Code books contain equations to design simple vessel shapes like cylindrical shells. What about shapes that are not found in code books? What about standard shapes used in arrangements or sizes not covered by the rules? This is the job for Finite Element Analysis (FEA).
A solid model is created. The model is split into small pyramids or cubes – a mesh of simple shapes that can be calculated by the laws of physics. Loads are applied to the mesh and displacements are calculated. Displacements are converted into stresses and both can be seen. Code rules separate areas of the model that are acceptable from those that are overstressed, and if required, the solid model is modified, and the process repeated until successful.
FEA can be used for much more. Wind and seismic loads can be input. Computational Fluid Dynamics (CFD) can determine shell temperature distributions which are used to calculate thermal displacement and stresses. Stresses are used to calculate the permissible cycle life (fatigue life).
The use of FEA is increasing. Users see the value in knowing the code permitted cycle life of their vessel. Designers can use irregular shapes more appropriate to their process needs. Inspectors are insisting on FEA for items that code rules do not do well – see the obround nozzle article below.
Introduction to FEA
If you are new to FEA we suggest starting with these pictorial guides.
Finite Element Analysis in Action
Finite Element Analysis (FEA) is used in this introductory sample to iteratively refine a pressurized elbow design and provide design alternatives. Computational Fluid Dynamics (CFD) is used to choose between the alternatives.
A Step By Step Introduction to FEA
This simple manifold block is analyzed to show the steps involved in a FEA study, including quality control. A good introduction to the steps required to make sure a FEA study is done right.
FEA Samples and Articles
These are our most read FEA samples and articles. More can be found in the FEA blogs below.
How Permissible Cycle Life (or Fatigue Life) is Calculated using FEA
From cycle life curves to FEA to a permissible cycle life for a vessel. How fatigue life calculations are done.
Designing Trouble-Free Large Obround Nozzles
ASME VIII-1 Code provides the required rules to design obround nozzles, but it also takes FEA to design a trouble free obround nozzle that does not leak.
Buckling of Dished Heads
ASME VIII-2 contains three analysis types to assess collapse from buckling. Per ASME VIII-2 article 5.4.1.2: (a) Type 1- If a bifurcation buckling analysis is performed using an elastic stress analysis without geometric nonlinearities in the solution to determine the pre-stress in the component, a minimum design factor of ΦB = 2/ ßcr shall be…
Heat Exchanger FEA with Thermal Loads Sample
The tubesheet stresses for this heat exchanger with differing tube sizes cannot be calculated by regular code rules. This FEA study combines thermal and pressure stress analysis as required by the ASME code, but FEA replaces the stress formulas that cannot function in this case. We regularly run this type of analysis on heat exchangers with non-circular tube patterns.
Sample - Seismic Analysis of a Propane Storage Sphere
This propane storage sphere is analyzed in multiple steps: 1) FEA provides the vibration frequency. 2) The building code base shear is calculated with a spreadsheet based on the FEA calculated frequency. 3) The base shear is added back into the FEA model and the stresses are compared with code allowables. A pass / fail assessment is made.
FEA Blogs
More samples and articles, validation of our software and methods by comparison with published articles and FEA techniques.
More FEA Samples
More Samples of FEA in use – Obround nozzles, unusual flanges, reverse dished heads and thermal analysis. Of interest to anyone trying to see if FEA can be used to solve their design or service problems.
SolidWorks Simulation Validation (Blog)
How do you know you are getting the correct FEA results? We compared our methods with published results in ASME PTB-3 and got the same results. CFD limitations and methods to work around them are also discussed.
FEA Methods (Blog)
A large collection of articles covering how to apply FEA to the design of pressurized equipment. Of interest to the FEA professional.