Thermo-Mechanical and Isothermal Low-Cycle Fatigue Behavior of Type 316L Stainless Steel in High-Temperature Water and Air

Abstract

Two unique facilities for isothermal low-cycle fatigue (LCF) and in-phase (IP) or out-ofphase (OP) thermo-mechanical fatigue (TMF) testing of tubular specimens under boiling water reactor (BWR) and pressurized water reactor (PWR) coolant conditions were set up and successfully tested. The systems allow both strain-and stress-controlled fatigue experiments with very small strain amplitudes or complex stress/strain profiles with superimposed rather rapid temperature changes (100 -340 °C) under flowing conditions. The present article introduces the new test facility and briefly discusses the first results of these experiments.In contrast to air, a strong effect of temperature on LCF and TMF lives was observed in de-oxygenated and hydrogenated high-temperature water environment, where both lives decrease with increasing temperature above 100 °C. The TMF life is between that of the isothermal LCF tests at minimum and maximum temperature. The IP TMF life is shorter than that of OP TMF and close to the LCF life at maximum temperature. The OP TMF life is close to that of LCF at minimum temperature. In hydrogenated environment, the LCF and TMF lives seem to be slightly shorter than predicted by the NUREG/CR-6909 approach of the US NRC Reg. Guide 1.207. Significant environmental effects were observed at 100 °C, which is significantly below the temperature threshold of 150 °C.

Correlation between Dislocation Structures and Mechanical Fatigue Response of 316L Austenitic Steel Loaded with and without Mean Stress at High Temperature in Air and Water Environment

“…A detailed description of the water loop facility employed for this study can be found in [4]. The load-controlled fatigue tests were performed at 288°C in air and in pressurized water environment characterized by high-purity, deoxygenated (nitrogen purging) water with 150 ppb dissolved hydrogen which is representative of boiling water reactor/hydrogen water chemistry.…”

“…Moreover, in some cases, dependent on temperature and environment, mean stresses could have significantly beneficial or detrimental effect on the fatigue life of austenitic steels. The effect of mean stress on fatigue life in water environment has been identified as one of the issues that is not sufficiently documented and that needs to be addressed [3,4].…”

Fatigue behavior of 316L austenitic stainless steel in air and LWR environment with and without mean stress

“…The facility for fatigue tests in high-temperature water ( Figure 6) consists of an Instron 8862 electro-mechanical fatigue test machine and a water loop that allows thermo-mechanical loading under BWR or PWR water chemistry conditions. A detailed description of the facility is described in [10]. The fatigue tests were conducted at 288°C and pressurized water was characterized by high-purity, hydrogenated water with 150 ppb dissolved hydrogen (BWR/HWC).…”