| With the oil and gas industry and geological exploration industry developing rapidly, when the drilling depth increasing constantly, the requirement for the properties of drill pipe is higher than before. In the conventional oil and geological drilling industry, steel pipes are usually utilized in the drilling, which could happen friction heat crack, stress corrosion fracture and hydrogen brittleness when in some special drilling conditions, such as in ultra-high drilling well and corrosive medium well et al. Compared with steel pipe, aluminum alloy pipe has excellent physical and mechanical properties to replace the steel pipe in drilling ultra-high well, horizontal well and large displacement well. The superiority of aluminum pipe main reflect in its excellent physical properties, light quality, high specific strength, sour corrosion resistance, small frictional resistance and no magnetic characteristic etc. Aluminum alloy pipe is suitable for bad drilling environment and can relieve hock load significantly, which make it attracted more and more attention in major diameter oil drilling well, ultra-high well, ultra-short radius horizontal directional well, large displacement well and so on. But the low hardness and bad abrasive resistance make the aluminum alloy difficult to screw and discharge the pipe frequently. So we need to connect the steel joint by interference fit on the aluminum alloy pipe both ends to relieve the injury of screw and discharge the pipe frequently, which also can relieve the contact friction between aluminum alloy pipe and well wall. The interference fit connection can provide inter-impacted pressure to form reliable and strong stationary fit, which is the guarantee of the reliable connection between aluminum alloy pipe and steel joint. The conventional method is called hot assembly, in which the steel joint is heated to 300-400℃, then screwed it on the aluminum alloy pipe, then the interference fit can be realized after cooling. The cold system is needed to reduce the high temperature effect on the properties of aluminum alloy, which also increases the complexity of assembly technology.In this paper, cold assembly technology between aluminum alloy pipe and steel joint had been studied. The screw thread section of aluminum alloy pipe was subzero treated with liquid nitrogen, and then screwed quickly into the steel joint which at the indoor temperature state to realize the interference fit connection. For testing the mechanical characteristic of assembly conveniently, in this paper, the 7XXX type aluminum alloy pipe with 50 mm diameter, 5mm wall thickness and steel joint with 58 mm diameter were as objects of study. The interference of the reliable connection between above pipe and joint dimensions is ranging ofmm3214.0mm0960.0 ≤≤ δ, which was defined by utilizing theoretical calculation of elastic mechanics. The cooling temperature and time for realizing the above interference were also defined by calculating. The liquid nitrogen vaporization subzero treatment case was used as the cold installation of aluminum alloy pipe and the screwing method was manual operation. The author used the 50 mm diameter aluminum alloy pipe and 58 mm steel joint to do the cold assembly tests. The designed interferences were 0.1mm, 0.15 mm and 0.2mm and the assemble time were 15-20 minutes.The tension and torsion tests of the assembly part had been done to evaluate the effect of cold assembly connection and the tension and torsion fractures had been analyzed. The result shows that the mechanical characteristics of aluminum alloy pipe and steel joint assembly were the best when the interference was 0.15 mm. The maximum tensile force of assembly could be 296.32 k N and the maximum torque could be 4162N?m. The fracture usually occurred in the first button of the initial screw thread of aluminum alloy pipe, which indicated that this place is the weakest part of the assembly.Based on the study of minor diameter aluminum alloy pipe and steel joint cold assembly, the cold assembly tests about 147 mm diameter and 9.1m length full size aluminum alloy pipe and the analysis of its mechanical characteristic had been done. The field drilling test had also been done based on the testing. During the field drilling test, the accumulated drilling depth of aluminum alloy pipe was 765 m which including the vertical interval, deflecting interval, angle increasing interval and angle maintaining interval of the testing well. It fitted the complicated well structure of the directional well successfully and had been used 38 hours continuously with no accident happened. The drilling rate was 20.1m/h. The aluminum alloy pipe and steel joint were keeping well and no obvious abrasion wear was found after lifting the pipe. |
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