United States
Environmental Protection
Agency
Office of Solid Waste
and Emergency Response
(5104)
EPA550-F-97-002a
May 1997
<>EPA
RUPTURE HAZARD OF PRESSURE
VESSELS
The Environmental Protection Agency (EPA| is issuing this^4/ert as part of its ongoing effort to
protect human health and the environment by preventing chemical accidents. Under CERCLA,
section 104(e) and Clean Air Act (CAA), EPA has authority to conduct chemical accident
investigations. Additionally, in January 1995, the Administration asked the Occupational Safety
and Health Administration (OSHA) and EPA to jointly undertake investigations to determine
the root causefs) of chemical accidents and to issue public reports containing recommendations
to prevent similar accidents. EPA has created a chemical accident investigation team to work
jointly with OSHA in these efforts. Prior to the release of a full report, EPA intends to publish
Alerts as promptly as possible to increase awareness of possible hazards. Alerts may also be
issued when EPA becomes aware of a significant hazard. It is important that facilities, SERCs,
LEPCs, emergency responders and others review this information and take appropriate steps
to minimize risk.
PROBLEM
Improperly operated or maintained
pressure vessels can fail
catastrophically, kill and injure
workers and others, and cause extensive
damage even if the contents are benign.
ACCIDENTS
In a 1996 accident, three workers were
killed and a number of others were
injured when a high-pressure vessel
containing air and water ruptured.
The vessel that ruptured was originally
designed with a working pressure of
1740 pounds per square inch (psi), but
was operating between 2000-3000 psi.
After a number of years of service, the
vessel developed a pin-hole leak. The
leak was repaired but not in adherence
with recognized codes. About a month
later, the vessel failed catastrophically at
the weld area. The vessel ripped apart
and rocketed through the roof. Major
pieces of shrapnel weighed from 1000 to
5000 pounds. Some pieces were thrown
a half mile away. Fortunately, people on
a nearby highway and a nearby
commuter railway narrowly missed
injury. Damage to the plant was
extensive and a portion of the state was
without phone and electrical services for
many hours.
This accident demonstrates the
potential danger of pressure
vessels if they are not properly
designed, constructed, operated,
inspected, tested, or repaired. The higher
the operating pressure and the larger the
vessel, the more energy will be released
in a rupture and the worse the
consequences. It should be emphasized
that the danger exists even if the vessel
contents are not flammable, reactive, or
explosive. In the case above, a vessel
containing only water and air ruptured
and released great energy. Had the
contents of the vessel been flammable
and/or toxic, the consequences would
probably have been magnified.
Factors In Pressure Vessel
Failure
The following conditions and factors
have played major roles in pressure
vessel accidents:
Operation above the maximum
allowable working and test pressures.
Chemical Emergency Preparedness and Prevention Office
> Printed on recycled paper
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Rupture Hazard of Pressure Vessels
Mai/1997
Improper sizing or pressure setting of relief
devices.
4- Improper operation of relief devices due to
faulty maintenance and failure to test
regularly.
4- Failure of the vessel due to fatigue from
repeated pressurization, general thinning
from corrosion or erosion, localized corro-
sion, stress corrosion cracking,
em.br.ittle.me.nl, holes and leaks.
4- Failure to inspect frequently enough.
4- Improper repair of a leak or other defect
involving welding and annealing that
embrittles and further weakens the vessel.
Hazards posed by a vessel can be worse if
repair welds are made without shutting
down and de-inventorying the vessel. If a
pressure vessel is repaired without remov-
ing the water, the quench effect of the water
can embrittle the steel.
4- Designing and constructing in accordance
with Section VIII of the ASME Boiler and
Pressure Vessel Code (ASME Code), "Rules
for Construction of Pressure Vessels" Divi-
sion 1, which covers vessels operating
between 15 psi and 3000 psi.
4 Marking the ASME Code on the vessel with
specified information that includes the
manufacturer, the serial number, the year
built, and the maximum allowable working
pressure for a specific temperature, and any
special suitability such as for low tempera-
ture and poisonous gases or liquids.
4- Having the vessel approved for installation
with the submission of drawings, specifica-
tions, welding details and calculations, and
having an authorized inspector be satisfied
with the welding and. witness the testing.
4- Operating at pressures below the maximum
allowable working pressure with pressure
relieving devices set according to the ASME
Code; testing at regular intervals.
4- Overpressuring and failure of the vessel
due to exothermic reaction or polymeriza-
tion.
Vessel exposure to fire.
Vessel
Requirements for pressure vessels vary widely
from state to state. Many states have a boiler
law, but others do not. Even for those states that
have a boiler law, typical practices (e.g.,
inspector requirements) for pressure vessels may
vary. State boiler laws that require general
adherence to American Society of Mechanical
Engineers (ASME) codes or National Board
Inspection Code (NBIC) usually require the
following for each pressure vessel:
4> Registering with the state boiler and. pres-
sure vessel department.
4> Periodically inspecting for corrosion and
defects, and testing according to the NBIC
"A Manual for Boiler and Pressure Vessel
Inspectors" or API 510, "Pressure Vessel
Inspection Code," for vessels in the petro-
chemical industry.
4- Repairing or altering only according to a
plan approved by an authorized inspector
and conducted by test-qualified welders.
The inspector must be satisfied, that the
repairs are performed according to NBIC or
API 510 and specify any necessary nonde-
structive and pressure testing. Increasing
the maximum allowable working pressure
or temperature is considered an alteration
whether or not physical work is done.
Authorized NBIC inspectors must be employees
of an authorized inspection agency such as (1) a
state boiler and pressure vessel department, (2)
an insurance company licensed to provide boiler
and pressure vessel insurance, or (3) an owner-
user who maintains a regularly established
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Rupture Hazard of Pressure Vessels
May 1997
inspection department, whose organization and
procedures meet National Board rules. API
authorized inspectors may also serve under
contract to an owner-user who maintains an
established inspection department. Inspectors
must qualify by written examination and NBIC
inspectors must hold a valid National Board
Commission.
In states with no pressure vessel law, good safety
practices require that similar precautions be
followed in the design, construction, welding,
testing, marking, operation, inspection, and
repair of any pressure vessel. The ASME Code
should be used for the design, construction,
initial testing, and operation of pressure vessels.
The NBIC or API 510 should be used for
maintenance and inspection and subsequent
testing. Boiler and machinery insurance
companies, some pressure vessel suppliers, or
jurisdiction-licensed independent contractors
can provide authorized inspectors.
Facilities, particularly those without formal
pressure vessel inspection programs,
should survey their vessels, review
pertinent history and data to identify hazards,
and prevent vessel rupture or catastrophic
failure. Among the questions to be asked and
answered are the following:
4> Does the vessel operate above 15 psi, and
was it designed, fabricated, and constructed
according to the ASME Code or other
applicable code? Is the vessel code labeled
or stamped? Is the operating pressure and
size of the vessel known?
4 Is the vessel maintained, inspected, and
repaired according to the NBIC and/or API 510?
4- Are the ratings and settings of the relieving
devices appropriate? Are the devices tested
regularly and how recently?
4- Is the vessel inspected periodically? What
are the criteria for inspection frequency?
When was it last inspected externally?
When was it last inspected internally? Did
the inspection disclose general thinning of
walls due to corrosion, localized corrosion,
stress corrosion cracking, embrittlement,
holes, leaks, or any other defects that re-
quired follow up? Were they followed up?
4> Has the vessel been repaired? Were the plan
of repair, welding techniques and safety
tests approved by a certified or authorized
inspector? Was the welding done by a
qualified welder? Were the welding perfor-
mance qualification tests approved by an
inspector? Was the vessel tested after the
repair was completed?
4- Was the vessel down rated and were the
necessary changes in operating conditions
and relief device settings made?
4> Are exothermic reactions carried out in the
vessel? Does the vessel have an emergency
relief system to handle runaway reactions?
Pressure vessels must comply with all
regulations, industry codes, and
standards to keep vessels in safe condition
to handle design pressures and temperatures.
Areas to review could include, but are not
limited to, the following:
Design
At a minimum, pressure vessels should be
designed in accordance with the ASME Code for
material contents of varying characteristics.
Facilities should address any added concerns
about the temperature and characteristics of
vessel contents (e.g., toxic, corrosive, reactive,
or flammable contents). When the vessel
contents are changed from those the vessel was
designed for, a risk analysis should be conducted
to determine if it is still safe for the new
materials.
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Certification of
In states with a pressure vessel law, all pressure
vessels must be certified by the relevant state
authority, such as a Chief Boiler and Pressure
Vessel Inspector, as meeting requirements of the
ASME Code. When a pressure vessel cannot
be constructed, to comply fully with the ASME
Code, however, the NBIC provides a procedure
by which the pressure vessel may get state
approval without bearing the ASME symbol.
This procedure includes submittal of drawings,
calculations, welding procedures, service
conditions, welding qualification and
performance tests, and professional engineering
certifications. This should be done before any
construction begins.
When a facility finds an unmarked vessel or is
about to bring one into a state, similar
information plus the repair history should be
submitted to the state pressure vessel authority
for review and approval before use begins or
continues.
On the other hand, when a pressure vessel is
located in a state without a pressure vessel law,
is not marked with the ASME symbol, and there
are doubts about the safety of the vessel, the
information listed above should be submitted
to a pressure vessel consulting engineer and
authorized inspector for a safety review.
Inspection
The NBIC and API. 510 require that vessels be
periodically inspected externally and internally.
External inspections are made more frequently
and involve visual and nondestructive
examination. An internal inspection is more
difficult to perform because it usually requires
a confined space entry and the vessel must be
taken out of service, cleaned, and prepared.
General or localized thinning of the internal
walls due to corrosion or erosion is a potential
problem and must be monitored, with records
kept of the rate of thinning. When the vessel is
reaching the end of its useful life, the period
between inspections is shortened so that the
vessel may be taken out of service before it can
become dangerous. An internal test may also
reveal stress corrosion, cracking, pitting,
embrittlement, and other defects that could
weaken the vessel. In addition to the vessel
itself, the relieving devices must also be tested.
When practical, this can be done in place for
vessels containing non-hazardous substances,
but for vessels containing hazardous substances
without special controls (e.g., scrubbers), safety
relief valves must be taken off to ascertain
whether their settings are correct. How this can
be done safely and conveniently should be
considered.
Maintenance
In addition to maintenance requirements, the
NBIC and API 510 include specific preheating
and postheating requirements. Large
temperature differences between the outside and
inside surfaces of the vessel - during repair or
other welding - must be avoided to minimize
embrittling or stressing the metal.
Nondestructive examinations may include
radiographic, ultrasonic, liquid penetrant,
magnetic particle, eddy current, visual checks,
and leak testing.
of
Operators should consider process start-up and
shutdown conditions, possible process upsets,
and any other unusual conditions that might
cause overpressure problems. The ASME Code
includes recommended pressure differentials
between safety valve set pressures and
maximum allowable working pressure, as well
as the pressure differential settings of the
relieving devices when there are multiple
devices.
The above listed information is generalized
guidance only. Some references that
contain information about the hazards of
pressure vessel ruptures and methods of
minimizing these hazards are listed below.
Regulations potentially applicable to pressure
vessels, and codes and standards that may be
relevant, are also listed below.
For more information consult the following:
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Section 112(r) of the Clean Air Act focuses on
prevention of chemical accidents. It imposes on
facilities with regulated substances or other extremely
hazardous substances a general duty to prevent and
mitigate accidental releases. Accident prevention
activities include identifying hazards and operating
a safe facility.
The America?!- Petroleum Institute (API) has vessel
standards, guidelines, and recommended practices.
American Petroleum Institute
1220 L St NW
Washington DC 20005
Phone: (202) 682-8000
Web site: http://www.api.org
EPA's Risk Management Program (RMP) Rule 140
CFR 68] is intended to prevent and mitigate
accidental releases of listed toxic and flammable
substances. Requirements under the RMP rule
include development of a hazard assessment, a
prevention program, and an emergency response
program.
The Occupational Safety and Health Administration
(OSHA) has the Process Safety Management
Standard, which includes regulations on tank
inspection and conduct during hot-work.
Relevant API standards include:
ANSI/API-510 — Pressure Vessel Inspection
Code-Maintenance Inspection, Rating, Repair,
and Alteration, seventh edition, 1992 (covers
vessels in the petroleum and chemical process
industries; see also ANSI/NB 23).
Supplement 2 to ANSI/API-510 — Pressure
Vessel Inspection Code-Maintenance
Inspection, Rating, Repair, and Alteration,
December 1994 (contains revisions to Sections
1, 2, 3,4, 5, and Appendices B and D).
Occupational Safety and Health Administration
Phone: (202) 219-8151 - Public Information
Web site: http://www.osha.gov
ANSI/API Recommended Practice 572 —
Inspection of Pressure Vessels, first edition,
January 1992.
Codes
The American National Standards Institute (ANSI)
has vessel inspection standards and codes, including
the NBIC. The purpose of the NBIC is to maintain
the integrity and safety of boilers and pressure vessels
after they have been placed in service by providing
rules and guidelines for inspection after installation,
repair, alteration, and rerating.
American National Standards Institute
655 15th St NW
Washington DC 20005
Phone: (202) 639-4090
or
11 West 42nd St
New York, NY 10036
Phone: (212) 642-4900
Web site: http://www.ansi.org
Relevant ANSI standards include:
ANSI/NB 23 — National Board Inspection
Code, 1995 (see also AP1-510).
API Standard 653 — Tank Inspection, Repair,
Alteration, and Reconstruction, second edition,
December 1995.
ANSI/ API-920—Prevention of Brittle Fracture
of Pressure Vessels, first edition, March 1990.
The American Society of Mechanical Engineers
(ASME) has the Boiler and Pressure Vessel Code
that establishes rules of safety governing the design,
fabrication, and inspection during construction of
boilers and pressure vessels.
American Society of Mechanical Engineers
1828 L St NW, Suite 906
Washington DC 20036
Phone: 1 (800) 843-2863 or (202) 785-3756
Publications and membership 1 (800) 843-2763
Codes and standards (212) 705-8500
Accreditation and certification programs (212)
705-8581
Web site: http://wivw.asme.org
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The American Society of Nondestructive Testing
(ASNT) certifies welding and. nondestructive
examination (NDE) and nondestructive testing
(NDT) inspectors.
American Society of Nondestructive Testing
P.O. Box 28518
1711 Arlingate Lane
Columbus, OH 43228
Phone: 1 (800) 222-2768 or (614) 274-6003
Web site: http://www.asnt.org
The American Welding Society (AWS) certifies
welding inspectors with the designation AWS QC-1
(Quality Control) Welding Inspector and has
guidelines on safe welding.
American Welding Society
550 NW Lejeune Rd
Miami, FL 33126
Phone: 1 (800) 443-9353 or (305) 443-9353
Web site: http://www.amweld.org
FOR MORE INFORMATION...
CONTACT THE EMERGENCY PLANNING AND
COMMUNITY RIGHT-TO-KNOW HOTLINE
(800) 424-9346 OR (703) 412-9810
TDD (800) 553-7672
MONDAY-FRIDAY, 9 AM TO 6 PM, EASTERN TIME
VISIT THE CEPPO HOME PACE ON THE WORLD
WIDE WEB AT:
http://www.epa.gov/swercepp/
The National Board of Boiler and Pressure Vessel
Inspectors promotes greater safety to life and property
through uniformity in the construction, installation,
repair, maintenance, and inspection of boilers and
pressures. A list of Chief Boiler and Pressure Vessel
Inspectors is available on the internet or through the
Board.
National Board of Boiler and Pressure Vessel
Inspectors
1055 Cruppe Avenue
Columbus, OH 43229
Phone: (614) 888-8320
Web site: http://www.nationalboard.org
NOTICE
The statements in this document are intended solely as guidance. This document does not substitute for EPA's or other
agency regulations, nor is it a regulation Itself. Site-specific application of the guidance may vary depending on process
activities, and may not apply to a giwen situation. EPA may rewoke, modify, or suspend this guidance in the future, as
appropriate.
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