Numerical Study on the Strain Capacity of Girth-Weld Pipes With Unequal Wall Thickness Transition Joints

Abstract

Abstract Girth-weld pipes with unequal wall thickness transition joints result in the misalignment of geometry, and the mismatched welding and heat-affected zone (HAZ) softening prompt inhomogeneity of material in the local area of girth weld. The misalignment of geometry and inhomogeneity of material are the main causes of local strain concentration in the girth weld, which greatly increases the possibility of crack initiation and propagation. In this paper, the numerical models of girth-welded pipe with cracks on the fusion line have been accurately constructed, referring to the crack size and location of the actual accident pipe. The influences such as the ratio of unequal wall thicknesses, the mis-matched coefficients and load conditions on the crack driving force curves have been investigated. The critical apparent fracture toughness has been selected as a failure criterion of girth welded pipe. Results show that an increase in the thickness ratio and a decrease in the weld strength will reduce the strain capacity of girth welded pipes, and the increase in internal pressure will weaken the strain capacity of girth welded pipes. The application of unequal wall thicknesses and low matching welding in the girth-weld pipes in engineering should be avoided or reduced.