Determination of Material Degradation at Various Environmental Conditions

There are growing interests in materials and system degradation at various environmental conditions, especially for structures in fossil fuel power station, nuclear power plants and petrochemical industry. Several testing and simulation approaches have been developed to determine the degradation of material properties with the influence of corrosion environment. A simulation technology is introduced to investigate the effects of irradiation on mechanical properties for a degraded reactor pressure vessel steel. The degradation procedure combines the application of cold prestrain together with high temperature heat treatment. It is found from the results of Charpy impact tests for degraded material that there is an increase of ductile-brittle transition temperature and a trend to a decrease of upper shelf energy because of irradiation embrittlement. Evaluation procedures of temper embrittlement and hydrogen-embrittlement are described for reactor pressure vessel steel exposed to hydrogen environment. A regular coupon sample test is adopted to determine the material degradation of hydrogen processing reactors. Numerical analysis and experimental hydrogen charging technique are explored to simulate the process of hydrogen embrittlement. A critical parameter of hydrogen concentration is defined to evaluate the susceptibility of hydrogen induced cracking for reactor steels. A fatigue testing system is designed to obtain the degradation of fatigue strength for materials under the low oxygen steam environment. The system couples a steam chamber with an axial force-controlled fatigue testing machine. The fatigue tests are performed for a titanium alloy with tension-compression loading up to 10⁷ cycles. Test results show that the fatigue strength is obviously influenced by the steam environment and the stress ratios.