Effect of Through-thickness Variation of Mechanical Properties on Stress Distribution in API X65 Linepipe Steel: An Experimental and Numerical Investigation

Alloying elements and temperature are non-uniformly distributed in the wall of a steel pipe during the manufacturing process. In this study, the effects of these non-uniform distributions on mechanical properties were evaluated macroscopically. Plate-type tensile specimens were cut from the wall of a steel pipe in a way that each specimen was separated from a specified location along the wall thickness. The results of tensile tests showed significant variation of mechanical properties in the thickness direction. To investigate the effect of this variation on the steel deformation, a thick tensile specimen with a thickness equal to the pipe wall thickness was then modeled as a multilayer structure based on the measured mechanical properties. First of all, with the help of finite element simulation and according to the obtained stress-strain curve from the tension test, GTN damage parameters have been calibrated for every single layer, and then, these parameters were used in modeling the multilayer specimen. According to the results, the numerical load-displacement curve obtained from multilayer modeling did not exactly match the experimental curve of the thick specimen; this can be due to different governing stress states in thin and thick specimens and also the effect of residual stresses.