Residual Stress Driven Creep Cracking in Type 316 Stainless Steel

A specially designed compact tension (CT) specimen has been used to simulate reheat cracking observed in plant components operating above 500°C. The specimens were deformed in compression beyond yield and unloaded to produce high tensile residual stresses at the notch root. Test specimens were machined from an ex-service AISI Type 316H austenitic stainless steel steam header. After residual stressing, one specimen was crept for 4500 h at 550°C. Residual strains along the ligament of the specimens were measured using synchrotron and neutron diffraction techniques before and after creep. A 3D finite element (FE) model was developed and used to predict the residual stress and strain fields in the two conditions. A good correlation has been found between measurements and FE predictions before and after creep. Application of a creep ductility-exhaustion model to the specimen predicts the onset of simulated reheat crack initiation during the test. The validity of this model will be assessed on destructive examination of the specimen.