ERW pipe (resistance welded pipe)
The name ERW is because such stainless steel pipes involve certain types of welding processes such as spot welding and seam welding. Seam welding is usually used when manufacturing round, square and rectangular stainless steel pipes. The stainless steel band is unwound from the coil and trimmed to control the width and adjust the edges for welding. The strip then passes through a series of shaped rolls that cold form the material into a circular (square or rectangular) shape. The edges are joined as butt joints under pressure and then welded by heating the material to a temperature above 2000°F. Wait until the flash weld that has been formed is removed from the outer diameter of the pipe. Once the weld has been tested, it can then pass through a series of sizing rolls to obtain the exact final dimensions, and then the stainless steel pipe is straightened and cut to the required length.
The welding state of the product during the manufacturing process (usually called the flash condition) means that when the flash of the weld stays inside the pipe, the ERW pipe is usually not removed or the production process is controlled.
Technically, DOM is not a steel pipe but the completion of a stainless steel pipe. It is considered a high quality pipe. The first stage of manufacture is the same as the stage for making an electric resistance welded pipe, but in the finishing stage, the entire flash weld is removed and the pipe is cold drawn on the mandrel. The cold drawing process provides the pipe with better dimensional tolerances, improved surface finish and the highest weld strength achievable. When the DOM actually does have a seam (though barely visible), the DOM is often incorrectly referenced as “seamless.”
Seamless steel pipe
Seamless steel pipes are manufactured using a method called “extrusion.” In the process, a solid steel rod passes through the center and uses a mold to turn the solid circle into a circular pipe.
There are basically two types of seamless steel pipes:
Cold drawn seamless (CDS), typically manufactured by SAE 1018, with precise tolerances and good surface finish; Hot Formed Seamless (HFS) is usually manufactured by SAE 1026, with less critical tolerances and scales, not as strong as CDS .
The advantages of Cold Drawn Seamless (CDS) are good surface finish, excellent processability, increased dimensional tolerances, and high strength to weight ratio. The advantages of seamless (HFS): cost-effective materials, good processability, a wide range of sizes.
Source: China Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)