Cyclic Behavior and Fatigue of Stainless Surge Line Material

Fatigue of Niobium stabilized austenitic stainless steel (X6CrNiNb1810mod) was studied using specimens extracted from a solution annealed and quenched φ360×32 mm pipe, which fulfils all the German KTA material requirements for primary components in BWR and PWR. An experimental strain life fatigue curve was determined as a base line for component specific evaluations and for comparison with the Langer and Chopra curves, which are the basis of the ASME III and NRC RG 1.207 design criteria. Stress strain responses in strain controlled tests were carefully measured to clarify the fatigue mechanisms. In the LCF regime our data lie within a common scatter band between the Langer and Chopra curves. When approaching HCF regime (> 100 000 cycles), the curves deviate and Chopra curve becomes highly conservative for this material. Strain controlled fatigue tests ranging to 10 million cycles in RT air indicated an endurance limit behavior for this alloy.