Points for Attention in Welding Technology of Longitudinal Welded Steel Pipes​ and Diameter Expansion Technology

Points for Attention in Welding Technology of Longitudinal Welded Steel Pipes and Diameter Expansion Technology

Longitudinal welded steel pipe diameter expansion is a pressure processing technology that uses hydraulic or mechanical means to apply force from the inner wall of the steel pipe to expand and expand the steel pipe radially outward. The mechanical method is simpler and more efficient than the hydraulic method. The expansion process of several large-diameter longitudinal welded pipelines in the world has been adopted. The process is as follows:

The mechanical expansion utilizes the split sector block at the end of the expander to expand in the radial direction so that the tube blank is stepped along the length direction to realize the process of plastic deformation of the entire tube length in sections. Divided into 5 stages

1. The preliminary rounding stage. The fan-shaped block is opened until all the fan-shaped blocks touch the inner wall of the steel pipe. At this time, the radius of each point in the inner tube of the steel pipe within the step length is almost the same, and the steel pipe is initially rounded.

2. Nominal diameter stage. The sector block starts to reduce the movement speed from the front position until it reaches the required position, which is the required inner circumferential position of the finished pipe.

3. Rebound compensation stage. The fan-shaped block will further slow down at the position of stage 2 until it reaches the required position, which is the position of the inner circumference of the steel pipe before rebounding as required by the process design.

4. Pressure maintaining and stable stage. The sector block remains stationary for some time before rebounding on the inner circumference of the steel pipe. This is the pressure-holding and stable stage required by the equipment and the diameter expansion process.

5. Unloading and returning stage. The sector block rapidly retracts from the position of the inner circumference of the steel pipe before the rebound, until it reaches the initial expansion position, which is the small contraction diameter of the sector block required by the diameter expansion process.

What are the advantages of using longitudinal welded pipes to transport fluids?

1. The cost of infrastructure is low. Compared with railway transportation, the cost of infrastructure can be saved by three points, and the transportation volume is twice that of the railway.

2. Simple construction, fast construction speed, generally laid underground, reliable and adaptable to various terrains.

3. The transportation operation cost is low, and it can be highly automated. Compared with other transportation methods, longitudinal welded pipe transportation is cheap, and the freight is only about 10% of the railway and about half of the waterway.

At present, the proportion of oil and gas transported by longitudinal welded pipes in the world is increasing, accounting for about 75%-95% of the total oil and gas. At present, the scope of transportation is gradually expanding, not only oil and gas, but also various chemical raw materials and Products, and has been studying the use of longitudinal welded pipes to transport solids.

What are the characteristics of welded pipe compared with seamless steel pipe?

1. The production process is simple.

2. Less equipment, simple structure, lightweight, easy to realize continuous, automated, and mechanized production.

3. The product cost is low.

4. It is suitable for a wide range of varieties and specifications, with a diameter of 6-3100mm and a wall thickness of 0.3-35mm.