Welded steel pipes, also known as weld pipes, are made by welding steel plates or strips after rolling and forming, typically in 6-meter lengths. The production process for welded steel pipes is simple, with high efficiency, a wide variety of types and specifications, and low equipment investment, although their strength is generally lower than that of seamless steel pipes. Since the 1930s, with the rapid development of continuous strip rolling production and advancements in welding and inspection technologies, the quality of welds has continuously improved, and the types and specifications of welded steel pipes have increasingly expanded, replacing seamless steel pipes in more and more fields. Welded steel pipes are classified by the shape of the weld into straight seam weld pipes and spiral seam weld pipes. By production method, they are categorized as: arc welding pipes, resistance welding pipes, (high-frequency, low-frequency) gas welding pipes, and furnace welding pipes.

Smaller diameter welded pipes are typically made using straight seam welding, while larger diameter pipes usually employ spiral welding; they are categorized into round and non-standard (square, rectangular, etc.) welded pipes based on the shape of the pipe ends; and into various types such as mining fluid conveyance welded pipes, galvanized welded pipes for low-pressure fluid conveyance, belt conveyor roller electric welded pipes, etc., depending on material and application. According to the specifications and dimensions table in the current national standard, they are sorted from smallest to largest by outer diameter multiplied by wall thickness. Common materials for standard welded pipes include Q235A, Q235C, Q235B, 16Mn, 20#, Q345, L245, L290, X42, X46, X60, X80, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, and more. Welded pipes use steel plates or strips as blanks, which are divided into furnace welded pipes, electric (resistance) welded pipes, and automatic arc welded pipes due to different welding processes. They are categorized into straight seam and spiral seam pipes based on the welding form, and into round and non-standard (square, flat, etc.) pipes based on the end shape. Welded pipes are further divided into several types based on material and application: GB/T3091-2008 (Welded pipes for low-pressure fluid conveyance): mainly used for conveying water, gas, air, oil, heating hot water or steam, and other low-pressure fluids and for other purposes. The representative material is Q235A steel. GB/T14291-2006 (Welded pipes for mining fluid conveyance): mainly used for straight seam焊接 pipes for mine ventilation, drainage, and shaft gas discharge. The representative materials are Q235A and B-grade steel. GB/T12770-2002 (Welded stainless steel pipes for mechanical structures): mainly used in machinery, automobiles, bicycles, furniture, hotel and restaurant decoration, and other mechanical components and structures. The representative materials include 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, and more. GB/T12771-1991 (Welded stainless steel pipes for fluid conveyance): mainly used for conveying low-pressure corrosive media. The representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, and more. Additionally, decorative welded stainless steel pipes (GB/T 18705-2002), stainless steel welding tubes for building decoration (JG/T 3030-1995), and welded pipes for heat exchangers (YB4103-2000).