Oil casing can be made of seamless steel pipe, high-frequency resistance welding (HFW), and high-frequency welding hot rolled Electric(SEW). Welded oil casing has been widely used in oil field production. HFW oil casing tube is made of hot-rolled coil/plate and after a series of processes such as extrusion forming, HFW welding, weld annealing and full pipe heat treatment. It has the advantages of good toughness, high dimensional accuracy and extrusion strength, but the performance of the weld microstructure is quite different from that of the base material, with high groove sensitivity.
Compared with other welding methods, HFW welds have no metal filler, and their weld performance depends on the welding process and heat treatment. The SEW casing pipe combination of HFW welding, hot stretch reducing and fully heat treatment process, namely welding low carbon low alloy TMCP hot-rolled coil/plate, heat by medium frequency induction heating speeds up the heating pipe (20 ℃ to 50 ℃) to Ac3 Austenitic phase transformation temperature (above 900 ℃ -- 1100 ℃), roll unit to reduce diameter brought about thermomechanical treatment, has good toughness and dimensional accuracy.
SEW can be considered as a mature and widely used oil casing manufacturing process. Compared with a seamless pipe of the same steel grade, SEW oil casing pipe has good toughness (impact toughness increased by about 30%), high geometric accuracy and small wall thickness tolerance, which can reduce steel pipe consumption by about 3% for Wells of the same depth and achieve continuous and efficient production of different specifications of the same pipe billet. The experiment shows that the strength of SEW N80Q tubing has been greatly reduced and the strength and toughness have been greatly improved after the heat treatment.
Yield strength /Mpa
Tensile strength /Mpa
0℃ Transverse impact work
Before hot stretch reducing
After hot stretch reducing
hot stretch reducing+tempering
API 5CT requirements
It can be confirmed that the performance of SEW casing is better than the ordinary casing. On the basis of meeting API standards, SEW casing has high geometric dimension accuracy and higher extrusion strength, which can meet the requirements of conventional oil Wells and ordinary injection Wells. At present, anti-extrusion N80*9.17mm SEW tubing and P110TT*10.54mm SEW tubing has been widely used in China under the sea with an average depth 2,000m.