A seamless pipe is a long strip of steel with a hollow section and no seams around it. According to different production methods, it can be divided into hot-rolled tubes, cold-rolled tubes, cold-drawn tubes, extruded tubes, etc. Generally used in fluid conveying pipes, boiler plants, engineering, mechanical processing plants.

Seamless steel pipe production process:

1. Hot rolling (extruded seamless steel pipe): round tube billet → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → stripping → sizing (or reducing) → cooling → straightening → hydraulic test (or flaw detection) → marking → warehousing

2. Cold drawn (rolled) seamless steel pipe: round tube blank→heating→piercing→heading→annealing→pickling→oiling (copper plating)→multi-pass cold drawing (cold rolling)→blank tube→heat treatment→straightening→water Pressure test (flaw detection) → marking → storage.

After the quality inspection of steel pipes, strict manual selection is required. Then spray the serial number, specification, production batch number, etc. with paint. And hoisted into the warehouse by crane.

Hot-rolled seamless pipes are generally produced on automatic pipe rolling units. After checking and removing surface defects, the solid tube blank is cut into the required length, centered on the perforated end face of the tube blank, then sent to the heating furnace for heating, and pierced on the piercing machine. Spin and advance the solid blank inside the process of piercing holes under the influence with the roller as well as the end. Then the solid blank is hollow finally, which is called gross pipe. Send to the automatic pipe rolling machine to continue rolling. Finally, the wall thickness is adjusted by the equalizing machine, and the size is sized by the sizing machine to meet the specification requirements. It is a more advanced method to produce hot-rolled seamless steel pipes by using continuous rolling mills.

If you want to obtain seamless pipes with smaller size and better quality, you must use cold rolling, cold drawing or a combination of both. Cold rolling is usually carried out on a two-roll mill, and the steel pipe is rolled in an annular pass formed by a circular hole groove with variable cross-section and a stationary tapered plug. Cold drawing is usually carried out on a single-chain or double-chain cold drawing machine of 0.5-100T.

The extrusion method is to place the heated tube blank in a closed extrusion cylinder, and the perforated rod and the extrusion rod move together to make the extruded part extrude from the smaller die hole. This method can produce steel pipes with smaller diameters.

Classification and material of seamless steel pipe