Advances in J-integral estimation of circumferentially surface cracked pipes

This paper describes enhanced J-integral estimation schemes for pipes with circumferential semi-elliptical cracks subjected to tensile loading, global bending and internal pressure. These schemes are given in two different forms to cover the wide ranges of geometries and material parameters; the modified GE/EPRI method and the modified reference stress method. In the former method, new plastic influence functions for fully plastic J-integral estimation are developed based on extensive three-dimensional finite element calculations. In the latter method, new optimized reference loads are suggested and utilized to predict the J values. To verify the feasibility of these two schemes, J-integral values obtained from further detailed FE analyses are compared to those from the proposed schemes. Because the estimated J-integrals agree fairly well with the detailed FE analysis results, the new solutions can be applied for accurate structural integrity assessment of different size pipes with a circumferential surface crack.