Evaluation of Failure Pressure of Locally Wall-Thinned Elbow by Real-Scale Pipe Tests

This study performed a series of burst tests using real-scale pipe elbows containing simulated wall-thinning defect, to evaluate the effects of local wall-thinning on the failure pressure of pipe elbows. The tests were conducted under simple internal pressure at room temperature. In the tests, various wall-thinning geometries, such as thinning depth, length, and circumferential angle, and thinning locations, extrados and intrados, were considered. From the results of tests, the effects of thinning geometries and locations on the failure pressure of local wall-thinned elbows were investigated. The dependences of failure pressure on the thinning length and depth in the wall-thinned elbow were similar to those in the wall-thinned straight pipe. The failure pressure clearly decreased with increasing circumferential thinning angle, which was different from the results of wall-thinned straight pipe. Also, the failure pressures were compared with the results predicted by existing evaluation models. The existing models showed excessive conservatism. For intrados wall-thinning case, especially, the conservatism was significant and the variation in failure pressure with thinning geometries could not be properly predicted. For extrados wall-thinning case, the existing models appropriately estimated the dependence of failure pressure on the thinning length and depth. All specimens tested were failed by bulging followed by axial cracking. For extrados and intrados wall-thinned elbows, the crack always occurred at the minimum wall-thinned area. For entire circumferential wall-thinned elbow, however, the crack location depended on the axial thinning length.