When normal design verification by ASME VIII formula based calculations is not sufficient to provide the necessary insight into the behaviour of a particular component, then Finite Element Analysis (FEA) provides a more analytical option. Welding Units has been performing FEA work for over ten years using LUSAS software and more recently, ANSYS software interfaced with AutoCAD Inventor.
FEA allows a greater insight into the behaviour of key components under analysis and is not just limited to conventional pipeline flanges. It can be used to provide conventional verification of any part against ASME VIII Div 2 code by the analysis of stress intensity values taken across key locations of the part, considering linear material properties. FEA can also be used to study particular areas of high strain, considering non-linear material properties to assess likelihood of failure due to rupture or excessive deformation. Fatigue analysis is a natural progression of the FEA, which allows very quick modifications and re-analysis to be performed in order to eliminate areas of concern.
The most common method of FEA is by axis-symmetric 2D analysis, which provides a reasonable level of accuracy in a relatively short period of time. This method can be improved by expanding the analysis to 3D and so the ability to consider the effect of bolt holes, bending moment gradient and other non-symmetric irregularities.
FEA has been used in conjunction with practical tests performed by Welding Units, in comparing strain gauge results taken during testing with theoretical results predicted by the analysis. This has resulted in some fine-tuning of the approaches taken during an analysis to ensure dependable results.
The FEA work regularly performed by Welding Units considers the following conditions:
- stress distribution within a flange body
- gasket behaviour under various load cases
- stress rise in bolting during service
- locations of high strain concentrations
- the effects of unusual configurations e.g. taper-bore, sharp hub angles, etc.
