Stress intensity factors for low aspect ratio longitudinal surface cracks in thin pipes

Finite element calculations of stress intensity factors for longitudinal external and internal semi-elliptical surface cracks in thin pipes (R/t of 10) and external edge cracks in thin pipes (R/t of 10, 20, 40) are presented. Constant, linear, parabolic and cubic stress distributions were applied to the crack face. Comparisons of flat plate and thin pipe stress intensity factor results are made for the deepest and surface points of the surface cracks, and for edge cracks. Recommendations are given regarding the limits of applicability of flat plate solutions. For a pipe with R/t of 10, the stress intensity factors for shallow semi-elliptical cracks and edge cracks (a/t less than 0.4) can be approximated to within 6% using the corresponding solutions for cracks in flat plates. For pipes with R/t larger than 40, the stress intensity factors for a wide range of crack depths, 0 ≤ a/t ≤ 0.8, can be approximated with good accuracy using the corresponding solutions for cracks in flat plates