Gas Turbine Compressor Corrosion and Erosion in Western Europe

It is shown that for gas turbines in the West European environment: (1) during operation hygroscopic salts - notably ammonium sulphate (originating from manure) and sodium and magnesium chloride (from sea salt) - are deposited on compressor components and (2) during shutdowns these wet deposits acidify owing to the absorption of the air pollutants NO2 and SO2. The response of the compressor metals can be broadly categorized as follows. Different steels show different degrees of corrosion. Especially pitting corrosion can lead to component rejection and compressor disintegration. This necessitates frequent washing and/or corrosion resistant coatings. Modern cleaners are environmentally friendly and contain a corrosion inhibitor. The performance of cleaners and coatings is discussed. Nickel-based superalloys and titanium alloys are not prone to corrosion in compressor applications. In order to avoid problems these materials should be used even for secondary components. This is exemplified by a crash due to stress corrosion of a component costing only a few dollars.

Compressor erosion as such is not a major problem in Western Europe. However, corrosion resistant coatings usually have a poor erosion resistance. Moreover, engine manufacturers and users prefer a general compressor coating for use in both corrosive and erosive environments. Developments with respect to compressor cleaners and coatings are discussed.