Oil well pipe G3 alloy

With the technological advancement and actual needs of the entire industrial field, nickel-based corrosion-resistant alloys have been widely used since the 1980s, including a large number of non-critical media such as seawater: use, the purpose of equipment Reliability and reduced maintenance costs. In view of the continuity of large-scale industrial production, when selecting structural materials for corrosion applications, it is necessary to consider not only the cost but also the equipment for easy maintenance, short operation time, long (not less than 20 years), and high reliability. . Therefore, the research, application range and usage of nickel-based corrosion-resistant materials with many superior properties are on the rise.
Years of application have shown that transition alloys are the best corrosion resistant materials that are best suited to harsh environments and are sometimes the only varieties available. In recent years, chemical production labor is complex and emphasizes environmental purification, so it has become increasingly difficult to select a project with sufficient corrosion resistance. Where stainless steel has been adapted, corrosion problems are now exacerbated by increasing operating temperatures and working pressures, increased chemical concentrations due to recycling, and more aggressive media using halogenated groups. In addition, modern structural materials must be able to withstand various forms of corrosion, including stress corrosion, which often limits the application of other alloy materials (Ti alloys, Cu alloys, etc.). The final choice often has to consider the use of nickel-based corrosion resistant materials with higher corrosion resistance. For example, in a medium-concentrated HC1 boiling solution, the corrosion rate of 316L stainless steel is more than four orders of magnitude higher than that of G3 nickel-based alloy.
G3 alloy is a corrosion-resistant alloy based on Ni-Cr-Fe and adding a certain amount of Mo and Cu, and
Other trace elements are added at the same time to improve their resistance to HAZ (heat affected zone) corrosion and to improve weldability. The higher Cr content makes the G3 alloy show better corrosion resistance in oxidizing acid and corrosive environment, and it also has good corrosion resistance to reducing medium due to the action of Ni and Cu elements. The lower C content increases the resistance to intergranular corrosion, while the addition of Mo provides excellent resistance to local corrosion. Therefore, G3 alloy is widely used in the working environment of phosphoric acid and sulfuric acid, such as flue gas desulfurization system, steam alloy generator heat transfer device, paper making and pulp industry. In recent years, the development of energy industry such as oil and natural gas has put forward higher requirements for the performance of reserve gold in high temperature and high oxidation corrosion environment. Nickel base alloy G3 has excellent resistance.
Corrosion ability, good processing properties and high strength just meet this requirement. Figure 1-8 shows the standard mechanical properties of the annealed G3 alloy of Special Metals. For the G3 alloy pipe, China is not yet fully industrialized, mainly because the G3 alloy can be processed at a narrow temperature range, and the high temperature thermoplastic is poor. It cannot be realized by hot rolling or hot perforation, and must be processed by hot extrusion. Since the G3 alloy does not have a precipitation strengthening mechanism, in order to improve the strength of the pipe, it is often difficult to control the degree of cold working by multi-pass cold working.

In the 1970s, Haynes used the argon-oxygen decarburization smelting technology to invent the G3 alloy, which can control the carbon content to a very low level without the addition of bismuth and antimony. G3 alloy is mainly used in acid oil and gas production and phosphoric acid steam generators. At present, in addition to Haynes, there are mainly US special steel companies, Sumitomo Metal Corporation of Japan, and V&M Company of Germany to research and produce G3 alloys. These companies have researched G3 alloys earlier, have many years of development and production experience, and have mastered the smelting and hot and cold processing technology of alloys. However, due to technical blockade and confidentiality, the smelting and forming technology of G3 alloys There are very few reports. Research on the corrosion resistance of G3 alloys in corrosive environments has just been reported. As the results of Hibne et al. show, the corrosion resistance of G3 alloy is better than that of 825 and 028 alloys in cold-worked nickel corrosion-resistant alloys. The G3 alloy has a temperature of 2201, pH = 3.3, a CP concentration of 15.175%, and a partial pressure of H2S and C02 of 2. The corrosion behavior of IMPa still shows good corrosion performance. In addition, Hibnei et al. also studied the effect of G3 alloy grain size on stress corrosion cracking and intergranular corrosion in a simulated acidic solution (25% NaCl + 1.03MPaH2S + 1.03MPaC02, temperature 218^) in the Gulf of Mexico. . The results of slow strain rate corrosion test show that the shrinkage and elongation of the G3 alloy are both greater than 92% and no secondary cracks. The G3_ alloy exhibits good resistance to corrosion cracking. When the grain size changes from 6 to 7. 5 to 4 to 5.5, its effect on stress corrosion cracking is small. The intergranular corrosion test shows that the corrosion rate of G3 alloy is about 0.27~0.36mm/a, which is significantly lower than the maximum allowable corrosion rate of chemical process (0.61mm/a). The influence of grain size on intergranular corrosion is also very good. Thompson et al. The pitting behavior of G3 alloy with an acid content of 100g/L and a temperature of 50T was studied by cyclic potentiometric scanning. The results show that the pitting potential of G3 alloy is 0.59V. When the potential exceeds this value, the corrosion is observed. The current increases rapidly and the corrosion resistance is greatly reduced. Due to the exploitation of highly acidic oil and gas fields in China, the demand for G3 corrosion resistant alloys is very large. Several units in China have carried out related research and development work on the alloys. The smelting of G3 alloy was carried out by vacuum induction furnace. The high temperature hot deformation behavior, the second phase precipitation and dissolution behavior were studied. The 133mmxl6mm waste pipe was produced by hot extrusion and centrifugal casting method, and it was cold-processed. Strengthened. The results show that the forged G3 alloy has high temperature plasticity and narrow deformation range. When the deformation temperature is lower than 1150 °C, the alloy contains a certain amount of carbides and precipitates, which makes the thermoplastics worse and increases with the heat distortion temperature. The second phase (M6C, M23C6 and 0 phase) is dissolved, and the plasticity of the alloy is gradually increased. When the temperature is higher than 1220 C, the grain growth of the alloy is obvious, resulting in a decrease in thermoplasticity. The state G3 alloy is in the range of 1150 C to 1220 C. The thermoplasticity of the enthalpy is good, and it is a suitable heat distortion temperature. The galvanic corrosion and the behavior of the passivation film of the G3 alloy in the environment containing C02, H2S and Cl are studied. Chen Changfeng et al. used XPS technology to study the passivation film of G3 alloy in different temperatures and pressures in C02 and H2S environments. The results show that G3 alloy is used in 2MPaC02, 3MPa H2S and 130C environment. When the surface of the alloy forms a passivation film with a two-layer structure, the surface of the passivation film is mainly Cr(OH)3, the inner layer is mainly composed of Cr2O3, Fe3O4 and various alloying elements, and the passivation film is bipolar np. The characteristics of the semiconductor, when the temperature and pressure of the medium gradually increase (3.5MPaC02, 3.5MPa H2S, the temperature is 205C, the passivation film is a three-layer structure, the outer layer is mainly sulfide, and the transition layer contains more hydrogen. Oxides and metal sulfides, the inner layer is mainly oxides and metal elements. As the pressure and temperature of the medium increase, the metal oxide film in the passivation film changes to the metal vulcanization film, resulting in a decrease in the corrosion resistance of the alloy. The effects of CO2, Cl-concentration and pH on the corrosion behavior of the alloy in high temperature and high pressure C02 and H2S environments were studied. The results show that the nickel-based alloy is easy to form occlusion corrosion micro-cells in corrosive medium. Disperse into the interior of the microbattery and form a compound with metal ions, causing an anode reaction. The anode reaction destroys the formation of the passivation film, accelerates the corrosion behavior, and reduces the corrosion resistance of the alloy. The pH of the corrosive medium increases. At the time, the self-corrosion potential of the alloy is lowered (potential negative shift), the corrosion current is gradually increased, the stability of the passivation film is destroyed, and the corrosion resistance of the alloy is gradually lowered.