Seamless steel pipe is a long steel strip with a hollow section and no joints around it.
Seamless steel pipes have a hollow cross-section and are widely used as pipelines for conveying fluids. Compared to solid steels such as round steel, steel pipes have a lower weight when their bending and torsional strength are the same. They are a type of economical cross-section steel and are widely used in the manufacture of structural and mechanical parts, such as petroleum drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolds used in construction.
Seamless steel pipes are widely used. Seamless steel pipes for general purposes are rolled from ordinary carbon structural steel, low alloy structural steel, or alloy structural steel, with the largest output, and are mainly used as pipes or structural parts for conveying fluids.

2. Supply is divided into three categories according to different uses:
   A. Supplied according to chemical composition and mechanical properties;
   B. Supplied according to mechanical properties;
   Supply according to hydraulic test. Steel pipes supplied in accordance with categories a and b, if used to withstand liquid pressure, should also undergo a hydraulic test.
3. There are various types of seamless pipes for special purposes, such as seamless pipes for boilers, seamless steel pipes for geology, and seamless pipes for petroleum.
   Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip after being crimped and welded. The production process of welded steel pipes is simple, with high production efficiency, multiple varieties and specifications, and less equipment capital. However, the strength is generally lower than that of seamless steel pipes.
   Since the 1930s, with the rapid development of high-quality strip steel continuous rolling production and the progress of welding and inspection technology, the quality of welds has been continuously improved, and the variety and specification of welded steel pipes have been increasing, replacing seamless steel pipes in more and more fields. Welded steel pipes are divided into straight welded pipes and spiral welded pipes in the form of welds.
   The production process of longitudinally welded pipe is simple, with high production efficiency, low cost, and rapid development. The strength of spiral welded pipes is generally higher than that of straight welded pipes. It is possible to produce welded pipes with larger pipe diameters using narrower billets, and it is also possible to produce welded pipes with different pipe diameters using billets of the same width.
   However, compared to straight seam pipes of the same length, the weld length increases by 30 to 100%, and the production speed is lower.
   Therefore, most of the smaller diameter welded pipes use straight seam welding, while most of the larger diameter welded pipes use spiral welding.