Prediction of wall thinning due to flow-accelerated corrosion at drift region in T-joint pipe

Abstract

Flow Accelerated Corrosion (FAC) is a pipe wall thinning phenomenon to be monitored and managed in the power plants with high priority. Its management has been conducted with conservative evaluation of thinning rate, and residual lifetime of piping based on wall thickness measurements. In T-joint with a curvature part called a "crotch" in the area where pipes meet, the radius of curvature of the crotch becomes small, especially when the pipe diameter is small, and the flat tip of the probe commonly used in conventional UT measurement cannot sufficiently contact the measurement surface of the crotch, making wall thickness measurement difficult. The purpose of this study is to develop a method for estimating the maximum wall thinning of a T-joint based on detailed wall thinning trends at and around the crotch, and to introduce a multiplication factor necessary for estimating the wall thinning. It was found that the local thinning distribution near the crotch changed depending on the inlet conditions of the branch and main pipes. The multiplication factor is greater than 1 under the condition of maximum wall thinning at the crotch, but this value also varies depending on the evaluation conditions, and is shown to be approximately 1.5 at maximum.