Unlike seamless steel pipe, the joint strength of pipe joint welding must be equal to or greater than the strength of the base metal. With the increase in strength of the steel pipe, high-strength weld metal is required. The more the amount of alloy is increased, the higher the strength of the weld metal and the better the correlation with the Pcm value. In general, as the strength increases, the toughness decreases, and the tensile strength rapidly decreases from 1000 MPa or more. The structure of 1000 MPa is upper bainite; 1150 MPa is the structure of strip-shaped martensite, and it can be seen that the influence of the morphology of the structure is large. X65 grade weld metal is widely used by adding B to the flux to suppress the intergranular ferrite formation of the weld metal and improve the low temperature toughness technology. When the tensile strength is 800 MPa or less, 30 ppm B of the weld metal using the B flux is added to suppress the intergranular ferrite, and the toughness is higher than that of the low B weld metal with B<15 ppm. However, the tensile strength is 800 MPa or more, but the low B toughness is high. This shows that the low-B weld metal structure contains acicular martensite at 1000 MPa. In addition, in order to achieve high strength and high toughness, it is effective to add Ni, and if the Ni content exceeds 3%, the high-temperature crack susceptibility improves.
Steel tube diameter, wall thickness, ellipticity and other automatic dimensioning have progressed. Steel pipe groove, weld bead shape measurement, automatic marking technology, and component tracking technology using image recognition have been developed, and the entire process data management can be performed for each steel pipe from the upstream process to the warehouse. In recent years, electronic data sharing with customers on the Internet has allowed us to keep abreast of the progress of management and the test results of shipments.
Progress of JCOE steel pipe manufacturing technology
The large-diameter lsaw steel pipe is mainly manufactured by the UOE method. When the diameter and wall thickness exceed the UOE manufacturing range, the three-roll bending method and the pressure bending method are used. In the mid-1990s, the JCOE large-diameter steel pipe plant was built with Germany, India, Russia, and China as the center, which is a detailed comparison with the UOE method.
JCOE steel pipe manufacturing process
The JCOE method was developed by SMS Meer, Germany. The process is: 1 rolling edge; 2 pre-bending; 3 bending one end of the press into a J shape, the other end is also formed into a J-shape, formed into a C-shape, and finally formed into a O-shaped open seam; 4 pipe seam welding ;5 expand tube. Compared with the UOE method, UO is partially replaced by 3 press bending. The maximum manufacturing range is 60 in. in diameter and 18 m in length. The wall thickness of ordinary steel pipe is 40 mm, and the maximum number of special tools is 65 mm. With a wall thickness of 40 mm, the press load of 12.2 m length is 65 MN, and the press load of 18.3 m length is 100 MN.
JCOE steel features
The JCOE method is characterized by low equipment costs. The investment amount for a production line is 1/8 of UOE and the output is 1/2. In particular, unlike the UOE method, the tooling of U-shaped presses and O-shaped presses of each size is low in tool cost and short in replacement time. Therefore, it is suitable for producing steel pipes with less variety. As the characteristics of the steel pipe, it is presumed that the residual stress is not significantly different from the UOE method due to the final expansion of the pipe. In the UOE method, the bent portion of the U-shaped press and the O-shaped press formed a polygonal shape at the initial stage of the press. The folded portion deforms greatly and has a deformation distribution in the circumferential direction. In the JCOE method, if the J-shape is carefully performed, the deformation distribution is small. How to carefully conduct J forming has a direct effect on productivity, but the actual operation is not clear. After positioning welding, it is the same as UOE steel pipe. After pipe expansion, the quality of steel pipes produced by JCOE method and UOE method is not much different.