Why Is There No Seam In Seamless Steel Pipes?

Why is there no seam in seamless steel pipes? Let's look at the manufacturing process!

How much do you know about seamless steel pipe? Seamless steel pipe is circular, square and rectangular hollow section steel pipe, without external joint. Seamless steel pipe is made of steel ingot or solid tube blank by piercing into capillary tube. It is then made by hot rolling, cold rolling or cold drawing. Seamless steel pipe has a hollow cross-section, which is usually used as a pipeline for conveying fluid. Compared with solid steel such as round steel, seamless steel pipe has the same bending and torsion strength and lighter weight. They are economical section steels and are widely used in the manufacture of structures, parts and mechanical parts, such as steel scaffolds for oil drilling.

Since 1953, China has been attaching great importance to the development of seamless steel pipe industry. The production system of rolling all kinds of large, medium and small pipes has been preliminarily formed. The process of cross rolling and piercing of ingot, rolling of pipe mill and drawing of coil are usually adopted for copper pipe.

Application and classification of seamless steel pipe
Application: seamless steel pipe is a kind of economic steel, which has a very important position in the national economy. It is widely used in petroleum, chemical industry, boiler, power station, ship, machinery manufacturing, automobile, energy, geology, construction and military industry and other departments.

Classification:
① According to the section shape: round section pipe, special section pipe.
② According to the connection mode: threaded pipe, fusion pipe.
③ According to the production method: hot rolling (extrusion, jacking, expanding) pipe, cold rolling (drawing) pipe.
④ According to the use: boiler tube, oil well tube, structure pipe, fertilizer pipe.

Production process of seamless steel pipe
① Production process of hot-rolled seamless steel pipe:
Preparation and inspection of tube blank → heating of tube blank → piercing → pipe rolling → reheating of waste pipe → fixing (reducing) diameter → heat treatment → straightening of finished pipe → finishing → inspection (nondestructive, physical and chemical, bench check) → warehousing.
② Production process of cold rolled seamless steel pipe:
Blank preparation → pickling and lubrication → cold rolling (stretching) → heat treatment → straightening → finishing → inspection.

Generally, seamless steel tubes are made of 10, 20, 30, 35, 45 and other carbon steels (such as 16Mn, 5MnV and other low alloy structural steels) or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other composite steels. Seamless pipes made of low carbon steel, such as 10 and 20, are mainly used for fluid conveying pipelines. Seamless tubes made of medium carbon steel (e.g. 45 and 40Cr) are used to manufacture mechanical parts. For example, for pressure parts of automobiles and tractors, seamless steel pipes are usually used for strength and flattening tests, hot-rolled steel pipes are delivered in hot-rolled or heat-treated state, and cold-rolled steel pipes are delivered in heat-treated state.

As the name implies, hot rolling is due to the high temperature of rolled parts. Therefore, the deformation resistance is small, and a large amount of deformation can be achieved. For example, the thickness of continuous casting slab is about 230mm, and the thickness after rough rolling and finishing rolling is 1-20mm. At the same time, because the width thickness ratio of steel plate is small, the dimensional accuracy requirement is relatively low, and the shape problem is not easy to occur. The crown is mainly controlled, and the microstructure is achieved by controlling the rolling and cooling, that is, controlling the initial rolling temperature of finish rolling.

Therefore, there is no seam in seamless steel pipes.