Tensile Strain Capacity of an X70 Pipe With Internal and External Semi-Elliptical Crack Under Bending and Tension

Abstract

This paper studies an in-depth examination of the tensile strain capacity (TSC) of an X70 pipeline containing an internal or external semi-elliptical crack when exposed to bending or tension. Comprehensive TSC evaluations were conducted through finite element analyses, incorporating initiation and ductile tearing criteria for different crack depths and magnitudes of internal pressure. During the analyses, crack-tip opening displacement (CTOD) and J-integral were calculated, taking into account the crack's depth and the magnitude of the internal pressure. The finite element results enabled a precise estimation of crack driving forces for both CTOD and J-integral, with respect to the remote strain of the pipeline. The findings revealed that, in bending scenarios, both internal and external cracks exhibited lower values of CTOD, and J-integral compared to tension conditions, resulting in a slightly higher tensile strain capacity. The disparities observed in CTOD and J-integral values between bending and tension conditions were relatively minor, suggesting that material and pipe properties may exert a more pronounced influence on their behavior than the specific loading condition in the pipeline. TSC calculations using initiation and ductile tearing methods indicated no significant differences for either external or internal cracks, under both bending and tension conditions. This study provides valuable insights into the TSC assessment of full-scale pipelines with semi-elliptical cracks, highlighting the significance of considering the specific loading conditions in such evaluations.