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Difference Between Seamless and Welded Pipe

What is the difference between welded pipe and seamless pipe?

The manufacturing process of a welded pipe begins at coils, which are cut by desired lengths and formed into steel plates and steel strips.
The steel plates and steels strips are rolled by a rolling machine, and then form into a circular shape. In the ERW process (Electric Resistance Welded), high-frequency electrical current is passed between the edges, causing them to fuse together. Once the welded pipe is manufactured, it will be straightened.

Normally the finished surface of the welded pipe is better than that of seamless pipe, because the manufacturing process of the seamless pipe is extrusion.

A seamless steel pipe is also called as a seamless tube. The seamless steel pipe can be made of carbon steel or stainless steel. Take a carbon steel for example, the seamless steel pipe is extruded and drawn from a solid cylindrical of steel, which is known as a billet. While heating, a billet is pierced through the center, turning the solid bar into a round pipe.

A seamless steel pipe is considered having better mechanical properties than a welded pipe. For example, a seamless steel pipe is able to withstand higher pressure, so it is common used in the industry of hydraulic, engineering and construction. Also, a seamless steel pipe DOES NOT have a seam, so it has a stronger resistance to corrosion, which extends the life of seamless steel pipe longer.