Estimation method of pipe wall thinning tendency at T tube in actual plant

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, in the actual plants, noticeable case of the wall thinning occurred in branch and junction piping (T tube). There is a problem to manage the wall thickness of the part covered by 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 flow 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 a localized wall thinning distribution occurs in the area where the reinforcement plate of the T tube exists. And this tendency is affected by pipe geometry and Reynolds number. In previous studies, a model that functionalized by pipe geometry and Reynolds number was introduced to predict this wall thinning trend. In this paper, the effectiveness of the proposed decay function was confirmed by comparing it with measurements taken in actual plants. It was shown that the maximum wall thinning rate at the T tube junction, including below the reinforcing plate, can be evaluated conservatively within an appropriate range by making corrections to the proposed decay function that take into account the causes of variation in the actual data.