Development of Life Estimation Method for Nozzle Welds in Large Scale Piping of Modified 9Cr-1Mo Steel -Part I: Experimental Study

Type IV creep damage has been frequently reported in longitudinal welds and nozzle welds. Many studies have been conducted on the longitudinal welds, and the applicability of life evaluation by non-destructive testing and numerical analysis has been examined. On the other hand, there are few studies on the nozzle welds, and the applicability of the existing life evaluation method is not clear. In this study, internal pressure creep test and numerical analysis were carried out on a large diameter pipe specimen which has several welded nozzles in order to clarify the applicability of the creep life evaluation method for the nozzle welds. This first report describes the experimental part. The internal pressure creep test at 650°C was performed on the large-diameter pipe specimen of modified 9Cr-1Mo (ASME P91) steel. The test was interrupted three times and nondestructive inspections were performed at each interruption. They included phased array ultrasonic testing, magnetic particle testing and replica observation. The test was completed when the test time reached about 20,000 hours and cross-sectional observations were performed after the specimen was cut into many pieces. Based on these efforts, the location and process of creep damage development in the nozzle welds and the effectiveness of non-destructive inspection were revealed.