What Is Seamless Steel Pipe? A Quick Guide

Seamless steel pipe is a long steel strip with a hollow cross-section and no seams around it. It is a tubular material made by punching a whole round steel bar. Compared with ordinary welded steel pipes, the most notable feature of seamless steel pipes is that there are no welds on their surface. This feature gives them obvious advantages in terms of pressure bearing capacity, structural integrity and service life. From the production process point of view, seamless steel pipes are made by heating solid pipe billets (ingots or round steel) and punching them, and then hot rolling, cold rolling or cold drawing. The entire forming process does not involve any welding process.

Seamless steel pipes differ significantly from ordinary welded steel pipes (also known as seamed steel pipes) in many aspects. From a manufacturing process perspective, seamless steel pipes are made by hot rolling or cold drawing solid round steel after perforation, with no welds throughout the entire process; whereas welded steel pipes are formed by welding steel plates or strips rolled into tubular shapes, with welds distributed longitudinally or spirally. This process difference results in differences in structural integrity between the two: the overall structure of seamless steel pipes is continuous and uniform, the material structure is dense, and there are no weak strength areas at the welds; whereas the weld areas of welded steel pipes often become the "weak points" of the structure, easily forming stress concentration sources, which require enhanced detection and treatment

Common Specifications and Standards of Seamless steel pipe

According to different production methods, seamless steel pipes can be divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, extruded pipes, jacking pipes, etc. According to the material type, seamless steel pipes can be divided into multiple categories such as carbon steel, alloy steel and stainless steel. Carbon steel seamless steel pipes can be further divided into ordinary carbon structural steel (such as Q215-A ~ Q275-A) and high-quality carbon structural steel (such as 10 ~ 50 steel). 20# seamless steel pipe is a typical representative of low-carbon steel pipes, with a carbon content of 0.17% ~ 0.20%, and has the characteristics of high cold deformation plasticity and good welding performance.

Alloy steel seamless steel pipes include low-alloy steel (such as 09MnV, 16Mn, etc.) and alloy structural steel (such as 40Cr, 30CrMnSi, etc.), with higher strength and better comprehensive performance. Stainless steel seamless steel pipes are made of various stainless steel materials (such as 304, 316L, etc.) by hot rolling or cold rolling, and have excellent corrosion resistance.

According to the classification of uses, seamless steel pipes have formed a more specialized product series. Seamless steel pipes for boilers are pipes specially used to manufacture boiler equipment. According to different working pressures, they are divided into low-pressure and medium-pressure boiler pipes and high-pressure boiler pipes. Seamless steel pipes for geological drilling and oil drilling are the main equipment for drilling operations, including core outer pipes, core inner pipes, casings, drill rods, etc. Petroleum cracking pipes are used for furnace tubes, heat exchangers and pipelines in oil refineries. In addition, there are many special seamless steel pipes such as carbon steel seamless steel pipes for ships, seamless steel pipes for automobile half-axle casings, and high-pressure oil pipes for diesel engines.

Thick-walled seamless steel pipes are an important category of seamless steel pipes, usually referring to products with an outer diameter of ≥325 mm and a wall thickness of ≥20 mm. This type of steel pipe is mainly made of steel ingots or solid billets, and is made through perforation, hot rolling and other processes. It is widely used in fluid transportation, machinery manufacturing, energy equipment and other fields

2. Available in three categories according to different uses:

3、Special-purpose seamless pipes include seamless pipes for boilers, chemical and electric power, geological seamless pipes, and petroleum seamless pipes. Seamless steel pipes have hollow sections and are widely used as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, coal gas, water and certain solid materials. Compared with solid steel materials such as round steel, steel pipes are lighter in weight when the bending and torsional strength is the same, and they are an economical cross-section steel material. It is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. The use of steel pipes to make ring parts can improve material utilization, simplify the manufacturing process, and save materials and processing. Steel pipes have been widely used for manufacturing.

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