Abstract: For steel tube made by a hot-rolling mill with one working process, its O.D. tolerance is typically ±0.75%, whereas for steel tube subjected to butt-welding connection, its O.D. tolerance is much stricter than that of the former. With proper groove design, it is possible to get O.D. tolerance of hot-rolled tube controlled within ±0.50%, while tube end O.D.deviation is limited to-0.40 mm~+1.59 mm, being satisfactory to requirements for relevant application.