Corrosion of coating materials in oxidizing and hydrogen chloride containing atmospheres

The boiler tubes in waste incinerator plants and power plants are mainly corrosive strained. This paper presents the corrosion behaviour of various coating materials in two corrosive atmospheres at 500 degreesC. In a first test, Ni-based materials applied by High Velocity Oxygen Fuel Flame (HVOF)-spraying and Atmospheric Plasma Spraying (APS) as well as Cr-based materials obtained by diffusion coating process are tested in oxidizing atmosphere with water saturation. The results of the corrosion test in this H2O-O-2-N-2-atmosphere show that NiCr applied by HVOF is less oxidized than that applied by APS-coating, whereas NiCrBSi coating by APS shows higher resistance than that applied by HVOF-spraying. The diffusion coating of Cr/Si is better than that of pure Cr. In a second test, metallic Mo and W-based materials applied by thermal spraying are tested to verify their corrosion resistance in HCl-H2O-O-2-N-2-atmosphere. It is shown that pure Mo applied by APS on 13 CrMo 44 and WCrNi sprayed on 15 Mo 3 by HVOF as well as on 13 CrMo 44 show relatively high corrosion resistance, whereas Mo sprayed by APS on 15 Mo 3 is not resistant. Both tungsten-cobalt-chromium mixtures show extremely high oxidation rates. Base materials in both tests were the standard boiler tube materials 15 Mo 3 and 13 CrMo 44. But even the low corrosion rates of the best materials in these tests are higher compared to those of materials already presented by Cha et al. in an earlier paper.