Manufacturing process of seamless steel pipe

Posted by zora li on February 9th, 2023

The seamless pipe is made of high-quality round steel as the main material, and then perforated on the round steel. The principle of perforation is to use high temperature to soften the round steel, and then use a plug to remove all the solid parts in the middle to become hollow round steel, that is, seamless steel pipe.

1. Manufacturing method of seamless pipe
According to different production methods, it can be divided into hot-rolled tubes, cold-rolled tubes, cold-drawn seamless tubes, extruded tubes, etc.
(1) Hot-rolled seamless pipes are generally produced on automatic pipe rolling units. After checking and removing surface defects, the solid tube blank is cut to the required length, centered on the perforated end face of the tube blank, sent to the heating furnace for heating, and pierced on the piercing machine. Under the action of the roller and the tip, the solid blank is rotated and pushed during the punching process. The solid blank is then finally hollow and is called a capillary. Sent to the automatic pipe rolling machine to continue rolling. Finally, the wall thickness is adjusted by the sizing machine, and the size is calibrated by the sizing machine to meet the specification requirements. It is a more advanced method to produce hot-rolled seamless steel pipes with a continuous rolling mill.
(2) In order to obtain seamless pipes with smaller size and better quality, cold rolling, cold drawing or a combination of the two must be used. Cold rolling is usually carried out on a two-roll mill, and the steel pipe is rolled in annular passes formed by circular bore grooves of variable cross-section and fixed tapered plugs. Cold drawing is usually carried out on a 0.5-100T single-chain or double-chain cold drawing machine.
(3) The extrusion method is to place the heated tube blank in a closed extrusion cylinder, and the perforation rod and the extrusion rod move together to make the extrusion part extrude from the smaller die hole. This method can produce steel pipes with smaller diameters.

2. Production process of seamless steel pipe:
(1) Hot rolling (extruded seamless steel pipe): round tube billet → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or reducing) → cooling → straightening → water pressure Test (or flaw detection) ) → marking → storage
(2) Cold drawn (rolled) seamless steel pipe: round tube billet → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → tube blank → heat treatment → straightening Straight → hydrostatic test (flaw detection) → marking → storage

Note: Detailed explanation of the two steel pipe production processes
(1) Using cold-drawn steel pipe as raw material, it is cold-rolled and rolled. Due to the cold hardening caused by continuous cold deformation, the strength and hardness of rolling rolls increase, and the toughness and plasticity indicators deteriorate, so the stamping performance deteriorates, and it can only be used for simple deformation parts. Hard-rolled coils can be used as raw materials for hot-dip galvanizing plants, because hot-dip galvanizing units are equipped with annealing lines. Rolling The rolling weight is generally 6-13.5 tons, and the inner diameter of the steel coil is 610mm.
(2) Hot-rolled steel pipes use continuous casting slabs or bloom slabs as raw materials, are heated in a walking heating furnace, and are descaled by high-pressure water before entering the roughing mill. After cutting the head and tail of the rough rolling material, it enters the finish rolling mill, and implements computer-controlled rolling. After final rolling, it is coiled into straight hair rolls by laminar flow cooling of the coiler. The head and tail of straight hair curlers are often tongue-shaped and fish-tail-shaped, with poor thickness and width precision, and the edges often have defects such as wavy, curled, and tower-shaped. The weight of the steel coil is relatively heavy, and the inner diameter of the steel coil is 760mm. Straight hair rolls are processed by finishing lines such as head cutting, tail cutting, edge trimming and multi-pass straightening, leveling, etc., and then cut or rewinded. That is to say: hot-rolled steel plate, hot-rolled flat steel coil, strip and other products. After the hot-rolled finish-rolled coil is pickled to remove scale and oiled, it becomes a hot-rolled pickled coil.