Flow-accelerated corrosion in low-pressure evaporator of heat recovery steam generator: Experiments and fluid dynamics simulation

Flow-accelerated corrosion (FAC) poses a significant challenge in the low-pressure evaporator (LP EVA) of heat recovery steam generators (HRSG), a critical component in district heating systems. In this study, wall thinning of the LP EVA tubes was observed, particularly in the upper and curved sections, with some areas showing residual thickness below 1.0 mm. Surface analysis identified phosphorus accumulation in the oxide layer, originating from water treatment agents, as a major factor in destabilizing the protective oxide and promoting FAC. Computational fluid dynamics (CFD) simulation highlighted imbalances in the interaction of boiler water and exhaust gas, exacerbating wall thinning. The corrosion rate of SA178 steel increased approximately fourteen times when the boiler water temperature changed from 110°C to 150°C under flow conditions, and mechanical testing showed a yield strength reduction from 374 MPa at room temperature to 242 MPa at 150°C. Mechanical tests demonstrated that SA178 steel, used in the tubes, suffers from deteriorated properties under operating conditions and is prone to pitting corrosion. It is suggested that localized turbulence and the destabilization of protective oxide layers drive FAC in LP EVA. These findings emphasize optimizing material selection, system design, and operational strategies to mitigate FAC and enhance HRSG reliability.