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Welded steel pipe
Welded steel pipes, also known as welded pipes, are manufactured by forming steel plates or strips and then welding them together. These pipes have a relatively simple production process, high manufacturing efficiency, a wide range of sizes and specifications, and require less initial investment in equipment. However, their overall strength is generally lower compared to seamless steel pipes. Since the 1930s, with the rapid development of high-quality strip steel continuous rolling technology and the improvement of welding and inspection techniques, the quality of welds has significantly improved. As a result, the variety and size range of welded steel pipes have expanded, and they have gradually replaced non-ferrous metal pipes in many applications.
Welded steel pipes can be classified into two main types based on the shape of the weld: straight seam welded pipes and spiral welded pipes. The production process of straight seam welded pipes is straightforward, efficient, and cost-effective, which has led to rapid development in this area. In contrast, spiral welded pipes typically offer higher structural strength. However, due to the longer weld length (approximately 30–100% longer than that of straight seam pipes), the production speed is slower. Therefore, smaller diameter pipes usually use straight seam welding, while larger diameter pipes tend to use spiral welding.
Welded steel pipes for low-pressure fluid transportation (GB/T 3091-2008) are commonly referred to as general welded pipes or "black pipes." They are used to transport low-pressure fluids such as water, gas, air, oil, and steam. These pipes come in different wall thicknesses, including standard and thickened versions, and pipe ends can be either unthreaded (smooth) or threaded. In addition to direct fluid transportation, these pipes are often used as the base material for galvanized welded steel pipes.
Galvanized welded steel pipes for low-pressure fluid transportation (GB/T 3091-2008), also known as galvanized electric welded pipes or "white pipes," are hot-dip galvanized welded pipes used for similar purposes. They are available in standard and thickened wall thicknesses, with both unthreaded and threaded ends. Their dimensions are indicated by nominal diameter in millimeters, though they are often expressed in inches, such as 1/2, 3/4, 1, 2, etc.
Other types include ordinary carbon steel wire conduits (YB/T 5305-2006), used in electrical installations; straight seam electric welded steel pipes (GB/T 13793-2008), suitable for general structures; and spiral submerged arc welded pipes (SY/T 5037-2000), designed for pressurized fluid transport. High-frequency spiral welded pipes (SY/T 5038-2000) and those for low-pressure fluid transport (SY/T 5039-2000) are also widely used. Additionally, spiral-welded steel pipes for piles (SY/T 5768-2000) are employed in civil engineering projects like bridges and wharves. These pipes are known for their high pressure resistance, good plasticity, and ease of welding, making them ideal for long-distance fluid transportation systems.