FE analysis of the creep of branched pipes

摘要

The results of steady-state creep finite element (FE) analyses, for three typical pipe/branch connection geometries, are presented. The chosen geometries are a hemi-spherical end cap with a branch, and pipes with single and double penetration branches, under internal pressure loading. For the hemi-spherical end cap, 2D axisymmetric FE modelling was used and welds were included using a three-material model comprising the parent material (PM), weld metal (WM) and heat-affected zones (HAZ). 3D FE modelling was used for the pipes with one and two branches, using a two-material model comprising the parent and weld materials. The material properties used for these analyses are those for a CrMoV pipe weldment at 640°C. From the results obtained, failure sites were identified, life estimations were carried out, and the effects of the various geometric parameters of the weld and pipe/branch connection were assessed. For the range of dimensions and material properties used, it has been shown that in all cases, the effects of the dimensions of the branch and the connection region, on the peak stresses, in the practical range, are significant. For a hemi-spherical end cap, a branch does not always cause a reduction in life, particularly when the axial loading is only caused by internal pressure on the end of the branch. However, when the axial loading is relatively high, failure may occur in the weld region and failure lives can be greatly reduced due to the presence of the weld. For a pipe with one or two branches, it was found that the existence of a weld has a negligible influence on the peak rupture stresses and their positions for the material properties used.