Development of Prediction Tool for Flow-Accelerated Corrosion: (2) Evaluation of Geometry Factor for Various Pipe Components

Abstract

Abstract Pipe wall thinning is an important issue in the maintenance of power plants. In particular, flow-accelerated corrosion (FAC) in carbon steel pipelines requires continuous monitoring because of its potential to cause catastrophic pipe rupture. In Japan, management rules for pipe wall thinning in power plants were established after the Mihama accident in 2004 based on pipe wall thickness measurements. However, this monitoring may lead to a large number of measurements for each outage in the power plants. In addition, because this approach assumes constant operating condition, some issues may occur when the plant operating conditions change and a decrease or increase in the FAC rate is expected. For the future improvement of pipe wall thinning management in Japanese power plants, the introduction of prediction methods or prediction codes for thinning rate and residual lifetime evaluation is expected, as already introduced in many other countries. Therefore, the authors conducted research to develop prediction methods for pipe wall thinning management for use in domestic power plants. In this study, to easily apply the FAC prediction model under single-phase water conditions to the actual piping system of nuclear power plants in Japan, we evaluated the geometry effect and the piping layout effect for the various piping components based on CFD parameter analysis. From the CFD results, the influence of the mass transfer coefficient on the parameters of the piping components such as the beta ratio of the orifice was evaluated. An original correlation was developed to enable prediction for the piping system of the actual plants, which consists of the various piping components.