Ratcheting Effect of Pressurized 90° Elbow Pipe under In-Plane Opening, Closing, and Reverse Bending

The effect of opening-bending, closing-bending, and reversed-bending loads on the ratcheting behavior of pressurized Z2CND18.12N stainless steel 90 degrees long-radius elbow pipe was studied using finite-element (FE) analysis. Three-dimensional elastoplastic analyses with the Chen-Jiao-Kim (CJK) kinematic hardening model, implemented in the FE software ANSYS, was used to simulate the ratcheting behavior of pressurized 90 degrees elbow pipe at flanks and intrados. The results indicated that ratcheting strain for single-step loading increased with increasing bending loading at the same internal pressure and that it increased with increasing internal pressure at the same bending loading. Multistep bending revealed that the ratcheting rate increased with increasing loading but decreased or even vanished at a lower bending level imposed after a higher bending level. Furthermore, the results generally indicated that the ratcheting strain of a 90 degrees elbow pipe subjected to in-plane opening-bending and closing-bending loads was larger than that with a reversed-bending load.