The plate in certain width after slitting line and stripping is unfolded and leveled. Then, they are sent into forming machine. Used the roller, the plate is bent into pipe state. The edge of the steel plate is melted by making use of the proximity effect and skin effect of high frequency current. Then, the plate is extruded and welded into the pipe by extruding roller. Straight seam welded pipe mill also is called ERW mill.

The forming styles of straight seam welded pipe can be divided into roll forming, flexible forming, full auto flexible forming. The mill developed by our company adopts roll forming when having small diameter （Φ≤114）. Flexible forming or full automatic flexible forming is adopted when having middle or large diameter（Φ≤711）.