Limit load solutions for pipes with local wall thinning based on finite element limit analysis

Analytical limit load solutions are available for straight pipes with circumferential and axial part-through wall cracks, subject to internal pressure, axial tension and global bending. Such solutions are based on equilibrium stress fields, and thus are lower bounds. Although it is believed that such lower bound solutions for cracked pipes would be better for pipes with local wall thinning, it has been reported that they are not appropriate. Noting that accurate limit load solutions are essential for residual strength and life estimates, detailed Finite Element (FE) limit analysis is performed for straight pipes with local wall thinning, subject to internal pressure, axial tension and global bending. Practically interesting ranges of pipe and defect geometries are considered. Based on the FE results, closed-form approximations of limit loads are proposed. Finally implication of the developed limit load solutions to defect assessment of locally wall-thinned pipes is discussed