How is Seamless Pipe Made? Steel Foundations
Using a variety of methods, seamless tubes and pipes are produced without a seam or weld in the pipe’s circumference. The most common method is piercing a solid cylindrical steel blank called a tube round, which has been prepared and heated to the proper temperature. Because of the extreme amount of material movement (deformation) required by the piercing process, it must be performed as a hot working process, where the metal is above its recrystallization temperature.
After reheating, the tube round is descaled using high-pressure water to remove any iron oxide surface scale. Then it enters the piercing mill, where a pair of rotating wheels forces the tube round to rotate and drive against a counter-rotating piercing head. The piercing head pushes a hole through the entire length of the tube round producing a seamless tube or pipe. After piercing, the tube is processed through a series of rolling mills where the pipe is finished to its prescribed dimensions.
To achieve better control of the tube’s inner diameter, outer diameter, and wall thickness, it can be put through an additional drawing process. Drawing the pipe through a fixed die and over mandrel is called the drawn over mandrel process, or DOM, which can produce tube and pipe with very exacting tolerances.
Seamless sizes over 14 inches in diameter are usually rotary rolled from 14-inch seamless shells that expand the diameter and reduce the wall thickness to the approximate required dimensions. Small sizes of seamless pipe are generally obtained using a stretch reduced mill. Seamless pipes and tubes go through various finishing operations including straightening, inspection, testing, and end finishing.
Seamless pipes are widely used in construction, oil refining, chemical and petrochemical industries, where a seam or weld in the pipe’s circumference is considered a weak point.