Acceptance criteria of local wall thinning in carbon steel pipe subjected to axial force

Structural evaluation of local wall thinning caused by erosion is important for integrity of a high energy piping system. Acceptance criteria are required if pipe wall thinning is found or suspected. The purpose of this paper is to provide acceptance criteria for local erosion thinning in pipes. The pipe of interest is a STS 42 carbon steel pipe loaded with an internal pressure together with an axial force. The thinned region is characterized by the length, width and depth of wall loss. The length and width correspond to axial and circumferential crack lengths. Allowable combinations of length and width of wall thinning are determined from leak and break behavior of crack growth in pipes. The allowable depth of wall thinning is determined from the local membrane stress rule. Based on the crack growth behavior and the stress rule, the allowable extent and depth of local wall thinning are proposed for carbon steel pipes. Consequently, double-ended fracture and split fracture of the pipe are prevented when the local wall thinning is limited to within the allowable sizes. (author)