Development of Predictive Evaluation Methods 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 thinning rate, and residual lifetime of piping based on wall thickness measurements. However, noticeable case of the wall thinning occurred in branch and junction piping (T-tube). There is a problem to manage the wall thickness beneath reinforcing plate of the T-tube, because measurement of this area is difficult to be conducted with ordinary ultrasonic testing devices due to the presence of the reinforcing plate. In this study, numerical analysis for the T-tube was conducted, and the wall thinning profile due to the FAC was evaluated by calculating the mass transfer coefficient. It was found that when the flows from the branch pipe and the main pipe merge or diverge, a localized wall thinning distribution occurs in the area where the reinforcement plate of the T-tube exists, and this tendency is affected by Reynolds number. It was suggested that the maximum amount of wall thinning in T-tube can be predicted by the flow rate ratio and the diameter ratio. In the future, we will confirm the effectiveness of the proposed decay function by comparing it with measurements taken in actual plants, and apply it to the management of wall thinning in actual plants.