Assessment of appropriate pressure vessel flange bolt tension by finite element modelling

Abstract

Flanged joints on large diameter flanges can prove problematic to seal successfully with many factors contributing to ensuring a successful operation. One such factor is stud bolt loading contributing to stress and deflection of the flanged joint. This investigation involves the use of finite element analysis (F.E.A) to predict levels of stress and deflection of a particular flanged joint when the stud bolts are tightened and flange pressurised. The level of stud bolt force selected must ensure the joint is sufficiently tight to avoid leakage. However, the force must not be excessive causing damage. The flanged joint is located on the channel head of a shell and tube heat exchanger. For the purposes of this project, the educational version of ANSYS 5.5 was used thus a number of critical assumptions were made to operate within the restrictions of the software. As a comparative check of the F.E.A method, a conventional method termed the target load bolt-up method was employed. The analysis results using both methods, when interpreted, indicated the flange was not excessively stressed. Field monitoring by observation of the flanged joint for signs of leakage and other detrimental effects indicates the stud bolt load selected is acceptable.