Differences in welded and seamless pipes

Both ERW and seamless steel pipe manufacturing methods have been in use for decades; over time, the methods used to produce each have advanced. So which is better?

Manufacturing welded pipe

Welded pipe starts out as a long, coiled ribbon of steel called a skelp. The skelp is cut to the desired length, resulting in a flat rectangular sheet. The width of that sheet’s shorter ends will become the pipe’s outside circumference, a value that can be used to calculate its eventual outside diameter.

The rectangular sheets are fed through a rolling machine that curls the longer sides up toward one another, forming a cylinder. In the ERW process, high-frequency electrical current is passed between the edges, causing them to melt and fuse together.

An advantage of ERW pipe is that no fusion metals are used and the weld seam cannot be seen or felt. That’s opposed to double submerged arc welding (DSAW), which leaves behind an obvious weld bead that must then be eliminated depending on the application.

Welded pipe manufacturing techniques have improved over the years. Perhaps the most important advancement has been the switch to high-frequency electric currents for welding. Prior to the 1970s, low-frequency current was used. Weld seams produced from low-frequency ERW were more prone to corrosion and seam failure.

Most welded pipe types require heat treatment after manufacture.

Manufacturing seamless pipe

Seamless piping begins as a solid cylindrical hunk of steel called a billet. While still hot, billets are pierced through the center with a mandrel. The next step is rolling and stretching the hollow billet. The billet is precisely rolled and stretched until it meets the length, diameter and wall thickness as specified by the customer order.

Some seamless pipe types harden as they’re manufactured, so heat treatment after manufacturing is not required. Others do require heat treatment. Consult the specification of the seamless pipe type you’re considering to learn whether it will require heat treatment.

Historical perspectives and use cases for welded vs. seamless steel pipe