Welded steel pipes, also known as welded tubes, are manufactured by rolling steel plates or strips into a cylindrical shape and then welding them together.

    Welded steel pipes feature a simple production process, high production efficiency, a wide variety of types and specifications, and low capital requirements; however, their strength is generally lower than that of seamless steel pipes. Since the 1930s, with the rapid development of continuous rolling for high-quality steel strips and advances in welding and inspection technologies, weld quality has continuously improved, and the variety and specifications of welded steel pipes have increased, leading them to replace seamless steel pipes in an ever-growing number of applications. Welded steel pipes are classified by weld type into straight-seam welded pipes and spiral-seam welded pipes.

    Longitudinal welded pipes feature a simple production process, high production efficiency, low costs, and rapid development. Spiral welded pipes generally have higher strength than longitudinal welded pipes; they can produce larger-diameter pipes using narrower strip stock, and can also produce pipes of different diameters using strip stock of the same width. However, compared to longitudinal welded pipes of the same length, the weld length increases by 30–100%, and the production speed is lower.

    Consequently, small-diameter welded pipes are mostly produced using the straight-seam welding method, while large-diameter welded pipes are predominantly produced using the spiral-seam welding method.

    Welded steel pipes for low-pressure fluid conveyance (GB/T 3092-1993), also known as general-purpose welded pipes and commonly referred to as “black pipes,” are used to convey water, gas, air, oil, heating steam, and other general-purpose low-pressure fluids, as well as for other applications. These pipes are classified by wall thickness into standard-wall and heavy-wall pipes; by end configuration, they are classified into plain-end (unthreaded) pipes and threaded pipes. The specifications of steel pipes are expressed in nominal diameter (mm), which is an approximate value of the inner diameter. It is customary to use inches for measurement, such as 1½. In addition to being used directly for fluid conveyance, welded steel pipes for low-pressure fluid conveyance are also extensively used as raw material for galvanized welded steel pipes for low-pressure fluid conveyance.

    1. Galvanized welded steel pipes for low-pressure fluid conveyance (GB/T 3091-1993), also known as galvanized electric-welded steel pipes and commonly referred to as “white pipes,” are hot-dip galvanized welded (furnace-welded or electric-welded) steel pipes used for conveying water, gas, air, oil, heating steam, hot water, and other general low-pressure fluids, as well as for other applications. These pipes are classified by wall thickness into standard galvanized steel pipes and heavy-wall galvanized steel pipes; by end configuration, they are classified into plain-end galvanized steel pipes and threaded-end galvanized steel pipes. Pipe specifications are expressed in nominal diameter (mm), which is an approximate value of the inner diameter. Conventionally, inches are often used, such as 1½, etc.

      2. Ordinary carbon steel electrical conduit (GB3640-88) is a steel pipe used to protect electrical wires in electrical installation projects for industrial and civil buildings, as well as in the installation of machinery and equipment.

    3. Longitudinally welded steel pipes (YB242-63) are steel pipes in which the weld seam runs parallel to the longitudinal axis of the pipe. They are typically classified into metric welded steel pipes, thin-walled welded pipes, transformer cooling oil pipes, and so on.

    4. Spiral-welded submerged-arc welded steel pipes for pressure fluid conveyance (SY5036-83) are manufactured from hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using a double-sided submerged-arc welding method. These spiral-welded steel pipes are used for conveying pressurized fluids. They feature high pressure-bearing capacity and excellent weldability, and after undergoing various rigorous scientific inspections and tests, they are safe and reliable for use. These pipes feature large diameters and high conveyance efficiency, while also reducing pipeline installation costs. They are primarily used in pipelines for transporting petroleum and natural gas.

    5. Spiral-welded high-frequency welded steel pipes for conveying pressurized fluids (SY5038-83) are manufactured using hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using the high-frequency lap welding method. These spiral-welded high-frequency welded steel pipes are designed for the conveyance of pressurized fluids. These steel pipes have strong pressure-bearing capacity and good plasticity, making them easy to weld and form; they undergo various rigorous and scientific inspections and tests, ensuring safe and reliable use. With large diameters, they offer high transport efficiency and can reduce the investment required for pipeline installation. They are primarily used for laying pipelines to transport petroleum, natural gas, and other fluids.

    6. Spiral-seam high-frequency welded steel pipes for general low-pressure fluid conveyance (SY5039-83) are manufactured using hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using the high-frequency lap welding method. They are designed for the conveyance of general low-pressure fluids.

    7. Spiral-welded steel pipes for piles (SY5040-83) are manufactured using hot-rolled steel coil as the pipe blank, formed into a spiral shape at room temperature, and welded using double-sided submerged arc welding or high-frequency welding. They are used for foundation piles in civil engineering structures, docks, bridges, and similar applications.