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　　ERW is a specifc type of welding process that is used to produce welded steel pipe, such as ERW steel pipe. Seam welding is commonly used during the

　　manufacturing of round, square and rectangular steel tubing. The steel strip is unwound from coils and side-trimmed to control width and condition the edges

　　for welding. The strip then passes through a series of contoured rollers which cold-form the material into a circular (square or rectangular) shape. The edges are forced together under pressure as a butt joint and then welded by heating the material to temperatures above 2000° F. The flash weld that has formed is now removed from the outside diameter of the tube. Once the weld has been tested the tube then passes through a series of sizing rolls to attain its precise finished size, after which the tube is then straightened and cut to length.

　　The seamless steel pipe is manufactured using a process called“extrusion". During this process a solid steel bar is pierced though the centre using a die,

　　turming the solid round into a round tube. Basically there are two types of seamless steel pipe. Cold Drawn Seamless normally made from SAE 1018,having precise tolerances and good surface finish. Hot Finished Seamless normally made from SAE 1026, having less critical tolerances and a scaly finish. It is not as strong as CDS. Cold Drawn Seamless has some benefits, such as good surface finish, superior machinability, increased dimensional tolerances and high strength to weight ratio. Hot Finish Seamless also has some advantages, including cost efective material, good machinability andwide range of sizes.

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