Hot End Cleaning - Corrosion Pitting of Turbine Discs

Over a period of years Rolls-Royce plc have experienced intermittent corrosion pitting of turbine discs manufactured from FV535. It was originally thought that this may have been caused by the acidic descaler. Recent work has shown that this corrosion pitting phenomenon is caused by low levels of alkaline permanganate, above 0.01% together with levels of chloride above 30 ppm on discs where there are areas of high chromium commensurate with low iron within the steel. The paper will describe the experimental work to substantiate these conclusions.