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Basic knowledge of welded steel pipes: Welded steel pipes, also known as welded tubes, are steel pipes that are made by welding steel plates or steel strips after rolling them into shape. Welded steel pipe has a simple production process, high production efficiency, a wide range of specifications, and requires less equipment; however, its strength is generally lower than that of seamless steel pipes. Since the 1930s, with the rapid development of continuous rolling for high-quality strip steel and advancements in welding and inspection technologies, weld quality has continued to improve. The variety and specifications of welded steel pipes have increased, and they are replacing seamless steel pipes in an ever-growing number of applications. Welded steel pipes are classified into straight-seam welded pipes and spiral-welded pipes according to the shape of the weld. Straight-seam welded pipe has a simple production process, high production efficiency, low costs, and is developing rapidly. The strength of spiral welded pipes is generally higher than that of straight-seam welded pipes. They allow for the production of pipes with larger diameters using narrower billets, and it is also possible to produce pipes with different diameters using billets of the same width. However, compared with straight-seam pipes of the same length, the weld length increases by 30–100%, and the production speed is lower. Therefore, smaller-diameter welded pipes are mostly welded by straight-seam welding, while larger-diameter welded pipes are mostly welded by spiral welding. I. Welded steel pipes for low-pressure fluid transport Welded steel pipes for low-pressure fluid transport (GB/T3092-1993) are also known as ordinary welded pipes, and are commonly referred to as black pipes. It is a welded steel pipe used for transporting fluids at relatively low pressures such as water, gas, air, oil, and heating steam, as well as for other purposes. Steel pipes are classified by wall thickness into ordinary steel pipes and thick-walled steel pipes ； The types of connection ends are divided into threaded steel pipes and unthreaded steel pipes (smooth pipes). The specification of steel pipes is indicated by the nominal diameter (mm), which is an approximate value of the inner diameter. *It is commonly expressed in inches, such as 11/2, etc. In addition to being used directly for transporting fluids, welded steel pipes for low-pressure fluid transport are also widely used as the base pipes for galvanized welded steel pipes used for the same purpose. II. Galvanized welded steel pipes for low-pressure fluid transport Galvanized welded steel pipes for low-pressure fluid transport (GB/T3091-1993) are also known as galvanized electric welding steel pipes, and are commonly referred to as white pipes. It is a hot-dip galvanized welded (furnace-welded or electrically welded) steel pipe used for transporting fluids at relatively low pressures such as water, gas, air, oil, heating steam, and hot water, or for other purposes. Steel pipe wall thickness is divided into ordinary galvanized steel pipes and thickened galvanized steel pipes ； The types of connection ends are divided into galvanized steel pipes without threads and galvanized steel pipes with threads. The specification of steel pipes is indicated by the nominal diameter (mm), which is an approximate value of the inner diameter. *It is commonly expressed in inches, such as 11/2, etc. III. Ordinary carbon steel wire sleeves: Ordinary carbon steel wire sleeves (GB3640-88) are steel tubes used to protect wires in electrical installation projects such as industrial and civil buildings and the installation of machinery and equipment. IV. Straight-seam electric welded steel pipes Straight-seam electric welded steel pipes (YB242-63) are steel pipes whose welds are parallel to the longitudinal direction of the pipe. They are generally classified into metric welded steel pipes, welded thin-walled pipes, transformer cooling oil pipes, and so on. V. Spiral-welded submerged-arc welded steel pipes: Spiral-welded submerged-arc welded steel pipes for transporting pressurized fluids (SY5036-83) are made by using hot-rolled steel strip coils as the pipe blanks, which are formed through spiral shaping at room temperature and then welded using double-sided submerged-arc welding; they are used as spiral-welded pipes for transporting pressurized fluids. Steel pipes have strong pressure resistance and good weldability; they have undergone various rigorous scientific inspections and tests, making them safe and reliable to use. Steel pipes have a large diameter, enabling high transportation efficiency and saving on investment in pipeline installation. Mainly used for pipelines transporting oil and natural gas. VI. High-frequency welded steel pipes with spiral seams – These are high-frequency welded steel pipes with spiral seams used for transporting pressurized fluids (SY5038-83). They are made by using hot-rolled steel strips as the tube blanks, which are then formed into tubes through spiral shaping; welding is carried out using a high-frequency lap welding method. Such pipes are utilized for transporting pressurized fluids. Steel pipes have strong pressure resistance, good plasticity, and are easy to weld and shape ； After various rigorous and scientific inspections and tests, it is safe and reliable to use; it features a large diameter for pipes, high transportation efficiency, and can help save on investment in pipeline installation. It is mainly used for laying pipelines to transport oil, natural gas, and other substances. VII. Spiral-welded submerged arc welded steel pipes: Spiral-welded submerged arc welded steel pipes for general low-pressure fluid transport (SY5037-83) are made by using hot-rolled steel strip coils as the pipe blanks, forming them in a spiral shape at room temperature, and then manufacturing them using double-sided automatic submerged arc welding or single-sided welding methods. These pipes are used for transporting low-pressure fluids such as water, gas, air, and steam. VIII. High-frequency welded steel pipes with spiral seams – Steel pipes with spiral seams for general low-pressure fluid transport (SY5039-83) are made by using hot-rolled steel strip coils as the tube blanks; they are formed by spiral shaping at room temperature and welded using a high-frequency lap welding method, and are thus used for transporting general low-pressure fluids. IX. Spiral-welded steel pipe for piles: The spiral-welded steel pipe for piles (SY5040-83) is made by using hot-rolled steel strip coils as the tube blank, forming it in a spiral manner at room temperature, and then welding it using double-sided submerged arc welding or high-frequency welding. It is used as steel pipes for foundation piles in civil engineering structures, docks, bridges, etc.