Flow Accelerated Corrosion Prediction in High Pressure Economizer of a Heat Recovery Steam Generator

This paper examines the flow accelerated corrosion in tubes downstream of an inlet header of the High-Pressure Economizer system using computational fluid dynamics (CFD). This problem was recently identified in a heat recovery steam generator. The k-ε RNG model with enhanced wall functions was employed. CFD results showed that, at the ends of inlet pipes, abrupt change in flow area resulted in recirculation and jet flow. Flow acceleration downstream of the inlet pipes caused strong recirculation at the entrance of two to three tubes extending from the inlet pipes’ centerline. This recirculation forced the flow in the remaining area to accelerate, causing higher wall shear stresses on the side opposite the recirculation. As high shear stresses correlate with the locations where the flow accelerated corrosion occurs severely in practice, the Chilton-Colburn analogy was applied for FAC rate prediction. Predicted rates and measured rates agreed, although some predicted values were overestimated. The distributions of predicted FAC rates matched the tubes thickness distributions. The maximum predicted rate was 0.739 mm/year on the left wall of tube 11 at an elevation 0.045 m below the header centerline. Lastly, a design of experiments was conducted, varying operating flow temperature, pressure, and velocity. ANOVA revealed that FAC in this case was most sensitive to flow velocity. The operating temperature, pressure and tube average velocity that resulted in the minimum FAC rate of 0.424 mm/year were 160.48°C, 190.76 bar, and 0.639 m/s, respectively.