Review of flow accelerated corrosion mechanism, numerical analysis, and control measures

Flow Accelerated Corrosion or FAC has been under investigated since 1980 s. However, with its well understood mechanism and developed preventive measures, the problem remains. This paper aims to provide a comprehensive review on the FAC mechanism and contributing factors, preventive measures and FAC management strategies. In addition, FAC rate prediction models employed in CFD studies are compared. The model that includes the effect of time-dependent roughness showed promising results, with only 12% maximum relative error of FAC rate compared to experimental results for flow in a bend. Roles of process modelling software in FAC analysis are explored. The ability of the software to replicate a warm start-up behavior of a combined-cycle heat recovery steam generator (HRSG) is demonstrated. Predictions from Apros are most accurate due to its heterogeneous mathematical models. Power Plant Simulator and Designer (PPSD) yields comparable results but takes the shortest calculation time of 30 min. Machine learning algorithms are also introduced. By applying them to predict FAC occurrence in a 90-degree bend, long-short term memory (LSTM) performed the best with 96% accurate results. Application of these algorithms and process modelling software proposes a promising methodology for FAC detection and monitoring system development. Moreover, a practical example of FAC in high-pressure (HP) economizer of HRSGs is presented. The damage occurs in tubes connecting to inlet headers where the flow cannot be evenly distributed. From preliminary investigation, the contributing factors include the geometry of the flow, turbulence, dissolved oxygen, susceptible material, and the operating temperature.