Blog

The ASME Boiler & Pressure Vessel Code permits the use of numerical methods, such as finite element analysis (FEA), in the design of pressure vessels. But who is permitted to perform these analyses and what are the basic requirements imposed by the Code?

Part 5 of Section VIII, Division 2 (Design by Analysis) of the ASME Code lists four failure modes to be investigated. The pressure vessel or component must be evaluated for each of these failure modes (as applicable). An overview of the methods used in evaluating for these failure modes is provided below.

When is the use of Design by Analysis methods, such as finite element analysis, permitted by the ASME Code in pressure vessel design? And what are the limitations imposed by the Code on its use?   

Imagining how a pressure vessel can fail due to excessive plastic deformation (plastic collapse), buckling, or fatigue is not too difficult. But what does the ASME Code mean by local failure? What exactly is the failure mechanism being considered in evaluating a component for local failure and why is it important?

Section VIII, Division 1 of the 2021 Edition of the ASME Boiler & Pressure Vessel Code introduced Mandatory Appendix 47 which specifies the qualification requirements of individuals involved in designing pressure vessels. Within this appendix is the requirement that fatigue assessments of pressure vessels are to be performed by, or under the direction of, a Certifying Engineer. This article discusses some of the things that are considered when conducting a fatigue assessment that go beyond being able to follow a procedure or properly use an equation.

The 2021 Edition of Section VIII, Division 1 of the ASME Boiler & Pressure Vessel Code has added Mandatory Appendix 47, “Requirements for Pressure Vessel Designers”. This mandatory appendix specifies the qualification requirements of those individuals involved in the design of pressure vessels. This article provides a general summary of Appendix 47 from the 2021 Edition of the ASME Boiler & Pressure Vessel Code.

Sometimes a customer specification requires you demonstrate your equipment can withstand shock or vibration loading. This could involve physical testing, engineering analysis, or both. If this is not a common requirement or if you generally subcontract out this type of work, you may be unfamiliar with the different types of finite element analyses (FEA) used to qualify equipment for shock and vibration. This article discusses the various types of finite element analyses used to evaluate equipment for shock and vibration loading, how they differ from each other, and when they are typically used.

When the cause of a failure of a structure or mechanical equipment is not apparent, a failure investigation is often conducted. While the details of how a failure investigation is conducted can vary depending on the individual conducting the investigation and the particular equipment or structure, the cause of nearly all failures can be grouped into one (or more) of the following five categories:

There are two commonly used methods of evaluating pressure vessels subjected to external nozzle loads. The first is using hand calculations and the method described in Welding Research Council (WRC) Bulletin 107, “Local Stresses in Spherical and Cylindrical Shells due to External Loadings”. The second is using finite element analysis. This article briefly discusses these two methods and some things to consider if you are unfamiliar with their use.

Several years ago, Section VIII, Division 2 of the ASME Boiler & Pressure Vessel Code started classifying Division 2 pressure vessels as either Class 1 or Class 2. The differences in the requirements and design basis between these two classes are not provided in a single location in Section VIII, Division 2 but rather spread out across the Code. This article presents a compilation of the differences between these two classifications.

Division 1 of Section VIII of the ASME Boiler & Pressure Vessel Code does not contain rules to cover all details of design and construction of pressure vessels. Where design rules do not exist, U-2(g) permits several courses of action, one of which is to use Mandatory Appendix 46. Appendix 46 provides the requirements for using Section VIII, Division 2 (Alternate Rules) in the design of Division 1 pressure vessels. This article provides a general overview of Appendix 46 from the 2019 Edition of the ASME Boiler & Pressure Vessel Code.

Depending on where your pressure vessel will be installed, a seismic analysis may be required. While design standards for storage tanks such as API 650 provide details on how to calculate and evaluate for seismic loads, the ASME Boiler & Pressure Vessel Code does not. Luckily, there are more than a few standards that provide details on how to evaluate pressure vessels for seismic loads.

If you’re considering evaluating a pressure vessel using finite element analysis (FEA) and haven’t done so before (or are fairly new at it), you may be ill-prepared and not even know it.

As a fabricator responsible for the design of a pressure vessel there may come a time when performing a finite element analysis is necessary to meet the requirements of the ASME Boiler & Pressure Vessel Code. You may come to this decision on your own or it may have been specifically required by your customer. If you are unfamiliar with finite element analysis with respect to pressure vessels this article should help.

Inspections of a pressure vessel, tank, or related equipment should be performed on a regular basis to ensure their continued operation is safe. But what happens when the inspection uncovers damage such that its continued safe operation is suspect? When the cost of repairing or replacing the vessel or equipment is not trivial a fitness-for-service evaluation may be performed. But what is a fitness-for-service evaluation and what can you expect if you have one performed?

Hiring a company to do a third-party evaluation may be required by a customer or deemed prudent rather than having the work done in-house. If you have never been down this road before, what considerations should you have, and what can you expect?

So, your pressure vessel or equipment has experienced a structural failure. But the question remains what caused the failure and what can be done so it doesn’t happen again? While you may understand the operation of your vessel or equipment very well, you may need to consult with someone outside of your company to determine the cause of the failure. So, you hire an outside person or firm to conduct a failure investigation. What can you expect?

As an ASME pressure vessel fabricator, you may be required from time to time to perform a finite element analysis (FEA) of the vessel. This may be because of some unusual geometric feature of the vessel, or perhaps some complex or cyclic loading conditions. If you are relying on an outside consultant to perform the finite element analysis, you will likely get some kind of a report documenting what was done. So, what can you typically expect in an FEA report and what does it all mean?

The Design By Analysis Requirements, Part 5 of Section VIII Division 2 of the ASME Boiler & Pressure Vessel Code, gives three acceptable analysis methods for ensuring the design of a pressure vessel is adequate against failure due to plastic collapse. These methods are: elastic stress analysis method, limit-load analysis method, and elastic-plastic stress analysis method.

Over the past several years I’ve had several Authorized Inspectors insist on adding a statement to the design report saying that the loads in UG-22 have been considered in the evaluation. At first, I thought these requests were a bit odd in that the report stated the design met the requirements of Section VIII, Division 1. Paragraph UG-22 is a part of Section VIII, Division 1 so adding this statement was unnecessary, right? Well, it seems that the AI’s concerns were based on some fabricators not being in compliance with the ASME Code in that they were claiming ignorance with respect to some of the loads listed in Paragraph UG-22.