. If an
    excessive amount of hot melt is being^ extruded out, it is an indication of either too
    much heat or too much pressure. Reduce the temperature and/or pressure to correct the
    situation.

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                                          "Squeeze-Out" or
                                         ^ "Flashing"
Figure 21.  Schematic Diagram of Cross Section of Dual (Spilt) Hot Wedge Seam Illustrating
           Squeeze-Out


    (c)  For FMLs of 40 mil thickness and less, a long, low sinusoidal wavelength pattern in
         the direction of the seam along its top surface is indicative of a proper weld.  If the
         wave peaks become too close together, the machine speed should be increased until a
         satisfactory pattern is present. The absence of this wavelength pattern indicates that the
         machine speed should be decreased. FML's  40 mils in thickness and less require
         considerable visual inspection. There will be no wavy pattern for FMLs greater than 40
         mils in thickness due to the inherent stiffness of the thicker material.

    (d)  Nip/drive roller marks will always show  on the surface when using knurled rollers.
         Their depth should be visually observable,  but just barely evident to the touch.

    (e)  The hot wedge device has  only a few  adjustments that can be made, but it is very
         important that they be checked regularly. Cleaning of machine should be done at least
         daily.

    (f)  Photographs of cross sections of different types of hot wedge seams follow in Figure
         22.
                                              36

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Figure 22. Photographs of Cross Sections of Hot Wedge Seams
          Upper:   Single Hot Wedge Seam with Acceptable Squeeze-Out
          Middle:  Dual Hot Wedgej Seam with Excessive Squeeze-Out
          Lower:   Dual Hot Wedge Seam with Acceptable Squeeze-Out
                                37

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                           8. CONCLUDING STATEMENT

     The preparation and construction of polyethylene FML field seams requires a balance
between adequate strength, uniform continuity, and long-term performance.  The first two of
these items are the usual focus of most CQC/CQA efforts. For example, removal of field seam
samples are commonplace and their shear and peel testing and evaluation  protocol is well
established.  Similarly, seam uniformity and continuity is generally evaluated by any one of a
number of nondestructive test methods, the most common being the vacuum box test.

     Long-term performance, however, can only be assured by treating the seam's preparation
and fabrication as carefully as that of the parent sheet's preparation and manufacture.  It is in this
regard that this technical guidance document is written. Hopefully it falls midway between a
FML installers guide and the usual CQC/CQA  manual.  Its goal is to aid all parties involved in
polyethylene field seam fabrication, inspection and final acceptance in gaining  the insight
necessary to understand the processes involved.  By so  doing  a genuine sensitivity and
awareness of this critical element in the long-term performance of polyethylene FMLs will be
enhanced.
                                          38


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                                 9. REFERENCES
 1.   Frobel, R. K., "Methods of Constructing and Evaluating Geomembrane Seams," Proc.
     Conf. on Geomembranes, Denver, Colorado, 1984, IFAI, pp. 359-364.
 2.   Lord, A. E. Jr., Koerner, R. M. and Crawford, R. B., "Nondestructive Testing Techniques
     to Assess Geomembrane Seam Quality!" Proc. Mgmt. of Uncontrolled Haz. Waste Sites
     Washington, DC, 1986, HMCRI, pp. 272-276.
;3.  Overmann, L. K., "Nondestructive Seam Testing:  CQC Perspectives," Proc. on the
    Seaming of Geosynthetics, GRI-3, Philadelphia, PA, 1989, (to be published).
4.  Richardson, G. N., "Nondestructive Seam Testing:  CQA Perspectives," Proc. on the
    Seaming of Geosynthetics, GRI-3, Philadelphia, PA, 1989 (to be published).
5.  Matrecon, Inc., "Lining of Waste  Containment and Other Impoundment Facilities,"
    EPA/600/2-88/052, Sept. 1988.
6.  U.S. EPA Technical Guidance Document, "Construction Quality Assurance for Hazardous
    Waste Land Disposal Facilities," EPA/530-SW-86-031, NTIS PB87-132825, Oct. 1986.
7.  Haxo, H. E. Jr.,"Quality Assurance of Geomembranes Used as Linings for Hazardous
    Waste Containment," Jour. Geotex. and Geomemb., Vol. 3, No. 4, 1986, pp. 225-248.
8.  Apse, J. I., "Polyethylene Resins for Geomembrane Applications," Proc. on Aging and
    Durability of Geosynthetics, R. M. Koerner, Ed., Elsevier Appl. Sci. Pub. Ltd.,  1989, pp.
    159-176.
9.  ASTM, Proposed Document for Task Committee D-4000 on Plastic Liners, June,  1989.
10. Koerner, R.  M., Designing  with Geosynthetics, 2nd Edition, Prentice Hall Publ. Co.,
    Englewood Cliffs, NJ, 1990.          I
11. Koerner, G. R. and Bove, J. A., "Construction Quality Assurance of HOPE Geomembrane
    Installations," Proc. Geosynthetics '89, San Diego, CA, JJFAI, pp. 70-83.
                                       39

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                             10.  GLOSSARY OF TERMS

Anvil —  In hot wedge seaming of FMLs, the anvil is the wedge of metal above and below
     which the sheets to be joined must pass. The temperature controllers and thermocouples of
     most hot wedge devices are located within the anvil.

Buffing — An inaccurate term often used to describe the grinding of polyethylene FMLs to
     remove surface oxides and waxes in preparation of extrusion seaming.

Construction  Quality Assurance  (CQA) — A planned system  of activities whose purpose
     is to provide a continuing evaluation of the quality control program, initiating corrective
     action where necessary.

Construction  Quality Control (CQC) — Actions that provide  a means of controlling and
     measuring the characteristics of the manufactured and installed product.

Destructive Tests —  Tests performed on FML samples cut out of a field installation to verify
     specification performance requirements, e.g., shear and peel tests of FML seams during
     which the specimens are destroyed.

Drive Rollers — Knurled or rubber rollers which grip the FML sheets via applied pressure
     and propel the seaming device at a controlled rate of travel.

Extrudate — The molten polymer which is emitted from an extruder during seaming using
     either extrusion fillet or extrusion flat methods. The extrudate is initially in the form of a
     ribbon, rod, bead or pellets.

Extruder (factory) — A stationary machine with a driver screw for continuous forming of
     polymeric  compounds by forcing through a die.  It is used to manufacture films and
     sheeting.

Extruder (field) —  A portable  device with a driver screw for continuous forming of  a
     ribbon, rod or bead of extrudate for making FML seams.

Factory Seams  — The seaming of FML rolls together to make large panels for transportation
      and field installation:  Note that this is rarely done for polyethylene which is made in
     relatively wide sheets.

Field Seams — The seaming of FML rolls or panels together in the field making a continuous
      liner system.

Flashing — The molten  extrudate  or sheet material which is extruded beyond the die edge or
      molten edge, also called "squeeze-out".

Flexible  Member Liner (FML)  — Synonymous term  for geomembrane  as used in the
      containment of solid, liquid and vapor materials.


                                          40

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Geomembrane — An essentially impermeable membrane used as a solid, liquid or vapor
     barrier with foundation, soil, rock, earth, or any other geotechnical engineering-related
  ,   material as an integral part of a hum'an-made project,  structure, or system. (ASTM
 ,  ,  definition)
Geotextile — Any permeable textile used
with foundation, soil, rock, earth, or any other
  .   geotechnical engineering-related material as an integral part of a human-made project,
-..-• structure, or system. (ASTM definition)

Grinding— The removal of oxide layers ar d waxes from the surface of a polyethylene sheet
     in preparation of extrusion filletor extrusion flat seaming.

Gun—• Synonymous term for hand held extrusion fillet device.
High Density Polyethylene (HDPE) — A
polyethylene with a resin density, according to
     ASTM D3350, of 0.941 to 0.960 g/cc ^see polyethylene). The FML industry, however,
     uses the term HDPE as being a liner with a. compound density above 0.941 g/cc.

Hook Blade — A shielded knife blade confined in such a way that the blade cuts upward or is
     drawn toward the person doing the cutting.

Horn —• The vibrating device used with ultrisonic seaming which vibrates at high frequency
     causing friction and a subsequent melting of the surfaces that it contacts.

Mouse — Synonymous term for hot wedge, or hot shoe, seaming device.

Nondestructive Test — A test method whidh does not require the removal of samples from,
     nor damage to, the installed liner system. The evaluation is done in an in-situ manner as
     with a vacuum box test.

Oxide Layer —• The taking of atmospheric oxygen in the  form  of a surface film after a
     polyethylene sheet is extruded or otherwise manufactured.
Pinholes — Small imperfections in sheet
     contained material, i.e. leaks.
  seamed FMLs which allow for escape of the
Polyethylene (PE) — A semicrystalline thermoplastic polymer made largely of ethylene,
     often incorporating lesser amounts of one or more comonomers.

Pressure Rollers — Rollers accompanying a seaming technique which apply pressure to the
     opposing FML sheets to be joined.  They closely follow the actual melting process and are
     self-contained within the seaming device
Puckering — The thermal distortion of the seamed region after completion and cooling of the
     seam. It is often observed on the under sjide of the seam.

Quality Assurance — see construction qua ity assurance.
Quality Control -— see construction quality

Shielded Blade — A knife within a housing
     open fashion, i.e. a protected knife.
control.

which protects, the blade from being used in an
                                         41

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Squeeze-Out — see  "flashing".

Tensiometer — A set of opposing grips used to place a FML seam in tension for evaluating its
     strength in shear or in peel. Many units are portable and can be used in the field for direct
     information feed-back to the parties involved.

Test Strips  — Trial sections of  seamed FMLs used to  establish machine setting of
     temperature, pressure and travel rate for a specific FML under a specific set of atmospheric
     conditions.

Test Welds — see "test strips".

Vacuum Box — A commonly used type of nondestructive  test method which develops a
     vacuum in a localized region of an FML seam in order to evaluate the seam's tightness and
     suitability.
   U.S.GOVERNMENT  PRINTING OFF ICEI 1 989-648-163/O0335
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