A representative example is provided by a type of helicopter jet engine compressor. The uncoated compressors experienced severe pitting problems in the Western European environment. Chemical analysis of collected rinsing water showed that the problem was mainly environmental. Because of spallation a salt layer deposited during flight never reached a visually detectable thickness but nevertheless caused pitting corrosion as manifested by the presence of metal ions. The most important deposited hygroscopic salts were found to be (NH4)2SO4 and MgCl2. The former derives from manure produced by intensive stock farming. Moisture absorbed by the hygroscopic salts was shown to be acidified by the air pollutants SO2 and NO2. Only MgCl2 is of a natural (marine) origin. This salt supplies the chloride ions that attack the protective oxide layer of stainless steels. For most engines conventional aluminium diffusion and spray coatings offer satisfactory protection. However, these coatings quickly erode away in helicopter jet engine compressors. Laboratory tests have established that the erosion resistance of these coatings is low. Therefore a number of new compressor coatings with supposedly high erosion resistance were investigated. Both the erosion and corrosion resistances of these coatings were investigated under simulated service conditions in the NLR compressor test rig. It is concluded - unfortunately - that the ideal compressor coating is not yet available.
Coatings for gas turbine compressors
Beschichtungen für Gasturbinenkompressoren
1989
7 Seiten, 6 Bilder, 5 Tabellen, 8 Quellen
Aufsatz (Konferenz)
Englisch
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