Cold-rolled pipes start as hot-rolled steel that has been annealed and descaled after initial shaping. The hot rolled steel is cooled to room temperature in the cold rolling mill and passed repeatedly between polished, unheated steel rollers.
The pressure applied by the rollers exceeds the yield strength of the steel, forcing it to plastically deform into thinner cross sections with each pass. This compressive cold working leads to up to a 40% reduction in thickness while elongating the steel.
The process is carefully controlled to achieve the stringent dimensional tolerances and surface finish requirements of cold-rolled pipes. The steel acquires its final shape of rounds, squares, or rectangles by the end.