Research On Butt Welding Process Of CT90 Coiled Tubing

Coiled tubing technology is recognized as an advanced method of oil and gas field operations in the world at present.With the development of coiled tubing technology to a higher level in China,such as drilling,deep well operations and so on,the tube to tube butt welding in the field is the unique means to ensure the length and solve the segmented transport of coiled tubing that required large diameter,high strength.Paper based on CNPC major engineering field test project-"the field test of lateral drilling technology and equipment with coiled tubing ",with CT90 coiled tubing butt welding as the research project,which is the highest strength(diameter of 2 inches,thickness of 3.96mm)in the domestic oil and gas field applications at present,using small welding line energy to ensure welded formation while reducing welding HAZ size and grain growth as the target,researching on coiled tubing butt welding process including welding current form,welding cooling methods and welding process parameters,the conclusions and datas about researching content and evaluation of real welding provided the basis for butt welding process to further improvements and applications of CT90 coiled tubing.The results showed:(1)When the welding line energy is same,the impulse current TIG penetration is larger than the direct current TIG,welding HAZ size is less than the direct current TIG,namely in the same penetration,impulse current TIG needed welding line energy is smaller and impulse current TIG is conducive to prevent grain growth and obtain smaller welding HAZ.(2)Cooling the welded joints by copper piece with room temperature circulatory water is conducive to reduce welding HAZ size and control grain growth.(3)Evaluating the welded joint with impulse current welding process,results show that the welded joint has good welded formation inside and outside,no size defect;welded joint strength and grain degree has reached the standard requirements,while the elongation and the welding HAZ microhardness is slightly lower than the standard requirements,to be further optimized for the microstructure control and welding process.