해양구조물용 API X80 강재의 해수환경에서 피로거동에 관한 연구
xi, 100 p.
S-N fatigue Fatigue crack propagation X80 steel weld metal seawater cathodic protection precorrosion;
- 원문 URL
In this study, the S-N fatigue and the fatigue crack propagation (FCP) behaviors of API X80 steel were examined in the each positions of base metal (BM), weld metal (WM) and heat affected zone (HAZ) and in artificial seawater (ASW) under various protection potentials. And the effects of pre-corrosion on the S-N fatigue behavior of X80 steel were examined. The X80 specimens were pre-corroded in FeCl3 solution for varying immersion times ranging from 0 to 96 hours and subsequently S-N fatigued in air. The slow strain rate test (SSRT) was also conducted on the X80 BM specimens in ASW under CP potential to identify the susceptibility of hydrogen affecting the FCP behavior. The resistance to S-N fatigue of X80 BM and WM specimen showed a strong dependency on the flow strength (½(yield strength + tensile strength)). The S-N fatigue curves of BM and WM were described by using a Basquin' law. The FCP rates of the X80 BM and the WM specimens were comparable with each other, while the HAZ specimen showed slightly better FCP resistance than the BM and the WM specimens, over the entire △K regime. Despite the varying microstructural characteristics of each weld location, the residual stress appeared to be a controlling factor to determine the FCP behavior. The CP potential of -850 and -1,050mVSCE suppressed the environmental effect of ASW on the FCP behavior of X80 BM and WM specimens, showing almost identical da/dN-△K curves for both air and ASW environments. The SSRT in ASW under CP potential of -1,050mVSCE suggested that the X80 BM specimen steel is susceptible to hydrogen embrittlement (HE), but the effect of hydrogen was believed to be marginal in affecting the FCP behavior of the X80 specimens at a loading frequency of 10 Hz. It was found that the resistance to S-N fatigue decreased abruptly with 1 hour immersion, while it became saturated with further increase in immersion time. The trend observed in the present study was relatively well explained by the stress concentration effect by the presence of corrosion damage on the surface. The in-situ S-N fatigue tests were also conducted on X80 steel in artificial seawater under applied potentials of -600, -850 and -1,050mVSCE. The CP potential of -850 and -1,050mVSCE suppressed the environmental effect of seawater on the S-N and FCP behavior of X80 BM and WM specimens.