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During piping stress analysis of a piping system, it sometimes seems that there is no major difference between ASME B31.3 and ASME B31.1. As simply changing the codes in the input spreadsheet is sufficient for analysis. But if we take a closer look at both B31.3 vs B31.1, we can understand that there are some major differences in the rules, applications, and guideline considerations between ASME B31.1 and ASME B31.3. In this article, we have listed down some major differences between the process piping (B31.3) and the power piping (B31.1) code.

What is ASME B31.3 or Process piping Code?

ASME B31.3 or Process Piping Code provides rules for piping design for petroleum refineries; onshore and offshore petroleum and natural gas production facilities; chemical, pharmaceutical, textile, paper, ore processing, semiconductor, and cryogenic plants; food and beverage processing facilities; and related processing plants and terminals. This code is known as the Bible for Process Piping Professionals. So this code dictates the design considerations of process plants.

What is ASME B31.1 or Power Piping Code?

ASME B31.1 or Power Piping Code provides rules for piping typically found in electric power generating stations, in industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems. This code is very important for Power piping Professionals as this code governs the design rules for power generation plants.

Difference Between ASME B31.3 and ASME B31.1 (B31.1 vs B31.3)

From the above discussions, it is clear that both ASME B31.3 and ASME B31.1 codes i.e Process Piping Code and Power Piping code are different. Both are related to piping design aspects but vary widely in design considerations. The following table lists out the major differences between ASME B31.3 and ASME B31.1.


  1. ASME B31.1 is written similar, and it stays parallel with Section I of the ASME B&PV Code on most issues.

  2. ASME B31.1 & ASME B31.3, both Codes spell out their intended scopes and their rules are "valid" for the intended scope. ASME B31 Pressure Piping Codes are "voluntary consensus Codes". When a local building Code (which is the law -jurisdiction) requires the use of one of the B31 Codes, only then does it have "the force of law”. Always check with your local jurisdiction to see what piping Code REQUIRED by the law is.

  3. Code in words don’t speak of factor of safety as 4 or 3, for example: The basic allowable stress S in B31.3 is typically based on lesser of one third tensile strength and two thirds yield strength. So, the 1/3 tensile at least gives a safety factor of three for S.

  4. Listed are few differences. Close comparison of ASME B31.3 and ASME B31.1 you will find vast differences in materials and fabrication.

  5. i = "In-plane" o = "Out-of-plane"" These terms relate to the direction of the applied moments. See Figures 319.4.4A and 4B in B31.3. The magnitude of stress in a component depends upon the direction of the applied moment. For example, an in-plane bending moment on an elbow will create a higher stress in an elbow than will an out-of-plane bending moment. B31.3 recognizes this difference by specifying different SIFs for the two moments. B31.1 takes a more simplified (and conservative) approach by specifying only one SIF (the greater of the two) for both moments (actually, the SIF applies to all three moments as B31.1 also intensifies torsional moments).


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