Introduction to welded steel pipe

　　Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or steel strip after crimping and forming. Welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment investment, but its general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of continuous rolling production of high-quality strip steel and the progress of welding and inspection technology, the weld quality has been continuously improved, the variety and specification of welded steel pipes have increased, and seamless steel pipes have been replaced in more and more fields. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of welds.

　　Longitudinal welded pipe has the advantages of simple production process, high production efficiency, low cost and rapid development. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. It can produce welded pipe with larger pipe diameter with narrow blank, and it can also produce welded pipe with different pipe diameters with blank of the same width. However, compared with the straight seam pipe with the same length, the weld length increases by 30~100%, and the production speed is low. Therefore, straight seam welding is mostly used for small-diameter welded pipes, while spiral welding is mostly used for large-diameter welded pipes.

　　Welded steel pipes for low-pressure fluid transmission (gb/t3091-2008) are also known as general welded pipes, commonly known as black pipes. It is a welded steel pipe used for conveying water, gas, air, oil, heating steam and other general low pressure fluids and other purposes. The wall thickness of steel pipe connection is divided into ordinary steel pipe and thickened steel pipe; The form of nozzle end is divided into non threaded steel pipe (smooth pipe) and threaded steel pipe. Welded steel pipes for low-pressure fluid transmission are not only directly used for fluid transmission, but also widely used as the original pipes of galvanized welded steel pipes for low-pressure fluid transmission.

　　1. Galvanized welded steel pipe for low-pressure fluid transmission (gb/t3091-2008) is also known as galvanized welded steel pipe, commonly known as white pipe. It is a hot-dip galvanized welded (furnace welding or electric welding) steel pipe used for conveying water, gas, air oil, heating steam, heating water and other general low pressure fluids or other purposes. The wall thickness of steel pipe connection is divided into ordinary galvanized steel pipe and thickened galvanized steel pipe; The form of nozzle end is divided into non threaded galvanized steel pipe and threaded galvanized steel pipe. The specification of steel pipe is expressed in nominal diameter (mm), which is the approximate value of inner diameter. Traditionally, it is usually expressed in inches, such as 1/2, 3/4, 1, 2, etc.

　　2 ordinary carbon steel wire sleeve (yb/t5305-2006) is a steel pipe used to protect wires in electrical installation projects such as industrial and civil buildings and installation of machinery and equipment.

　　3. Straight seam electric welded steel pipe (gb/t13793-2008) is a steel pipe whose weld is longitudinally parallel to the steel pipe. For general structures, it is usually divided into metric electric welded steel pipes, electric welded thin-walled pipes, etc.

　　4. Spiral seam submerged arc welded steel pipe (sy/t5037-2000) for pressure fluid transmission is a spiral seam steel pipe used for pressure fluid transmission, which takes hot-rolled steel strip coil as pipe blank, often warm spiral forming, and welding with double-sided submerged arc welding. The steel pipe has strong pressure bearing capacity and good welding performance. After various strict scientific inspections and tests, it is safe and reliable to use. The steel pipe has large diameter, high transmission efficiency, and can save the investment in laying pipelines. It is mainly used for pipelines transporting oil and natural gas.

　　5. Spiral seam high-frequency welded steel pipe (sy/t5038-2000) for pressure fluid transmission is a spiral seam high-frequency welded steel pipe for pressure fluid transmission, which takes hot-rolled steel strip coil as pipe blank, is often formed by warm spiral, and is welded by high-frequency lap welding method. The steel pipe has strong pressure bearing capacity and good plasticity, which is convenient for welding and processing; After various strict and scientific inspections and tests, it is safe and reliable to use, with large diameter steel pipes, high transmission efficiency, and can save the investment in laying pipelines. It is mainly used for laying pipelines for transporting oil, natural gas, etc.

　　7. Spiral seam high-frequency welded steel pipe (sy/t5039-2000) for general low-pressure fluid transmission is made of hot-rolled steel strip coil, which is often formed by warm spiral and welded by high-frequency lap welding method. It is used for spiral seam high-frequency welded steel pipe for general low-pressure fluid transmission.

　　8. Spiral welded steel pipe for pile (sy/t5768-2000) is made of hot-rolled steel strip coil as pipe blank, often warm spiral forming, and is made of double-sided submerged arc welding or high-frequency welding. It is used for steel pipe for foundation piles such as civil building structures, wharves, bridges, etc.