Bureau of Special Equipment Safety

To reduce the waste of austenitic stainless steels due to their low yield strengths, the strain hardening technology is used to significantly improve their yield strength, in order to increase the elastic load carrying capacity of austenitic stainless steel pressure vessels. The basic principle of strain-hardening for austenitic stainless steel pressure vessels and two common models of strain hardening, including Avesta Model for ambient temperature and Ardeform Model for cryogenic temperature, were briefly introduced. However, it was fully established by experiments, the lack of a necessary theoretical foundation and the safety concern affect its widespread use. In this study, we investigated the load carrying capacity of strain-hardening austenitic stainless steel pressure vessels under hydrostatic pressure, based on the elastic-plastic theory. To understand the effects of strain hardening on material behavior, the plastic instability loads of a round tensile bar specimen were also derived under two different loading paths and validated by experiments. The results of theoretical, experimental and finite element analyses illustrated, considering the effect of material strain hardening and structural deformation, at ambient temperature, the static load carrying capacity of pressure vessels does not relate to the loading paths. To calculate the plastic instability pressures, a method was proposed so that the original dimension and original material parameters prior to strain hardening can be used either by the theoretical formula or finite element analysis. The safety margin of austenitic stainless steel pressure vessels under various strain hardening degrees was quantitatively analyzed by experiments and finite element method. A 5% strain as the restrictive condition of strain hardening design for austenitic stainless steel pressure vessels was suggested.