A Note on Ratcheting in High Temperature Applications

Pressurized components are typically subjected to a combination of cyclic thermal and mechanical loads. The combination of primary and secondary stresses can exceed the yield limit of the material without causing immediate plastic failure of the component. Cyclically recurring load transients that exceed the yield limit of the material can cause deformations to accumulate with each cyclic load application, which is a ratcheting condition. The phenomena becomes more complex under elevated temperature. Design by analysis rules for pressure vessels and piping of elevated temperature codes provide requirements to avoid a ratcheting condition under cyclic loading. This paper reviews these requirements and further explores the technical basis for these rules.