This study proposes a low-cycle fatigue life derived from measurement points on pipe elbows, which are components that are vulnerable to seismic load in the interface piping systems of nuclear power plants that use seismic isolation systems. In order to quantitatively define limit states regarding leakage, i.e., actual failure caused by low-cycle fatigue, in-plane cyclic loading tests were performed using a sine wave of constant amplitude. The test specimens consisted of SCH40 6-inch carbon steel pipe elbows and straight pipes, and an image processing method was used to measure the nonlinear behavior of the test specimens. The leakage lines caused by low-cycle fatigue and the low-cycle fatigue curves were compared and analyzed using the relationship between the relative deformation angles, which were measured based on each of the measurement points on the straight pipe, and the moment, which was measured at the center of the pipe elbow. Damage indices based on the combination of ductility and dissipation energy at each measurement point were used to quantitatively express the time at which leakage occurs due to through-wall cracking in the pipe elbow.

Materials design and processing development proposed in this study, aims at contributing to high wear resistant and friction characteristics. To find wear resistant and friction with inner elbow pipe, it is needed hardness and frictional condition test to be capable of supplying with high Cr casting steel. The result of HTV(heat treatment in vacuum) shows that hardness increased with increasing Cr content in % carbide phase. It was about 7∼10% of hardness improvement compared to original casting elbow pipe. This behavior of the hardness of Cr casting steel was explained by the types of chemical bonds that hold atoms together in Cr carbide phase. Through the friction coefficient and wear loss test, with the increasing of Cr wt% reduction in the coefficient of friction and wear loss.

In this study, a PTZ(Pan-Tilt-Zoom) system was applied as the methods for measuring the deformation angle of a steel pipe elbow. An image of the steel pipe elbow was enhanced using an image filter processing algorithm. To measure the deformation angle, the Hough transform was applied to the enhanced image to facilitate line recognition. In this study, the limit state of the elbow was defined as rupture or leakage. To verify the validity of measuring the deformation angle of a steel pipe elbow by using a PTZ system, an in-plane cyclic loading test was conducted so that deformation angles that are too large to measure using a conventional sensor could be measured effectively.