Development of a plastic collapse assessment procedure in the p–M diagram method for pipe bends with a local thin area under combined internal pressure and external in-plane bending moment

Pipe bends are common elements in piping systems such as power or process piping, and local thinning typically occurs on pipe bends due to erosion and/or corrosion. Therefore, it is important to establish the plastic collapse condition for pipe bends having a local thin area (LTA) under combined internal pressure and external bending moment. In this paper, a simplified plastic collapse assessment procedure in the p–M (internal pressure ratio and external bending moment ratio) diagram method for pipe bends with a local thin area simultaneously subjected to internal pressure, p, and external in-plane bending moment, M, due to earthquake, etc., is proposed, which is based on the reference stresses derived from the Tresca theory under a three axes condition. The plastic collapse loads derived from the proposed p–M diagram method are ascertained by comparing with the results of experimental testing with full-scale pipe bends and those of FEA for the same sized pipe bends with an LTA having various dimensions as well.

► A simplified plastic collapse assessment procedure for pipe bends with a local thin area is proposed. ► Conditions under combined internal pressure and external in-plane bending moment are considered. ► The procedure is using the p–M diagram method (pressure ratio and external bending moment ratio). ► The p–M diagram is derived from the reference stresses based on the Tresca theory. ► The plastic collapse loads are ascertained by results of the full scale testing with pipe bends and FEA.