1. Seamless Steel Pipe 

The typical method for making seamless tubes is the Mannesmann method, in which a rod-like billet is heated to a high temperature, and then compressed from the periphery and perforated at the center using a tool called a "perforating mandrel". This manufacturing method is suitable for mass production. It can make large diameter steel pipe and is also suitable for thick wall steel pipe. Because there are no joints, the original properties of the material can be maintained. However, in terms of manufacturing methods, the dimensional accuracy is not very good.

2. Welded Steel Pipe 

The material of welded pipe does not use bar billets but uses steel strips (coils). For example, for seam pipe welded with resistance welding, the process is to use the uncoiler to continuously pull out the steel strip and make it cylindric. The joint part of the cylinder is changed into a high-temperature state with a large current, and the joint is welded by strong rolling and resistance welding. After melting welding, do not use welding wire because it uses materials from itself. Finally, remove the welding bead of the welding part (weld bulge). After cooling, go on straightening and drawing processing.

This method is suitable for small batch production, and it features flexible size settings and high dimensional accuracy.