Creep-fatigue lifetime modelling of bellows made of AISI 316

Expansion joints including metallic bellows are used in plant piping systems in order to accommodate thermal strains. Thus, many bellows are subjected to creep-fatigue loading due to start-up and shut-down. Tests on small scale bellows made of AISI 316 with hold times up to 120 minutes at a temperature of 600 °C have been performed by Tsukimori et al. [1]. In the present paper finite element simulations have been performed on an axisymmetric bellow model to recalculate these component tests. Therefor Abaqus Standard deformation models and a fracture mechanics based lifetime model developed at Fraunhofer IWM have been used. For the calibration of the deformation model parameters LCF tests with hold times were performed. The lifetime model was adjusted to creep-fatigue lifetime data from lit erature ([3],[4]). However, therefor steady state stress vs. strain hysteresis loops are required, but typically not published in literature. Thus, they were computed using the adjusted deformation model. The fracture mechanics based lifetime model is able to describe creep-fatigue data with hold times up to 1000 minutes within a scatter band of factor 3. With the adjusted models the influence of hold time on the bellow life in the small scale tests from literature could be reasonably described.