실 배관 파열시험을 통한 감육 Elbow의 손상압력 평가

Abstract

Wall thinning defect due to flow-accelerated corrosion (FAC) is one of the degradation mechanisms of carbon steel piping component in nuclear power plant (NPP), and it results in reducing load carrying capacity and fatigue resistance of the piping components. Especially, the wall-thinning defect leads to abrupt rupture of piping components under normal operating pressure. Thus, it is important to accurately evaluate the failure pressure of piping components containing an internal wall-thinning defect for ensuring integrity of piping system of NPP. Unfortunately, the failure pressure data on the internally wall-thinned pipe are very rear. For wall-thinned elbow, especially, there are no published data up to this time. Therefore, this study performed failure tests using real-scale elbows containing simulated wall-thinning defect under internal pressure and combined internal pressure and bending moment. Based on the results of experiments, the effect of thinning depth, thinning length, circumferential thinning angle and bending moment on the failure pressure was investigated. Also, these results were compared with failure pressure predicted by existing models. The results of failure tests showed that the failure pressure decreased with increasing depth and it was decreased and saturated with increasing axial thinning length. There tendencies are similar as those observed from the straight pipe with local wall-thinning. Also, the failure pressure decreased with increasing circumferential thinning angle. This is different from that observed in the results of studies on the wall-thinned straight pipe. The effect of bending moment on the failure pressure was negligible. The comparison of failure pressures obtained from experiment and predicted by models showed that the existing models conservatively estimated the failure pressure of wall-thinned elbow, and reasonably predicted the effect of wall thinning length and depth. However, the models could not appropriately consider the effect of circumferential thinning angle and thinning location on the failure pressure.