| Boiler is used widely in power, paper, metallurgy and chemical process etc industries. Because the boiler tubes including waterwall, superheater, reheater and economizer tubes are exposed to erosive environment of high temperature, super-high pressure, corrosion and fume erosion, high temperature corrosion and erosion will lead to the high wastage of tubes easily. The direct hazard is to cause the leakage and burst of boiler tubes that will affect the running safety of boiler severely and make the huge loss of economy. The protection from the leakage and burst of four tubes of boiler has become a technical problem that should be solved urgently. In this paper, the new alloy and cermet coatings applied to boiler tubes were designed and their performance was researched according to the research item "the study of application and performance of the new cermet coatings applied to boiler superheater tube" for Wuhan Steel and Electricity Ltd.For lightening high temperature corrosion and erosion in boiler, some thermal spraying coatings have been developed and applied in the corrosion and erosion resistance for boiler tubes abroad since eighties and it is a trend to develop new NiCr alloy and cermet coatings for protection of boiler tubes. Based on analyzing the failure mechanism of boiler tubes, a kind of NiCr alloy coating and three kinds of NiCr-Cr3C2 cermet coatings which possess excellent performance of corrosion and erosion resistance on the service condition of large boiler at home were designed in this paperAt present, the coatings applied to boiler tubes are produced mainly by arc spray, plasma spray and high velocity oxy-fuel spray (HVOF). Although arc spraying has the advantages of high deposition efficiency and low cost, only electrically conductive wire materials can be adopted for arc spraying. The quality of coatings produced with plasma spraying and HVOF is high, but large volume of plasma spraying equipment makes it difficult to be used on site, and the high investment of equipment, the large consumption in fuel and high cost prevent from spreading of HVOF. The coatings deposited with subsonic flame spraying possess high bonding strength, low porosity and is low costly, at the same time it is applied to the worksite of boiler tubes specially. The coatings applied to boiler tubes were deposited by subsonic flame spraying in this study.For NiCr alloy coating and three kinds of NiCr-Cr3C2 cermet coatings with different content of Cr3C2, high temperature oxidation and corrosion, erosion, bonding strength and hardness of coating, thermal cycling andthermal shock tests were carried out in this study. The mechanism of corrosion and erosion resistance of NiCr alloy and cermet coatings were explored and their performance were compared with the coatings of FeCrAl, NiCrTi, NiCr-Cr3C2 used widely at present and three kinds of boiler tuber materials including 20G, 102G and 15CrMoG by analyzing the microstructure and distributing of element of coatings with the techniques of metallographic analysis, Scanning Electron Microscope (SEM) and Electron Probe Micro-Analysis (EPMA) in this paper.In general, there exists certain porosity in the coatings and this would affect the coatings' performance of high temperature corrosion, thermal cycling and thermal shock. In these tests, FeCrAl, NiCrTi and NiCr-50%Cr3C2 coatings were sealed with Si-resins in the study. The effect on the performance of coatings due to sealing process was researched and the mechanism of effect on the performance of coatings due to sealant was explored in this paper.When coating materials are deposited on boiler tubes, their temperature distribution and heat transmission would be affected to some extent and this would influence the boiler economic benefit. The temperature distribution and heat transmission of boiler tubes with sprayed coatings and metal anti-erosion tile were calculated and their effects were compared with each other.
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