Influence of flow velocity and temperature on flow accelerated corrosion rate at an elbow pipe

Abstract Flow accelerated corrosion (FAC) is one of the important issues that must be considered for aging fossil and nuclear power plants. To understand the effect of thermal flow field on FAC, FAC rates at an elbow pipe were measured under different flow velocity and temperature conditions. The elbow test section was made of stainless steel (diameter D  = 49.5 mm) and FAC rates were measured using corrosion sensors made of carbon steel. The dissolved oxygen concentration was kept under 0.1 μg/kg, and pH was nearly neutral (about 7.0) at room temperature. The mean cross-sectional velocity was changed from 0.39 to 5.74 m/s (Reynolds number, about 1.0e6). When the water temperature was about 150 °C, the FAC rate was smaller at the intrados of the elbow pipe than at other circumferential locations. This tendency continued downstream. The FAC rates at the elbow pipe were larger than those upstream and downstream from the elbow pipe and the FAC rates downstream from the elbow pipe decreased along the flow direction. FAC rates increased as flow velocity increased and their relationship was not linear. The ratios of the maximum FAC rate at the elbow to the FAC rate in the upstream straight pipe ranged from about 1.7 to 2.9. When temperature decreased to 100 °C, FAC rate at the intrados became the largest of the other circumferential sensors. When temperature decreased further to 50 °C, FAC rate also decreased, but the value was not negligible. The influence of flow velocity was negligibly small at 50 °C and remarkable at 100 °C and 150 °C. The combination effect of flow velocity and temperature was different from place to place and particularly strong at the elbow.