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16
16.1 BACKGROUND AND GENERALINFORMATION
This chapter is based on the 2007 edition of ASME B31.1,Power
Piping Code. As changes, some very significant, are madeto the Code
every year, the reader should refer to the Code forany specific
requirements. This chapter should be considered toprovide
background information and not specific, current Coderules.
References herein to Sections I, II, III, V, VIII, and IX are
ref-erences to Sections of the ASME Boiler and Pressure VesselCode.
References to a para. are generally to a paragraph in ASMEB31.1 or
to a paragraph in this book.
The equations that are numbered in this chapter use the
samenumbers as are used in ASME B31.1. Equations that are not
num-bered are either not in ASME B31.1 or are not numbered
therein.
Published references are listed at the end of each major
sectionof this chapter. Reference documents other than codes and
stan-dards are numbered. Codes and standards, such as those
providedby the ASME, API, AWWA, and ASTM, are simply listed at
theend of each reference section.
16.1.1 History of B31.1 In 1926, the American Standards
Institute initiated Project B31
to develop a piping Code. The ASME was the sole
administrativesponsor. The first publication of this document,
AmericanTentative Standard Code for Pressure Piping, occurred in
1935.From 1942 through 1955, the Code was published as theAmerican
Standard Code for Pressure Piping, ASA B31.1. It con-sisted of
separate sections for different industries.
These sections were split off, starting in 1955, with the
GasTransmission and Distribution Piping Systems, ASA B31.8.
ASAB31.3, Petroleum Refinery Piping Code, was first published
in1959. A number of separate documents have been prepared, mostof
which have been published. The various designations follow:
(1) B31.1, Power Piping (2) B31.2, Fuel Gas Piping (withdrawn in
1988) (3) B31.3, Process Piping (4) B31.4, Pipeline Transportation
Systems for Liquid
Hydrocarbons and Other Liquids (5) B31.5, Refrigeration Piping
(6) B31.6, Chemical Plant Piping (never published; merged into
B31.3) (7) B31.7, Nuclear Piping (moved to B&PV Code Section
III) (8) B31.8, Gas Transmission and Distribution Piping Systems
(9) B31.9, Building Services Piping
(10) B31.10, Cryogenic Piping (never published; merged
intoB31.3)
(11) B31.11, Slurry Piping With respect to the initials that
appear in front of B31.1, these
have been ASA, ANSI, and ASME. It is currently correct to
referto the Code as ASME B31.1. The initial designation ASA
referredto the American Standards Association. This became the
UnitedStates of America Standards Institute and then the
AmericanNational Standards Institute (ANSI) between 1967 and 1969;
thus,ASA was changed to ANSI. In 1978, the Standards Committeewas
reorganized as a committee operating under ASME proce-dures with
ANSI accreditation. Therefore, the initials ASME nowappear in front
of B31.1. These changes in acronyms have notchanged the committee
structure or the Code itself.
16.1.2 Scope of B31.1 The ASME B31.1 Code was written with power
piping in
mind. It was intended to cover the fuel gas and oil systems in
theplant (downstream of the meters), central and district heating
sys-tems, in addition to the water and steam systems in power
plants.The 1998 edition specifically listed systems that are
included andthose that are excluded. However, the ASME B31
StandardsCommittee has directed that the B31 Codes be revised to
permitthe Owner to select the piping code most appropriate to their
pip-ing installation; this change is incorporated in the 1999
addenda.The Introduction to ASME B31.1 (as well as the
Introductions tothe other B31 Codes) states the following:
It is the Owners responsibility to select the Code Sectionwhich
most nearly applies to a proposed piping installation.Factors to be
considered by the Owner include: limitations ofthe Code Section;
jurisdictional requirements; and the applic-ability of other Codes
and Standards. All applicable require-ments of the selected Code
Section shall be met.
The applications considered in the preparation of ASME
B31.1include piping typically found in electric-generating
stations,industrial and institutional plants, geothermal heating
systems,and central and district heating and cooling systems. It
alsoincludes the following:
(1) central and district heating systems for the distribution
ofsteam and hot water away from the plant; and
(2) fuel gas or fuel oil piping from where it is brought into
theplant site from a distribution system, downstream from theoutlet
of the plant meter set assembly, unless the meter setassembly is
located outside of the plant property.
B31.1, POWER PIPINGCharles Becht IV
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The following items are excluded from coverage:
(1) pressure equipment covered by the ASME Boiler andPressure
Vessel Code;
(2) building heating and distribution steam piping designed
for15 psig [100 kPa (gage)] or less, or hot-water heatingsystems
designed for 30 psig [200 kPa (gage)] or less;
(3) piping for hydraulic or pneumatic tools and their
compo-nents downstream of the first block or stop valve off
thesystem distribution header; and
(4) piping for marine or other installations under
federalcontrol.
Note that piping for nuclear power installations is covered
bythe ASME Boiler and Pressure Vessel Code Section III. ASMEB31.1
is also not intended to be applied to the following items,which
were listed as exclusions in the 1998 edition:
(1) roof and floor drains, plumbing, sewers, and sprinkler
andother fire protection systems;
(2) building services piping within the property limits or
build-ings of industrial and institutional facilities, which is
withinthe scope of ASME B31.9 (piping outside of the scope ofB31.9,
such as due to pressure and/or temperature limita-tions, falls
within ASME B31.1.);
(3) fuel gas piping inside industrial and institutional
buildings,which is within the scope of ANSI Z223.1, National
FuelGas Code; and
(4) pulverized fuel piping, which is within the scope of
NFPA8503.
These exclusions were removed in the 1999 addenda andreplaced by
the general statement that it is the Owners responsi-bility to
select the most applicable Code Section. While ASMEB31 now permits
the Owner to select the Code Section that he orshe thinks is most
appropriate to the piping installation, theASME B31.1 Section
Committee has generally considered indus-trial and institutional
piping, other than process piping, to bewithin the scope of ASME
B31.1. In process facilities, most allpiping, including utilities,
generally is constructed in accordancewith ASME B31.3. In other
industrial and institutional facilities,ASME B31.9 should generally
be the Code of choice unless thesystem is not within the coverage
limitations of ASME B31.9.Some of these limits are given below.
(1) Maximum size and thickness limitations, depending
onmaterial: (a) Carbon steel: NPS 30 (DN 750) and 0.50 in. (12.5
mm) (b) Stainless steel: NPS 12 (DN 300) and 0.50 in. (12.5 mm) (c)
Aluminum: NPS 12 (DN 300) (d) Brass and copper: NPS 12 (DN 300)
[12.125 in. OD
(308 mm) for copper tubing] (e) Thermoplastics: NPS 14 (DN 350)
(f) Ductile iron: NPS 18 (DN 450) (g) Reinforced thermosetting
resin: 14 in. (DN 350)
(2) Maximum pressure limits: (a) Boiler external piping for
steam boilers: 15 psig
(105 kPa) (b) Boiler external piping for water heating units:
160 psig
(1,100 kPa) (c) Steam and condensate: 150 psig (1,035 kPa) (d)
Liquids: 350 psig (2,415 kPa) (e) Vacuum: 1 atm external pressure
(f) Compressed air and gas: 150 psig (1,035 kPa)
(3) Maximum temperature limits: (a) Boiler external piping for
water heating units: 250F
(120C) (b) Steam and condensate: 366F (185C) (c) Other gases and
vapors: 200F (95C) (d) Other nonflammable liquids: 250F (120C)
The minimum temperature for ASME B31.9 piping is 0F(18C). Toxic
and flammable gases and toxic liquids are alsoexcluded from the
scope of ASME B31.9.
High pressure and/or temperature steam and water piping with-in
industrial and institutional buildings should generally be
con-structed to ASME B31.1. One of the reasons that B31.1 is
per-haps a better choice for these facilities than B31.3 is that
B31.3places significant responsibility on the Owner. For users of
B31.3,the Owner should have a depth of knowledge that may
wellexceed what the Owners of many industrial and institutional
facil-ities have. B31.1, on the other hand, is more prescriptive
and doesnot place the same responsibility for decisions on the
Owner.
A boiler has three types of piping: boiler proper piping,
boilerexternal piping, and nonboiler external piping. A discussion
ofboiler piping classification and the history behind it is
providedby Bernstein (1998) [1]. Boiler proper piping is entirely
coveredby Section I of the Boiler and Pressure Vessel Code. Boiler
properpiping is actually part of the boiler (e.g., downcomers,
risers,transfer piping, and piping between the drum and an
attachedsuperheater). It is entirely within the scope of Section I
and is notcovered at all by ASME B31.1.
Boiler external piping includes piping that is considered to
bepart of the boiler, but is external to the boiler. It covers
pipingfrom the boiler to the valve or valves that are required by
Section I.Example systems include feedwater, main steam, vent,
drain,blowoff, and chemical feed piping. It includes the connection
tothe boiler proper piping and the valves, beyond which is the
non-boiler external piping. The technical requirements for this
pipingwere transferred from Section I to ASME B31.1 in
1972.However, the administrative requirements remain with Section
I,as this piping is considered to be part of the boiler. Because
thetechnical requirements differ between Section I and ASMEB31.1,
this sometimes results in confusion and error. Reference[1]
provides a detailed comparison of key differences.
Nonboiler external piping is the piping beyond the boiler
thatis, the balance of plant piping beyond the block valve(s)
thatdefine the boundary of the boiler. For this piping, the rules
fallentirely within ASME B31.1.
Figures 16.1.1 and 16.1.2 illustrate the jurisdictional limits
ofboiler proper, boiler external, and nonboiler external
piping.
Because the Code is written for a very specific application
power plant pipingvery detailed piping systemspecific rulesare
provided. This differs, for example, from ASME B31.3, whererules
are written with respect to service conditions (e.g.,
pressure,temperature, flammable, and toxic) rather than specific
systems(e.g., main steam, hot reheat, blowoff, and blowdown).
16.1.3 Intent The ASME B31.1 Code provides minimum requirements
for
safety. It is not a design handbook; furthermore, it is for
design ofnew piping. However, it is used for guidance in the
repair, replace-ment, or modification of existing piping. See
NonmandatoryAppendix V, Recommended Practice for Operation,
Maintenance,and Modification of Power Piping Systems, para. V-8.1,
whichstates the following:
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Piping and piping components which are replaced, modified,
oradded to existing piping systems are to conform to the editionand
addenda of the Code used for design and construction ofthe original
systems, or to later Code editions or addenda asdetermined by the
Operating Company. Any additional pipingsystems installed in
existing plants shall be considered as newpiping and shall conform
to the latest issue of the Code. Further clarification on the issue
of using a more recent edition
of the Code for replacement, modification, or addition is
providedin Interpretation 26-1, Question (2).
Question (2): If a Code edition or addenda later than
theoriginal construction edition (and applicable addenda) isused,
is a reconciliation of the differences required?
Reply (2): No. However, the Committee recommends that theimpact
of the applicable provisions of the later edition oraddenda be
reconciled with the original Code edition andapplicable
addenda.
Some of the philosophy of the Code is discussed in theForeword.
ASME B31.1 is intended to parallel the Boiler andPressure Vessel
Code Section I, Power Boilers, to the extent thatit is applicable
to power piping.
The Foreword states that the Code is more conservative thansome
other piping Codes; however, conservatism consists ofmany aspects,
including allowable stress, fabrication, examina-tion, and testing.
When comparing ASME B31.1 with ASMEB31.3, covered in Chapter 17
herein, one will find that ASME
FIG. 16.1.1 CODE JURISDICTION LIMITS FOR PIPINGFORCED-FLOW STEAM
GENERATOR WITHOUT FIXED STEAM ANDWATER LINE [Source: ASME B31.1,
Fig. 100.1.2(A)]
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B31.1 is more proscriptive and, depending on the circum-stances,
more or less conservative. For example, wall-thicknessof ASME B31.1
will generally be the same or greater. Degree ofexamination will be
more or less, depending on the service.Hydrotest pressure will be
lower, but pneumatic test pressurewill be higher.
The Foreword also contains the following additional
paragraph:
The Code never intentionally puts a ceiling limit on
conser-vatism. A designer is free to specify more rigid
requirementsas he feels they may be justified. Conversely, a
designer whois capable of a more rigorous analysis than is
specified in theCode may justify a less conservative design, and
still satisfythe basic intent of the Code.
In the Introduction, the following paragraph is provided:
The specific design requirements of the Code usually
revolvearound a simplified engineering approach to a subject. It
isintended that a designer capable of applying more completeand
rigorous analysis to special or unusual problems shallhave latitude
in the development of such designs and the eval-uation of complex
or combined stresses. In such cases, thedesigner is responsible for
demonstrating the validity of hisapproach.
Thus, while ASME B31.1 is largely very proscriptive, it
pro-vides the latitude for good engineering practice when
appropriateto the situation. Note that designers are essentially
required to
FIG. 16.1.2 CODE JURISDICTIONAL LIMITS FOR PIPINGDRUM-TYPE
BOILERS [Source: ASME B31.1, Fig. 100.1.2(B)]
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demonstrate the validity of their approach to the Owners and,
forboiler external piping, the Authorized Inspectors
satisfaction.This is addressed in Interpretation 1113, Question
(1).
Question (1): To whom should a designer justify a less
con-servative design by more rigorous analysis to satisfy the
basicintent of the Code as allowed in the Foreword
andIntroduction?
Reply (1): The Owner of a piping installation has
overallresponsibility for compliance with the B31.1 Code, and
forestablishing the requirements for design, construction,
exam-ination, inspection, and testing. For boiler external
piping,the requirements of para. 136.3 shall also be satisfied.
Adesigner capable of more rigorous design analysis than isspecified
in the B31.1 Code may justify less conservativedesigns to the Owner
or his agent and still satisfy the intentof the Code. The designer
is cautioned that applicable juris-dictional requirements at the
point of installation may have tobe satisfied.
Chapter VII, Providing Operation and Maintenance require-ments,
was added in the 2007 edition. See 16.16.
16.1.4 Responsibilities (a) Owner The Owners first
responsibility is to determine
which Code Section should be used. The Owner is also
responsiblefor imposing requirements supplementary to those of the
selectedCode Section, if necessary, to ensure safe piping for the
proposedinstallation. These responsibilities are contained in the
Introduction.
The Owner is responsible for inspection of nonboiler
externalpiping to ensure compliance with the engineering design and
withthe material, fabrication, assembly, examination, and test
require-ments of ASME B31.1.
(b) Designer While not specifically stated in ASME B31.1,
thedesigner is responsible to the Owner for assurance that the
engineer-ing design of piping complies with the requirements of the
Codeand with any additional requirements established by the
Owner.
(c) Manufacturer, Fabricator, and Erector While not
specificallystated in ASME B31.1, the manufacturer, fabricator, and
erectorof piping are responsible for providing materials,
components,and workmanship in compliance with the requirements of
theCode and of the engineering design.
(d) Inspector The inspector is responsible to the Owner,
fornonboiler external piping, to ensure compliance with the
engi-neering design and with the material, fabrication,
assembly,examination, and test requirements of the Code.
An Authorized Inspector, which is a third party, is required
forboiler external piping. The manufacturer or assembler is
requiredto arrange for the services of the Authorized Inspector.
TheAuthorized Inspectors duties are described in para. 16.13.1
here-in. The qualifications of the Authorized Inspector are
specified inSection I, PG-91, as follows:
An Inspector employed by an ASME accredited AuthorizedInspection
Agency, that is, the inspection organization of astate or
municipality, of the United States, a Canadianprovince, or of an
insurance company authorized to writeboiler and pressure vessel
insurance. They are required tohave been qualified by written
examination under the rules ofany state of the United States or
province of Canada whichhas adopted the Code (Section I).
16.1.5 How Is B31.1 Developed and Maintained? ASME B31.1 is a
consensus document. It is written by a com-
mittee that is intended to contain balanced representation from
avariety of interests. Membership includes the following:
(1) Manufacturers (2) Owners/Operators (3)
Designers/Constructors (4) Regulatory Agents (5)
Insurers/Inspectors (6) General Interest Parties The members of the
committee are not intended to be represen-
tatives of specific organizations; their membership is
consideredbased on qualifications of the individual and desire for
balancedrepresentation of various interest groups.
B31.1 is written as a consensus Code and is intended to
reflectindustry practice. This differs from a regulatory approach
inwhich rules may be written by a government body.
Changes to the Code are prepared by the B31.1 SectionCommittee.
Within the Section Committee, responsibility forspecific portions
of the Code are split among Task Groups. Theseare the
following:
(1) Task Group on General Requirements (TG/GR) (2) Task Group on
Materials (TG/M) (3) Task Group on Design (TG/D) (4) Task Group on
Fabrication, Examination, and Erection
(TG/FEE) (5) Task Group on Intercode Liaison (TG/IL) (6) Task
Group on Special Assignments (TG/SA) (7) Task Group on Piping
System Performance (TG/SA) To make a change to the Code, the
responsible Task Group pre-
pares documentation of the change, which is then sent out as a
bal-lot to the entire Section Committee to vote on. Anyone who
votesagainst the change (votes negatively) must state their reason
fordoing so, which is shared with the entire Section Committee.
Theresponsible Task Group usually makes an effort to resolve
anynegatives. A two-thirds majority is required to approve an
item.
Any changes to the Code are forwarded to the B31
StandardsCommittee along with the written reasons for any negative
votes.In this fashion, the Standards Committee is given the
opportunityto see any opposing viewpoints. If anyone on the B31
StandardsCommittee votes negatively on the change, on first
consideration,the item is returned to the Section Committee with
written rea-sons for the negative. The Section Committee must
consider andrespond to any negatives, either by withdrawing or
modifying theproposed change or by providing explanations that
respond to thenegative. If the item is returned to the Standards
Committee forsecond consideration, it requires a two-thirds
approval to pass.
Once an item is passed by the Standards Committee, it is
for-warded to the Board on Pressure Technology Codes andStandards,
which is the final level at which the item is voted onwithin ASME.
Again, any negative vote at this level returns theitem to the
Section Committee, and a second considerationrequires two-thirds
approval to pass.
While the Board on Pressure Technology Codes and
Standardsreports to the Council on Codes and Standards, the Council
doesnot vote on changes to the Code.
The final step is a public review process. Availability
ofdocument drafts is announced in two publications: ANSIsStandards
Action and ASMEs Mechanical Engineering. Copies
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of the proposed changes are also forwarded to the B31Conference
Group and B31 National Interest Review Group forreview. Any
comments from the public or the Groups are consid-ered by the
Section Committee.
While there are a lot of steps in the process, an item can
bepublished as a change to the Code within one year of approval
bythe Section Committee, assuming it is passed on first
considera-tion by the higher committees. The procedures provide for
carefulconsideration and public review of any change to the
Code.
16.1.6 Code Editions and Addenda A new edition of the B31.1 Code
is issued every three years.
Addenda are issued every year except the year in which a
newedition is published.
Addenda are designated a and b. Addenda and the new edi-tion
include the following:
(1) technical changes that have been approved by letter ballot;
(2) editorial changes, which clarify the Code but do not change
technical requirements; and (3) errata items. The issuance of
only two addenda was a change instituted as of
the 1998 edition. Prior policy was to issue three addenda,
withone addenda being issued in the same year as that in which
thenew edition was published. All technical changes were made
inaddenda, and only editorial changes and errata were included
inany new edition.
This chapter is prepared based on the 2007 edition. Significant
changes can occur each addenda and, naturally,
between editions. An engineer whose practice includes
powerpiping should keep current Codes. ASME sells new editions
ofthe B31.1 Code, which include delivery of the associated
addenda,errata, and interpretations.
16.1.7 How Do I Get Answers to Questions About the Code?
The B31.1 Section Committee responds to all questions aboutthe
Code via the inquiry process. Instructions for writing a requestfor
an interpretation are provided in Appendix H. The Committeewill
provide a strict interpretation of the existing rules.
However, as a matter of policy, the Committee will not
approve,certify, rate, or endorse any proprietary device, nor will
it act as aconsultant on specific engineering problems or the
general under-standing or application of Code rules. Furthermore,
it will not pro-vide explanations for the background or reasons for
Code rules. Ifyou need any of the above, you should engage in
research or edu-cation, read this chapter, and/or hire a
consultant, as appropriate.
The Section Committee will answer any request for
interpreta-tion with a literal interpretation of the Code. It will
not createrules that do not exist in the Code, and will state that
the Codedoes not address an item if it is not specifically covered
by ruleswritten into the Code.
Inquiries are assigned to a committee member who develops
aproposed question and reply between meetings. Although the
pro-cedures permit these to be considered between meetings, the
prac-tice is for the Section Committee as a whole to consider
andapprove interpretations at the Section Committee meetings.
Theapproved question and reply is then forwarded to the inquirer
bythe ASME staff. Note that the inquiry may not be considered atthe
next meeting after it is received (the person responsible
forhandling the inquiry may not have prepared a response yet).
Interpretations are published with addenda for the benefit of
allCode users.
16.1.8 How Can I Change the Code? The simplest means for trying
to change the Code is to write a
letter suggesting a change. Any requests for revision to the
Codeare considered by the Code Committee.
To be even more effective, the individual should come to
themeeting at which the item will be discussed. ASME B31.1Section
Committee meetings are open to the public, and participa-tion of
interested parties is generally welcomed. Having a personexplain
the change and the need for it can be more effective than aletter
alone. If you become an active participant and have appro-priate
professional and technical qualifications, you could beinvited to
become a member.
Your request for a Code change may be passed to one of
twotechnical committees under ASME B31. These are the
Fabricationand Examination Technical Committee and the Mechanical
DesignTechnical Committee, which are technical committees intended
toprovide technical advice to and consistency among the variousCode
Sections.
16.1.9 References 1. Bernstein, M.D., and Yoder, L. W., Power
Boilers: A Guide to Section I
of the ASME Boiler and Pressure Vessel Code; The American
Societyof Mechanical Engineers, 1998.
ASME B31.1, Power Piping; The American Society ofMechanical
Engineers.
ASME B31.3, Process Piping; The American Society ofMechanical
Engineers.
ASME B31.4, Pipeline Transportation Systems for
LiquidHydrocarbons and Other Liquids; The American Society
ofMechanical Engineers.
ASME B31.5, Refrigeration Piping; The American Society
ofMechanical Engineers.
ASME B31.8, Gas Transmission and Distribution PipingSystems; The
American Society of Mechanical Engineers.
ASME B31.9, Building Services Piping; The American Society
ofMechanical Engineers.
ASME B31.11, Slurry Piping; The American Society ofMechanical
Engineers.
ASME Boiler and Pressure Vessel Code Section I, Power
Boilers;The American Society of Mechanical Engineers.
ASME Boiler and Pressure Vessel Code Section III, Rules
forConstruction of Nuclear Power Plant Components; The
AmericanSociety of Mechanical Engineers.
16.2 ORGANIZATION OF B31.1 16.2.1 Boiler External and Nonboiler
External Piping
The Code has separate requirements for boiler external
andnon-boiler external piping. Boiler external piping is actually
with-in the scope of Section I of the Boiler and Pressure Vessel
Code.Section I refers to ASME B31.1 for technical
requirements.Nonboiler external piping falls entirely within the
scope of ASMEB31.1. Thus, boiler external piping is treated as part
of the boiler
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and subject to the Boiler and Pressure Vessel Code, whereas
non-boiler external piping is not.
Boiler external piping is considered to start at the first weld
forwelded pipe, flange-face for flanged piping, or threaded joint
forthreaded piping outside of the boiler. It extends to the valve
orvalves required by Section I (and B31.1 para. 122). Both the
jointwith the boiler proper piping and the valve(s) at the end of
thepiping fall within the scope of boiler external piping.
16.2.2 Code Organization Since the systems in a power plant are
well defined, require-
ments are given for specific piping systems. This differs
fromB31.3, which describes requirements in terms of more
generalfluid services. Specific requirements for a piping system,
includ-ing the basis for determining the design pressure and
temperaturefor specific systems, can be found in Chapter II, Part 6
(para.122). The following systems are covered:
(1) boiler external piping including steam, feedwater,
blowoff,and drain piping;
(2) instrument, control, and sampling piping; (3) spray-type
desuperheater piping for use on steam generators
and reheat piping; (4) piping downstream of pressure-reducing
valves; (5) pressure-relief piping; (6) piping for flammable and
combustible liquids; (7) piping for flammable gases, toxic gases or
liquids, or
nonflammable nontoxic gases; (8) piping for corrosive liquids
and gases; (9) temporary piping systems;
(10) steam-trap piping; (11) pump-discharge piping; and (12)
district heating and steam distribution systems. The Code consists
of six chapters and 13 appendices.
Appendices with a letter designation are mandatory; those with
aRoman numeral designation are nonmandatory.
The paragraphs in the Code follow a specific numbering
scheme.All paragraphs in the Code are in the 100 range. The
100-seriesparagraphs are the ASME B31.1 Code Section of the ASME
B31Code for Pressure Piping.
16.2.3 Nonmandatory Appendices ASME B31.1 contains several
nonmandatory appendices.
These are described below, but are not covered in detail, except
asotherwise noted.
Appendix II: Nonmandatory Rules for the Design of SafetyValve
Installations provides very useful guidance for the design
ofsafety-relief-valve installations. In addition to general
guidanceon layout, it provides specific procedures for calculating
thedynamic loads that occur when these devices operate.
Appendix III: Nonmandatory Rules for Nonmetallic Pipingprovides
rules for some of the services in which nonmetallic pip-ing is
permitted by ASME B31.1. It does not cover all
potentialnon-metallic piping system applications within the scope
ofASME B31.1. Appendix III is discussed in greater detail inSection
16.15.
Appendix IV: Nonmandatory Corrosion Control for ASMEB31.1 Power
Piping Systems contains guidelines for corrosioncontrol both in the
operation of existing piping systems and thedesign of new piping
systems. Though nonmandatory, Appendix IVis considered to contain
minimum requirements. It includes
discussions of external corrosion of buried pipe, internal
corro-sion, external corrosion of piping exposed to the atmosphere,
anderosioncorrosion.
Appendix V: Recommended Practice for Operation, Maintenance,and
Modification of Power Piping Systems provides minimumrecommended
practices for maintenance and operation of powerpiping. It includes
recommendations for procedures; documenta-tion; records; personnel;
maintenance; failure investigation andrestoration; piping position
history and hanger/support inspection;corrosion and/or erosion;
piping addition and replacement; safety,safety-relief, and relief
valves; considerations for dynamic loadand high-temperature creep;
and rerating.
Appendix VI: Approval of New Materials offers guidanceregarding
information generally required to be submitted to theASME B31.1
Section Committee for the approval of new materials.
Appendix VII: Nonmandatory Procedures for the Design
ofRestrained Underground Piping provides methods to evaluate
thestresses in hot underground piping where the thermal expansionof
the piping is restrained by the soil. It includes not only theaxial
compression of fully restrained piping, but also the calcula-tion
of bending stresses that occur at changes of direction, wherethe
piping is only partially restrained by the soil.
16.2.4 References ASME B31.1, Power Piping; The American Society
ofMechanical Engineers.
ASME B31.3, Process Piping; The American Society ofMechanical
Engineers.
ASME Boiler and Pressure Vessel Code Section I, Power
Boilers;The American Society of Mechanical Engineers.
ASME Boiler and Pressure Vessel Code Section VIII, Division
1,Pressure Vessels; The American Society of Mechanical
Engineers.
16.3 DESIGN CONDITIONS AND CRITERIA 16.3.1 Design Conditions
Design conditions in ASME B31.1 are specifically intended
forpressure design. The design pressure and temperature are themost
severe coincident conditions that result in the greatest
pipewall-thickness or highest required pressure class or other
compo-nent rating. Design conditions are not intended to be a
combina-tion of the highest potential pressure and the highest
potentialtemperature unless such conditions occur at the same
time.
While it is possible for one operating condition to govern
thedesign of one component in a piping system (and be the
designcondition for that component) and another to govern the
design ofanother component, this is a relatively rare event. If
this case wereencountered, the two different components in a piping
systemwould have different design conditions.
16.3.1.1 Design Pressure In determining the design pressure,all
conditions of internal pressure must be considered. Theseinclude
thermal expansion of trapped fluids, surge, and failure ofcontrol
devices. The determination of design pressure can besignificantly
affected by the means used to protect the pipe fromoverpressure. An
example is the piping downstream of a pressure-reducing valve. Per
para. 122.5, this piping must either be provid-ed with a
pressure-relief device or the piping must be designed forthe same
pressure as the upstream piping.
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8 Chapter 16
In general, piping systems are permitted to be used
withoutprotection of safety-relief valves. However, in the event
that noneare provided on the pipe (or attached equipment that would
alsoprotect the pipe), the piping system must be designed to
safelycontain the maximum pressure that can occur in the piping
sys-tem, including consideration of failure of any and all
controldevices.
ASME B31.1 dictates how the design pressure is determinedin
para. 122 for specific systems. For example, for boiler exter-nal
feedwater piping, the design pressure is required to exceedthe
boiler design pressure by 25% or 225 psi (1,550 kPa),whichever is
less. These requirements are based on system-specific experience.
For example, the aforementioned 25% high-er pressure is required
because this piping is considered to be inshock service and subject
to surge pressure from pump tran-sients.
While short-term conditions such as surge must be
considered,they do not necessarily become the design pressure. The
Codepermits short-term pressure and temperature variations per
para.102.2.4. If the event being considered complies with the
Coderequirements of para. 102.2.4, the allowable stress and/or
compo-nent pressure rating may be exceeded for a short time, as
dis-cussed in 16.3.3. While this is often considered to be an
allowablevariation above the design condition, the variation
limitations arerelated to the maximum allowable working pressure of
the piping,not the design conditions, which could be lower than the
maxi-mum allowable pressure at temperature.
16.3.1.2 Design Temperature It is the metal temperature that
isof interest in establishing the design temperature. The design
tem-perature is assumed to be the same as the fluid temperature,
unlesscalculations or tests support use of other temperatures. If a
lowertemperature is determined by such means, the design metal
tem-perature is not permitted to be less than the average of the
fluidtemperature and the outside surface temperature.
Boilers are fired equipment and therefore subject to
possibleovertemperature conditions. Paragraph 101.3.2(C) requires
thatsteam, feedwater, and hot-water piping leading from fired
equip-ment have the design temperature based on the expected
continu-ous operating condition plus the equipment manufacturers
guar-anteed maximum temperature tolerance. Short-term operation
attemperatures in excess of that condition fall within the scope
ofpara. 102.2.4 covering permitted variations.
ASME B31.1 does not have a design minimum temperature forpiping,
as it does not contain impact test requirements. This isperhaps
because power piping generally does not run cold.Certainly,
operation of water systems below freezing is not a real-istic
condition to consider.
16.3.2 Allowable Stress The Code provides allowable stresses for
metallic piping in
Appendix A. These are, as of addend a to the 2004 edition,
thelowest of the following with certain exceptions:
(1) 1/3.5 times the specified minimum tensile strength (which
isat room temperature);
(2) 1/3.5 times the tensile strength at temperature (times 1.1);
(3) two-thirds specified minimum yield strength (which is at
room temperature); (4) two-thirds minimum yield strength at
temperature; (5) average stress for a minimum creep rate of
0.01%/1,000 hr.;
(6) two-thirds average stress for creep rupture in 100,000
hr.;and
(7) 80% minimum stress for a creep rupture in 100,000 hr.
Specified values are the minimum required in the Material
Specifications. The minimum at temperature is determined
bymultiplying the specified (room temperature) values by the
ratioof the average strength at temperature to that at room
temperature.The allowable stresses listed in the Code are
determined by theASME Boiler and Pressure Vessel Code Subcommittee
II, and arebased on trend curves that show the effect of strength
on yield andtensile strengths (the trend curve provides the
aforementionedratio). An additional factor of 1.1 is used with the
tensile strengthat temperature.
An exception to the above criteria is made for austenitic
stain-less steel and nickel alloys with similar stressstrain
behavior,which can be as high as 90% of the yield strength at
temperature.This is not due to a desire to be less conservative,
but is a recogni-tion of the differences between the behaviors of
these alloys. Thequoted yield strength is determined by drawing a
line parallel tothe elastic loading curve, but with a 0.2% offset
in strain. Theyield strength is the intercept of this line with the
stressstraincurve. Such an evaluation provides a good yield
strength value ofcarbon steel and alloys with similar behavior, but
it does not rep-resent the strength of austenitic stainless steel,
which has consid-erable hardening and additional strength beyond
this value.However, the additional strength is achieved with the
penalty ofadditional deformation. Thus, the higher allowable
stresses rela-tive to yield are only applicable to components that
are not defor-mation sensitive. Thus, while one might use the
higher allowablestress for pipe, it should not be used for flange
design.
The allowable stress for Section I of the ASME Boiler
andPressure Vessel Code was revised to change the factor on
tensilestrength from to in 1999. Code Case 173 was issued in 2001to
permit use of the higher allowable stresses, while new allow-able
stress tables were under preparation for B31.1 The newallowable
stress tables were issued with addenda 2005a (issued in2006) to the
2004 edition.
The increase in allowable stress for Section I was not applied
tobolting. Bolting remains at one-fourth tensile strength.
For cast and ductile iron materials, the behavior is brittle
andthe allowable stress differs accordingly. For cast iron, the
basicallowable stress is the lower of one-tenth of the specified
mini-mum tensile strength (at room temperature) and one-tenth of
theminimum strength at temperature, also based on the trend
ofaverage material strength with temperature. For ductile iron,
afactor of one-fifth is used rather than a factor of one-tenth, and
thestress is also limited to two-thirds times the yield strength.
Theseare in accordance with Section VIII, Division 1, Appendix P,
andTables UCI-23 and UCD-23.
16.3.3 Allowances for Temperature and PressureVariations
While the Code does not use the term maximum allowableworking
pressure, the concept is useful in discussion of theallowances for
variations. Pressure design of piping systems isbased on the design
conditions. However, since piping systemsare an assembly of
standardized parts, there is quite often signifi-cant pressure
capacity in the piping beyond the design conditionsof the system.
The allowances for variations are relative to themaximum
permissible pressure for the system. The allowances
13.5
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for variations are not used in sustained (longitudinal),
occasional(wind, earthquake), nor displacement (thermal expansion)
stressevaluations. They are only used in pressure design.
Increases in pressure and temperature above the design
condi-tions are permitted for short-term events as long as several
condi-tions are satisfied, one of which is that this maximum
allowableworking pressure is not exceeded by more than some
percentage.Thus, the variation can be much higher than the design
condi-tions, yet remain permissible.
ASME B31.1 does not allow use of the variations provision ofthe
Code to override limitations of component standards or thosegiven
by manufacturers of components.
The circumferential pressure stress may exceed the
allowablestress provided by ASME B31.1, Appendix A, by the
following:
(1) 15% if the event duration occurs for no more than 8 hr atany
one time and no more than 800 hr/year; or
(2) 20% if the event duration occurs for no more than 1 hr atany
one time and no more than 80 hr/yr.
There is no provision requiring Owners approval, nor
anyrequiring the designer to determine that the system is safe
withthe variations.
Use of the variations for piping containing toxic fluid is
prohib-ited [see para. 122.8.2(F)].
16.3.4 Overpressure Protection As discussed in the prior section
on design pressure, the piping
system must either be designed to safely contain the
maximumpossible pressure, considering such factors as failure of
controldevices and dynamic events such as surge, or be provided
withoverpressure protection such as a safety-relief valve.
Specificexamples are provided in the Systems (Part 6) part of
Chapter IIfor pressure-reducing valves (para. 122.5) and pump
dischargepiping (para. 122.13), as well as elsewhere in specific
system dis-cussions.
For example, if a 600 psi system goes through a pressure
let-down valve (irrespective of fail-closed features or other
safe-guards) to a 300 psi system, if no safety-relief devices are
provid-ed, the 300 psi system would have to be designed to
safelycontain 600 psi.
If a pressure-relieving device is used, ASME B31.1 refers
toSection I for boiler external piping and nonboiler external
pipingreheat systems, and to Section VIII, Division 1, for
nonboilerexternal piping. See para. 16.5.2 herein.
Block valves are prohibited from the inlet lines to
pressure-relieving safety devices, and diverter or changeover
valves forredundant protective devices are permitted under certain
condi-tions (para. 122.6.1). Block valves are also prohibited from
use inpressure-relieving device discharge piping (para.
122.6.2).
16.3.5 References ASME B31.1, Power Piping; The American Society
ofMechanical Engineers.
ASME Boiler and Pressure Vessel Code Section I, Power
Boilers;The American Society of Mechanical Engineers.
ASME Boiler and Pressure Vessel Code Section II, Materials;The
American Society of Mechanical Engineers.
ASME Boiler and Pressure Vessel Code Section VIII, Division
1,Pressure Vessels; The American Society of Mechanical
Engineers.
16.4 PRESSURE DESIGN 16.4.1 Methods for Internal Pressure
Design
The ASME B31.1 Code provides four basic methods for designof
components for internal pressure, as described in para. 102.2.
(1) Components in accordance with standards listed in Table
126.1for which pressure ratings are provided in the standard,
suchas ASME B16.5 for flanges, are considered suitable byASME B31.1
for the pressure rating specified in the standard.Note that the
other methods of pressure design provided inASME B31.1 can be used
to determine pressure ratings abovethe maximum temperature provided
in the standard if thestandard does not specifically prohibit
that.
(2) Some listed standards, such as ASME B16.9 for pipe
fittings,state that the fitting has the same pressure rating as
matchingseamless pipe. If these standards are listed in Table
126.1,the components are considered to have the same
allowablepressure as seamless pipe of the same nominal
thickness.Note that design calculations are not usually performed
forthese components; design calculations are performed for
thestraight pipe, and matching fittings are simply selected.
(3) Design equations for some components such as straight
pipeand branch connections are provided in para. 104 of ASMEB31.1.
These can be used to determine the required wall-thickness with
respect to internal pressure of components.Also, some specific
branch connection designs are assumedto be acceptable.
(4) Specially designed components that are not covered by
thestandards listed in Table 126.1 and for which design formu-las
and procedures are not given in ASME B31.1 may bedesigned for
pressure in accordance with para.104.7.2. Thisparagraph provides
accepted methods, such as burst testingand finite element analysis,
to determine the pressure capac-ity of these components.
The equations in the Code provide the minimum thicknessrequired
to limit the membrane and, in some cases, bendingstresses in the
piping component to the appropriate allowablestress. To this
thickness must be added mechanical and corro-sion/erosion
allowances. Finally, the nominal thickness selectedmust be such
that the minimum thickness that may be provided,per specifications
and considering mill tolerance, is at least equalto the required
minimum thickness.
Mechanical allowances include physical reductions in
wall-thickness such as from threading and grooving the
pipe.Corrosion and erosion allowances are based on the
anticipatedcorrosion and/or erosion over the lifespan of the pipe.
Suchallowances are derived from estimates, experience, or
referencessuch as NACE publications. These allowances are added to
thepressure design thickness to determine the minimum
requiredthickness of the pipe or component when it is new.
For threaded components, the nominal thread depth (dimension hof
ASME B1.20.1, or equivalent) is used for the mechanicalallowance.
For machined surfaces or grooves, where the toleranceis not
specified, the tolerance is required to be assumed as in.(0.40 mm)
in addition to the depth of the cut.
Mill tolerances are provided in specifications. The most
commontolerance on wall-thickness of straight pipe is 12.5%. This
means thatthe wall-thickness at any given location around the
circumference ofthe pipe must not be less than 87.5% of the nominal
wall-thickness.Note that the tolerance on pipe weight is typically
tighter, so that
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volume of metal and its weight may be there but a thin region
wouldcontrol design for hoop stress from internal pressure.
Note that the appropriate specification for the pipe must
beconsulted to determine the specified mill tolerance. For
example,plate typically has an undertolerance of 0.01 in. (0.25
mm).However, pipe formed from plate does not have this
undertoler-ance; it can be much greater. The pipe specification,
which canpermit a greater undertolerance, governs for the pipe. The
manu-facturer of pipe can order plate that is thinner than the
nominalwall-thickness for manufacturing the pipe, as long as the
pipespecification mill tolerances are satisfied.
16.4.2 Pressure Design of Straight Pipe for Internal
Pressure
Equations for pressure design of straight pipe are provided
inpara. 104.1. The minimum thickness of the pipe selected,
consid-ering manufacturers minus tolerance, must be at least equal
to tm,as calculated using equation (3) or (3A).
(3)
where
additional thicknesspipe outside diameter (not nominal
diameter)internal design gage pressuremaximum allowable stress in
material from internalpressure and joint efficiency (or casting
quality factor)at design temperature from Appendix A minimum
required thickness including additional thick-ness, Acoefficient
provided in Table 104.1.2(A) of the Code andTable 16.4.1 herein
The additional thickness, A, is to compensate for
materialremoved in threading and grooving; to allow for corrosion
and/or
y =
tm =
SE = P =
Do = A =
tm =PDo
2(SE + Py) + A
erosion; to account for cast iron pipe, [0.14 in. (3.56 mm) for
cen-trifugally cast and 0.18 in. (4.57 mm) for statically cast];
and toaccommodate other variations, as described in para. 102.4.4,
suchas local stresses from pipe support attachments.
When equation (3) or (3A) is used for a casting, SF
(basicmaterial allowable stress, S, multiplied by casting quality
factor, F),is used rather than SE.
Note that the equation is based on the outside, rather than
theinside diameter, which is used in pressure vessel Codes. This
isfor a very good reason: the fact that the outside diameter of
pipeis independent of wall-thickness that is, an NPS 6 pipe will
havean outside diameter of 6.625 in. regardless of the
wall-thickness.Therefore, the wall-thickness can be directly
calculated when theoutside diameter is used in the equation.
The foregoing equation is an empirical approximation of themore
accurate and complex Lam equation. The hoop or circum-ferential
stress is higher toward the inside of the pipe than towardthe
outside. This stress distribution is illustrated in Fig. 16.4.1.The
Lam equation can be used to calculate the stress as a func-tion of
location through the wall-thickness. Equation (3) is theBoardman
equation [1]. While it has no theoretical basis, it pro-vides a
good match to the more accurate and complex Lam equa-tion for a
wide range of diameter-to-thickness ratios. It becomesincreasingly
conservative for lower D/t ratios (thicker pipe).
The Lam equation for hoop stress on the inside surface of pipeis
given in the following equation. Note that for internal
pressure,the stress is higher on the inside than the outside. This
is becausethe strain in the longitudinal direction of the pipe must
be con-stant through the thickness, so that any longitudinal strain
causedby the compressive radial stress (from Poissons effects and
con-sidering that the radial stress on the inside surface is equal
to thesurface traction of internal pressure) must be offset by a
corre-sponding increase in hoop tensile stress to cause an
offsettingPoissons effect on longitudinal strain.
sh = P c0.5(Do>t)2 - (Do>t) + 1
(Do>t) - 1 d
TABLE 16.4.1 VALUES OF COEFFICIENT y [Source: ASME B31.1, Table
104.1.2(A)]
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where
sh = hoop stress
The Boardman empirical representation of this simply basesthe
calculation of pressure stress on some intermediate diame-ter
between the inside and outside diameters of the pipe,
asfollows:
where
y = 0.4
Simple rearrangement of the above equation, and substitutingSE
for sh, leads to the Code equation (3). Furthermore,
insidediameterbased formulas add 0.6 times the thickness to the
insideradius of the pipe rather than subtract 0.4 times the
thickness fromthe outside radius. Thus, the inside diameterbased
formula in thepressure vessel Codes and equations (3) and (3A) of
the pipingCode are consistent.
A comparison of hoop stress calculated using the Lam equa-tion
versus the Boardman equation (3) is provided in Fig.
16.4.2.Remarkably, the deviation of the Boardman equation from
theLam equation is less than 1% for D/t ratios greater than
5.1.Thus, the Boardman equation can be directly substituted for
themore complex Lam equation.
For thicker wall pipe, ASME B31.1 provides the followingequation
for the calculation of the y factor in the definition of y inNote
(b) of Table 104.1.2(A). Use of this equation to calculate yresults
in equation (3) matching the Lam equation for heavy wallpipe as
well.
The factor y depends on temperature. At elevated tempera-tures,
when creep effects become significant, creep leads to a
y =d
Do + d
sh = P cDo - 2yt2t dmore even distribution of stress across the
pipe wall-thickness.Thus, the factor y increases, leading to a
decrease in the calculat-ed required wall-thickness (for a constant
allowable stress).
The following additional equation is in ASME B31.1.
(3A)
where
d = inside diameter
Equation (3A) is the same as (3) but with (d + 2t)
substitutedfor D and the equation rearranged to keep thickness on
the leftside. This equation can provide a different thickness than
equation(3) because equation (3A) implicitly assumes that the
additionalthickness, A, is on the inside, whereas equation (3A)
implicitlyassumes it is on the outside. If it were assumed to be on
theinside, there would be an additional P2A added to the
numeratorof equation (3A). Alternatively, d could be taken as the
insidediameter in the corroded condition.
The thickness of gray and ductile iron pipe in other than
steamservice may, as an alternate to equation (3), be determined
fromrelevant standards. See para. 104.1.2(B). The thickness in
steamservice must be determined using equation (3).
The following additional minimum thickness requirements
arespecified to provide added mechanical strength, beyond what
isrequired to satisfy burst requirements, in para. 104.1.2(C):
tm =Pd + 2SEA + 2yPA
2[SE + Py - P]
FIG. 16.4.1 STRESS DISTRIBUTION THROUGH PIPEWALL-THICKNESS FROM
INTERNAL PRESSURE
FIG.16.4.2 COMPARISON OF LAME AND BOARDMANEQUATIONS
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16.4.3 Pressure Design for Straight Pipe UnderExternal
Pressure
For straight pipe under external pressure, there is a
membranestress check in accordance with equation (3) or (3A) of
ASMEB31.1 (the equation for internal pressure) as well as a
bucklingcheck in accordance with the external pressure design rules
of theB&PV Code Section VIII, Division 1 (paras. UG-28, UG-29,
andUG-30).
Flanges, heads, and stiffeners that comply with Section
VIII,Division 1, para. UG-29 are considered stiffeners. The
lengthbetween stiffeners is the length between such components.
Thebuckling pressure is a function of geometry parameters and
mate-rial properties.
Buckling pressure calculations in Section VIII, Division
1require first calculation of a parameter A, which is a function
ofgeometry, and then a parameter B, which depends on parameterA and
a material property curve. The charts that provide the
parameter B account for plasticity that occurs between
theproportional limit of the stressstrain curve and the 0.2% offset
yieldstress. The chart for determination of parameter A is provided
inFig. 16.4.3. A typical chart for B is provided in Fig.
16.4.4.
Two equations are provided for calculating the maximum
permis-sible external pressure. The first uses the parameter B, as
follows:
where:
parameter from material curves in Section II, Part D,Subpart 3
inside diameter (note that the B&PV Code takes dimen-sions as
in the corroded condition) allowable external pressure pressure
design thickness
The second equation is for elastic buckling and is necessary to
usewhen the value of parameter A falls to the left of the material
prop-erty curves that provide parameter B. This equation is as
follows:
p =4AE
3
t = p =
D =
B =
p =4B
3D>t
where:
parameter from geometry curves in Section II, Part D,Subpart 3,
Fig. G (included herein as Fig. 16.4.3) elastic modulus from
material curves in Section II, PartD, Subpart 3.
The second equation is based on elastic buckling, so the
elasticmodulus is used. Note that a chart of parameter B could be
used,with the linear elastic portion of the curve extended to
lowervalues of B, but this would unnecessarily enlarge the charts.
Thecharts provided in ASME B31.5 have this form, with the
elasticlines extended.
The Section VIII procedures include consideration of the
allow-able out-of-roundness in pressure vessels, and use the design
mar-gin of 3. While pipe is not generally required to comply with
thesame out-of-roundness tolerance as is required for pressure
vessels,this has historically been ignored, and has not led to any
apparentproblems.
The basis for the Section VIII approach is provided in
refs.[2][6].
A new buckling evaluation procedure, provided in Code Case2286,
is more relevant to piping as it permits consideration of com-bined
loads, including external pressure, axial load, and gross bend-ing
moment. It is not presently explicitly recognized in ASMEB31.1, but
could be considered as permitted by the Introduction.
16.4.4 Pressure Design of Welded BranchConnections
The pressure design of branch connections is based on a
rathersimple approach, although the resulting design calculations
arethe most complex of the design-by-formula approaches providedin
the Code. A branch connection cuts a hole in the run pipe. Themetal
removed is no longer available to carry the forces due tointernal
pressure. An area replacement concept is used for thosebranch
connections that do not either comply with listed standardsor with
certain designs (see para. 16.4.7 herein). The area of metalremoved
by cutting the hole, to the extent that it was required forinternal
pressure, must be replaced by extra metal in a regionaround the
branch connection. This region is within the limits
ofreinforcement, defined later.
The simplified design approach is limited to branches where
theangle (angle between branch and run pipe axes) is at least 45
deg.
Where the above limitations are not satisfied, the designer
isdirected to para. 104.7 (see para. 16.4.15 herein). Alternatives
inthat paragraph include proof testing and finite element
analysis.
The area A7 is the area of metal removed and is defined as
follows:
A7 = (tmh - A)d1(2 - sina)where:
inside centerline longitudinal dimension of the finishedbranch
opening in the run of the pipe required minimum thickness of run
pipe as determinedfrom equation 3angle between branch and run pipe
axes
In this equation, d1 is effectively the largest possible
insidediameter of the branch pipe. It is appropriate to use the
insidediameter of the pipe in the fully corroded condition.
The angle is used in the evaluation because a lateral
connec-tion, a branch connection with an a other than 90 deg.,
creates alarger hole in the run pipe. This larger hole must be
considered in
a =
tmh =
d1 =
E =
A =
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FIG. 16.4.3 TYPICAL CHART TO DETERMINE A (Source: Fig. G,
Section II, Part D, Subpart 3 of the ASME B&PV Code)
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d1. For a lateral, d1 is the branch pipe inside diameter,
consideringcorrosionerosion allowance, divided by sin a. The (2 -
sina)term in the equation for A7 is used to provide additional
reinforce-ment that is considered to be appropriate because of the
geometryof the branch connection.
The required minimum thickness, tmh, is the pressure
designthickness of the run pipe per equation (3), with one
exception. Ifthe run pipe is welded and the branch does not
intersect the weld,the weld quality factor E should not be used in
calculating thewall-thickness. The weld quality factor only reduces
the allowablestress at the location of the weld.
Only the pressure design thickness is used in calculating
therequired area since only the pressure design thickness
wasrequired to resist internal pressure. Corrosion allowance and
milltolerance at the hole are obviously of no consequence.
The area removed, A7, must be replaced by available area
aroundthe opening. This area is available from excess
wall-thickness thatmay be available in the branch and run pipes as
well as added rein-forcement, and the fillet welds that attach the
added reinforcement.This metal must be relatively close to the
opening of the run pipe toreinforce it. Thus, there are limits,
within which any metal areamust be to be considered to reinforce
the opening. The areas andnomenclatures are illustrated in Fig.
16.4.5.
The limit of reinforcement along the run pipe, taken as
adimension from the centerline of the branch pipe where it
inter-sects the run pipe wall is d2, defined as follows:
(However, d2 is not permitted to exceed Dh.) where
allowance (mechanical, corrosion, erosion) outside diameter of
header pipe measured or minimum thickness of branch
permissibleunder purchase specification
Tb = Dn = A =
d2 = greater of [d1, (Tb - A) + (Th - A) + d1>2]
measured or minimum thickness of header permissibleunder
purchase specification half-width or reinforcing zone
The limit of reinforcement along the branch pipe measuredfrom
the outside surface of the run pipe is L4. L4 is the lesser
of2.5(Th - A) and 2.5(Tb - A) + tr ,
where:
thickness of attached reinforcing pad (when the rein-forcement
is not of uniform thickness, it is the height ofthe largest 60 deg.
right triangle supported by the run andbranch outside diameter
projected surfaces and lyingcompletely within the area of integral
reinforcement; seeFig. 16.4.5, Example C)
The reinforcement within this zone is required to exceed A7.This
reinforcement consists of excess thickness available in therun pipe
(A1); excess thickness available in the branch pipe (A2);additional
area in the fillet weld metal, (A3); metal area in ring,pad, or
integral reinforcement (A4); and metal in a reinforcingsaddle along
the branch (A5). (See Fig. 16.4.5, Example A.) Thesecan be
calculated as follows:
A3 is the area provided by deposited weld metal beyond the
out-side diameter of the run and branch and for fillet weld
attachmentsof rings, pads, and saddles within the limits of
reinforcement.
A4 is the area provided by a reinforcing ring, pad, or
integralreinforcement.
A5 is the area provided by a saddle on 90 deg. branch
connec-tions. See Fig. 16.4.5, Example A.
A2 = 2L4(Tb - tmh)>sin a A1 = (2d2 - d1)(Th - tmh)
tr =
d2 =
Th =
FIG. 16.4.4 TYPICAL CHART TO DETERMINE B (Source: Fig. CS-2,
Section II, Part D, Subpart 3 of the ASME B&PV Code)
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FIG
.16.
4.5
BR
AN
CH C
ONN
ECTI
ON
NOM
ENCL
ATUR
E [S
ourc
e:AS
ME
B31.
1, F
ig.1
04.3
.1 (D
)]
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16 Chapter 16
FIG
.16.
4.5
(CON
TINUE
D)
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The area A4 is the area of properly attached reinforcement
andthe welds that are within the limits of reinforcement. For the
to beconsidered effective, it must be welded to the branch and
runpipes. Minimum acceptable weld details are provided in Fig.
127.4.8(D). The ASME B31.1 Code does not require thedesigner to
specify branch connection weld size because general-ly acceptable
minimum sizes are specified by the Code.Furthermore, the ASME B31.1
Code differs from the B&PVCode in that strength calculations
for load paths through the weldjoints are not required.
If metal with a lower allowable stress than the run pipe is
usedfor reinforcement, the contributing area of this
reinforcementmust be reduced proportionately. No additional area
credit is pro-vided for reinforcement materials with a higher
allowable stress.
Note that branch connections of small bore pipe by creating
asocket or threaded opening in the run pipe wall are permitted
withcertain limitations, as stated in 104.3.1(B.3) and (B.4).
16.4.5 Pressure Design of Extruded Outlet Header An extruded
outlet header is a branch connection formed by
extrusion, using a die or dies to control the radii of the
extrusion.Paragraph 104.3.1(G) provides area-replacement rules for
suchconnections; they are applicable for 90 deg. branch
connectionswhere the branch pipe centerline intercepts the run pipe
center-line,and where there is no additional reinforcement. Figure
16.4.6[ASME B31.1, Fig. 104.3.1(G)] shows the geometry of an
extrudedoutlet header.
Extruded outlet headers are subject to minimum and
maximumexternal contour radius requirements, depending on the
diameterof the branch connection.
A similar area-replacement calculation as described in
para.16.4.4 for fabricated branch connections is provided,
exceptthat the required replacement area is reduced for
smallerbranch-to-run diameter ratios. The replacement area is from
addi-tional metal in the branch pipe, additional metal in the run
pipe,and additional metal in the extruded outlet lip.
16.4.6 Additional Considerations for BranchConnections Under
External Pressure
Branch connections under external pressure are covered in
para.104.3.1. The same rules described in paras. 16.4.4 and 16.4.5
aboveare used. However, only one-half of the area described in
para.16.4.4, covering welded branch connections, requires
replacement.In other words, only one-half of the area A7 requires
replacement.Also, the thicknesses used in the calculation are the
requiredthicknesses for the external pressure condition.
16.4.7 Branch Connections That Are Presumed to Be Acceptable
Some specific types of branch connections are presumed to
beacceptable. This includes fittings listed in Table 126.1
(e.g.,ASME B16.9 tees, MSS SP-97 branch outlet fittings) and the
fol-lowing [para. 104.3.1(C)]:
(1) For branch connections NPS 2 or less that do not
exceedone-fourth of the nominal diameter of the run pipe, thread-ed
or socket welding couplings or half couplings (Class3000 or
greater) are presumed to provide sufficient rein-forcement as long
as the minimum thickness of the couplingwithin the reinforcement
zone is at least as thick as theunthreaded branch pipe.
(2) Small branch connections, NPS 2 or smaller as shown inASME
B31.1 Fig. 127.4.8(F) (these are partial penetra-tion weld branch
connections for NPS 2 and smallerbranch fittings), provided the
thickness of the weld joint(not including the cover fillet) is at
least equal to thethickness of schedule 160 pipe of the branch
size, areacceptable.
Integrally reinforced fittings and integrally reinforced
extrudedoutlets that satisfy the area replacement requirements or
are qualifiedby burst or proof tests or calculations substantiated
by successfulservice of similar design [para. 104.3.1(D.2.7)] are
also acceptable.
16.4.8 Pressure Design of Bends and Elbows Bends are required to
have, after bending, a wall-thickness at
least equal to either the required wall-thickness for straight
pipein para. 104.1.2(A) (para. 104.2 refers to para. 102.4.5
whichrefers to para. 104.1.2(A), or to satisfy equations 3B and
3C.These equations are based on the Lorenz equation.
Paragraph17.4.8, herein, discusses the Lorenz equation, which
provides theactual pressure stresses in a pipe bend or elbow.
Because of the bending process, the thickness tends to
increasein the intradors, or inside curve of the elbow, and
decrease on theextrados, or outside curve of the elbow. ASME B31.1
providesminimum recommended thickness of the pipe, prior to
bending, inTable 102.4.5, which, based on experience, results in a
pipe thick-ness after bending that is at least equal to the
required wall thick-ness of straight pipe.
Elbows in accordance with standards listed in Table 126.1
(e.g.,B16.9 elbows) are acceptable for their rated pressure
temperature.
16.4.9 Pressure Design of Miters Miter joints and miter bends
are covered by para. 104.3.3.
Miters in a miter bend are either widely spaced or closely
spaced.The criteria for closely spaced versus widely spaced are
containedin Table D-1. If the following equation is satisfied, the
miter isclosely spaced; otherwise it is widely spaced.
where mean radius of pipe chord length between miter joints,
taken along pipe centerline one-half angle between adjacent miter
axes (see Fig. 16.4.7;the axes are the extension of the line of
miter cuts towhere they intercept)
If the miters are widely spaced and the half-angle satisfies
thefollowing equation, no further consideration is required.
Themiter cut is simply considered to be equivalent to a girth
butt-welded joint.
where
nominal wall-thickness of the pipe
The required wall-thickness of other miters depends onwhether
they are closely spaced or widely spaced. For closely
tn =
u 6 9Atnr
u = s = r =
s 6 r (1 + tan u)
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18 Chapter 16
spaced miter bends, the required pressure design wall-thickness
isper the following equation:
where
bend radius of miter bend minimum required thickness for
straight pipe tm =
R =
ts = tm 2 - r>R
2(1 - r>R)
For widely spaced miters, the following equation provides
therequired pressure design wall-thickness:
This equation must be solved iteratively since the
requiredthickness is on both sides of the equation.
There are additional pressure limitations for miters. These
are10 psi (70 kPa) and less, above 10 psi (70 kPa) but not
exceeding100 psi (700 kPa), and above 100 psi (700 kPa). The
above
ts = tm(1 + 0.641r>ts tan u)
FIG. 16.4.6 EXTRUDED OUTLET HEADER NOMENCLATURE [Source: ASME
B31.1, Fig. 104.3.1 (G)]
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equations can be used for design of the miter bends up to 100
psiunder the following conditions: the thickness is not less
thanrequired for straight pipe; the contained fluid is
nonflammable,nontoxic, and incompressible, except for gaseous vents
to atmos-phere; the number of full pressure cycles is less than
7,000 duringthe expected lifetime of the piping system; and full
penetrationwelds are used in joining miter segments.
For above 100 psi, or when the above conditions are
notsatisfied, the design is required to be qualified per para.
104.7,with additional qualifications to the para. 104.7
requirements statedin para. 104.3.3(C).
For use up to 100 psi, the following requirements must
besatisfied:
(1) Angle must not exceed 22.5 deg. (e.g., 2 cut miter for 90deg
bend, minimum).
(2) The minimum length of the miter segment at the crotch
(theshortest length in a miter segment), B, must be at least
6tnwhere tn is the pipe nominal wall thickness.
The above two conditions need not be satisfied if the pressureis
limited to 10 psi (70 kPa).
16.4.10 Pressure Design of Closures Closures are covered in
para. 104.4.1. Components in accor-
dance with standards listed in Table 126.1, such as ASME
B16.9pipe caps, can be used for closures within their specified
pressure-temperature ratings. The other options provided in ASME
B31.1are to either design the closure in accordance with either
Section I,PG-31, or to Section VIII, Division 1, UG-34 and UW-13,
or toqualify it as an unlisted component in accordance with
para.104.7 (see para. 16.4.15 herein).
Openings in closures are covered in para. 104.4.2.
Theserequirements are summarized as follows:
(1) If the opening is greater than one-half of the inside
diame-ter of the closure, it is required to be designed as a
reducerper para. 104.6. While not an ASME B31.1 requirement,
theASME B31.3 requirement that if the opening is in a flat
clo-sure, it be designed as a flange, is appropriate and should
beconsidered.
(2) Small openings and connections using branch
connectionfittings that comply with para. 104.3.1(C) (by the
referenceto para. 104.3.1) are considered to be inherently
adequatelyreinforced.
(3) The required area of reinforcement is the inside diameter
ofthe finished opening times the required thickness of the
u
closure. The Section VIII, Division 1 rules that only
requireone-half of that area for flat heads are not applicable.
(4) The available area of reinforcement should be calculated
perthe rules in ASME B31.1 contained in para. 104.3.1.
(5) Rules for multiple openings follow para. 104.3.1(D.2.5)
rulesfor multiple openings (by the reference to para. 104.3.1).
16.4.11 Pressure Design of Flanges (para. 104.5.1) Most flanges
are in accordance with standards listed in
Table 126.1, such as ASME B16.5 and, for larger flanges,
ASMEB16.47. When a custom flange is required, design by analysis
ispermitted by para. 104.5.1. ASME B31.1 refers to the rules
forflange design contained in Section VIII, Division 1, Appendix
2,but uses the allowable stresses and temperature limits of
ASMEB31.1. In addition, the fabrication, assembly, inspection, and
test-ing requirements of ASME B31.1 are governing.
16.4.12 Pressure Design of Blind Flanges (para. 104.5.2)
Most blind flanges are in accordance with standards listed
inTable 126.1, such as ASME B16.5. When designing a blindflange,
the rules of Section I for bolted flat cover plates are applic-able
(these are contained in PG-31). Additionally, the ASMEB31.1 design
pressure and allowable stresses are to be used.
16.4.13 Pressure Design of Blanks Blanks are flat plates that
get sandwiched between flanges to
block flow. A design equation for permanent blanks is provided
inpara. 104.5.3, as follows:
(7)
where
inside diameter of gasket for raised or flat-face flanges, orthe
gasket pitch diameter for retained, gasketed flanges
Other terms are as defined in para. 16.4.2 herein. Mechanical
and corrosionerosion allowances must be added
to the pressure design thickness calculated from equation (7).
Blanks used for test purposes are required to be designed per
the foregoing equation, except that the test pressure is used
andSE may be taken, if the test fluid is incompressible (e.g., not
apneumatic test), at 95% of the specified minimum yield strengthof
the blank material.
16.4.14 Pressure Design of Reducers Most reducers in piping
systems are in accordance with the
standards listed in Table 126.1. This is the only provision
forreducers in para. 104.6 (which is not helpful when one is
referredfrom para. 104.4.2 to this paragraph for large-diameter
openingsin closures). However, pressure design per 104.7 is also an
option.
16.4.15 Specially Designed Components If a component is not in
accordance with a standard listed in
Table 126.1, and the design rules provided elsewhere in para.
104are not applicable, para. 104.7.2 is applicable. This
paragraphrequires that some calculations be done in accordance with
thedesign criteria provided by the Code and be substantiated by
one
d6 =
t = d6A3p
16 SE
FIG. 16.4.7 ILLUSTRATION OF MITER BEND SHOWINGNOMENCLATURE
(Source: ASME B31.1, Table D-1)
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20 Chapter 16
of several methods. The most important element of this paragraph
isconsidered to be the substantiation; the aforementioned
calculationsare not generally given much consideration. The methods
to verifythe pressure design include the following: (Note that this
paragraphwas substantially changed in the 1999 addenda, including
the addi-tion of detailed stress analysis as an option for
substantiation.
(1) Extensive, successful service experience under
comparableconditions with similarly proportioned components of
thesame or like material.
(2) Experimental stress analysis, such as described in
theB&PV Code Section VIII, Division 2, Appendix 6.
(3) A proof test conducted in accordance with ASME B16.9,MSS
SP-97, or Section I, A-22. The option for witnessingby the
Authorized Inspector was removed in the 1999addenda. This prior
provision was not necessarily practicaland could create difficulty
for the manufacturer, since prooftests may be conducted to qualify
a line of components wellbefore being sold for any specific piping
system.
(4) Detailed stress analysis (e.g., finite element method)
withresults evaluated in accordance with Section VIII, Division
2,Appendix 4 except the basic allowable stress fromAppendix A is
required to be used in place of Sm. These arethe design-by-analysis
rules in the B&PV Code.
Of the above, the methods normally used to qualify new unlist-ed
components are proof testing and detailed stress analysis.
It should be noted that the Code permits interpolation
betweensizes, wall-thicknesses, and pressure classes, and also
permitsanalogies among related materials. Extrapolation is not
permitted.
The issue of how to determine that the above has been done ina
satisfactory manner is addressed in the 1999 addenda.
Earliereditions of the Code only provided for witnessing of the
proof testfor boiler external piping. However, this is not
practical when themanufacturer performs proof tests to qualify a
line of piping com-ponents. Obviously, all the potential future
Authorized Inspectorscould not be gathered for this event.
Furthermore, the other meth-ods are of at least equal concern, and
their review may be moreappropriately done by an engineer rather
than an Inspector. As aresult of these concerns, the requirement
was added that docu-mentation showing compliance with the above
means of pressuredesign verification must be available for the
Owners approvaland, for boiler external piping, available for the
AuthorizedInspectors review. The Owners review could be done by
anInspector or some other qualified individual.
While MSS SP-97 and ASME B16.9 provide a clear approachfor
determining that the rating of a component is equivalent orbetter
to matching straight pipe, they do not provide defined pro-cedures
for determining a rating for a component that may have aunique
rating, which may differ from matching straight pipe. Theprocedure
generally used here is to establish a pressure-temperaturerating by
multiplying the proof pressure by the ratio of the allow-able
stress for the test specimen to the actual tensile strength ofthe
test specimen. In the proposed ASME B31H Standard, thiswould be
reduced by a testing factor depending on the number oftests. An
example of this approach is provided in ref. [7].
The proposed standard ASME B31H, Standard Method toEstablish
Maximum Allowable Design Pressure for PipingComponents, is under
development by the ASME and will even-tually add to or replace the
existing proof test alternatives in para.104.7.2. This standard
provides procedures to either determine ifa component has a
pressure capacity at least as great as a matching
straight pipe, or to determine a pressure-temperature rating for
acomponent.
16.4.16 References 1. Boardman, H.C., Formulas for the Design of
Cylindrical and
Spherical Shells to Withstand Uniform Internal Pressure, The
WaterTower, Vol. 30, 1943.
2. Bergman, E. O., The New-Type Code Chart for the Design of
VesselsUnder External Pressure, Pressure Vessel and Piping
Design,Collected Papers 19271959, The American Society of
MechanicalEngineers, 1960, pp. 647654.
3. Holt, M., A Procedure for Determining the Allowable
Out-of-Roundness for Vessels Under External Pressure, Pressure
Vessel andPiping Design, Collected Papers 19271959, The American
Societyof Mechanical Engineers, 1960, pp. 655660.
4. Saunders, H. E., and Windenburg, D., Strength of Thin
CylindricalShells Under External Pressure, Pressure Vessel and
Piping Design,Collected Papers 19271959, The American Society of
MechanicalEngineers, 1960, pp. 600611.
5. Windenburg, D., and Trilling, C., Collapse by Instability of
ThinCylindrical Shells Under External Pressure, Pressure Vessel
andPiping Design, Collected Papers 19271959, The American Societyof
Mechanical Engineers, 1960, pp. 612624.
6. Windenburg, D., Vessels Under External Pressure: Theoretical
andEmpirical Equations Represented in Rules for the Construction
ofUnfired Pressure Vessels Subjected to External Pressure,
PressureVessel and Piping Design, Collected Papers 19271959,
TheAmerican Society of Mechanical Engineers, 1960, pp. 625632.
7. Biersteker, M., Dietemann, C., Sareshwala, S., and Haupt, R.
W.,Qualification of Nonstandard Piping Product Form for ASME
Codefor Pressure Piping, B31 Applications, Codes and Standards
andApplications for Design and Analysis of Pressure Vessels and
PipingComponents, PVP-Vol. 210-1, The American Society of
MechanicalEngineers, 1991.
ASME B1.20.1, Pipe Threads, General Purpose (Inch); The
AmericanSociety of Mechanical Engineers.
ASME B16.5, Pipe Flanges and Flanged Fittings; The American
Societyof Mechanical Engineers.
ASME B16.9, Factory-Made Wrought Steel Butt-Welding Fittings;
TheAmerican Society of Mechanical Engineers.
ASME B16.47, Large-Diameter Steel Flanges: NPS 26 through NPS
60;The American Society of Mechanical Engineers.
ASME B31.1, Power Piping; The American Society of
MechanicalEngineers.
ASME B31.3, Process Piping; The American Society of
MechanicalEngineers.
ASME B31.5, Refrigeration Piping; The American Society of
MechanicalEngineers.
ASME B31H, Standard Method to Establish Maximum Allowable
DesignPressures for Piping Components; The American Society of
MechanicalEngineers (to be published). ASME Boiler and Pressure
Vessel Code Section I, Power Boilers; TheAmerican Society of
Mechanical Engineers.
ASME Boiler and Pressure Vessel Code Section II, Part D,
Materials,Properties; The American Society of Mechanical
Engineers.
ASME Boiler and Pressure Vessel Code Section VIII, Division 1,
PressureVessels; The American Society of Mechanical Engineers.
ASME Boiler and Pressure Vessel Code Section VIII, Divisions 1
and 2,Code Case 2286, Alternative Rules for Determining
Allowable
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Compressive Stresses for Cylinders, Cones, Spheres, and Formed
Heads;The American Society of Mechanical Engineers.
MSS SP-97, Integrally Reinforced Forged Branch Outlet
FittingsSocketWelding, Threaded, and Butt-Welding Ends; The
ManufacturersStandardization Society of the Valve and Fittings
Industry, Inc.
16.5 LIMITATIONS ON COMPONENTSAND JOINTS
16.5.1 Overview ASME B31.1 includes limitations on components
and joints in
the design chapter, Chapter II. These are contained in Part
3,Selection and Limitations of Piping Components; and in Part
4,Selection and Limitations of Piping Joints. This section
(16.5)combines the limitations with pressure design and other
consider-ations, on a component-by-component basis.
16.5.2 Valves Most valves in ASME B31.1 piping systems are in
accordance
with standards listed in Table 126.1. These standards include
thefollowing:
(1) ASME B16.10, Face-to-Face and End-to-End Dimensionsof
Valves
(2) ASME B16.34, ValvesFlanged, Threaded, and WeldingEnd
(3) AWWA C500, Metal-Seated Gate Valves for Water SupplyService
(with limitation regarding stem retention)
(4) AWWA C504, Rubber-Seated Butterfly Valves (5) MSS SP-42,
Class 150 Corrosion-Resistant Gate, Globe,
Angle, and Check Valves With Flanged and Butt-WeldedEnds (with
limitation regarding stem retention)
(6) MSS SP-67, Butterfly Valves (with limitation regardingstem
retention)
(7) MSS SP-80, Bronze Gate, Globe, Angle and Check Valves Listed
valves are accepted for their specified pressure ratings.
Valves that are not in accordance with one of the listed
standardscan be accepted as unlisted components in accordance with
para.102.2.2. The pressure-temperature rating for such valves
shouldbe established in accordance with para. 104.7.2. The
manufacturersrecommended rating is not permitted to be
exceeded.
Additional requirements are provided in para. 107. Theseinclude
the following:
(1) requirements for marking (para. 107.2); (2) requirement for
use of outside screw threads for valves NPS
3 (DN 75) and larger for pressure above 600 psi (4,150
kPa)(para. 107.3);
(3) prohibition of threaded bonnet joints where the seal
dependson the thread tightness for steam service at pressure
above250 psi (1,750 kPa) (para. 107.5); and
(4) requirements for bypasses (para. 107.6). Additional
requirements for valves in boiler external piping
(steam-stop valves, feedwater valves, blowoff valves, and
safetyvalves) are provided in para. 122.1.7.
Requirements for safety-relief valves for ASME B31.1 pipingare
also covered in para. 107.8. Safety-relief valves on boilerexternal
piping are required to be in a accordance with Section I(by
reference to para. 122.1.7(D.1). Safety-relief valves for
non-boiler external piping are required to be in accordance
with
Section VIII, Division 1, paras. UG-126 through UG-133.
Anexception for valves wit set pressures 15 psig (100 kPa
(gage))and lower is that ASME Code Stamp and capacity
certificationare not required. Safety-relief valves for nonboiler
external reheatpiping are required to be in accordance with Section
I, PG-67through PG-73.
Appendix II provides nonmandatory rules for the design
ofsafety-valve installations.
For piping containing toxic fluids [para. 122.8.2(D)],
steelvalves are required, and bonnet joints with tapered threads
areprohibited. Also, special consideration should be given to
valvedesign to prevent stem leakage. Permitted bonnet joints
includeunion, flanged with at least four bolts; proprietary,
attached bybolts, lugs, or other substantial means, and having a
design thatincreases gasket compression as fluid pressure
increases; orthreaded with straight threads of sufficient strength,
with metal-to-metal seats and a seal weld.
16.5.3 Flanges Most flanges in ASME B31.1 piping systems are in
accordance
with listed standards. These listed standards include the
following:
(1) ANSI B16.1, Cast Iron Pipe Flanges and Flanged Fittings (2)
ASME B16.5, Pipe Flanges and Flanged Fittings (3) ASME B16.24, Cast
Copper Alloy Pipe Flanges and Flanged
Fittings Class 150, 300, 400, 600, 900, 1500, and 2500 (4) ASME
B16.42, Ductile Iron Pipe Flanges and Flanged
Fittings, Classes 150 and 300 (5) ASME B16.47, Large Diameter
Steel Flanges, NPS 26
through NPS 60 (6) AWWA C115, Flanged Ductile-Iron Pipe with
Threaded
Flanges (7) AWWA C207, Steel Pipe Flanges for Water Works
Service,
Sizes 4 Inch through 144 Inch (100 mm through 3,600 mm) (8) MSS
SP-51, Class 150LW Corrosion-Resistant Cast
Flanges and Flanged Fittings (9) MSS SP-106, Cast Copper Alloy
Flanges and Flanged
Fittings, Class 125, 150, and 300
Flanges that are listed in Table 126.1 are accepted for
theirspecified pressure ratings. Flanges that are not in accordance
withone of the listed standards can be designed using the rules
ofSection VIII, Division 1, Appendix 2, with appropriate
allowablestress and design pressure (see para. 104.5.1), or
qualified usingpara. 104.7.2. ASME B31.1 states that the Section
VIII rules arenot applicable when the gasket extends beyond the
bolt circle,which is also a limitation stated in Section VIII.
Paragraphs 104.5, 108, 112, and 122.1.1 provide
additionalrequirements for flanges, including the following:
(1) ASME B16.5 slip-on flanges are not permitted for higherthan
Class 300 flanges [para. 104.5.1(A)].
(2) When bolting Class 150 steel flanges to matching cast
ironflanges, the steel flange is required to be flat face to
preventoverloading the cast iron flange (para. 108.3). Use of
full-face gaskets with flat-face flanges helps the flange
resistrotation from the bolt load.
(3) Class 250 cast iron are permitted to be used with
raised-faceClass 300 steel flanges (para. 108.3).
(4) Table 112 provides detailed requirements for flange
bolt-ing, facing, and gaskets. These depend on f