Patent attributes
A seamless tube producing method uses a piercing/rolling plug wherein piercing/rolling is performed with an inclined rotary piercing mill while the seamless tube piercing/rolling plug is used as a piercing tool. In one mode, a front part and a rear part of the split plug are held as an integral plug, the front part being made of low alloy steel, and oxide films are formed on surfaces of the front part and rear part. In a second mode, the front part and/or rear part are replaceable via a removable mounting wherein a mandrel bar holding the plug goes through the rear part, the mandrel bar being coupled with the front part. A thickness of the oxide film formed in the front part can be 200 μm or more and the oxide film of the front part can be thicker than the oxide film of the rear part.
