LSAW pipes, or straight seam submerged arc welded steel pipes, are widely used in oil and gas transportation, municipal engineering, and other fields due to their large diameter, thick walls, and high pressure resistance. Their manufacturing process centers on precision forming and strict quality control, undergoing multiple processes to achieve high performance and high reliability.
Raw material pretreatment is the foundation of the process and directly determines the quality of subsequent production. After the steel plate enters the production line, it first undergoes full-plate ultrasonic testing to check for internal defects and ensure that the material meets standards. Then, according to the steel pipe specifications, the steel plate is cut to the corresponding size using flame or plasma cutting equipment. Next, the edges are milled on both sides by a milling machine to create a uniform bevel and flat edges, creating conditions for precise welding. Finally, a pre-bending machine presses the plate edges to a curvature that matches the pipe diameter, avoiding stress concentration in the weld area after forming.
The forming process is the core of LSAW steel pipe manufacturing, with the mainstream processes being JCOE and UOE. The JCOE process employs progressive molding, first stamping one half of a pre-bent steel plate into a "J" shape, then symmetrically pressing the other half into a "C" shape, and finally joining the seams under pressure to form an open "O"-shaped tube blank. This process offers advantages such as flexible specifications and uniform stress distribution. The UOE process, on the other hand, uses a two-step pressing process with both a U-shaped press and an O-shaped press, making it suitable for mass production and standardization, resulting in higher efficiency. Both processes ensure the geometric accuracy of the tube blank, laying a solid foundation for subsequent welding.
Welding and quality control determine the structural strength of the steel pipe. After forming, pre-welding is performed using gas shielded welding to fix the tube blank shape and ensure a tight seam. The core welding utilizes double-sided submerged arc welding technology, with multi-wire longitudinal welding systems operating on both the inner and outer sides. The flux layer isolates air, reduces defects, and forms a deep penetration weld, combining toughness and sealing. After welding, double non-destructive testing is required: ultrasonic testing to check for defects in the weld and base material, and X-ray industrial television inspection to achieve full-coverage imaging of the weld, ensuring the absence of internal cracks, porosity, and other problems.
