Patent ID: 7506526

Claim:
A seamless tube piercing/rolling plug in which a split plug composed of a plug front part and plug rear part is used by holding the plug front part and plug rear part as an integral plug by means of a mandrel bar going through the plug rear part, wherein said plug front part and plug rear part are replaceable and independently rotatable about a centerline axis thereof without generating any trouble jointing said plug parts into the complete split plug during a seamless tube making process in on-line operation; said plug front part is made in a one-piece structure and diameters thereof continuously and smoothly progressively increase as they go from a front end to a rear end; a front end portion of said plug front part does not have an opening lest the mandrel bar should go through and stick out when said plug front part and said plug rear part are held as the integral plug; and at least said plug front part is made of low alloy steel and oxide films are formed on surfaces of the plug front part and plug rear part.