Performing an FEA in Section VIII, Division 1 to Qualify an Article U-2(g) Component

Performing an FEA in Section VIII, Division 1 to Qualify an Article U-2(g) Component


While there are currently no explicit rules on how to perform a finite element analysis (FEA) if you are doing so in support of an ASME Section VIII, Division 1 vessel, there is good practice. Regarding rules, all you have is from Article U-2(g), which says:

This Division of Section VIII does not contain rules to cover all details of design and construction. Where complete details are not given, it is intended that the Manufacturer, subject to the acceptance of the Inspector, shall provide details of design and construction which will be as safe as those provided by the rules of this Division.

So, how exactly does an engineer perform an FEA, for which Section VIII, Division 1 has absolutely no rules, that is “as safe as” the rules otherwise provided in Section VIII, Division 1? Luckily, I’m not the first person to think about this. In fact, there is some pretty decent guidance in API 579/ASME FFS-1. Also, the ASME Section VIII Code Committee has formed a Task Group on U-2(g). I have attended (as a visitor) meetings of that Task Group, and can report that they are looking at far more than this topic. However, they have drafted something which is exactly what I would recommend as good practice.

So, here’s my take on what constitutes good practice:

  • The allowable stress for all product forms except bolting needs to be from Section II, Part D, Table 1 and Table 1A (i.e. the allowable stress for Section VIII Division 1 construction).
  • For bolting materials the allowable stress needs to be determined from Section II, Part D, Table 3.
  • Limiting values that are not calculated using the allowable stress, S, such as fatigue and compressive allowable stresses, can be determined from the current rules in Section VIII Division 2.
  • The weld joint efficiency needs to be established in accordance with UW-11 and UW-12 of Section VIII Division 1. (more on this item in another post)
  • The Design By Analysis Rules in ASME Section VIII, Division 2, Part 5 should be followed. This is only possible for temperatures not in the creep regime. If your vessel has operating temperatures into the creep regime (indicated by the allowable stress being in italics in Table 1 or Table 1A), I would suggest that you retain the services of an expert, because there are NO rules right now for that situation.
  • ALL of the load case combinations of the applicable Division 2 assessment procedure need to be considered in addition to any other combinations defined by the User. In evaluating load cases involving the pressure term, P, the effects of the pressure being equal to zero needs to be considered (this ought to be standard practice of anyone using Part 5, but it is worth stating, again).
  • All of failure mechanisms in 5.2, 5.3, 5.4, and 5.5 of Part 5 need to be evaluated. In 5.3, a component is exempt from the Local Failure Criteria evaluation if the component design is in accordance with the standard details of Part 4. That said, there are many details permitted in Division 1 that are not permitted in Division 2. If the component being evaluated is not covered by a standard detail from Part 4, then an evaluation per 5.3 is required.
  • When elastic-plastic analysis is performed, the required load case combinations from ASME FFS-1/API-579 Table B1.4 Note 6 need to be used.
  • Evaluation of the test condition per paragraph of Section VIII, Division 2 is not mandatory, but consideration of the test condition per UG-22(j) of Section VIII, Division 1 is mandatory.

All other requirements for construction need to comply with Section VIII, Division 1.

It is my opinion that if a designer chooses to apply U-2(g) and then uses a Design-By-Analysis approach, then Appendix KK ought to become Mandatory. However, it is unlikely that will be required by the Codes. Therefore, it is good practice for the engineer performing the FEA to ask for as much detail as they will need to perform the analysis – especially Protection Against Failure From Cyclic Loading.

Remember that an FEA cannot be used to supersede existing rules in the Code. This is true not just for basic design calculations such as wall thickness, but also for weld details, PWHT requirements, NDE requirements, etc.

 [readon2 url=”index.php?option=com_rsform&view=rsform&formId=4&Itemid=620″]Click to Request Info[/readon2]


About The Author

Mr. Seipp, an ASME Fellow, has over 22 years of experience in design, analysis, review and failrue analysis of process and power equipment, vessels, piping, and structures. He has extensive analytical experience including linear and non-linear finite element analysis using ANSYS and ABAQUS, buckling analyses, steady-state and transient heat transfer and thermal stress analysis of pressure vessels and piping, fitness-for-service evaluations, and fatigue assessments. Mr. Seipp has worked for clients all around the world, who are in many different industries such as oil sands, refining, chemicals, mining, metals processing, pressure vessel and piping fabrication, and aerospace. Mr. Seipp is an author/co-author of over 30 journal and conference papers and presentations.  He is also very involved in ASME Codes and Standards, currently serving on the following: ASME Board on Pressure Technology Codes and Standards Subgroup on Design of Section VIII Subgroup on Interpretations of Section VIII Working Group on Design By Analysis of Section VIII Vice-Chair of the ASME Pressure Vessels and Piping Division Technical Program Chair for the ASME Pressure Vessels and Piping Conference - 2019 Conference Chair for the ASME Pressure Vessels and Piping Conference - 2020 Mr. Seipp is a licensed professional engineer in the Canadian Provinces of Alberta, Saskatchewan, and Ontario.  He is also a Responsible Member for Becht Engineering's Alberta Permit to Practice and the Saskatchewan and Ontario Certificates of Authorization.

Authors Recent Posts

Performing an FEA in Section VIII, Division 1 to Qualify an Article U-2(g) Component

8 thoughts on “Performing an FEA in Section VIII, Division 1 to Qualify an Article U-2(g) Component

  1. Thank you for this review. I have used this approach for conformable pressure vessels where you need FEA to address the abnormal geometry that is not covered in Division 1 or 2. This is a good summary.

  2. Good review ! really useful. i have 2 questions?

    1. What does ASME says about allowable deformation for a pressure vessel or vacuum vessel

    2. What is the limiting value for Directional acceleration based on the input spectra provided in a Response Spectrum Analysis – FEA

  3. Shino Ulahannan – thank you for your questions.

    “1. What does ASME say about allowable deformations for a pressure vessel or vacuum vessel.” Well, there is very little in the way of guidance for deformations. The only rule that I am aware of is UG-99(d) in Division 1 that says, during the hydrostatic test, there may be no permanent deformations visible to the inspector. In Division 2, for the Elastic-Plastic analysis method for confirming Protection Against Plastic Collapse, the User may define a serviceability criteria, which would be deformation-based.

    “2. What is the limiting value for Directional acceleration based on the input spectra provided in a Response Spectrum Analysis – FEA” Seismic excitation is, unfortunately, not one of my specialties. Although the ASME Code indicates that seismic loads must be considered, they are not prescriptive on exactly how that can be performed; mostly due to the wide variety of national/regional requirements. In general, I would say that local requirements would supersede BPV Code anyway.

  4. Thanks for the reply & details noted !

    Pls let me know your opinion on ‘ can we take the % strain or corresponding deformation against allowable stress(S – as defined by part D) from the stress strain plot of the material as the permissible deformation value at a specific temperature?’

  5. “can we take the % strain or corresponding deformation against allowable stress(S – as defined by part D) from the stress strain plot of the material as the permissible deformation value at a specific temperature?”
    This is not something that I have encountered before.

    It appears to me that you are attempting to formulate a “serviceability criteria” as described in Table 5.5 of Division 2. In that context, I would not apply such an arbitrary approach – rather I would recommend that any limit on deformation be based on criteria specific to the operability of the individual vessel. If you are looking for a strain limit, I would apply the rules in Section 5.3: Protection Against Local Failure.

  6. Thanks for your time & the details provided!

    My concern is to identify ‘ what should be the extra thickness to be provided over the minimum required thickness to make the vessel safe against deformation or other failure loads like fatigue, buckling etc. [b]As code says nominal thickness to be more than required thickness, but doesnt specify how much more?[/b] (say) whether nominal thickness/required thickness = 1.5 for a shell 5m ID with spherical heads a safe call, if stress & deformation values evaluated also with FEA is under the safe limits as per operational criteria.

    Please advise me, For the design of a new spherical vessel of 16m ID what are the guidelines to choose a safety margin on thickness required? My idea was to take safe stress from part D & deciding on safe deformation values as per failure & operational criteria, do FEA to substantiate the selected thickness(nominal) against various load combinations of div 2. hence an opinion from code on safety margin of thickness will be vital information.

    Kindly advise !

  7. The design margins provided in Part 5 are sufficient for protecting against the failure modes. The most important thing to remember is to follow the rules exactly as-written. Please take a look at my new post – – for some additional thoughts on Plastic collapse and ratcheting.

    Based on your comments, it sounds like you might benefit significantly from my ASME Section VIII, Division 2, Part 5 course. Please keep an eye on our Training Section – – for updates on when and where that course will be held. And, I can always come to your place of work and teach the course in-house.

Comments are closed.

Let Becht Turn Your Problem
Into Peace of Mind