Modelling Crack Propagation and Arrest in Gas Pipes Using CTOA Criterion

Abstract

In this paper, the resistance to ductile crack extension is discussed in terms of Charpy or DWTT energy, R curve and CTOA. Methods used in numerical simulations of ductile crack extension are presented including the cohesive zone model, a critical damage with the Gurson–Tvergaard–Needleman model, critical damage given by SRDD model or a critical crack opening angle (CTOA). Selection of CTOA is based on the reduced number of parameters and the low sensitivity to pipe geometry. Numerical simulations of crack propagation and arrest based on CTOA, use the node release technique, which is described. Results on a pipe made in steel API L X65 are presented. The influence of geometrical and material parameters on crack arrest and velocity using this technique are presented. Finally, an arrest pressure equation similar to the BTCM’s equation but including critical CTOA is introduced. For the same decompression wave pressure, the crack propagation velocity is inversely proportional to the resistance to crack extension of the material, which is the dominant parameter. The crack velocity versus decompression is expressed by a CTOAc function of resistance to crack extension.