Development of Wall-Thinning Evaluation Procedure for Nuclear Power Plant Piping — Part 1: Quantifi cation of Thickness Measurement Deviation

Pipe wall thinning by flow-accelerated corrosion and various types of erosion is a significantand costly damage phenomenon in secondary piping systems of nuclear power plants(NPPs). Most NPPs have management programs to ensure pipe integrity due to wall thinningthat includes periodic measurements for pipe wall thicknesses using nondestructiveevaluation techniques. Numerous measurements using ultrasonic tests (UTs; one of thenondestructive evaluation technologies) have been performed during scheduled outages inNPPs. Using the thickness measurement data, wall thinning rates of each component aredetermined conservatively according to several evaluation methods developed by theUnited States Electric Power Research Institute. However, little is known about theconservativeness or reliability of the evaluation methods because of a lack of understandingof the measurement error. In this study, quantitative models for UT thicknessmeasurement deviations of nuclear pipes and fittings were developed as the first step forestablishing an optimized thinning evaluation procedure considering measurement error. In order to understand the characteristics of UT thickness measurement errors of nuclearpipes and fittings, round robin test results, which were obtained by previous researchersunder laboratory conditions, were analyzed. Then, based on a large dataset of actual plantdata from four NPPs, a quantitative model for UT thickness measurement deviation isproposed for plant conditions. KCI Citation Count: 1