Welded Vs. Seamless Steel Pipe

While there are a variety of pipe manufacturing methods, the most prominent discussion in the industry is comparing electric resistance welded (ERW) steel pipe and seamless (SMLS) steel pipe.Welded pipe starts out as a long, coiled strip of steel, called a strip. The strip is cut to the desired length, resulting in a flat, rectangular plate. The width of the shorter end of the plate becomes the outer circumference of the pipe, a value used to calculate its final outside diameter. The rectangular plate is passed through a rolling mill, where the longer sides are rolled toward each other to form a cylinder. In the ERW process, a high-frequency current is passed between the edges, causing them to melt and fuse together. One advantage of ERW pipe is that no fusion metal is used, and the weld is invisible and untraceable. This is in contrast to double submerged arc welding (DSAW), which leaves a noticeable weld bead that must then be removed depending on the application. Over the years, welded pipe manufacturing technology has continued to improve. Perhaps the most significant advancement was the move to using high-frequency currents for welding. Prior to the 1970s, low-frequency currents were used. Low-frequency ERW produces welds that are more susceptible to corrosion and weld fracture. Most welded pipe types require heat treatment after manufacturing.

Seamless pipe starts out as a solid, cylindrical piece of steel called a billet. While the billet is still hot, a mandrel is used to pierce the billet through the center. The next step is to roll and stretch the hollow billet. The billet is precisely rolled and stretched until it reaches the length, diameter, and wall thickness specified by the customer's order.
Some seamless pipes harden during the manufacturing process, so they do not require heat treatment after manufacturing. Other pipes do require heat treatment.

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