To evaluate the fatigue behavior of the austenitic cladding of pressurized components, the fatigue design curves are usually based on experiments on specimens taken from plates, pipes or bars. Due to rapid heat transport into the ferritic base material, the cladding has a distinctive anisotropic structure that results from the manufacturing process. Therefore, it may not be assumed a priori that the fatigue curves of the various austenitic product forms used in the Safety Standards are also representative for the material of austenitic cladding. It is therefore necessary to determine and assure experimentally a fatigue curve of the cladding material and compare the results with the database of austenitic stainless steels used in German NPPs.
Flat specimens specially adapted to the geometric conditions were prepared out of the austenitic cladding of a RPV which had been manufactured according to nuclear specifications. To check a possible influence of the specimen geometry, flat specimens were prepared in advance from an austenitic pipe of known fatigue behavior and tested at different strain amplitudes. A comparison of the results with the fatigue curve determined with cylindrical specimens showed no influence at the higher strain amplitudes. Altogether, the fatigue data with flat specimens made of the austenitic cladding fit well into the scatter of the fatigue database of austenitic base materials tested with cylindrical specimens.
