Load-independent creep constraint analysis and solutions for surface cracks in pressurized pipes

Abstract

Using load-independent creep constraint parameters Q* and Qm*, the variations of crack front stress field and constraint level are analyzed for various crack sizes of pipelines containing internal surface cracks under high temperature conditions. The results show that the trends of stress changes in the axial and circumferential internal surface crack front for different crack sizes are similar. For axial internal surface cracks, when the crack depth to length ratio a/c is the same, the maximum values of crack front Q* and Qm* are shifted from the deepest part of the crack (2Φ/π = 1) to the vicinity of the free surface (2Φ/π = 0.2) as the crack depth a/t increases. As for the circumferential inner surface cracks, when the crack depth a/t exceeds 0.2, the locations where the maximum values of crack fronts Q* and Qm* appear are mainly concentrated in the deepest part of the crack (2Φ/π = 1). Based on the calculation results of the constraint parameters, the empirical formulas for the engineering calculation of the relationship between the average constraint parameters (Qavg* and Qm‐avg*) and the crack size are obtained by fitting.