Things You Should Know Before You Start Evaluating Pressure Vessels Using FEA
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), there are a few things you should know.
How Hard Can It Be?
On the surface, evaluating pressure vessels using FEA may not look too difficult. You may have used FEA in your design classes in school and may have used it at work to evaluate mechanical or structural components not governed by the ASME Boiler & Pressure Vessel Code. By contemplating using FEA to evaluate pressure vessels, you are likely already fairly well-versed with the Design by Rule methods in ASME Section VIII, Division 1. Part 5 of Section VIII, Division 2 provides the requirements and acceptance criteria for using FEA in the design and analysis of pressure vessels so how hard could it be? As it turns out, underestimating the training and experience necessary to correctly use the Design by Analysis methods in Section VIII, Division 2 is a common, critical mistake.
I’ve seen more than a few engineers make significant mistakes using FEA and the Design by Analysis methods in Section VIII, Division 2 of the ASME Code. It’s not that they were incompetent engineers but rather inexperienced in correctly analyzing and evaluating pressure vessels using this part of the ASME Code. If you are lacking experience with the Design by Analysis methods and requirements, it is all too easy to make mistakes which can lead to an unsafe design. Analyzing and evaluating pressure vessels using FEA is a niche that requires a particular set of skills and experience to do it correctly.
Qualifications of the Analyst
There are three areas of expertise an engineer should have before using FEA to evaluate a pressure vessel. The first is knowledge of finite element analysis. The engineer should have a thorough understanding of finite element analysis, know its limitations, and understand those things that can affect the accuracy of results.
The engineer should also have experience in the FEA software being used. Not being experienced with the software being used can result in improperly defining a wide variety of parameters and controls leading to erroneous results.
Lastly, the engineer should be experienced with the Design by Analysis methods in Section VIII, Division 2. This experience should consist of: 1) knowing the requirements and limitations of the particular method described in the Code, 2) understanding the reasoning behind the details of the method’s requirements and limitations, and 3) having successfully and correctly used the Design by Analysis methods in the Code. Yes, this last one is a bit of a Catch-22.
A Plan of Action
So what should you take away from all of this? Basically, if you don’t have the experience, don’t go into this alone. Having access to an engineer already experienced in evaluating pressure vessels using FEA is essential in avoiding mistakes and correctly using the Code.
Well that’s fine if you work in a larger company, but what if you work for a small company and there isn’t anyone to fill that role? The following is a course of action to get the training and experience you need when you are largely on your own.
1. Educate yourself on finite element analysis and the finite element method
There are numerous resources describing the finite element method and finite element analysis. Whether the resource is a textbook or information found online, you should acquire at least a basic understanding of the mathematics behind the finite element method. More importantly, learn about the aspects of finite element analysis that have the potential for producing inaccurate or erroneous results. These include: how loads and boundary conditions are applied, element shape and size, element mesh density, and singularities to name a few.
2. Take an ASME Training Course
Without a mentor it is very easy to make a critical mistake. There are references and companion guides to the ASME Code discussing the Design by Analysis methods in Section VIII, Division 2, but they are largely only helpful to engineers who already have some level of experience using these methods. My recommendation is to take a course that specifically trains you in the requirements and use of the Design by Analysis methods in Section VIII, Division 2.
3. Get training in the FEA software
The learning curve for FEA software is steep. A lot of time, grief, and frustration can be avoided by taking a class or two offered by your software provider. If you have little or no experience with the software I strongly recommend taking an introductory class. Afterwards, you can determine whether taking a class more specific to your analysis needs would be beneficial.
4. Hire a consultant to help you
Even if you do all of the above, I highly recommend hiring a consultant experienced in analyzing and evaluating pressure vessels to assist you. There will likely be gaps in your training and you will have questions as you progress through analyzing and evaluating the pressure vessel. Hiring a consultant will help you avoid pitfalls and making mistakes. This could entail having the consultant assist you every step along the way, or reviewing your work when you are done to make sure everything is fine. As you gain experience with each project, your reliance on an outside consultant will become less frequent.
In conclusion, the use of the Design by Analysis methods in Section VIII, Division 2 of the ASME Boiler & Pressure Vessel Code should only be undertaken by engineers experienced in these methods or those working under the supervision of someone who is. If you do not have the necessary expertise, get the appropriate training and hire a consultant to assist you until you do.