Seamless Pipe
Seamless pipe is a wrought steel pipe manufactured by a seamless process. A large percentage of tubulars and high quality pipes are manufactured in this way. In the seamless process, a billet is pierced by a mandrel and the pierced tube is subsequently rolled and re-rolled until the finished diameters are obtained (Fig. 1.3). The process may involve a plug mill or mandrel mill rolling. In a plug mill, a heated billet is introduced into the mill, where it is held by two rollers that rotate and advance the billet into the piercer. In a mandrel mill, the billet is held by two obliquely oriented rotating rollers and pierced by a central plug. Next, it passes to the elongator where the desired length of the pipe is obtained. In the plug mills the thickness of the tube is reduced by central plugs with two single grooved rollers.
In mandrel mills, sizing mills similar in design to the plug mills are used to produce a more uniform thickness of pipe. Finally, reelers similar in design to the piercing mills are used to burnish the pipe surfaces and to produce the final pipe dimensions and roundness.