Based on welding methods, welded steel pipes can be categorized into arc-welded pipes, high-frequency or low-frequency resistance-welded pipes, gas-welded pipes, furnace-welded pipes, Bundy tubes, etc.
Electric Welded Steel Pipes: Used in oil drilling, machinery manufacturing, and other industries.
Furnace-Welded Pipes: Can be utilized as water and gas pipes, with large-diameter straight-seam welded pipes suitable for high-pressure oil and gas transportation, and spiral-welded pipes applied in oil and gas transmission, pipe piles, bridge piers, etc.
According to the shape of the weld seam, welded steel pipes can be divided into straight-seam welded pipes and spiral-welded pipes.
Straight-Seam Welded Pipes: Featuring simple production processes, high production efficiency, and low costs, they have developed rapidly.
Spiral-Welded Pipes: Typically stronger than straight-seam welded pipes, they can produce larger-diameter pipes from narrower billets and pipes of varying diameters from the same width billet. However, compared to straight-seam pipes of the same length, the weld seam length increases by 30-100%, and the production speed is lower. Therefore, smaller-diameter pipes mostly adopt straight-seam welding, while larger-diameter pipes predominantly use spiral welding.
Spiral-seam welded steel pipes are further classified into automatic submerged arc welded steel pipes and high-frequency welded steel pipes.
a. Automatic Submerged Arc Welded Steel Pipes with Spiral Seams are divided into Class A and Class B pipes based on the pressure of the conveyed medium. Class A pipes are generally welded with ordinary carbon steel Q235, Q235F, and ordinary low-alloy structural steel 16Mn, while Class B pipes are welded with Q235, Q235F, Q195, and other steels, used for low-pressure fluid transportation.
b. High-Frequency Welded Steel Pipes with Spiral Seams have not yet established a unified product standard and are generally manufactured from ordinary carbon steel Q235, Q235F, etc.
Based on their applications, welded steel pipes can be further classified into general welded pipes, galvanized welded pipes, oxygen-blowing welded pipes, electrical wire conduit pipes, metric welded pipes, idler pipes, deep-well pump pipes, automotive pipes, transformer pipes, electric welded thin-wall pipes, electric welded special-shaped pipes, and spiral-welded pipes.
General Welded Pipes: Used for transporting low-pressure fluids, made from Q195A, Q215A, Q235A steel, or other easily weldable mild steel. Subject to hydraulic, bending, and flattening tests, they have specific surface quality requirements. Typically delivered in lengths of 4-10m, often to specified or multiple lengths. Their specifications are indicated by nominal diameters (in millimeters or inches), which may differ from actual diameters. According to wall thickness, they are classified as regular and thickened pipes, and by end forms, as threaded or unthreaded.
Galvanized Steel Pipes: To enhance corrosion resistance, regular steel pipes (black pipes) are galvanized, either by hot-dip galvanizing (thicker coating) or electro-galvanizing (lower cost).
Oxygen-Blowing Welded Pipes: Small-diameter welded pipes used in steelmaking oxygen blowing, ranging from 3/8" to 2" in diameter, made from 08, 10, 15, 20, or Q195-Q235 steel strips. Some undergo aluminizing for corrosion protection.
Electrical Wire Conduit Pipes: Ordinary carbon steel electric welded pipes used in concrete and various structural power distribution projects, with common nominal diameters ranging from 13-76mm. Featuring thin walls, they are often coated or galvanized before use and require cold bending tests.
Metric Welded Pipes: Specified in seamless pipe format, indicated by outer diameter * wall thickness (in millimeters), welded from hot-rolled or cold-rolled strips of ordinary carbon steel, high-quality carbon steel, or low-alloy steel, or cold-drawn after welding. Metric welded pipes are classified as regular and thin-walled, with the former used for structural components like transmission shafts or fluid transportation, and the latter for furniture, lighting fixtures, etc. They must meet strength and bending test requirements.
