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Thu Mar 18, 2010 12:45 am

now you say that to be DOM the tubing needs to be cold drawn. typically any "cold rolled" steel, be it plate or solid bar stock is smooth and "hot rolled" will have a scale on it. the process of heating the billet to 2300 and then drawing it, would that create the same scale as the typical hot rolled process?

now talking 1.5 od .120 wall 1020, erw vs seamless cold drawn or "DOM" is there any real benifit to the seamless? explain please?

Fri Mar 19, 2010 6:27 pm

Cold drawing is done cold. The billets are only heated to 2300 when they are pierced and then they are allowed to cool before being "pickled" in sulfuric acid, to remove any scale that is incured while it is red hot. Following the pickle, the tubes are "doped" in animal fat to provide a dry lubricant for the cold drawing process. The dope is a dry powder that is mixed with water and it is heated to a continuos 170 degrees, The tubs are about 6 X 6 X 60 feet so they are quite large. After tubes are pulled, they are stress relieved at 900 to 1100 degrees, depending on their final use, and run thru the finish line, where they are straightened, amalog tested for defects in the OD, cut to length and packed in hex bundles. The 4130 tubing has more strength, but is expensive because of the cost of the raw billets plus seamless is more costly because of the heat used to get the tubes ready for piercing. Even the welded tubes are pickled in acid, for a shorter time, before they are doped and drawn. Any DOM tubing is stronger than direct from the mill tubing, because of the property changes that occur when a tube is drawn.