When Should the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used?

When Should the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used?

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This posting (November 2019) is an update to an October 2013 post which reflects changes to the ASME B31.3 Code relative to severe cyclic service that have occurred since the original post.

There has been a fair amount of confusion as to when the rules for severe cyclic conditions in ASME B31.3 should be used, and the rules themselves can be somewhat confusing to apply. In the 2016 edition of ASME B31.3 the definition of when the rules for severe cyclic service are applicable were changed, which may reduce the confusion.  The definition as to when the rules of severe cyclic apply is in the 300.2, Definitions.  Prior to the 2016 edition, it stated that severe cyclic conditions are:

  • Conditions applying to specific piping components or joints in which SE computed in accordance with para. 319.4.4 exceeds 0.8SA (as defined in para. 302.3.5); and
  • The equivalent number of cycles (N in para. 302.3.5) exceeds 7000;
  • Or, other conditions that the designer determines will produce an equivalent effect.

So, by this definition, severe cyclic conditions applied to piping systems with a lot of displacement cycles, which are rare in most continuous operation process plants, and the calculated displacement stress is close to the allowable displacement stress.  For these piping systems, fatigue is a greater concern. Following the rules for severe cyclic conditions generally results in piping systems with greater fatigue resistance.

In the 2016 edition, consideration of calculated stress and number of cycles was eliminated in the definition, and it was changed to: conditions applying to specific piping components or joints for which the owner or the designer determines that construction to better resist fatigue loading is warranted.  So, for systems where experience has shown fatigue is a greater concern, such as highly cyclic units, the owner or designer can designate severe cyclic service to get a constructed piping system that is more resistant to fatigue failure.

While it appears that some of the rules in the code are written with the idea that severe cyclic conditions may apply to an entire piping system, the rules only apply to the specific components.  In the past it was those that are over 80% of the allowable stress or otherwise designated by the designer.  With the change to the new definition, it only applies to components and joints designated by the owner or designer.

The prior rules led to some puzzling circumstances.  For example, there are some components that are prohibited for use in severe cyclic service for which stresses are not calculated.  An example is slip-on flanges.  The stress in the pipe at that location could be over 80% of the allowable stress, but this is highly unlikely in most systems, as components such as elbows and tees typically govern in the flexibility analysis.  And the rules called for considering the stress in the component, something that was not available for a slip-on flange.  With the change in the definition, things are clearer.  If the owner or designer designates a flanged joint as in severe cyclic service, slip-on flanges are prohibited.

If a component or weld is determined to be in serve cyclic conditions, the following additional requirements apply:

  • The rules prohibit the use of less fatigue resistant components and joints for use with severe cyclic conditions
  • There are some fabrication requirements, such as 328.5.6 which states that “A welding procedure shall be employed which provides a smooth, regular, fully penetrated inner surface.”
  • 100% visual examination of fabrication is required
  • 100% volumetric examination of butt and miter groove welds
  • Socket welds and other branch connections welds examined by magnetic particle or liquid penetrant examination
  • The acceptance criteria for welds is more stringent, for example, prohibiting any undercutting

The following example illustrates how the rules worked prior to the change in the 2016 edition:

Assume there is a system with 10,000 equivalent displacement cycles, so it is more than 7,000, and the calculated stress in one location, an unreinforced fabricated tee, exceeds 80% of the allowable stress (but as required by code, is less than the allowable stress).  To start with, you probably don’t want to use an unreinforced fabricated tee in such a service anyway, so you would reinforce it or replace it with a welding tee, the calculated stress will undoubtedly drop below 80% of the allowable, and it is no longer in severe cyclic conditions.  With the 2016 edition, the calculation of stress and the number of cycles is no longer relevant but assume now that the owner designated the tee as being in severe cyclic service.  For the purposes of looking at the rules, let’s assume that you went ahead with the unreinforced fabricated tee. 

Per 328.5.6, you are requried to use an appropriate weld procedure.  Looking at 341.4.3, you can note that all threaded, bolted, and other joints shall be examined.  Well, the tee doesn’t have any joints, other than the weld joint itself, which should be examined.  And 341.4.3 (a) (3) requires all dimensions, alignment, springs, guides, etc be checked.  It is not very clear what should be included since only the tee is considered to be in severe cyclic conditions, but it is reasonable to assume that it should be those that may affect the stress in the subject tee.  The joint requires 100% magnetic particle or liquid penetrant examination, and more stringent acceptance criteria apply than for normal fluid service.

With the change in the definition of severe cyclic service in the 2016 edition of ASME B31.3, some of the confusing aspects of applying the rules have been eliminated.  The intent is if there is an elevated concern for fatigue failure in a system, generally considered to be as a result of thermal displacement cycling, the owner or designer can designate specific components or joints as in severe cyclic service to get more fatigue resistant piping construction.

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Dr. Becht, Fellow ASME, former Chairman of the ASME B31.3, Process Piping Code, is a recognized authority in pressure vessels, piping, expansion joints, and elevated temperature design. He has more than 40 years of experience in design, design review, analysis, check-out, mechanical integrity, development, troubleshooting, and failure analysis. He has been a member of 14 Codes and Standards committees, five of which he has chaired. He has more than 60 publications including two books (on B31.3 and B31.1 piping) and seven patents and is a frequent speaker and chairman in technical forums. He received the ASME Dedicated Service Award in 2001, the 2009 ASME Pressure Vessel and Piping Medal, the 2014 J. Hall Taylor Medal, and the 2022 ASME B31 Forever Medal for Excellence in Piping. He is CEO of Becht, CEO of Helidex, LLC, and Chairman of Becht Industrial Group.

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When Should the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used?

12 thoughts on “When Should the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used?

  1. Dear Mr. becht,
    Interesting subject about this fatigue analysis in ASME B31.3.
    But how about Process piping system that will induced by Low cycle and High cycle phenomena like in FPSO? Does the paragraph 301.10 intrepretation of “other Cyclic Loading” include the effect of Low Cycle fatigue and high cycle fatigue for Process piping in FPSO. If yes, the method defined in B31.3 only for secondary stress, meanwhile for FPSO we will deal also with the Primary stress in fatigue.
    So far we are refering to DNV RP C203 or BS PD5500 to accomodate this piping fatigue analysis for FPSO.
    Is there any possibility that ASME B31.3 will address the primary stress fatigue?
    Thank you.

  2. There is an new Appendix being voted on for high cycle fatigue, which is suitable for use with FPSO’s. However, I believe it’s focus will be stresses due to displacement loading. Perhaps it will be ready for the 2016 edition.

    Note that the existing B31.3 rules give a methodology for combined low cycle and high cycle events, the high cycle events are converted into an equivalent number of low cycle events. Note that there has been some work that shows that the present extension of the f factor into the very high cycle range may not be conservative.

  3. Dear Mr.Becht,
    as you mentioned in the post:
    It states that it is severe cyclic conditions are:

    • Conditions applying to specific piping components or joints in which SE computed in accordance with para. 319.4.4 exceeds 0.8SA (as defined in para. 302.3.5), and

    • the equivalent number of cycles (N in para. 302.3.5) exceeds 7000;

    • or other conditions that the designer determines will produce an equivalent effect.

    Is this 0.8SA criteria applied only when f factor is equal to 1.2 ?
    When ASME cover the high cycle sress due o displacements, as the presen f facor is no conservaive anmore, does it makes the crieria for 0.8SA also not conservative?

  4. Severe cyclic applies when the number of cycles exceeds 7000 so the f factor will be 1 or lower, not 1.2.

    The 0.8 factor is a committee judgement type factor, a judgement that as one gets closer to the allowable, additional inspection is required. If the fatigue curves change, the 0.8Sa will change along with it, since Sa will change.

  5. “Severe cyclic” as per ASME B31.3 2016 has now been revised to address excessive vibration. Its previous definition on the matter was only to address systems that may experience more than 7,000 thermal cycles in a 20 year design life. To meet this new criteria an M7 (DA3) would be required as per API 618 for recip compressors. The previous requirement was max stress below 80% and confirmation of design life not exceed start-up shut-down once per day ( 7,000 thermal cycles, 20 year life). Although the end user/customer has the choice to have this implemented to the study, they now have the code to enforce /justify this request. Basically this would just be a heads up to the recip packagers moving forward how to handle packages that are released without an M7 analysis. Feel free to let me know your thoughts on the matter and if this has recently come up in any of your projects.

  6. The B31.3 code has changed the criteria to a more subjective one, and I will address that in a future blog. But it does not specify any specific analysis approach. Further, what severe cyclic service does is make the construction more fatigue resistant if fatigue is a concern (e.g. prohibit any weld undercut). This can be specified simply based on experience with similar systems, no specific analysis is required.

    When originally conceived, designation of severe cyclic service was strictly based on number of displacement cycles and a set percent of allowable displacement stress. This was of course generally avoidable in design by designing for lower displacement stress range. What the new rules do is simply leave to the owner or designer to designate severe cyclic service for systems for which high cycle fatigue is a concern.

    With respect to vibration, the current code provides what is essentially an endurance limit for design for vibration. The next edition will have Appendix W which will more specifically address high cycle conditions such as vibration.

  7. Normal is a fluid service, basically most everything. Severe cyclic is not a fluid service. It is a condition where fatigue failures are more likely so that additional precautions against fatigue failure are taken.

  8. Dear Mr Becht,
    We have P4 materials which was 4x PWHTed due to repair result after NDT.
    *IS THIS APPLICABLE?

    Thanks

    Could you please the QW-407-1 BELOW
    Post Weld Heat Treatment: (qw-407)
    Temperature Range: 704°C to 730°C
    Time Range: 2.4mins/mm; 2HRS Minimum
    Heating Rate: 200°C/hr, Cooling rate 148°C/hr

    BASE METAL: P-4 to P4 Group 1
    Specification type and grade: A182 Grade F11, A335 P11, A691 C1-C22 Gr 1-1/4 Cr,
    A234 Grade WP11, A387 Gr 11 & equivalent
    To Specification type and grade: A182 Grade F11, A335 P11, A691 C1-C22 Gr 1-1/4 Cr,
    A234 Grade WP11, A387 Gr 11 & equivalent
    Thickness Groove: 5mm – 50.8mm
    Welding Process: GTSM

    The procedure qualification test shall be subjected to
    PWHT essentially equivalent to that encountered in the
    fabrication of production welds, including at least 80%
    of the aggregate times at temperature(s). The PWHT total
    time(s) at temperature(s) may be applied in one heating
    cycle.

  9. Dear Mr Becht
    We have P4 materials which was 4x PWHTed due to repair result after NDT.
    *IS THIS APPLICABLE IN ASME B31.3?

    *COULD YOU PLEASE INTERPRET THE QW-407 BELOW WITH REGARDS TO PWHT*
    QW-407. The procedure qualification test shall be subjected to
    PWHT essentially equivalent to that encountered in the
    fabrication of production welds, including at least 80%
    of the aggregate times at temperature(s). The PWHT total
    time(s) at temperature(s) may be applied in one heating
    cycle.

    Thanks

    Below is the summarize of our approved WPS

    Post Weld Heat Treatment: (QW-407)
    Temperature Range: 704°C to 730°C
    Time Range: 2.4mins/mm; 2HRS Minimum
    Heating Rate: 200°C/hr, Cooling rate 148°C/hr

    BASE METAL: P-4 to P4 Group 1
    Specification type and grade: A182 Grade F11, A335 P11, A691 C1-C22 Gr 1-1/4 Cr,
    A234 Grade WP11, A387 Gr 11 & equivalent
    To Specification type and grade: A182 Grade F11, A335 P11, A691 C1-C22 Gr 1-1/4 Cr,
    A234 Grade WP11, A387 Gr 11 & equivalent
    Thickness Groove: 5mm – 50.8mm
    Welding Process: GTSM

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  11. This appears to be a request for consulting services. Rather than making a blog post, if you are interested in consulting services please submit a request via one of the info request buttons on the site.

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