Changes In the 2012 Edition of ASME B31.3

Changes In the 2012 Edition of ASME B31.3

In addition to the many clarifications, updated references to codes and standards, updates to basic allowable stresses, and added listed materials, there are several substantive changes to the 2012 Edition of ASME B31.3, Process Piping. These changes are:

Category D Fluid Service

The definition was revised to include piping with design minimum temperatures below -29⁰C (-20⁰F) if the cause of the lower temperature is from ambient conditions.

Allowable Displacement Stress Range

The allowable displacement stress range was limited to 60,000 psi (414 MPa) in the 2012 edition. High strength steels have higher yield and tensile strengths and thus higher allowable stresses. Therefore, they also have higher calculated allowable displacement stress ranges when calculated using the old formula. However, these materials have fatigue strengths similar to the more common steels, which is why the limit was added.

Flexibility Stress Equation

The axial stress was added to the flexibility stress equation. While axial stress in not important in most piping systems, it can be important for piping that is jacketed or buried. The 2010 edition required that it be considered, but it was not in the equation.

Welding Qualification

Restrictions to acceptance of previously qualified welding procedures were removed. Specific language about use of standard welding procedures as permitted by ASME BPV Code, Section IX was added.


The 2012 edition changed “recommended” preheat temperatures to “required” preheat temperatures. All metals must now be preheated to 10⁰C (50⁰F) or higher before welding.

Owner’s Inspector

The qualification requirements for an Owner’s Inspector were broadened in the 2012 Edition.

MPa Stress Table

The MPa allowable stress table first appears in the print version in the 2012 edition. This table is still just for information. The psi allowable stress values are the requirement.

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About The Author

Mr. Frikken is an internationally recognized authority in piping systems, valves, and the development of standards and specifications. His work with Becht includes designing new piping systems, analyzing existing piping systems, assisting manufacturers with respect to code compliance issues, and providing instruction on process piping and piping flexibility analysis courses. Don has received a number of awards including the ASME B31 Forever Medal for Excellence in Piping, and the ASME Melvin R. Green Codes and Standards Medal in 2002, which recognizes outstanding contributions to the development of documents used in ASME programs of technical codification, standardization and certification. He received the ASME Fellow Award in 1994 and the ASME Dedicated Service Award in 1995. Prior to joining Becht Engineering, Don spent 34 years with Solutia, Inc. and Monsanto Company working on a wide range of activities including piping and mechanical design, project engineering, and engineering standards. Mr. Frikken is a registered PE in Missouri.

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Changes In the 2012 Edition of ASME B31.3

18 thoughts on “Changes In the 2012 Edition of ASME B31.3

  1. Dear Don,

    Thanks for your article, very informative. Referring to your comment on the allowable displacement stress range. I can see within ASME B31.3-2012, the change which imposes a maximum limit for Sc and Sh of 138MPa.

    With reference to Equation 1a, can you explain how the maximum displacement stress range could ever be 414MPa? I would have thought it to be:

    Sa = f (1.25*138 + 0.25*138) = f*207 MPa

    Kind Regards,

    Byron Laird

  2. Bryon,

    If you use Equation 1b, the result can be as high as 414 MPa when SL = 0 and f = 1.2.

    Sa = f [1.25(138 + 138) – 0] = 414 MPa max.

    Have fun!

    Don Frikken

  3. B31.3 is clear in stating that Imperial units are mandatory (interpolation to be done from the imperial units table).
    ASME B16.5 (ratings) and ASME Section II (stresses) states that the Metric tables can be used, inclusive interpolation.
    Our view on this matter is that only imperial table data should be used for interpolation to obtain data at other temperatures (same approach as B31.3).
    We assume that the tensile tests where done (now and in the past) at the °F temperatures, and that the stress data where derived from these.
    Therefore, one should not interpolate between interpolated Metric data.
    We launched an interpretation request to the ASME B16.5 committee adressing this problem.

  4. The ASME B16.5 ratings are based on data supplied by the B&PV Code Section II Committee. In some cases, the MPa values are derived from the psi values. In other cases, the MPa values are derived from the same raw data as the psi values are derived from. So for B16.5 ratings, it is permissible to interpolate using either the bar or psi tables. I believe B16 Subcommittee C will respond to your inquiry along those lines. Keep in mind that for B16.5, you must use all US customary units or all metric units. That is not true (yet) for B31.3.

  5. For a unclassified ASME IX material, which cannot fulfill the requirements of ASME IX for bend test (cannot bend at 180° at room temp), how can we realize a PQR according to ASME IX & ASME B31.3?
    Previously, it was possible to realize a specimen in the base metal.

  6. I’m not familiar enough with ASME B&PV Code Section IX to know if there is an exception to the rule you describe. If the material is not sufficiently ductile to withstand the bend test, it may not be suitable for use as a piping material, at least is some applications. Note that the material might still be used for piping without welding according to ASME B31.3 if it can be otherwise qualified.

  7. Thank you for this prompt reply. These specific materials are used for petrochem furnace, due to good properties for creep resistance and also oxydation resistance.
    The design code of these furnaces is mainly API 530 referring to ASME B31.3. Before the revision 2012, I was able to achieve the PQR with the bend tests by stating the para 328.2.1 of ASME B31.3 (prior to 2012 edition) to pass the PQR. I’m now very confused about that! These possibility was also stated in ASTM A488 (casting products). I cannot find any information about the changement of ASME B31.3.

  8. That revision was made as part of a general update to para. 328. I’m pretty sure no one recognized the problem with the deletion of the provision. I will recommend that the committee consider reinstating the old para. 328.2.1(b), but if it is approved, it won’t appear until the 2016 or 2018 editions. Two approaches you can take for now: 1) Many people do not consider the piping you describe as being within the scope of B31.3. If you can take that approach, then you could write your own rules for welder qualification. 2) You can use the rule described in para. 300(c)(3) to justify qualification by the old requirement.

  9. Thank you for your help. I think temporary both solutions can help myself. Do you know how explain my request to the committee?

  10. I sent the request to the committee. I already have a response from Phil Flenner. He says:
    The test bend requirements of Section IX is actually slightly less restrictive than the requirements that were in 328 for bends. If the base materials have a ductility less than 20%, QW-466.1 allows an adjustment for the bends per Note 1 that was somewhat less restrictive than 328 bend test requirements.

  11. Hello. As per Sec 302.3.5 of B31.3 V2012 &2014, the max. allowable stress of Sc & Sh to 20000psi
    can you please explain the reason for keeping the limiting value for the high yield material to 20000psi. More ever, most of the plant process plant works within 7000 cycle.

  12. High strength steels have about the same fatigue resistance as low strength steels, especially for low cycle fatigue. Using the higher values of Sc and Sh when calculating SA gave higher allowable stress ranges for the high strength steels than the materials were capable of accepting. Limiting Sc and Sh to 20,000 psi corrects this problem.

  13. Thanks for your reply. I am still not clear on,
    1. Why to consider fatigue when in general the displacement stress range is with the consideration of shake down to elastic cycling
    2. This can be valid if f>1(Sc & Sh be limited to 20000psi)
    3. Most of the plant is designed for f

  14. Even when the stress range is less than two times yield, the materials cannot be cycled forever without failure. That is why the Code has the stress range factor, f, as part of the equaiton. Figure 302.3.5 illustrates this point.
    When f is greater than one, the limit on Sc and Sh applies as you say.,
    I agree that, in general, 90 plus percent of piping in process plants has f greater than or equal to 1.

  15. Dear Sir,
    Regarding the statement.
    “The allowable displacement stress range was limited to 60,000 psi (414 MPa) in the 2012 edition. High strength steels have higher yield and tensile strengths and thus higher allowable stresses. Therefore, they also have higher calculated allowable displacement stress ranges when calculated using the old formula. However, these materials have fatigue strengths similar to the more common steels, which is why the limit was added.”

    My doubt is Sc and Sh was limited to
    a maximum of 138 MPa (20 ksi) when using a
    value of f > 1.0 in 2010 edition itself. Then why did you mentioned this point in the changes occurred in 2012 edition.

    Please Clarify

  16. Limiting Sc and Sh to 138 MPa applies no matter what the value of f is. Without this limit, the allowable stress range could be higher than 414 MPa for high strength steels when f = 1.0 or less. For example, SA could be as high as 617 MPa for X80 material.

  17. Hi Don,

    Appreciate your efforts in providing these useful information. Do you have a summary of all the substantial changes to ASME B 31.3 since 2004 edition all the way up to 2016 edition? It would be a great help as we are planning to use the latest edition of this code for a project, however the regulation still list 2004 edition.

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