Research on the New Low Temperature Self-Protective Paste Boronizing Processes of Thermal Power Plant Economizer Pipe Jianjun HE, Jian CHEN, Yanjie REN, Wei QIU, Beier LUO School of energy and power engineering, Changsha University of Science and Technology, Changsha, 410114, China * Corresponding author: hejianjun329@126.com Abstract: Power plant boiler economizer pipe tend to crack rapidly due to the erosion of high temperature flue gas. In this paper, the power plant boiler economizer pipe (annealing 20 steel) was chosen as the research materials, three new formulations of self-protective paste in which quartz powder, fly ash and coal gangue were as the main ingredients were investigated,what’s more,the low temperature self-protective paste boronizing technology with the rare earth added was studied. The experimental results show that the quartz powder, fly ash and coal gangue protective layer sintered at the boride temperature have the virtues of high strength, good sealing and easier peeling off, and these protective layers also brought good boronizing effect. 9wt% rare earth addition can bring good boronizing effect, when the boronizing temperature down to 700 , ℃ the rare earth added self-protection paste boronizing process can still achieve boronizing layer. The wear-resisting and corrosion resistant performance of the economizer pipe after boronizing process obviously improved. Keywords Self-protective paste boronizing, Protective coating, rare earth, economizer pipe, low temperature 1 Introduction Economizer is an important heat-absorbing surface in the power plant boiler. It is usually equipped in the flue and absorbs the quantity of heat of flue gas in order to heat the boiler. But the existence of the large number of solid particles and corrosive gases in flue gas will cause the high temperature erosion wear and hot corrosion to the economizer tube and even leads to abnormal tube wall thinning and premature failure, frequent detonation tube leakage thus become serious threat to the safe and economic operation of boilers [1]. In coal-fired power plants, boiler accidents accounted for more than half of the power plant accident, while economizer of boiler tube blasting accidents accounted for 45% ~ 50%, among those economizer abrasions leakage is a main reason [2, 3]. So the improvement on the operational process of economizer pipe outer surface erosion and hot corrosion resistance is of great significance to improve the service life of the power plant boiler economizer, boost the reliability of boiler and prolong average trouble-free operation time of the boiler. Boronizing is a kind of important chemical heat treatment technology. Take steel material for an example, after dealing with boron, its wear resistance, corrosion resistance, and the rigid and high oxidation resistance can be improved. Paste boronizing is a technological method in which the boron agent, activator, and filler are mixed through the use of the binder paste to be applied to the clean metal surface, and then sealed, packed, heated and preserved heat to achieve the boronizing layer [4,5]. Self-protection paste boron which overcomes the shortcomings that the traditional medicinal extract boron needs seal packing or the protection of the atmosphere, adapts the paste outer take cover [6,7],then in boronizing temperature a glaze shell generates on the paste coating surface to achieve self protection in the process of boronizing. The technology has the characteristics of simple process, fast boron permeability speed, good effect and low cost [8-10], which is suitable various shapes of the workpiece. It is a promising surface treatment technology [8]. The paste boronizing temperature of boron treatment is commonly in 800 ~ 1000 , ℃ in such a high temperature, the traditional boronizing agent generates active boron atom which is essential to the boronizing process. But generally such a high temperature may reach to the austenitic temperature of steel tube. what’s more, considerable changes in the organization of the original material took place, affected the performance of the matrix, then restricted the development and application of
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