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With the increasing demand for oil and gas resources worldwide, more and more oil and gas wells need to be developed. The US Department of Energy has increased the depth of global oil and gas wells by 1 time since the 1978. And continue to show a rapid growth trend. The increase of well depth and the increase of temperature and pressure have put forward many new and higher requirements for oil casing. Deep and ultra-deep wells with depths of several kilometers are deeply buried and complex. They contain a large amount of H2S, CO2 and C1-media and are accompanied by high temperature and high pressure environments. When the well conditions are so severe, they must use Fe-Ni or Ni. alloy. Hastelloy G-3 alloy was introduced in the 1980s as Ni-Cr-Mo-Cu alloy, which can be used in iron-based Cr-Ni or Cr-Ni-Mo stainless steel, non-metallic materials and other unusable corrosive media. It has excellent mechanical properties and has been widely used in many fields such as petroleum, chemical industry and environmental protection. The main constituent elements of Hastelloy G-3 alloy are expensive and scarce. From the perspective of short-term benefits, the oil casings in the oil and gas field industry are mainly made of carbon steel and low alloy steel. Failure formation based on corrosion, wear, corrosion fatigue, cracking, etc. originates on the surface of the material. If a layer of alloy with the same or close composition as the Hastelloy G-3 alloy is prepared on the surface of the carbon steel oil casing, the surface alloying gradient is used. The replacement of expensive overall corrosion-resistant alloys by materials is tempting both in terms of engineering application prospects and economic efficiency.
At present, industry experts have successfully prepared Ni-based alloy layers on the surface of P110 steel for oil casings by using hot-dip plating technology in the chemical heat treatment. The coating layer is uniform, continuous and dense, and the outermost layer alloy The content of the element is the highest, and gradually decreases as the distance from the surface increases, that is, the gradient from the surface to the inside shows a distinct deposition layer + diffusion layer morphology. The results of 5% NaC1 neutral salt spray corrosion test and 5% NaC1 immersion corrosion test show that the corrosion rate of Ni-based alloy layer is slightly higher than that of Hastelloy G-3 alloy, but much lower than that of untreated P110 steel. It can be seen that the hot-dip Ni-based alloy layer significantly improves the corrosion resistance of P110 steel.
Thermal infiltration technology is also attributed to the surface alloying process. The principle is to deposit or coat metal or non-metal (solute atoms) on the surface of the base metal, and diffuse into the surface of the base metal under high temperature, when the surface of the substrate When the rate of adsorption of alloying elements exceeds the rate of diffusion of alloying elements into the matrix, the surface of the substrate usually forms a composite layer of deposited layer + diffusion layer, and the chemical composition and phase structure of the surface change, giving the surface a higher resistance. Corrosive, wear resistant and high temperature oxidation resistance. There is a strong metallurgical bond between the galvanized layer and the substrate, and there is no problem of peeling or peeling off of the alloy layer; the alloying elements in the permeable layer are distributed in a gradient from the surface to the inside, and the hardness of the permeable layer is also distributed in a gradient, which can avoid the cause under high load conditions. The base material has low bearing capacity and surface damage or failure.