2D PIV study of flow accelerated corrosion downstream a typical industrial gate valve

Abstract

A critical degradation mechanism of piping systems in either nuclear power plant is Flow Accelerated Corrosion (FAC), which causes wall thinning of pipes and component shells from inside. The valves which are frequently used in power plant piping systems are mostly subjected to FAC. A Gate vale in the feed water piping system of a typical nuclear power plant that it’s downstream had been damaged due to the FAC was considered as a reference. In this study the effect of the mean flow velocity and the opening percentage of gate valve on the flow field downstream the valve was investigated by using 2D PIV. The locus where flow turbulences happen downstream the gate valve was determined by 2D PIV. It is found that there is a very good coincidence between the locus in which the maximum wall thinning measured by Ultrasonic Technique (UT) and that the flow turbulences happen downstream the gate valve determined by 2D PIV.It is observed that the locus of flow turbulences and intense velocity gradients is in the upper part of the pipe and over the domain of 0.2 <L/D < 2.4 along the pipe downstream the gate valves where the minimum wall thickness was measured by using UT. Flow turbulences and velocity gradients near the upper pipe wall result in higher wall shear stress and maximize the mass transfer from the pipe inner wall in turn result in wall thinning. The results of this paper can be useful for optimizing inspection plans in identifying and predicting the vulnerable FAC locations downstream the gate valves.