Shakedown analysis of 90-degree mitred pipe bends

Abstract

Abstract The behaviours of smooth 90-degree pipe bends under cyclic loading have received substantial attention in recent years where shakedown and ratchetting domains have been determined. However, such data are considerably lacking for mitred pipe bends. In the current research, the lower bound shakedown limit loads of 90-degree mitred pipe bends are determined via a simplified direct non-cyclic numerical technique recently developed by Abdalla et al. (2007) The analysed mitred pipe bends are subjected to the combined effect of steady internal pressures and cyclic in-plane or out-of-plane bending moments. Both in-plane closing and opening bending moment cases are considered. The shakedown boundaries of three mitred pipe bend geometries with one, two, and three welded joints are determined and compared with the shakedown boundary of a smooth 90-degree pipe bend. All analysed bends have diameter to thickness ratio of 25 and bend radius of 1.5 times the pipe mean diameter. The results indicate that the shakedown boundaries of mitred bends have reduced domains compared with the smooth pipe bend of similar geometrical parameters. Shakedown domains of mitred bends increase in size as the number of welded joints increase until it approaches the shakedown boundary of the smooth pipe bend simulating a mitred bend with infinite number of welded joints. The percentage of the area under shakedown domain for the mitred pipe bends to that of the smooth pipe bend ranges from 20% for the single mitred pipe bend to 75% for the 3-weld mitred bend. Results also revealed that reducing the number of mitred welded joints, dominates reversed plasticity response at the expense of ratchetting response. Out-of-plane bending generally showed larger shakedown domain than the in-plane bending shakedown domain. Additionally, the shakedown domains for in-plane closing and opening moments are quite similar.