Stress Concentration Factors Due to Misalignment at Girth Welds in Bi-Layer Pipes

Abstract

In recent years, bi-layer pipes, composed of an inner layer and an outer layer, have been widely used in offshore engineering. In this study, the governing equation for a bi-layer pipe subjected to axisymmetric loadings is derived based on classical shell theory. Then, the equation is used to develop stress concentration factor formulations for girth welds in bi-layer pipes with fabrication tolerances and thickness transitions. Axisymmetric finite element analysis is carried out to verify the accuracy of the proposed formulations. It is noted that these formulations can be well suited for determining the stress concentration factors for a wide range of thickness ratios (ratio of the inner layer thickness to the total thickness in a bi-layer pipe) varying from 0.0 to 1.0. They can also obtain accurate stress concentration factors whether the elastic modulus of the inner layer is smaller or larger than that of the outer layer.