Scope of ASME B31.3 

The ASME B31.3 code is not a design handbook and many engineering decisions that are required to be made to produce a sound piping installation are not specified in detail within this code. Futher, the code specifies a simplified approach for many of its requirements and the designer may choose to adopt a more rigorous analysis to develop the design and construction requirements. 


Rules for ASME B31.3 code have been developed considering piping typically found in the following facilities: 

  • Petroleum refineries
  • Onshore and offshore petroleum and natural gas production facilities
  • Chemical plants
  • Pharmaceutical, textile, paper, ore processing and semiconductor plants
  • Cryogenic plants
  • Food and beverage processing facilities
  • Related processing plants and terminals
  • Piping interconnecting pieces or stages within packaged equipment assembly

Fluid Services

The code covers a wide range of services including

  • Raw, intermediate and finished chemicals
  • Petroleum products
  • Gas, steam, air and water
  • Fluidized solids
  • Refrigerants
  • Cryogenic fluids

ASME B31.3 Exclusions

The following facilities are excluded from the scope of ASME B31.3 in accordance with para 300.1.3:

  • Piping systems handling service that is nonflammable, nontoxic and not damaging to human tissues, designed for internal gage pressure greater than 0 but less than 15 psi (105 kPa).
  • Power boilers as per ASME BPVC Section I and boiler external piping that is required to conform to ASME B31.1.
  • Tubes, tube headers, crossovers and manifolds of fire heaters that are internal to the heater enclosure.
  • Pressure vessels, heat exchangers, pumps, compressors and other fluid handling or processing equipment, including internal piping and connections for external piping.
  • Operation, examination, inspection, testing, maintenance, or repair of piping that has been placed in service.

Code Intent

300(c)(3) Engineering requirements of this code, while considered necessary and adequate for a safe design, generally employ a simplified approach to the subject. A designer capable of applying a more rigorous analysis shall have the latitude to do so, but must be able to demonstrate the validity of that approach.

300(c)(4) Piping elements should insofar as practicable, conform to the Specifications and Standards listed in this code. Piping elements neither specifically approved nor specifically prohibited by this code may be used provided they are qualified for use as set forth in applicable chapters of this code.

300(c)(5) The engineering design shall specify any unusual requirements for a particular service. Where service requirements necessitate measures beyond those required by this code, such measures shall be specified by the engineering design. Where so specified, the code requires that they be accomplished.


Balanced representation of the following interests is preferred:

  • Manufacturers
  • Owners/Operators
  • Designer/Constructors
  • Regulatory Agencies
  • Insurance/Inspection
  • General Interest

Members do not represent organisations.

Membership is considered based on qualifications of the individual.

Interested persons and organizations may participate.

How the Code is revised

The Section committee votes on technical changes by letter ballot (2/3 of committee members must approve). Efforts are made to resolve all negative ballots.

Ballots approved by the section committee are forwarded to the B31 main committee, along with any negative ballots and the reasons for the disapproval. If there are any negative votes at the main committee, the ballot is returned to the section committee for reconsideration. Efforts are made to resolve all disapprovals.

Second consideration at the main committee - 2/3 of members must approve.

Public review - availability of drafts is announced in ASME "Mechanical Engineering" and ANSI "Standards Action." All comments are considered.

Code Issues and Addenda

  • New editions of the code are issued every two years.
  • Addenda issued one and two years after the new edition.
  • Addenda are designated as a and b.
  • Addenda and new editions includes:
    • Technical changes approved by letter ballot
    • Editorial changes which clarify the code but do not change technical requirements
    • Errata to correct misspellings, etc.
  • Technical changes typically take about one year from approval by section committee to be included in code.

Technical Inquiries

Guidelines for preparing technical inquiries regarding the code are provided in Appendix Z. The ASME B31 Committee Code for Pressure Piping considers written requests for interpretations and revisions of the Code rules, and develop new rules if dictated by technological developments. Interpretations previously issued are available at New Inquiries may be submitted through the online Interpretation Submittal Form through The code also provides email contact and address for submittal of enquiries by hard copy.

Inquiries shall be limited strictly to interpretations of the rules or to the consideration of revisions to the present rules on the basis of new data or technology.

  • The B31.3 committee prepares responses to specific questions on the code. These responses are literal interpretations based on a specific edition of the code.
  • If the code, as written, does not address an issue, the response will so state.
  • Rapid preparation of responses is a priority and they are published as interpretations that are issued at the same time as the addenda.
  • Questions must address code requirements. The committee does not:
    • Act as as a consultant on specific engineering problems or on the general application or understanding of the code rules.
    • Approve, certify, rate or endorse any item, construction, propriety device or activity and accordingly inquiries requesting such consideration are returned.

History of ASME B31.3 

The need for a national code of pressure piping became increasingly evident from 1915 to 1925. To meet this need, in March 1926, at the request of The American Society of Mechanical Engineers (ASME), the American Standards Association initiated Project B31 to develop a piping code with ASME as the sole administrative sponsor. After several years work by the Sectional Committee B31 and its subcommittees, the first edition was published in 1935 as an American Tentative Standard code for Pressure Piping. It was composed of separate sections for different industries. A revision of the original tentative standard begun in 1937. Several more years' effort was given to securing uniformity between sections and to eliminating divergent requirements and discrepancies as well as to keeping the code abreast of developments in welding technique, stress computations and reference to new dimensional and materials standards. This work culminated in the 1942 American Standard Code for Pressure Piping.

The Sectional Committee B31 was reorganized and an extensive review of the 1942 code was made. A revision was prepared which was finally approved as American Standard in February, 1951, with the designation B31.3 -1951. The American Standards Association further reviewed the code and a revision was isssued in 1955.

The first edition of ASA B31.3 - Petroleum Refinery Piping Code was published in 1959. Subsequent editions of ASA B31.3 were published in 1962 and 1966. The Americal Standards Association was reorganized in 1967 and renamed as American National Standards Institute. The next edition of the code was designated as ANSI B31.3 - Petroleum Refinery Piping Code and published in 1973. 

A code for Chemical Plant Piping, B31.6, sponsored by Chemical Manufacturers Association was completed in 1974. However, it was decided to merge the requirements of B31.6 and B31.3 because the two codes  were closely related. The new edition of code designated as ANSI B31.3 - Chemical Plant and Petroleum Refinery Piping, was published in 1976. It was at this time that items such as fluid service categories such as Category M, non-metallic piping and safeguarding were introduced into ASME B31.3.

In 1980 the non-metals portions of the B31.3 Code were gathered and included into Chapter VII. Chapter VII of ASME B31.3: 2018 covers nonmetallic piping and piping lined with nonmetals.

A draft code for Cryogenic Piping had been prepared by section Committee B31.10 and was ready for approval in 1981. However, since the coverage overlapped with B31.3, it was decided to merge the and develop a single inclusive code. This code was issued in 1984. 

In addition, in 1984 another potentially separate code was added as new chapter to B31.3, High-Pressure Piping, Chapter IX.

The resulting document is a Code that is very broad in scope. It covers fluids ranging from water to category M fluids. It covers temperatures from cryogenic conditions to 1500°F and beyond. It covers pressures from vacuum and atmospheric to high pressure piping (Chapter IX). There is a great deal of responsibility placed with the Owner and latitude to use good engineering. The Owner of a piping installation has overall responsibility for compliance with this Code.

Previous versions of the code have been prefixed with ASA and ANSI. The initial designation ASA referred to the American Standards Association. The code with ANSI designation referred to the American National Standards Institute and was first published in 1973. The current version of the code has ASME prefix and is referred to as ASME B31.3. 

The various ASME piping codes published as on date of this article are listed below:

  • B31.1 Power Piping
  • B31.2 Fuel Gas Piping (withdrawn in 1988)
  • B31.3 Process Piping (previously referred to as Chemical Plant and Petroleum Refinery Piping Code
  • B31.4 Pipeline Transportation Systems for Liquids and Slurries
  • B31.5 Refrigeration Piping and Heat Transfer Components
  • B31.6 Chemical Plant Piping (never published)
  • B31.7 Nuclear Piping (moved to B&PV Code Section III)
  • B31.8 Gas Transmission and Distribution Piping Systems
  • B31.9 Building Services Piping
  • B31.10 Cryogenic Piping (never published)
  • B31.11 Slurry Piping (superseded by ASME B31.4)
  • B31.12 Hydrogen Piping and Pipelines