Since the industrial applications have become complex and evolved a lot, the piping products are also changing to stay in the race. Although there are many pipe processing techniques, the industry’s most influential controversy between electrical resistance welded and seamless steel pipe.
For decades, welded and seamless steel pipe production techniques have been in use by industrial pipe suppliers; the techniques used to manufacture each has evolved over time. Which is better, then?
Welded pipe manufacturing
The welded pipe begins as a long, coiled steel ribbon, called a skelp. The skelp, which results in a flat rectangular board, is cut to the desired length. The width of the shorter ends of that sheet will become the outer circumference of the pipe, a value that can be used to measure its eventual outer diameter.
The rectangular sheets go through a rolling machine forming a cylinder, curls the longer sides up to each other. A high-frequency electrical current is transmitted between the edges in the ERW process, causing them to melt and fuse together.
A benefit of the ERW pipe is that no fusion metals are used and it is not possible to see or feel the weld seam. This is compared to double submerged arc welding (DSAW), which leaves behind an apparent weld bead that, depending on the application, must then be removed.
Over the years, welded pipe manufacturing methods have changed. The transition to high-frequency electrical currents for welding was maybe the most significant development. Low-frequency current was used prior to the 1970s. Weld seams made from low-frequency ERW were more susceptible to seam failure and corrosion.
After manufacturing, most welded pipe forms require heat treatment.
Seamless pipe welding
Seamless piping starts off as a solid steel cylindrical hunk called a billet. While still hot, a mandrel is pierced through the middle by billets. Rolling and stretching the hollow billet is the next step. As defined by the customer order, the billet is rolled and stretched to meet the diameter, length and wall thickness.
As they are produced, some seamless pipe types harden, so heat treatment after production is not needed. Others need thermal therapy. Consult the seamless pipe form specification you are considering to learn if heat treatment would be needed.