Carbon steel tubing is the most common material used for process piping. It has the advantage of wide availability, high strength and a variety of connection options, e.g. screwed, socket-welded and butt-welded. Steel tubing should be selected for the strength and durability required for the application, as well as the ductility and machinability required to be joined into tubing coils. The tubing must withstand the pressure, temperature, and corrosion conditions of the application.
Carbon steel tubing can be manufactured using a variety of techniques, each producing a tube with specific properties. These properties include strength, wall thickness, corrosion resistance, and temperature and pressure limitations. For example, tubes that have the same wall thickness but are manufactured using different processes may vary in strength and pressure limits. Manufacturing processes that we will mention include seamless, butt-welded, and spiral-welded tubing.
A seamless tube is formed by piercing a solid, nearly molten steel rod, called a billet, with a mandrel to create a tube with no seams or joints.
A butt-welded pipe is formed by passing a hot plate of steel through formers, which roll it into a hollow circular shape. When the two ends of the panel are pressed together, a fused joint or seam is formed.
The least common of the three methods is a spiral welded pipe. Spiral welded tubing is formed by twisting strips of metal into a spiral shape, similar to a barber pole, and then welding where the edges meet to form a seam. This type of tube is limited to piping systems that use low pressures due to its thin wall thickness.