The expansion is a pressure processing process that uses hydraulic or mechanical means to force the steel pipe to expand radially outward from the inner wall of the steel pipe. The mechanical method is simpler than the hydraulic method, and the equipment is simpler and more efficient. Several advanced large-diameter lsaw steel pipe control pipeline expansion steps have been adopted in the world. The process is: mechanical expansion using the splitting of the end of the expanding machine The fan-shaped block is radially expanded, so that the tube blank is stepwisely formed in a lengthwise manner to realize a process of plastic deformation of the entire pipe length.

This process is divided into five phases:
1. Initial rounding stage. The fan-shaped block is opened until all the fan-shaped blocks are in contact with the inner wall of the steel pipe. At this time, the radius of each point in the inner pipe of the steel pipe is almost the same in the step length, and the steel pipe is initially rounded.
2. Nominal inner diameter stage. The segment reduces the speed of movement from the front position until it reaches the desired position, which is the desired inner circumference of the finished tube.
3. The rebound compensation stage. The fan-shaped block begins to move at a lower speed in the 2-stage position until it reaches the required position, which is the inner circumferential position of the steel pipe before the rebound of the process design.
4. The pressure stabilization phase. The fan-shaped block remains in the inner circumferential position of the steel pipe for a period of time before the rebound, which is the pressure-stabilizing stage required by the equipment and the expansion process.
5. Unloading return phase. The segment is rapidly retracted from the inner circumferential position of the steel pipe before the rebound until it reaches the position of the initial expansion, which is the small contraction diameter of the segment required by the expansion process.

Seamless steel pipes are used in a wide range of applications. The general-purpose seamless steel pipe is rolled from ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, and has a large output, and is mainly used as a pipe or a structural part for conveying a fluid. According to the use, there are three types of supply: a, supply according to chemical composition and mechanical properties; b, supply according to mechanical properties; c, supply according to water pressure test. Steel pipes supplied in categories a and b, if used to withstand liquid pressure, are also subjected to hydrostatic testing.

Special-purpose seamless pipes include boiler seamless pipes, chemical power, geological seamless steel pipes and petroleum seamless pipes. Seamless steel tubes have a hollow section and are used as a conduit for conveying fluids. They can replace spiral submerged arc welded steel pipes for transporting oil, natural gas, gas, water and certain solid materials.

Compared with solid steel such as round steel, the steel pipe has a lighter weight when it has the same bending and torsional strength, and is an economical section steel. Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automotive drive shafts, bicycle frames and steel scaffolding used in construction, such as steel scaffolding, to make ring parts, improve material utilization, simplify manufacturing processes, save materials and processing In working hours, steel pipes have been widely used for manufacturing.