1. Tube blank qualityERW steel pipe special steel has high purity. Through de-S, de-P, de-aeration, Ca treatment and other methods, the S and P content can be controlled below 0.005%, the N content can be controlled below 0.008%, the shape of the inclusions can be controlled to be spherical and the number can be greatly reduced. The C content is controlled below 0.1%, which has good welding performance, and the increase in strength is to prevent the growth of austenite grains by adding trace alloy elements such as Nb, V, Ti, etc., while increasing the gap strengthening to improve the steel Toughness and strength. The billet of SML steel pipe is generally made of A3, 20 steel, 16Mh and other materials. The purity of the material is poor, and the C content is high, generally about 0.2%, which is not conducive to girth welding during construction, and the strength is acceptable. But toughness is poor.ERW steel tube blanks are manufactured by cold-rolling hot-rolled steel strips, while SML steel tube blanks are perforated in round steel in the hot-rolled state. The grain size and microstructure density of SML tube blanks formed by hot rolling are far from those of ERW tube blanks.2....