A new method to determine elasto-plastic j-integral for steel pipes with longitudinal semi-elliptical surface cracks

Steel pipes have been widely used in the water and petroleum industries where crack-like flaws have long been recognised as a major cause of their failures. This paper intends to develop a new method for determining the elasto-plastic J-integral of cracked pipes made of all types of steel. A solution to elasto-plastic J-integrals is derived for external longitudinal semi-elliptical surface cracks in pressurised steel pipes. A meshing technique is developed in the detailed three-dimensional finite element analysis that incorporates the mixed types of quadratic tetrahedron and hexahedron elements. The developed method is verified with detailed finite element results. It is found in the paper that the general trend of normalised fully plastic J-integral changes with the change of crack depths and aspect ratios, and the magnitude of normalised fully plastic J-integrals can be significantly affected by material properties and pipe dimensions. The developed method can provide a useful tool for the failure assessment of pressurized steel pipes, allowing for a wide range of pipe dimensions, crack geometries and material properties.