Performance of Detonation Gun-Sprayed Ni-20Cr Coating on ASTM A213 TP347H Steel in a Boiler Environment
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G. Kaushal, H. Singh, and S. Prakash (Submitted November 21, 2011; in revised form February 13, 2012) Detonation gun-sprayed coatings are known for their high density, high bond strength, moderate substrate heating, superior surface finish, better wear/corrosion resistance, and low cost. In this study, detonation gun-spraying technique was used to deposit Ni-20Cr coating on a commonly used boiler steel ASTM A213 TP347H. The specimens with and without coating were subjected to cyclic oxidation testing at an elevated temperature of 700 °C in actual boiler environment to ascertain the usefulness of the coating. The mass change technique was used to establish the kinetics of erosion-corrosion. XRD and SEM/EDS techniques were used to analyze the exposed samples. The uncoated sample suffered from erosion, and a significant mass loss was recorded. It was observed that overall mass loss was reduced by 83% and thickness loss by 53% after the application of the coating. The detonation gun-sprayed Ni-20 Cr coating was found to be suitable to impart erosion resistance to the given steel in the actual boiler environment.
Keywords
boiler environment, D-Gun, erosion-corrosion, high-temperature oxidation, protective coating
1. Introduction The conventional boilers, where various grades of stainless steel are used as the base materials for their tubes, face the acute problem of degradation by high-temperature oxidation of hot-section components, which is accompanied by erosion as well (Ref 1-6). The atmosphere in power plant boilers has a sufficient free oxygen content to account for a combined erosion-corrosion (E-C) process, consisting of an oxidizing gas at elevated temperature carrying erosive fly ash which impact against metallic surfaces (Ref 7). The combination of high temperatures with contaminants of environment and low-grade fuels, such as sodium, sulfur, vanadium, and chlorine, require special attention to the phenomenon of high-temperature corrosion. This form of corrosion consumes the material unpredictably at very rapid rate (Ref 8). Oxidation and high-temperature corrosion resistance of these materials used in the high-temperature regions is improved by the application of protective coatings. Thermal spray coating
G. Kaushal, RIMT-Institute of Engineering & Technology Mandi Gobindgarh, Punjab, India; H. Singh, Indian Institute of Technology Ropar, Rupnagar, Punjab, India; and S. Prakash, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India. Contact e-mails: [email protected] and gagankaushal@ rimt.ac.in.
Journal of Thermal Spray Technology
can be applied to overcome the oxidation/corrosion problems since it alters the surface without affecting the bulk material properties (Ref 9-12). These coatings can offer an alternative to diffusion coatings. Although protective surface treatments are widely used at low temperature, the application of these at elevated temperature is relatively recent. Detonation gun (D-Gun) spraying, developed in the late quarter of the 1900s, owns the same virtues as the
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