Experimental and computational failure analysis of a valve in a nuclear power plant

A parallel slide valve of a nuclear power plant failed before its designed life. The failed part was on the belt eye (BE), which was manufactured from ASTM 216 WCB. In this paper, a failure analysis of the valve was performed by visual inspection, Vickers hardness measurement, scanning electron microscopy observation and Energy Dispersive Spectroscope analysis of the BE metal and oxide scale. Computational fluid dynamics method was employed to calculate the possible effect of cavitation erosion on the failed BE and to define the sensitive regions.The experimental results showed that the failure mode of the BE was a combination of flow-accelerated corrosion (FAC) and cavitation erosion. The FAC characteristic “orange peel” appearance was observed on the inner surface of the BE. Significant wall thinning occurred due to formation of an unprotective oxide on the metal. Simulation results showed that it is not the Venturi-like shape inside the valve but the misalignment between the reducer and the BE in the valve that caused the cavitation erosion. Moreover, cavitation enhanced the turbulence intensity and eventually increased the local FAC rate.

► The failure mode of the valve is a combination of FAC and cavitation erosion.
► FAC and cavitation erosion enhance with each other if they occur simultaneously.
► The misalignment between components can cause severe local wall thinning.
► The most sensitive section for cavitation erosion was calculated by CFD method.