Characteristic of pipe wall thinning by flow accelerated corrosion at drift region in junction piping

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 the thinning rate and the residual lifetime of the piping based on the wall thickness measurements. However, noticeable case of the wall thinning was occurred in branch and junction piping (tee tube). It is a problem to manage the section beneath the reinforcing plate of the tee tube; the region where measurement is difficult to conduct with ordinary ultrasonic testing device. In this study, numerical analysis for the tee tube was conducted, and the wall thinning profile due to the FAC was evaluated by calculating the mass transfer coefficient. In the case of the union flow, local wall thinning profile was found near the junction where is covered by the reinforcing plate. This profile showed the tendency of increase in association with increasing of the flow amount from the branch pipe. And, the profiles also have smooth decay tendency from the junction to downstream of the main pipe. Therefore, the amount of the wall thinning beneath the reinforcing plate can be predicted from the location where is deviated from the plate.