Limiting plastic load for a pressure vessel with a tangential branch pipe

Abstract

This paper presents results of elasto-plastic analysis of a vessel with a tangential branch pipe subject to internal pressure. The finite-element method in the two-dimensional statement and the yield theory with isotropic hardening are employed for nonlinear analysis. Different means and characteristic curves are examined for determination of limiting plastic pressure. The influence exerted by various geometric parameters on limiting pressure is demonstrated.Pressure vessels and equipment fitted with branch pipes are widely used in chemical and petrochemical machine building. Pressure vessels with radial branch pipes are most widely employed (we will call this position of the branch pipe tangential). Results of elastic analysis [1], which indicate a high level of stress concentration in the vessel and branch pipe owing to the abrupt change in the surface geometry of the design, are known primarily for vessels with a tangential branch pipe. In addition to elastic stress analysis for the designs under consideration, determination of the limiting plastic load based on inelastic analysis is a critical problem [2].This study presents results of elasto-plastic deformation and determination of the limiting plastic pressure of a cylindrical vessel with a branch pipe (Fig. 1).The structural coupling between the branch pipe and housing of the vessel is considered a tangential connection between intersecting cylindrical shells [1]. The elasto-plastic deformation of such a connection is investigated by the finite-element method (FEM) using two-dimensional shell elements, and the theory of plastic flow with isotropic hardening. The specialized computer program SAIS, some results of the testing of which are presented in [3][4][5], has been developed for elasto-plastic analysis of connections between intersecting shells.For tangential connections subject to elastic analysis, the maximum stresses in the shell will depend on the following set of relative parameters: