| The drill steel G105 was selected as the research object, the corrosion fatigue behavior of the drill steel G105 was investigated in detail, the coating process was probed, and the coating's properties were evaluated preliminary, the requirement of preventing the corrosion fatigue on the inner surface of drill pipe was achieved.Based on the theoretical analysis, macro and micro analysis of the fractures of drill pipe were done by different experiments, and physical and chemical properties of materials of the drill pipe were studied in depth. The results show the failure behavior of drill pipe belongs corrosion fatigue which is caused by oxygen. The corrosion product of G105 drill pipe on the inner surface is analyzed by X-ray diffraction, and then the corrosion product is a mixture of several oxides containing Fe. the corrosion products is porous and loose, and adhesive ability is poor, corrosive media can pass through this film easily, thereby failure occurred. In addition, the oxide, sulfide reduces the impact toughness of the steel drill pipe and promoteds the expansion of corrosion fatigue crack. The corrosion fatigue properties of material are deteriorated result in premature failure of drill pipes.The internal coating is proposed as a preventive measures to corrosion fatigue, and the coating process is explored, shot peening is used as the pre-treatment process of inner surface of drill pipes, afterwards, the high pressure and airless spray is used to prepare the coating; the performances of the coating are measured by a series of experiments. The results show that the coating with a best thickness can improve the resistance of corrosion fatigue, and the service life of drill pipe can be increased greatly.
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