Long-term low-cycle corrosion fatigue of steel 08Kh18N10T and its welded joints in water of high parameters

Steel 08Kh18N10T (similar to steel 321SS) and the weld metal of full-scale pipe of the WWER-440 main circulation pipeline were tested for fatigue in air environment (300 degC) and in deoxygenated water (9 MPa, 300 degC). Cantilevered specimens were loaded in a displacements-controlled symmetrical triangular cycle. The strain rate during tests in water was 1.1x10-3 to 6.7x10-2 % s-1. Given equal strain amplitudes, the number of cycles to failure in water, as compared with air testing, is reduced by a factor of 8-13 at the most with strain rate decrease. The results of testing steels 18-8 in PWR water show fair agreement with fatigue curves according to the equation based on the ANL model. This paper presents equations for calculating curves in case of loading in water and air, as well as design fatigue curves for austenitic stainless steels 18-8 under the given conditions. Fatigue crack growth was studied as found in the base metal and the weld in air, with the asymmetry coefficient R = 0.1 and 300 degC. The results were compared with the design curves for conditions of air and PWR water environment as well as with the design curve in air, calculated by the ASME Code. (author)