Hot corrosion behavior of thermal spray coatings on superalloy in coal-fired boiler environment
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Korada Viswanatha Sharma Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Bander Seri Iskander, Tronoh 32610, Malaysia
Rengaswamy Jayaganthan and Satya Prakash Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India (Received 12 December 2014; accepted 10 August 2015)
Coal is an attractive fuel owing to its low price linked to its worldwide availability but combustion of coal generates very corrosive media especially near the superheater tubes. The present investigation is an attempt to evaluate the hot corrosion behavior of detonation-gun sprayed coatings of Cr3C2–NiCr, NiCrAlY 1 0.4 wt% CeO2, and NiCoCrAlYTa on superfer 800H, exposed to low temperature super-heater zone of the coal-fired boiler. The specimens were hanged in the platen super-heater of coal-fired boiler where the gas temperature was around 900 °C 6 10 °C. Hot corrosion experiments were performed for 10 cycles, each cycle consisting of 100 h exposure followed by 1 h cooling at ambient temperature. All three coatings deposited on superfer 800H imparted better hot corrosion resistance than the bare uncoated one. The Cr3C2–NiCr coated superalloy performed better than the other two coatings in the given boiler environment.
I. INTRODUCTION
The worldwide demand for electrical energy has been increasing steadily. The consumption of conventional fuels, such as coal, oil, and gas in thermal power plants, is rapidly increasing thereby depleting the fossil resources. For energy sustainability and economic reasons, residual fuel oil can be used along with coal in electricity generation using the conventional thermal systems, such as furnaces, boilers, and turbine components. Coal is an attractive fuel owing to its low price linked to its worldwide availability and anticipated future shortage of other fossil fuel reserves, such as oil and gas. But the combustion of coal generates corrosive gases near the superheater tubes.1 The high resistance of high-chromium, nickel–chromium alloys to high-temperature oxidation and corrosion makes them widely used for welded and thermally sprayed coatings in fossil fuel-fired boilers.2 The surface degradation of metal containment walls and heat exchanger tubes by combined erosion–corrosion (E–C) mechanism has been experienced in certain boilers, particularly fluidized bed combustors.3 Hot corrosion
became a topic of importance and popular interest in the late 1960s as the phenomenon had been observed frequently on the high temperature components of coal conversion system.4 Metallic components in coal-gasification plants are exposed to severe corrosive atmospheres and high temperatures, the corrosive nature of the gaseous environments (i.e., environments containing O, S, and C) may cause rapid material degradation and result in the premature failure of components.5 Detonation-gun (D-gun) is capable of producing the highest pressure, velocity, and density in the gas flow, which is not achievable by all other spraying techniques; as a resul
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