High-Temperature Behavior of a NiCr-Coated T91 Boiler Steel in the Platen Superheater of Coal-Fired Boiler
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JTTEE5 22:838–847 DOI: 10.1007/s11666-013-9899-6 1059-9630/$19.00 ASM International
High-Temperature Behavior of a NiCr-Coated T91 Boiler Steel in the Platen Superheater of Coal-Fired Boiler Sukhpal Singh Chatha, Hazoor S. Sidhu, and Buta S. Sidhu (Submitted September 30, 2012; in revised form December 21, 2012) Ni-20Cr coating was deposited on T91 boiler tube steel by high-velocity oxy-fuel (HVOF) process to enhance high-temperature oxidation resistance. High-temperature performance of bare, as well as HVOF-coated steel specimens was evaluated for 1500 h under in the platen superheater zone of coalfired boiler, where the temperature was around 900 °C. Experiments were carried out for 15 cycles, each of 100-h duration followed by 1-h cooling at ambient temperature. The extent of degradation of the specimens was assessed by the thickness loss and depth of internal corrosion attack. Ni-20Cr-coated steel performed better than the uncoated steel in actual boiler environment. The improved degradation resistance of Ni-20Cr coating can be attributed to the presence of Cr2O3 in the top oxide scale and dense microstructure.
Keywords
boiler steel, coal-fired boilers, high-temperature oxidation, HVOF process, Ni-20Cr
1. Introduction Degradations due to high-temperature oxidation, hot corrosion, and erosion are the main failure modes of components in the hot sections of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces, and petrochemical installations (Ref 1-3). Failure of heat exchanger tubes in coal-fired boilers due to high-temperature oxidation and erosion caused by the impact of fly ashes has become a key material issue in the design and operation of thermal power plants. It is recognized as one of the main causes of downtime (Ref 4, 5). Depending on the plant, the conditions could be very severe, but in the recent years, the temperatures have been increased worldwide to produce more energy, and the life-time of steel superheater tubes has decreased (Ref 6). Maintenance costs for replacing broken tubes are also very high (Ref 4). Attempts to decrease the maintenance costs of these components have led to the increased interest in shielding them with protective coatings (Ref 1). Protective coatings are being used on structural alloys in energy conversion and utilization systems to protect surface from oxidation and erosion (Ref 7, 8). Thermal spraying has emerged as a suitable and effective, alternative surface Sukhpal Singh Chatha and Hazoor S. Sidhu, Yadavindra College of Engineering, Punjabi University Guru Kashi Campus, Talwandi Sabo, Punjab 151302, India; and Buta S. Sidhu, Punjab Technical University, Jalandhar, Punjab 144601, India. Contact e-mail: [email protected].
838—Volume 22(5) June 2013
engineering technology to be used for the application of protective coatings on the boiler tubes, without affecting any other properties of the component (Ref 7, 9, 10). The high-velocity oxy-fuel (HVOF) thermal-spray process has been widely adopted by many industries because of its fle
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