Development of a method for estimating wall thinning tendency due to flow-accelerated corrosion in tee joint piping

Flow-Accelerated Corrosion (FAC) is a pipe wall thinning phenomenon to be monitored and managed in 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 tee 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 (Ultrasonic Testing) 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 tee 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 depending on the flow pattern, the maximum amount of wall thinning occurs at the crotch. It is suggested that the angular position of the tee joint curvature where the maximum value appears can be determined by the design value of the piping. The trend of the multiplication factor can be arranged according to the design value of the piping, and its maximum value was found to be approximately 1.5.