Development of Modelling Guidelines for Stress Analysis of Pressure Vessel Bolted Closures

This paper describes some of the outcomes of the development of finite element modelling guidelines for the stress analysis of bolted joints in pressure vessels and piping. The modelling methods originally developed at Rolls-Royce typically used 2D axisymmetric models as this was deemed adequate at the time. However, computing software and hardware improvements have subsequently been made which enable more realistic 3D bolted joint models to be solved where a greater level of geometric detail is required. For example the bolts, nuts and perforated flanges can now be represented more realistically reducing the degree of geometric abstraction that is required. Also, modern finite element codes such as ABAQUS and ANSYS now offer gasket elements which enable the initial compression, in-service performance and unloading of the joint to be modelled more realistically. Additionally, contact techniques can also be used to simulate the axial and radial distribution of thread load in the joint which will affect the stress distribution remote from the threaded region. Consequently, the modelling guidelines have been updated and provide guidance for stress engineers to decide which degree of model complexity is warranted.