Wisconsin Administrative Code › Department of Safety and Professional Services › SPS 301-399 - Safety, Buildings, and Environment › SPS 326-360 - General, Part II › Chapter SPS 341 - Boilers And Pressure Vessels › Appendix C - EXCERPTS FROM: ASME BOILER AND PRESSURE VESSEL CODE

Current through June 24, 2024
SECTION VIII - RULES FOR CONSTRUCTION OF PRESSURE
					 VESSELS 2010 EDITION
INTRODUCTION
SCOPE
U-1 SCOPE
U-1 (a)
U-1(a)(1) The Foreword provides the basis for the rules
					 described in this Division.
U-1(a)(2)
For the scope of this Division,
					 pressure vessels are containers for the containment of pressure, either
					 internal or external. This pressure may be obtained from an external source, or
					 by the application of heat from a direct or indirect source, or any combination
					 thereof.
U-1(a)(3)
This Division contains mandatory
					 requirements, specific prohibitions, and nonmandatory guidance for pressure
					 vessel materials, design, fabrication, examination, inspection, testing,
					 certification, and pressure relief. The Code does not address all aspects of
					 these activities, and those aspects which are not specifically addressed should
					 not be considered prohibited. Engineering judgment must be consistent with the
					 philosophy of this Division, and such judgments must never be used to overrule
					 mandatory requirements or specific prohibitions of this Division. See also
					 informative and nonmandatory guidance regarding metallurgical phenomena in
					 Appendix A of Section II, Part D.
U-1(b)
This Division is divided into three
					 Subsections, Mandatory Appendices, and Nonmandatory Appendices. Subsection A
					 consists of Part UG, covering the general requirements applicable to all
					 pressure vessels. Subsection B covers specific requirements that are applicable
					 to the various methods used in the fabrication of pressure vessels. It consists
					 of Parts UW, UF, and UB dealing with welded, forged, and brazed methods,
					 respectively. Subsection C covers specific requirements applicable to the
					 several classes of materials used in pressure vessel construction. It consists
					 of Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT, ULW, and ULT dealing with carbon
					 and low alloy steels, nonferrous metals, high alloy steels, cast iron, clad and
					 lined material, cast ductile iron, ferritic steels with properties enhanced by
					 heat treatment, layered construction, and low temperature materials,
					 respectively. Section II, Part D also contains tables of maximum allowable
					 stress values for these classes of materials.
The Mandatory Appendices address specific subjects not
					 covered elsewhere in this Division, and their requirements are mandatory when
					 the subject covered is included in construction under this Division. The
					 Nonmandatory Appendices provide information and suggested good
					 practices.
U-1 (c)
U-1(c)(1)
The scope of this Division has
					 been established to identify the components and parameters considered in
					 formulating the rules given in this Division. Laws or regulations issued by
					 municipality, state, provincial, federal, or other enforcement or regulatory
					 bodies having jurisdiction at the location of an installation establish the
					 mandatory applicability of the Code rules, in whole or in part, within their
					 jurisdiction. Those laws or regulations may require the use of this Division of
					 the Code for vessels or components not considered to be within its Scope. These
					 laws or regulations should be reviewed to determine size or service limitations
					 of the coverage which may be different or more restrictive than those given
					 here.
U-1(c)(2)
Based on the Committee's
					 consideration, the following classes of vessels are not included in the scope
					 of this Division; however, any pressure vessel which meets all the applicable
					 requirements of this Division may be stamped with the Code U Symbol:
(a) those within the scope of other Sections;
(b) fired process tubular heaters;
(c) pressure containers which are integral parts or
					 components of rotating or reciprocating mechanical devices, such as pumps,
					 compressors, turbines, generators, engines, and hydraulic or pneumatic
					 cylinders where the primary design considerations and/or stresses are derived
					 from the functional requirements of the device;
(d) except as covered in U-l(f), structures whose primary
					 function is the transport of fluids from one location to another within a
					 system of which it is an integral part, that is, piping systems;
(e) piping components, such as pipe, flanges, bolting,
					 gaskets, valves, expansion joints, fittings, and the pressure containing parts
					 of other components, such as strainers and devices which serve such purposes as
					 mixing, separating, snubbing, distributing, and metering or controlling flow,
					 provided that pressure containing parts of such components are generally
					 recognized as piping components or accessories;
(f) a vessel for containing water1 under pressure,
					 including those containing air the compression of which serves only as a
					 cushion, when none of the following limitations are exceeded: - See PDF for
					 table
1 The water may contain
					 additives provided the flash point of the aqueous solution at atmospheric
					 pressure is 185°F or higher, The flash point shall be determined by the
					 methods specified in ASTM D 93 or in ASTM D 56, whichever is
					 appropriate.
(1) a design pressure of 300 psi (2 MPa);
(2) a design temperature of 210°F (99°C);
(g) a hot water supply storage tank heated by steam or any
					 other indirect means when none of the following limitations is exceeded:
(1) a heat input of 200,000 Btu/hr (58.6 kW);
(2) a water temperature of 210°F (99°C);
(3) a nominal water containing capacity of 120 gal (450
					 L);
(h) vessels not exceeding the design pressure, at the top
					 of the vessel, (see 3.2) limitations below, with no limitation on size [see
					 UG-28(f), 9-l(c)]:
(1) vessels having an internal or external pressure not
					 exceeding 15 psi (100 kPa);
(2) combination units having an internal or external
					 pressure in each chamber not exceeding 15 psi (100 kPa) and differential
					 pressure on the common elements not exceeding 15 psi (100 kPa) [see
					 UG-19(a)];
(i) vessels having an inside diameter, width, height, or
					 cross section diagonal not exceeding 6 in. (152 mm), with no limitation on
					 length of vessel or pressure;
(j) pressure vessels for human occupancy.2 - See PDF for
					 table
2 Requirements for pressure
					 vessels for human occupancy are covered by ASME PVHO-1.
U-1(d)
The rules of this Division have
					 been formulated on the basis of design principles and construction practices
					 applicable to vessels designed for pressures not exceeding 3000 psi (20 MPa).
					 For pressures above 3000 psi (20 MPa), deviations from and additions to these
					 rules usually are necessary to meet the requirements of design principles and
					 construction practices for these higher pressures. Only in the event that after
					 having applied these additional design principles and construction practices
					 the vessel still complies with all of the requirements of this Division may it
					 be stamped with the applicable Code symbol.
U-1(e)
In relation to the geometry of
					 pressure containing parts, the scope of this Division shall include the
					 following:
U-1(e)(1)
where external piping; other
					 pressure vessels including heat exchangers; or mechanical devices, such as
					 pumps, mixers, or compressors, are to be connected to the vessel:
(a) the welding end connection for the first
					 circumferential joint for welded connections [see UW-13(g)];
(b) the first threaded joint for screwed
					 connections;
(c) the face of the first flange for bolted, flanged
					 connections;
(d) the first sealing surface for proprietary connections
					 or fittings;
U-1(e)(2)
where nonpressure parts are
					 welded directly to either the internal or external pressure retaining surface
					 of a pressure vessel, this scope shall include the design, fabrication,
					 testing, and material requirements established for nonpressure part attachments
					 by the applicable paragraphs of this Division;3 - See PDF for table
3 These requirements for design,
					 fabrication, testing, and material for nonpressure part attachments do not
					 establish the length, size, or shape of the attachment material. Pads and
					 standoffs are permitted and the scope can terminate at the next welded or
					 mechanical joint.
U-1(e)(3)
pressure retaining covers for
					 vessel openings, such as manhole and handhole covers;
U-1(e)(4)
the first sealing surface for
					 proprietary fittings or components for which rules are not provided by this
					 Division, such as gages, instruments, and nonmetallic components.
U-1(f)
The scope of the Division includes
					 provisions for pressure relief devices necessary to satisfy the requirements of
					 UG-125 through UG-137 and Appendix 11.
U-1(g)(1)
Unfired steam boilers shall be
					 constructed in accordance with the rules of Section I or this Division [see UG-
					 125(b) and UW-2(c)].
U-1(g)(2)
The following pressure vessels
					 in which steam is generated shall not be considered as unfired steam boilers,
					 and shall be constructed in accordance with the rules of this Division:
U-1(g)(2)(a)
vessels known as evaporators
					 or heat exchangers;
U-1(g)(2)(b)
vessels in which steam is
					 generated by the use of heat resulting from operation of a processing system
					 containing a number of pressure vessels such as used in the manufacture of
					 chemical and petroleum products;
U-1(g)(2)(c)
vessels in which steam is
					 generated but not withdrawn for external use.
U-1(h)
Pressure vessels or parts subject
					 to direct firing from the combustion of fuel (solid, liquid, or gaseous), which
					 are not within the scope of Sections I, III, or IV may be constructed in
					 accordance with the rules of this Division [see UW-2(d)].
U-1(i)
Gas fired jacketed steam kettles
					 with jacket operating pressures not exceeding 50 psi (345 kPa) may be
					 constructed in accordance with the rules of this Division (see Appendix
					 19).
U-1(j)
Pressure vessels exclusive of those
					 covered in U-l(c), U-l(g), U-l(h), and U-l(i) that are not required by the
					 rules of this Division to be fully radiographed, which are not provided with
					 quick actuating closures (see UG-35), and that do not exceed the following
					 volume and pressure limits may be exempted from inspection by Inspectors, as
					 defined in UG-91, provided that they comply in all other respects with the
					 requirements of this Division:
U-1(j)(1)
5 cu ft (0.14 m3) in volume and
					 250 psi (1.7 MPa) design pressure; or
U-1(j)(2)
3 cu ft (0.08 m3) in volume and
					 350 psi (2.4 MPa) design pressure;
U-1(j)(3)
1½ cu ft (0.04 m3) in
					 volume and 600 psi (4.1 MPa) design pressure.
In an assembly of vessels, the limitations in (1) through
					 (3) above apply to each vessel and not the assembly as a whole. Straight line
					 interpolation for intermediate volumes and design pressures is permitted.
					 Vessels fabricated in accordance with this rule shall be marked with the "UM"
					 Symbol in Fig. UG-116 sketch (b) and with the data required in UG-116.
					 Certificates of Compliance shall satisfy the requirements of UG-120(a).
U-1 (k)
The degree of nondestructive
					 examination(s) and the acceptance standards beyond the requirements of this
					 Division shall be a matter of prior agreement between the Manufacturer and user
					 or his designated agent.
GENERAL
U-2 GENERAL
(a) The user or his designated agent4 shall establish the
					 design requirements for pressure vessels, taking into consideration factors
					 associated with normal operation, such other conditions asstartup and shutdown,
					 and abnormal conditions which may become a governing design consideration (see
					 UG-22). - See PDF for table
4 For this Division, the user's
					 designated agent may be either a design agency specifically engaged by the
					 user, the Manufacturer of a system for a specific service that includes a
					 pressure vessel as a part and that is purchased by the user, or an organization
					 that offers pressure vessels for sale or lease for specific services.
(1) the need for corrosion allowances;
(2) the definition of lethal services. For example, see
					 UW-2(a).
(3) the need for postweld heat treatment beyond the
					 requirements of this Division and dependent on service conditions;
(4) for pressure vessels in which steam is generated, or
					 water is heated [see U-l(g) and (h)], the need for piping, valves, instruments,
					 and fittings to perform the functions covered by PG-59 through PG-61 of Section
					 I.
(b)
Responsibilities5
- See PDF for table
5 See UG-90(b) and UG-90(c)(l)
					 for summaries of the responsibilities of the Manufacturer and the duties of the
					 Inspector.
(1) The Manufacturer of any vessel or part to be marked
					 with the Code Symbol has the responsibility of complying with all of the
					 applicable requirements of this Division and, through proper certification, of
					 assuring that all work done by others also complies. The vessel or part
					 Manufacturer shall have available for the Inspector's review the applicable
					 design calculations. See 10-5 and 10-15(d).
(2) Some types of work, such as forming, nondestructive
					 examination, and heat treating, may be performed by others (for welding, see
					 UW-26 and UW-31). It is the vessel or part Manufacturer's responsibility to
					 ensure that all work so performed complies with all the applicable requirements
					 of this Division. After ensuring Code compliance, the vessel or part may be
					 Code stamped by the appropriate Code stamp holder after acceptance by the
					 Inspector.
(c) A vessel may be designed and constructed using any
					 combination of the methods of fabrication and the classes of materials covered
					 by this Division provided the rules applying to each method and material are
					 complied with and the vessel is marked as required by UG-116.
(d) When the strength of any part cannot be computed with a
					 satisfactory assurance of safety, the rules provide procedures for establishing
					 its maximum allowable working pressure.
(e) It is the duty of the Inspector to make all of the
					 inspections specified by the rules of this Division, and of monitoring the
					 quality control and the examinations made by the Manufacturer. He shall make
					 such other inspections as in his judgment are necessary to permit him to
					 certify that the vessel has been designed and constructed in accordance with
					 the requirements. The Inspector has the duty of verifying that the applicable
					 calculations have been made and are on file at Manufacturer's plant at the time
					 the Data Report is signed. Any questions concerning the calculations raised by
					 the Inspector must be resolved. See UG-90(c)(l).
(f) The rules of this Division shall serve as the basis for
					 the Inspector to:
(1) perform the required duties;
(2) authorize the application of the Code Symbol;
(3) sign the Certificate of Shop (or Field Assembly)
					 Inspection.
(g) This Division of Section VIII does not contain rules to
					 cover all details of design and construction. Where complete details are not
					 given, it is intended that the Manufacturer, subject to the acceptance of the
					 Inspector, shall provide details of design and construction which will be as
					 safe as those provided by the rules of this Division.
(h) Field assembly of vessels constructed to this Division
					 may be performed as follows.
(1) The Manufacturer of the vessel completes the vessel in
					 the field, completes the Form U-1 or U-1A Manufacturer's Data Report, and
					 stamps the vessel.
(2) The Manufacturer of parts of a vessel to be completed
					 in the field by some other party stamps these parts in accordance with Code
					 rules and supplies the Form U-2 or U-2A Manufacturer's Partial Data Report to
					 the other party. The other party, who must hold a valid U Certificate of
					 Authorization, makes the final assembly, required NDE, final pressure test;
					 completes the Form U-1 or U-1A Manufacturer's Data Report; and stamps the
					 vessel.
(3) The field portion of the work is completed by a holder
					 of a valid U Certificate of Authorization other than the vessel Manufacturer.
					 The stamp holder performing the field work is required to supply a Form U-2 or
					 U-2A Manufacturer's Partial Data Report covering the portion of the work
					 completed by his organization (including data on the pressure test if conducted
					 by the stamp holder performing the field work) to the Manufacturer responsible
					 for the Code vessel. The vessel Manufacturer applies his U Stamp in the
					 presence of a representative from his Inspection Agency and completes the Form
					 U-1 or U-1A Manufacturer's Data Report with his Inspector.
In all three alternatives, the party completing and signing
					 the Form U-1 or U-1A Manufacturer's Data Report assumes full Code
					 responsibility for the vessel. In all three cases, each Manufacturer's Quality
					 Control System shall describe the controls to assure compliance for each Code
					 stamp holder.
(i) For some design analyses, both a chart or curve and a
					 formula or tabular data are given. Use of the formula or tabular data may
					 result in answers which are slightly different from the values obtained from
					 the chart or curve. However, the difference, if any, is within practical
					 accuracy and either method is acceptable.
U-3 STANDARDS REFERENCED BY THIS
DIVISION
(a) Throughout this Division references are made to various
					 standards, such as ANSI standards, which cover pressure-temperature rating,
					 dimensional, or procedural standards for pressure vessel parts. These
					 standards, with the year of the acceptable edition, are listed in Table
					 U-3.
(b) Rules for the use of these standards are stated
					 elsewhere in this Division.
U-4 UNITS OF
					 MEASUREMENT6
6 Guidance for conversion of
					 units from U.S.Customary to SI is found in Nonmandatory Appendix GG.
Either U.S. Customary, SI, or any local customary units may
					 be used to demonstrate compliance with all requirements of this edition, e.g.,
					 materials, design, fabrication, examination, inspection, testing,
					 certification, and overpressure protection.
In general, it is expected that a single system of units
					 shall be used for all aspects of design except where unfeasible or impractical.
					 When components are manufactured at different locations where local customary
					 units are different than those used for the general design, the local units may
					 be used for the design and documentation of that component. Similarly, for
					 proprietary components or those uniquely associated with a system of units
					 different than that used for the general design, the alternate units may be
					 used for the design and documentation of that component.
For any single equation, all variables shall be expressed
					 in a single system of units. When separate equations are provided for U.S.
					 Customary and SI units, those equations must be executed using variables in the
					 units associated with the specific equation. Data expressed in other units
					 shall be converted to U.S. Customary or SI units for use in these equations.
					 The result obtained from execution of these equations may be converted to other
					 units.
Production, measurement and test equipment, drawings,
					 welding procedure specifications, welding procedure and performance
					 qualifications, and other fabrication documents may be in U.S. Customary, SI,
					 or local customary units in accordance with the fabricator's practice. When
					 values shown in calculations and analysis, fabrication documents, or
					 measurement and test equipment are in different units, any conversions
					 necessary for verification of Code compliance and to ensure that dimensional
					 consistency is maintained, shall be in accordance with the following:
(a) Conversion factors shall be accurate to at least four
					 significant figures.
(b) The results of conversions of units shall be expressed
					 to a minimum of three significant figures.
Conversion of units, using the precision specified above
					 shall be performed to assure that dimensional consistency is maintained.
					 Conversion factors between U.S. Customary and SI units may be found in the
					 Nonmandatory Appendix, Guidance for the Use of U.S. Customary and SI Units in
					 the ASME Boiler and Pressure Vessel Code. Whenever local customary units are
					 used the Manufacturer shall provide the source of the conversion factors which
					 shall be subject to verification and acceptance by the Authorized Inspector or
					 Certified Individual.
Material that has been manufactured and certified to either
					 the U.S. Customary or SI material specification (e.g., SA-516M) may be used
					 regardless of the unit system used in design. Standard fittings (e.g., flanges,
					 elbows, etc.) that have been certified to either U.S. Customary units or SI
					 units may be used regardless of the units system used in design.
All entries on a Manufacturer's Data Report and data for
					 Code-required nameplate marking shall be in units consistent with the
					 fabrication drawings for the component using U.S. Customary, SI, or local
					 customary units. It is acceptable to show alternate units parenthetically.
					 Users of this Code are cautioned that the receiving jurisdiction should be
					 contacted to ensure the units are acceptable.
TABLE U-3YEAR OF ACCEPTABLE EDITION OF
								  REFERENCED STANDARDS IN THIS DIVISION
Title
Number
Year
Seat Tightness of Pressure Relief Valves
API Std. 527
1991 (R2002) (1)
Unified Inch Screw Threads (UN and UNR Thread
								  Form)
ASME B1.1
2003
Pipe Threads, General Purpose (Inch)
ANSI/ASME B1.20.1
1983 (R2006) (1)
Cast Iron Pipe Flanges and Flanged Fittings,
								  Classes 25, 125,and 250
ASME B16.1
1998
Pipe Flanges and Flanged Fittings
ASME B16.5
2003 (2)
Factory-Made Wrought Buttwelding Fittings
ASME B16.9
2007
Forged Fittings, Socket-Welding and
								  Threaded
ASME B16.11
2005
Cast Bronze Threaded Fittings, Classes 125 and
								  250
ASME B16.15
1985 (R2004) (1)
Metallic Gaskets for Pipe Flanges - Ring-Joint,
								  Spi-ral-Wound, and Jacketed
ASME B16.20
2007
Cast Copper Alloy Pipe Flanges and Flanged
								  Fittings, Class150, 300, 400, 600, 900, 1500, and 2500
ASME B16.24
2001
Ductile Iron Pipe Flanges and Flanged Fittings,
								  Class 150and 300
ASME B16.42
1998
Large Diameter Steel Flanges, NPS 26 Through NPS
								  60
ASME B16.47
1996
Square and Hex Nuts (Inch Series)
ASME B18.2.2
1987 (R1999) (1)
Welded and Seamless Wrought Steel Pipe
ASME B36.10M
2004
Guidelines for Pressure Boundary Bolted Flange
								  JointAssembly
ASME PCC-1
2000
Repair of Pressure Equipment and Piping
ASME PCC-2
2006
Pressure Relief Devices
ASME PTC 25
2001
Qualifications for Authorized Inspection
ASME QAI-1
2003 (3)
ASNT Central Certification Program
ACCP
Rev 3, November1997
ASNT Standard for Qualification and Certification
								  of Non-destructive Testing Personnel
ANSI/ASNT CP-189
2006
Recommended Practice for Personnel Qualification
								  and Cer-tification in Nondestructive Testing
SNT-TC-1A
2001
Standard Test Methods for Flash Point by Tag
								  Closed Tester
ASTM D 56
2002a
Standard Test Methods for Flash Point by
								  Pensky-MartensClosed Tester
ASTM D 93
2002a
Pressure Relieving and Depressuring
								  Systems
ANSI/API Std.521
5th Ed., January2007
Reference Photographs for Magnetic Particle
								  Indications onFerrous Castings
ASTM E 125
1963 (R1985) (1)
Hardness Conversion Tables for Metals
ASTM E 140
2007
Standard Reference Radiographs for Heavy-Walled
								  (2 to 4½-in. (51 to 114-mm)) Steel Castings
ASTM E 186
1998
Method for Conducting Drop-Weight Test to
								  DetermineNil-Ductility Transition Temperature of Ferritic Steels
ASTM E 208
2006
Standard Reference Radiographs for Heavy-Walled
								  (4½ to12-in. (114 to 305-mm) Steel Castings
ASTM E 280
1998
Standard Reference Radiographs for Steel Castings
								  up to 2in. (51 mm) in Thickness
ASTM E 446
1998
Marking and Labeling Systems
ANSI/UL-969
1991
Charpy Pendulum Impact Test Part 1: Test
								  Method
ISO 148-1
2006
Charpy Pendulum Impact Test Part 2: Verification
								  of TestMachines
ISO 148-2
1998
Charpy Pendulum Impact Test Part 3: Preparation
								  and Char-acterization of Charpy V Reference Test Pieces for Verificationof Test
								  Machines
ISO 148-3
1998
Metric Standards
Metric Screw Thread - M Profile
ASME B1.13M
2001
Metric Screw Thread - MJ Profile
ASME B1.21M
1997
Metric Heavy Hex Screws
ASME B18.2.3.3M
1979 (R2001)
Metric Hex Bolts
ASME B18.2.3.5M
1979 (R2001)
Metric Heavy Hex Bolts
ASME B18.2.3.6M
1979 (R2001)
Metric Hex Nuts, Style 1
ASME B18.2.4.1M
2002
Metric Hex Nuts, Style 2
ASME B18.2.4.2M
1979 (R1995)
Metric Heavy Hex Nuts
ASME B18.2.4.6M
1979 (R2003)
NOTES:
(1) R - Reaffirmed.
(2) See UG-11 (a) (2).
(3) See UG-91 and UG-117 (f).
PRESSURE RELIEF DEVICES
UG-125 GENERAL
(a) All pressure vessels within the Scope of this Division,
					 irrespective of size or pressure, shall be provided with pressure relief
					 devices in accordance with the requirements of UG-125 through UG- 137.
(1) It is the responsibility of the user to ensure that the
					 required pressure relief devices are properly installed prior to initial
					 operation.
(2) It is the responsibility of the user or his/her
					 designated agent to size and select the pressure relief device(s) based on its
					 intended service. Intended service considerations shall include, but not
					 necessarily be limited to, the following:
(a) normal operating and upset conditions
(b) fluids
(c) fluid phases
(3) These pressure relief devices need not be supplied by
					 the vessel Manufacturer.
(4) Unless otherwise defined in this Division, the
					 definitions relating to pressure relief devices in Section 2 of ASME PTC 25
					 shall apply.
(b) An unfired steam boiler, as defined in U-1(g), shall be
					 equipped with pressure relief devices required by Section I insofar as they are
					 applicable to the service of the particular installation.
(c) All pressure vessels other than unfired steam boilers
					 shall be protected by a pressure relief device that shall prevent the pressure
					 from rising more than 10% or 3 psi (20 kPa), whichever is greater, above the
					 maximum allowable working pressure except as permitted in (1) and (2) below.
					 (See UG-134 for pressure settings.)
(1) When multiple pressure relief devices are provided and
					 set in accordance with UG-134(a), they shall prevent the pressure from rising
					 more than 16% or 4 psi (30 kPa), whichever is greater, above the maximum
					 allowable working pressure.
(2) When a pressure vessel can be exposed to fire or other
					 unexpected sources of external heat, the pressure relief device(s) shall be
					 capable of preventing the pressure from rising more than 21% above the maximum
					 allowable working pressure. Supplemental pressure relief devices shall be
					 installed to protect against this source of excessive pressure if the pressure
					 relief devices used to satisfy the capacity requirements of UG-125(c) and
					 UG-125(c)(1) have insufficient capacity to provide the required protection. See
					 Nonmandatory Appendix M, para. M-13 for cases where the metal temperature due
					 to fire or other sources of external heat can cause vessel failure prior to
					 reaching the MAWP.
(3) Pressure relief devices, intended primarily for
					 protection against exposure of a pressure vessel to fire or other unexpected
					 sources of external heat installed on vessels having no permanent supply
					 connection and used for storage at ambient temperatures of nonrefrigerated
					 liquefied compressed gases42 are excluded from the requirements of (c)(1) and
					 (c)(2) above, provided: - See PDF for table
42 For the purpose of these
					 rules, gases are considered to be substances having a vapor pressure greater
					 than 40 psia (300 kPa absolute) at 100°F (40°C).
(a) the pressure relief devices are capable of preventing
					 the pressure from rising more than 20% above the maximum allowable working
					 pressure of the vessels;
(b) the set pressure marked on these devices shall not
					 exceed the maximum allowable working pressure of the vessels;
(c) the vessels have sufficient ullage to avoid a liquid
					 full condition;
(d) the maximum allowable working pressure of the vessels
					 on which these pressure relief devices are installed is greater than the vapor
					 pressure of the stored liquefied compressed gas at the maximum anticipated
					 temperature43 that the gas will reach under atmospheric conditions; and - See
					 PDF for table
43 Normally this temperature
					 should not be less than 115°F (45°C).
(e) pressure relief valves used to satisfy these provisions
					 also comply with the requirements of UG-129(a)(5), UG-131(c)(2), and
					 UG-134(d)(2).
(d) Pressure relief devices shall be constructed, located,
					 and installed so that they are readily accessible for inspection, replacement,
					 and repair and so that they cannot be readily rendered inoperative (see
					 Appendix M).
(e) Pressure relief valves or nonreclosing pressure relief
					 devices44 may be used to protect against overpressure. Nonreclosing pressure
					 relief devices may be used either alone or, if applicable, in combination with
					 pressure relief valves on vessels. - See PDF for table
44 A
pressure relief
					 valve
is a pressure relief device which is designed to reclose and
					 prevent the further flow of fluid after normal conditions have been restored.
					 A
nonreclosing pressure relief device
is a pressure relief
					 device designed to remain open after operation.
Note:
Use of nonreclosing pressure relief
					 devices of some types may be advisable on vessels containing substances that
					 may render a pressure relief valve inoperative, where a loss of valuable
					 material by leakage should be avoided, or where contamination of the atmosphere
					 by leakage of noxious fluids must be avoided. The use of rupture disk devices
					 may also be advisable when very rapid rates of pressure rise may be
					 encountered.
(f) Vessels that are to operate completely filled with
					 liquid shall be equipped with pressure relief devices designed for liquid
					 service, unless otherwise protected against overpressure.
(g) The pressure relief devices required in (a) above need
					 not be installed directly on a pressure vessel when either of the following
					 conditions apply:
(1) the source of pressure is external to the vessel and is
					 under such positive control that the pressure in the vessel cannot exceed the
					 maximum allowable working pressure at the operating temperature except as
					 permitted in (c) above (see UG-98), or under the conditions set forth in
					 Appendix M.
(2) there are no intervening stop valves between the vessel
					 and the pressure relief device or devices except as permitted under
					 UG-135(d).
Note:
Pressure reducing valves and similar
					 mechanical or electrical control instruments, except for pilot operated
					 pressure relief valves as permitted in UG-126(b), are not considered as
					 sufficiently positive in action to prevent excess pressures from being
					 developed.
(h) Pressure relief valves for steam service shall meet the
					 requirements of UG- 131(b).
UG-126 PRESSURE RELIEF
					 VALVES45
45 A
safety valve
is a pressure relief valve actuated by inlet static pressure and
					 characterized by rapid opening or pop action. A
relief valve
is a pressure relief valve actuated by inlet static pressure which
					 opens in proportion to the increase in pressure over the opening pressure. A
safety relief valve
is a pressure relief valve characterized
					 by rapid opening or pop action, or by opening in proportion to the increase in
					 pressure over the opening pressure, depending on application. A
pilot
					 operated pressure relief valve
is a pressure relief valve in which the
					 major relieving device is combined with and is controlled by a self-actuated
					 auxiliary pressure relief valve.
(a) Safety, safety relief, and relief valves shall be of
					 the direct spring loaded type.
(b) Pilot operated pressure relief valves may be used,
					 provided that the pilot is self-actuated and the main valve will open
					 automatically at not over the set pressure and will discharge its full rated
					 capacity if some essential part of the pilot should fail.
(c) The spring in a pressure relief valve shall not be set
					 for any pressure more than 5% above or below that for which the valve is
					 marked, unless the setting is within the spring design range established by the
					 valve Manufacturer or is determined to be acceptable to the Manufacturer. The
					 initial adjustment shall be performed by the Manufacturer, his authorized
					 representative, or an Assembler, and a valve data tag shall be provided that
					 identifies the set pressure capacity and date. The valve shall be sealed with a
					 seal identifying the Manufacturer, his authorized representative, or the
					 Assembler performing the adjustment.
(d) The set pressure tolerances, plus or minus, of pressure
					 relief valves shall not exceed 2 psi (15 kPa) for pressures up to and including
					 70 psi (500 kPa) and 3% for pressures above 70 psi (500 kPa).
UG-127 NONRECLOSING PRESSURE RELIEF
					 DEVICES
(a)
Rupture Disk
					 Devices
46
46
A rupture disk device
is a nonreclosing pressure relief device actuated by inlet static
					 pressure and designed to function by the bursting of a pressure containing
					 disk. A
rupture disk
is the pressure containing and pressure
					 sensitive element of a rupture disk device. Rupture disks may be designed in
					 several configurations, such as plain flat, prebulged, or reverse buckling. A
rupture disk holder
is the structure that encloses and clamps
					 the rupture disk in position.
(1)
General.
Every rupture disk shall
					 have a marked burst pressure established by rules of UG- 137(d)(3) within a
					 manufacturing design range47 at a specified disk temperature48 and shall be
					 marked with a lot49 number. The burst pressure tolerance at the specified disk
					 temperature shall not exceed ±2 psi (±15 kPa) for marked burst
					 pressure up to and including 40 psi (300 kPa) and ±5% for marked burst
					 pressure above 40 psi (300 kPa). - See PDF for table
47 The
manufacturing
					 design range
is a range of pressure within which the marked burst
					 pressure must fall to be acceptable for a particular requirement as agreed upon
					 between the rupture disk Manufacturer and the user or his agent. The
					 manufacturing design range must be evaluated in conjunction with the specified
					 burst pressure to ensure that the marked burst pressure of the rupture disk
					 will always be within applicable limits of UG-134. Users are cautioned that
					 certain types of rupture disks have manufacturing ranges that can result in a
					 marked burst pressure greater than the specified burst pressure.
48 The specified disk
					 temperature supplied to the rupture disk Manufacturer shall be the temperature
					 of the disk when the disk is expected to burst.
49 A
lot of rupture
					 disks
is those disks manufactured of a material at the same time, of
					 the same size, thickness, type, heat, and manufacturing process including heat
					 treatment.
(2)
Relieving Capacity.
The rated flow
					 capacity of a pressure relief system which uses a rupture disk device as the
					 sole relief device shall be determined by a value calculated under the
					 requirements of (a) using a coefficient of discharge or (b) using flow
					 resistances below.
(a) When the rupture disk device discharges directly to
					 atmosphere and
(1) is installed within eight pipe diameters from the
					 vessel nozzle entry; and
(2) with a length of discharge pipe not greater than five
					 pipe diameters from the rupture disk device; and
(3) the nominal diameters of the inlet and discharge piping
					 are equal to or greater than the stamped NPS designator of the device, the
					 calculated relieving capacity of a pressure relief system shall not exceed a
					 value based on the applicable theoretical flow equation [see UG-131(e)(2) and
					 Appendix 11] for the various media multiplied by a coefficient of discharge
K
equal to 0.62. The area
A
in the
					 theoretical flow equation shall be the minimum net flow area50 as specified by
					 the rupture disk device Manufacturer. - See PDF for table
50 The
minimum net flow
					 area
is the calculated net area after a complete burst of the disk with
					 appropriate allowance for any structural members which may reduce the net flow
					 area through the rupture disk device. The net flow area for sizing purposes
					 shall not exceed the nominal pipe size area of the rupture disk device.
(b) The calculated capacity of any pressure relief system
					 may be determined by analyzing the total system resistance to flow. This
					 analysis shall take into consideration the flow resistance of the rupture disk
					 device, piping and piping components including the exit nozzle on the vessels,
					 elbows, tees, reducers, and valves. The calculation shall be made using
					 accepted engineering practices for determining fluid flow through piping
					 systems. This calculated relieving capacity shall be multiplied by a factor of
					 0.90 or less to allow for uncertainties inherent with this method. The
					 certified flow resistance51
K
R
for the rupture
					 disk device, expressed as the velocity head loss, shall be determined in
					 accordance with UG-13 1(k) through (r). - See PDF for table
51 The
certified flow
					 resistance K
R
is a dimensionless factor used to
					 calculate the velocity head loss that results from the presence of a rupture
					 disk device in a pressure relief system.
(3)
Application of Rupture Disks
(a) A rupture disk device may be used as the sole pressure
					 relieving device on a vessel.
Note:
When rupture disk devices are used, it
					 is recommended that the design pressure of the vessel be sufficiently above the
					 intended operating pressure to provide sufficient margin between operating
					 pressure and rupture disk bursting pressure to prevent premature failure of the
					 rupture disk due to fatigue or creep.
Application of rupture disk devices to liquid service
					 should be carefully evaluated to assure that the design of the rupture disk
					 device and the dynamic energy of the system on which it is installed will
					 result in sufficient opening of the rupture disk.
(b) A rupture disk device may be installed between a
					 pressure relief valves52 and the vessel provided: - See PDF for table
52 Use of a rupture disk device
					 in combination with a pressure relief valve shall be carefully evaluated to
					 ensure that the media being handled and the valve operational characteristics
					 will result in opening of the valve coincident with the bursting of the rupture
					 disk.
(1) the combination of the pressure relief valve and the
					 rupture disk device is ample in capacity to meet the requirements of UG-133(a)
					 and (b);
(2) the marked capacity of a pressure relief valve (nozzle
					 type) when installed with a rupture disk device between the inlet of the valve
					 and the vessel shall be multiplied by a factor of 0.90 of the rated relieving
					 capacity of the valve alone, or alternatively, the capacity of such a
					 combination shall be established in accordance with (3) below;
(3) the capacity of the combination of the rupture disk
					 device and the pressure relief valve may be established in accordance with the
					 appropriate paragraphs of UG-132;
(4) the space between a rupture disk device and a pressure
					 relief valve shall be provided with a pressure gage, a try cock, free vent, or
					 suitable telltale indicator. This arrangement permits detection of disk rupture
					 or leakage.53 - See PDF for table
53 Users are warned that a
					 rupture disk will not burst at its design pressure if back pressure builds up
					 in the space between the disk and the pressure relief valve which will occur
					 should leakage develop in the rupture disk due to corrosion or other
					 cause.
(5) the opening50 provided through the rupture disk, after
					 burst, is sufficient to permit a flow equal to the capacity of the valve [(2)
					 and (3) above], and there is no chance of interference with proper functioning
					 of the valve; but in no case shall this area be less than the area of the inlet
					 of the valve unless the capacity and functioning of the specific combination of
					 rupture disk device and pressure relief valve have been established by test in
					 accordance with UG-132. - See PDF for table
50 The
minimum net flow
					 area
is the calculated net area after a complete burst of the disk with
					 appropriate allowance for any structural members which may reduce the net flow
					 area through the rupture disk device. The net flow area for sizing purposes
					 shall not exceed the nominal pipe size area of the rupture disk device.
(c) A rupture disk device may be installed on the outlet
					 side 54 of a pressure relief valve which is opened by direct action of the
					 pressure in the vessel provided: - See PDF for table
54 This use of a rupture disk
					 device in series with the pressure relief valve is permitted to minimize the
					 loss by leakage through the valve of valuable or of noxious or otherwise
					 hazardous materials, and where a rupture disk alone or disk located on the
					 inlet side of the valve is impracticable, or to prevent corrosive gases from a
					 common discharge line from reaching the valve internals.
(1) the pressure relief valve will not fail to open at its
					 proper pressure setting regardless of any back pressure that can accumulate
					 between the pressure relief valve disk and the rupture disk. The space between
					 the pressure relief valve disk and the rupture disk shall be vented or drained
					 to prevent accumulation of pressure, or suitable means shall be provided to
					 ensure that an accumulation of pressure does not affect the proper operation of
					 the pressure relief valve.55 - See PDF for table
55 Users are warned that many
					 types of pressure relief valves will not open at the set pressure if pressure
					 builds up in the space between the pressure relief valve disk and the rupture
					 disk device. A specially designed pressure relief valve such as a diaphragm
					 valve, pilot operated valve, or a valve equipped with a balancing bellows above
					 the disk may be required.
(2) the pressure relief valve is ample in capacity to meet
					 the requirements of UG-125(c);
(3) the marked burst pressure of the rupture disk at the
					 specified disk temperature plus any pressure in the outlet piping shall not
					 exceed the design pressure of the outlet portion of the pressure relief valve
					 and any pipe or fitting between the valve and the rupture disk device. However,
					 in no case shall the marked burst pressure of the rupture disk at the specified
					 disk temperature plus any pressure in the outlet piping exceed the maximum
					 allowable working pressure of the vessel or the set pressure of the pressure
					 relief valve.
(4) the opening provided through the rupture disk device
					 after breakage is sufficient to permit a flow equal to the rated capacity of
					 the attached pressure relief valve without exceeding the allowable
					 overpressure;
(5) any piping beyond the rupture disk cannot be obstructed
					 by the rupture disk or fragment;
(6) the system is designed to consider the adverse effects
					 of any leakage through the pressure relief valve or through the outlet side
					 rupture disk device, to ensure system performance and reliability.56 - See PDF
					 for table
56 Some adverse effects
					 resulting from leakage may include obstructing the flow path, corrosion of
					 pressure relief valve components, and undesirable bursts of the outlet side
					 rupture disk.
(7) the bonnet of a balancing bellows or diaphragm type
					 pressure relief valve shall be vented to prevent accumulation of pressure in
					 the bonnet.
(b)
Breaking Pin Device
57 - See PDF for
					 table
57 A
breaking pin device
is
a
nonreclosing pressure relief device actuated by
					 inlet static pressure and designed to function by the breakage of a
					 load-carrying section of a pin which supports a pressure containing member. A
breaking pin
is the load-carrying element of a breaking pin
					 device. A
breaking pin housing
is the structure which encloses
					 the breaking pin mechanism. The material of the housing shall be listed in
					 Section II and be permitted for use in this Division.
(1) Breaking pin devices shall not be used as single
					 devices but only in combination between the pressure relief valve and the
					 vessel.
(2) The space between a breaking pin device and a pressure
					 relief valve shall be provided with a pressure gage, a try cock, a free vent,
					 or suitable telltale indicator. This arrangement permits detection of breaking
					 pin device operation or leakage.
(3) Each breaking pin device shall have a rated pressure
					 and temperature at which the pin will break. The breaking pin shall be
					 identified to a lot number and shall be guaranteed by the Manufacturer to break
					 when the rated pressure, within the following tolerances, is applied to the
					 device:
Rated Pressure, psi (kPa)
Tolerance, Plus or
Min.
Max.
Minus, psi (kPa)
30 (200)
150 (1 000)
5 (35)
150 (1 000)
275 (1 900)
10 (70)
275 (1 900)
375 (2 600)
15 (100)
(4) The rated pressure of the breaking pin plus the
					 tolerance in psi shall not exceed 105% of the maximum allowable working
					 pressure of the vessel to which it is applied.
(5) The rated pressure at the specified temperature58 shall
					 be verified by breaking two or more sample breaking pins from each lot of the
					 same material and the same size as those to be used. The lot size shall not
					 exceed 25. The test shall be made in a device of the same form and pressure
					 dimensions as that in which the breaking pin is to be used. - See PDF for
					 table
58 The specified temperature
					 supplied to the breaking pin manufacturer shall be the temperature of the
					 breaking pin when an emergency condition exists and the pin is expected to
					 break.
(c)
Spring Loaded Nonreclosing Pressure Relief
					 Device
(1) A spring loaded nonreclosing pressure relief device,
					 pressure actuated by means which permit the spring loaded portion of the device
					 to open at the specified set pressure and remain open until manually reset, may
					 be used provided the design of the spring loaded nonreclosing device is such
					 that if the actuating means fail, the device will achieve full opening at or
					 below its set pressure. Such a device may not be used in combination with any
					 other pressure relief device. The tolerance on opening point shall not exceed
					 ±5%.
(2) The calculated capacity rating of a spring loaded
					 nonreclosing pressure relief device shall not exceed a value based on the
					 applicable theoretical formula (see UG-131) for the various media, multiplied
					 by:
K
= coefficient = 0.62.
The area
A
(square inches) in the
					 theoretical formula shall be the flow area through the minimum opening of the
					 spring loaded nonreclosing pressure relief device.
(3) In lieu of the method of capacity rating in (2) above,
					 a Manufacturer may have the capacity of a spring loaded nonreclosing pressure
					 relief device design certified in general accordance with the procedures of
					 UG-131, as applicable.
UG-128 LIQUID PRESSURE RELIEF VALVE
S
Any liquid pressure relief valve used shall be at least NPS
					 ½ (DN 15).
UG-129 MARKING
(a)
Safety, Safety Relief, Relief, Liquid Pressure
					 Relief, and Pilot Operated Pressure Relief Valves.
Each safety,
					 safety relief, relief, liquid pressure relief, and pilot operated pressure
					 relief valve NPS ½ (DN 15) and larger shall be plainly marked by the
					 Manufacturer or Assembler with the required data in such a way that the marking
					 will not be obliterated in service. The marking may be placed on the valve or
					 on a plate or plates that satisfy the requirements of UG-119:
(1) the name, or an acceptable abbreviation, of the
					 Manufacturer and the Assembler;
(2) Manufacturer's design or type number;
(3) NPS size (DN) _____ (the nominal pipe size of the valve
					 inlet);
(4) set pressure _____ psi (kPa), and, if applicable per
					 UG-136(d)(4), cold differential test pressure _____ psi (kPa);
(5) certified capacity (as applicable):
(a) lb/hr (kg/hr) of saturated steam at an overpressure of
					 10% or 3 psi (20 kPa), whichever is greater for valves certified on steam
					 complying with UG-131 (b); or
(b) gal/min of water at 70°F (20°C) at an
					 overpressure of 10% or 3 psi (20 kPa), whichever is greater for valves
					 certified on water; or
(c) SCFM [standard cubic feet per minute at 60°F and
					 14.7 psia] (M3/min, cubic meters per minute at 20°C and 101 kPa), or lb/min
					 (kg/min), of air at an overpressure of 10% or 3 psi (kPa), whichever is
					 greater. Valves that are capacity certified in accordance with UG-131 (c) (2)
					 shall be marked "at 20% overpressure."
(d) In addition to one of the fluids specified above, the
					 Manufacturer may indicate the capacity in other fluids (see Appendix
					 11).
(6) year built, or alternatively, a coding may be marked on
					 the valve such that the valve Manufacturer or Assembler can identify the year
					 the valve was assembled or tested;
(7) ASME Symbol as shown in Fig. UG-129.1. The pilot of a
					 pilot operated pressure relief valve shall be plainly marked by the
					 Manufacturer or Assembler showing the name of the Manufacturer, the
					 Manufacturer's design or type number, the set pressure in pounds per square
					 inch (kPa), and the year built, or alternatively, a coding that the
					 Manufacturer can use to identify the year built.
On valves smaller than NPS ½ (DN 15), the markings
					 may be made on a metal tag attached by wire or adhesive meeting the
					 requirements of UG-119 or other means suitable for the service
					 conditions.
(8) Restricted lift _____ in. (mm) (For restricted lift
					 valves only)
(b) Safety and safety relief valves certified for a steam
					 discharging capacity under the provisions of Section I and bearing the official
					 Code Symbol Stamp of Section I for safety valves may be used on pressure
					 vessels. The rated capacity in terms of other fluids shall be determined by the
					 method of conversion given in Appendix 11. [See UG- 13l(h).]
(c)
Pressure Relief Valves in Combination With
					 Rupture Disk Devices
. Pressure relief valves in combination with
					 rupture disk devices shall be marked with the capacity as established in
					 accordance with UG-127(a)(3)(b)(2) (using 0.90 factor) or the combination
					 capacity factor established by test in accordance with UG-132(a) or (b), in
					 addition to the marking of UG-129(a) and (f) below. The marking may be placed
					 on the pressure relief valve or rupture disk device or on a plate or plates
					 that satisfy the requirements of UG-119. The marking shall include the
					 following:
(1) name of Manufacturer of valve;
(2) design or type number of valve;
(3) name of Manufacturer of rupture disk device;
(4) design or type number of rupture disk device;
(5) capacity or combination capacity factor;
(6) name of organization responsible for this
					 marking.
This shall be either the vessel user, vessel Manufacturer,
					 rupture disk Manufacturer, or pressure relief valve Manufacturer.
(d)
Pressure Relief Valves in Combination With
					 Breaking Pin Devices.
Pressure relief valves in combination with pin
					 devices shall be marked with the capacity as established in accordance with
					 UG-127 (b) (3) (b) (2) (using 0.90 factor) or the combination capacity factor
					 established by test in accordance with UG-132 (a) or (b), in addition to the
					 marking of UG-129 (a) and (f) below. The marking may be placed on the pressure
					 relief valve or pin device or on a plate or plates that satisfy the
					 requirements of UG-119. The marking shall include the following:
(1) name of Manufacturer of valve.
(2) design or type number of valve.
(3) name of Manufacturer of pin device.
(4) design or type number of pin device.
(5) capacity or combination capacity factor.
(6) name of organization responsible for this
					 marking.
This shall be either the vessel user, vessel Manufacturer,
					 pin device Manufacturer, or pressure relief valve Manufacturer.
See PDF for
					 diagram
(e)
Rupture Disk Devices.
Every rupture
					 disk shall be plainly marked by the Manufacturer in such a way that the marking
					 will not be obliterated in service. The rupture disk marking may be placed on
					 the flange of the disk or on a metal tab that satisfies the requirements of
					 UG-119. The marking shall include the following:
(1) the name or identifying trademark of the
					 Manufacturer;
(2) Manufacturer's design or type number;
(3) lot number;
(4) disk material;
(5) size _____ [NPS (DN) of rupture disk holder];
(6) marked burst pressure _____ psi (kPa);
(7) specified disk temperature _____ °F
					 (°C);
(8) minimum net flow area _____sq in. (sq mm);
(9) certified flow resistance (one or more as
					 applicable);
(a)
K
RG
_____ for
					 rupture disk certified on air or gases;
(b)
K
RL
_____ for rupture
					 disk certified on liquid;
(c)
K
RGL
_____ for
					 rupture disk certified on air or gases, and liquid;
(10) ASME symbol as shown in Fig. UG-129.2;
(11) year built, or alternatively, a coding may be marked
					 on the rupture disk such that the rupture disk device Manufacturer can identify
					 the year the rupture disk device was assembled and tested.
Items (1), (2), (5), (10), and (11) above and flow
					 direction shall also be marked on the rupture disk holder.
(f)
Pin Devices and Pin Actuated Pilot Operated
					 Pressure Relief Devices.
Pin devices shall be plainly marked by the
					 Manufacturer with the required data in such a way that the marking will not be
					 obliterated in service. The marking may be placed on the device housing or on a
					 plate or plates that satisfies the requirements of UG-119. The marking shall
					 include the following:
(1) the name, or an acceptable abbreviation of the
					 Manufacturer
(2) Manufacturer's design or type number
(3) NPS (DN) size (the nominal pipe size of the device
					 inlet)
(4) set pressure psi (kPa)
(5) flow direction
(6) pin to pin device identifier
(7) for capacity certified devices
(a) lb/hr of saturated steam at an overpressure 10% or 3
					 psi (20 kPa), whichever is greater for devices certified on steam complying
					 with UG-131(b), or
(b) gal/min of water at 70°F (20°C) at an
					 overpressure of 10% or 3 psi (20 kPa), whichever is greater for devices
					 certified on water, or
(c) SCFM [standard cubic feet per minute at 60°F and
					 14.7 psia (20°C and 101 kPa)], or lb/min, of air at an overpressure of 10%
					 or 3 psi, whichever is greater. Devices that are capacity certified in
					 accordance with UG-131 (c) (2) shall be marked "at 20% overpressure."
(d) In addition to one of the fluids specified above, the
					 Manufacturer may indicate the capacity in other fluids (see Appendix
					 11).
(8) for flow resistance certified devices:
(a) minimum net flow area _____ in2 (mm2)
(b) certified flow resistance (one or more as
					 applicable)
(1)
K
RG
_____ for pin
					 devices certified on air or gases
(2)
K
RL
_____ for pin
					 devices certified on liquid
(3)
K
RGL
_____ for pin
					 devices certified on air or gases, and liquid
(9) ASME symbol as shown in Fig. UG-129.2
(10) year built, or alternatively, a coding may be marked
					 on the device such that the device Manufacturer can identify the year the
					 device was tested
(11) The pin shall be marked according to one of the
					 following methods:
(a) for pin devices using a replaceable pin to control set
					 pressure, the pin shall be marked with its lot number, pin temperature °F
					 (°C) and the information required by (f) (l), (f) (4), (f) (6), (f) (10),
					 or
Note:
When the pin size or configuration does
					 not permit the use of an attached metal tag, a metal tag may be attached using
					 a nonmetallic connector with an adhesive that complies with Appendix 18 of this
					 Division.
(b) for pin devices that are single use and permanently
					 assembled, the marking requirements of (f) (8) (a), (f) (8) (b), and (f) (11)
					 (a) shall be applied to the device, or
(c) for pin devices that have a replaceable pin within the
					 sealed body per UG-138, the pin shall be marked with its lot number.
(g)
Spring Loaded Nonreclosing Pressure Relief
					 Devices.
Spring loaded nonreclosing pressure relief devices shall be
					 marked in accordance with (a) above except that the Code Symbol Stamp is to be
					 applied only when the capacity has been established and certified in accordance
					 with UG-127 (c) (3) and all other requirements of UG-130 have been met.
(h) For units other than those included above, see
					 U-4.
UG-130 CODE SYMBOL STAMP
Each pressure relief device59 to which the Code Symbol (see
					 Figs. UG-129.1 and UG-129.2) will be applied shall have been fabricated or
					 assembled by a Manufacturer or Assembler holding a valid Certificate of
					 Authorization (UG-117) and capacity certified in accordance with the
					 requirements of this Division. A Certified Individual (CI) shall provide
					 oversight as required by UG-117(a). Each use of the Code Symbol shall also be
					 documented on a Certificate of Conformance Form UV-1 or UD-1, as appropriate. -
					 See PDF for table
59 Vacuum relief devices are not covered by Code Symbol
					 Stamp requirements.
UG-133 DETERMINATION OF PRESSURE RELIEVING
					 REQUIREMENTS
(a) Except as permitted in (b) below, the aggregate
					 capacity of the pressure relief devices connected to any vessel or system of
					 vessels for the release of a liquid, air, steam, or other vapor shall be
					 sufficient to carry off the maximum quantity that can be generated or supplied
					 to the attached equipment without permitting a rise in pressure within the
					 vessel of more than 16% above the maximum allowable working pressure when the
					 pressure relief devices are blowing.
(b) Pressure relief devices as permitted in UG-125(c)(2),
					 as protection against excessive pressure caused by exposure to fire or other
					 sources of external heat, shall have a relieving capacity sufficient to prevent
					 the pressure from rising more than 21% above the maximum allowable working
					 pressure of the vessel when all pressure relief devices are blowing.
(c) Vessels connected together by a system of adequate
					 piping not containing valves which can isolate any vessel, and those containing
					 valves in compliance with Appendix M, M-5, may be considered as one unit in
					 figuring the required relieving capacity of pressure relief devices to be
					 furnished.
(d) Heat exchangers and similar vessels shall be protected
					 with a pressure relief device of sufficient capacity to avoid overpressure in
					 case of an internal failure.
(e) The official rated capacity, or the certified flow
					 resistance and minimum net flow area, of a pressure relief device shall be that
					 which is stamped on the device and guaranteed by the Manufacturer.
(f) The rated pressure relieving capacity of a pressure
					 relief valve for other than steam or air shall be determined by the method of
					 conversion given in Appendix 11.
(g) The relieving capacity of a pressure relief device for
					 compressible fluids may be prorated at any relieving pressure greater tha
					 n
					 1.10
p
, as permitted under UG-125, by
					 applying a multiplier to the official relieving capacity as follows:
(U.S. Customary Units)
See PDF for
					 diagram
where
P
= relieving pressure, psig(kPa
					 gage)
p = set pressure, psig(kPa gage)
For steam pressures above 1,500 psig (10 MPa gage), the
					 above multiplier is not applicable. For steam valves with relieving pressures
					 greater than 1,500 psig (10 MPa gage) and less than or equal to 3,200 psig
					 (22.1 MPa gage), the capacity at relieving pressures greater tha
					 n
					 1.10
p
shall be determined using the
					 equation for steam and the correction factor for high pressure steam in UG-131
					 (e) (2) with the permitted absolute relieving pressure and the coefficient
K
for that valve design.
(h) When sizing and selecting valves, the restricted lift
					 nameplate capacity shall be determined by multiplying the capacity at full
					 rated lift as defined in UG-131 (e) (3) by the ratio of the restricted lift to
					 the full rated lift.
UG-134 PRESSURE SETTINGS AND PERFORMANCE
					 REQUIREMENTS
(a) When a single pressure relief device is used, the set
					 pressure61 marked on the device shall not exceed the maximum allowable working
					 pressure of the vessel. When the required capacity is provided in more than one
					 pressure relief device, only one pressure relief device need be set at or below
					 the maximum allowable working pressure, and the additional pressure relief
					 devices may be set to open at higher pressures but in no case at a pressure
					 higher than 105% of the maximum allowable working pressure, except as provided
					 in (b) below. - See PDF for table
61 The
set pressure
is the value of
					 increasing inlet static pressure at which a pressure relief device displays one
					 of the operational characteristics as defined by opening pressure, popping
					 pressure, start-to-leak pressure, burst pressure, or breaking pressure. (The
					 applicable operating characteristic for a specific device design is specified
					 by the device Manufacturer.)
(b) For pressure relief devices permitted in UG-125(c)(2)
					 as protection against excessive pressure caused by exposure to fire or other
					 sources of external heat, the device marked set pressure shall not exceed 110%
					 of the maximum allowable working pressure of the vessel. If such a pressure
					 relief device is used to meet the requirements of both UG-125(c) and
					 UG-125(c)(2), the device marked set pressure shall not be over the maximum
					 allowable working pressure.
(c) The pressure relief device set pressure shall include
					 the effects of static head and constant back pressure.
(d) (l) The set pressure tolerance for pressure relief
					 valves shall not exceed ±2 psi (15 kPa) for pressures up to and
					 including 70 psi (500 kPa) and ±3% for pressures above 70 psi (500 kPa),
					 except as covered in (d)(2) below.
(2) The set pressure tolerance of pressure relief valves
					 which comply with UG-125(c)(3) shall be within -0%, +10%.
(e) The burst pressure tolerance for rupture disk devices
					 at the specified disk temperature shall not exceed ±2 psi (15 kPa) of
					 marked burst pressure up to 40 psi (300 kPa) and ±5% of marked burst
					 pressure 40 psi (300 kPa) and over.
(f) Pressure relief valves shall be designed and
					 constructed such that when installed per UG-135, the valves will operate
					 without chattering and shall not flutter at the flow-rated pressure in a way
					 that either would interfere with the measurement of capacity or would result in
					 damage.
UG-135 INSTALLATION
(a) Pressure relief devices intended for relief of
					 compressible fluids shall be connected to the vessel in the vapor space above
					 any contained liquid or to piping connected to the vapor space in the vessel
					 which is to be protected. Pressure relief devices intended for relief of
					 liquids shall be connected below the liquid level. Alternative connection
					 locations are permitted, depending on the potential vessel overpressure
					 scenarios and the type of relief device selected, provided the requirements of
					 UG-125(a)(2) and UG-125(c) are met.
(b)(1) The opening through all pipe, fittings and
					 nonreclosing pressure relief devices (if installed) between a pressure vessel
					 and its pressure relief valve shall have at least the area of the pressure
					 relief valve inlet. The characteristic of this upstream system shall be such
					 that the pressure drop will not reduce the relieving capacity below that
					 required or adversely affect the proper operation of the pressure relief
					 valve.
(2) The opening in the vessel wall shall be designed to
					 provide unobstructed flow between the vessel and its pressure relief device
					 (see Appendix M).62 - See PDF for table
62 Users are warned that the proper operation of various
					 rupture disk devices depends upon following the Manufacturer's installation
					 instructions closely with regard to the flow direction marked on the device.
					 Some device designs will burst at pressures much greater than their marked
					 burst pressure when installed with the process pressure on the vent side of the
					 device.
(c) When two or more required pressure relief devices are
					 placed on one connection, the inlet internal cross-sectional area of this
					 connection shall be either sized to avoid restricting flow to the pressure
					 relief devices or made at least equal to the combined inlet areas of the safety
					 devices connected to it. The flow characteristics of the upstream system shall
					 satisfy the requirements of (b) above. (See Appendix M.)
(d) There shall be no intervening stop valves between the
					 vessel and its pressure relief device or devices, or between the pressure
					 relief device or devices and the point of discharge, except:
(1) when these stop valves are so constructed or positively
					 controlled that the closing of the maximum number a of block valves possible at
					 one time will not reduce the pressure relieving capacity provided by the
					 unaffected pressure relief devices below the required relieving capacity;
					 or
(2) under conditions set forth in Appendix M.
(e) The pressure relief devices on all vessels shall be so
					 installed that their proper functioning will not be hindered by the nature of
					 the vessel's contents.
(f) Discharge lines from pressure relief devices shall be
					 designed to facilitate drainage or shall be fitted with drains to prevent
					 liquid from lodging in the discharge side of the pressure relief device, and
					 such lines shall lead to a safe place of discharge. The size of the discharge
					 lines shall be such that any pressure that may exist or develop will not reduce
					 the relieving capacity of the pressure relief devices below that required to
					 properly protect the vessel, or adversely affect the proper operation of the
					 pressure relief devices. [See UG- 136(a)(8) and Appendix M.]