Chemistry in surface boundary layers as related to flow accelerated corrosion of carbon steel in high temperature water

摘要

Flow accelerated corrosion (FAC) is divided into two processes: the corrosion (chemical) process and the flow dynamics (physical) process. The former is the essential cause of FAC, while the latter accelerates its occurrence. Chemistry in the surface boundary layers was analyzed to evaluate FAC rates. First flow pattern and temperature in each elemental volume along the flow path were obtained with 1-3D computational flow dynamics (CFD) codes, next [O_2] and [Fe~(2+)] were calculated with a chemical reaction model based on the obtained flow pattern, and then calculated [Fe~(2+)] was fed back to the environmental factors for the wall thinning calculation, at all points of interest, using the modified double oxide layer model. The effects of candidates for dcountermeasures, e.g., O_2 injection and increasing pH, on FAC mitigation could be evaluated. Future wall thinning trends could also be predicted by the model.