Numerical predictions of crack growth in a pressure vessel with welded nozzles

Abstract

Most structural elements that represent parts of equipment and machines in the process industry are subjected to strength calculations. Structural materials and welded joints typically contain flaws and microcracks, from which cracks are initiated. Exploitation conditions can lead to the occurrence of cracks, even in cases when there are no flaws in the material, typically at locations with stress concentration. Penetration of two cylinders is the most commonly encountered form of geometric discontinuity of cylindrical surfaces which results in stress concentration. On a pressure vessel with two nozzles of different geometries, critical areas (i.e. stress concentration areas) are determined by experimental 3D Digital Image Correlation (DIC) method. Then, the numerical analysis of the equivalent 3D model is performed and the obtained results are comparable to experimental values. Since the fatigue cracks are expected in the high stress areas, in one of them - next to the nozzle in the numerical model - a crack has initiated. Then, crack growth is simulated using extended finite element method (XFEM). The aim of this paper is to show that it is possible to predict the crack growth direction and critical length of the crack which can occur in the pressure vessel, based on values of stress intensity factors (SIFs) evaluated in the numerical simulation.