The Influence of System Design, Station Operations and Cycle Chemistry on Corrosion Product Generation and Flow-Accelerated Corrosion (FAC) at Coryton Combined Cycle Gas Turbine (CCGT) Power Station

A systematic study of the influence of system design, station operations and cycle chemistry on corrosion product generation and flow-accelerated corrosion (FAC) was carried out at Intergen’s Coryton CCGT in Essex, UK. Coryton is a modern 779 MW two-by-one combined-cycle natural gas plant equipped with an air-cooled condenser (ACC). The plant was designed and constructed for operational flexibility and functional efficiency in a merchant power environment, which in practice means a cycling operation with occasional two-shifting. The study was instigated by the frequent occurrence of FAC in combined cycle power plants and the retrospective nature of non-destructive testing (NDT). The station wanted to invest in advanced monitoring techniques with the objective of reducing corrosion in the air-cooled condenser and the potential for FAC in the heat recovery steam generator (HRSG) during normal and cycling operations, and to determine the impact of cycling operation on unit life expectancy and reliability. Of special interest was the evaluation of the use of all-volatile treatment oxidising (AVT-O) versus all-volatile treatment reducing (AVT-R) chemistry control in the all-steel system as a means to reduce FAC in the HRSG and iron pick-up in the air-cooled condenser. On-line “at-temperature” Oxidation-Reduction Potential and Particle Monitor instruments were applied to supplement the standard array of chemistry and operational monitoring. The study should allow Coryton Power to identify the best cycle chemistry control specifications to minimise FAC and ACC corrosion, leading to more reliable, efficient and lower cost generation for the life of the plant.