Production principle of hot-rolled seamless steel pipe

The production process of hot-rolled solid ingots is to roll them into hollow tubes with no seams around them. Carbon steel, alloy tubes, high alloy steel, and some non-ferrous metal seamless steel pipes can be produced by hot rolling, with an outer diameter range of 16 to 1600 mm and a wall thickness of 2 to 200 mm.

In addition to round-section tubes, there are also various special-section tubes and variable-section tubes. In addition to being finished tubes, hot-rolled seamless steel pipes can also be used as pipe materials for cold drawing and cold-rolled tubes (see cold rolling and cold drawing of tubes). Seamless steel pipes produced by hot rolling account for 80% to 90% of the output of seamless steel pipes.

The tube billets used for hot-rolled steel pipes include ingots, continuous casting billets, rolled billets, forged billets, and hollow casting billets. The basic process of hot-rolled steel pipes is:
(1) Punch the ingot or billet into a hollow thick-walled rough tube on a piercing machine. The methods of perforating tube billets are divided into two-roller oblique rolling perforation, pressure perforation, push rolling perforation, three-roller oblique rolling perforation, etc.
(2) The rough tube is rolled thin on the stretching machine and stretched into a rough tube with a wall thickness close to that of the finished tube. The methods of rough tube stretching, i.e. rough tube rolling, include: rolling on an automatic tube rolling mill, rolling on a continuous tube rolling mill, oblique rolling on a three-roll and two-roll tube rolling mill, rolling on a periodic tube rolling mill, and jacking on a jacking machine.
(3) The rough tube is finished on the finishing mill to become a finished tube. Finishing rolling of rough tubes includes tube leveling and tube sizing to improve quality, as well as tube diameter reduction and hot expansion to expand product specifications.

The units for producing hot-rolled seamless steel tubes can vary according to the production methods and equipment used in the three basic processes of piercing, stretching, and finishing rolling. Different units are named after the mill that stretches the rough tube into the rough tube. For example, an automatic pipe rolling mill is called an automatic pipe rolling mill unit, a continuous pipe rolling mill is called a continuous pipe rolling mill unit, a machine that rolls rough pipes on a three-roll (or two-roll) inclined rolling and stretching mill is called a three-roll (or two-roll) pipe rolling mill unit, a machine that rolls pipes on a periodic pipe rolling mill is called a periodic pipe rolling mill unit, and a machine that rolls pipes on a CPE pipe jacking machine is called a CPE pipe jacking unit.