Steel pipes have been a crucial component in the development of modern infrastructure. Dating back to ancient times, humans have recognized the importance of channeling fluids and gases efficiently and safely. However, it was not until the 19th century that steel pipes emerged as a game-changer in this field. The invention of steel pipes revolutionized various industries, including transportation, construction, and manufacturing. Steel's durability and strength made it an ideal material for constructing pipelines that could withstand high pressure and extreme temperatures. This innovation allowed for the efficient transportation of oil, gas, water, and other fluids over long distances. Steel pipes played a pivotal role in the construction industry by providing structural support for buildings and bridges. The use of steel pipes in these structures ensured their stability and longevity. Additionally, steel pipes were instrumental in facilitating industrial processes such as steam power generation. Furthermore, advancements in technology have further enhanced the versatility of steel pipes. Today, they are used extensively in various applications such as plumbing systems, sewage disposal networks, irrigation systems, and even underground mining operations.
 
A steel pipe is a kind of economical steel and an important product in the steel industry, usually accounting for about 10% of all steel. It is widely used in the national economy. Since steel pipes have a hollow section, they are most suitable for fluid delivery pipes. At the same time, compared with round steel of the same weight, steel pipes have a greater section coefficient and greater bending and torsional strength, making them an important material in various machinery and building structures. A large number of various steel pipes are especially used in oil drilling, smelting and transportation, followed by the chemical industry, construction industry, machinery industry, aircraft and automobile manufacturing, as well as boilers, medical equipment, furniture and bicycles. In recent years, with the development of new technologies such as atomic energy, rockets, missiles and the aerospace industry, steel pipes have become increasingly important in the national defense industry, science and technology and economic construction, and are known as the "blood vessels" of industry. 
 
There are many types of steel pipes with different uses, resulting in different technical requirements and different production methods. The outer diameter of steel pipes currently produced ranges from 0.1 to 4500 mm, and the wall thickness ranges from 0.01 to 250 mm.
 
Steel pipes are divided into two categories, namely, seamless pipes and welded pipes according to the production method. Seamless steel pipes can be divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes and extruded pipes; cold drawn and cold roll are the secondary processing of steel pipes; welded pipes are divided into straight seam welded pipes and spiral welded pipes. 
 
Steel pipes can be divided into round pipes and special-shaped pipes according to the cross-sectional shape. Special-shaped pipes include rectangular pipes, rhombus pipes, oval pipes, hexagonal pipes, octagonal pipes and various pipes with asymmetrical cross-sections.
 
Steel pipes can be classified into equal-section pipes and variable-section pipes according to the longitudinal cross-section shape; variable-section pipes include tapered pipes, stepped pipes and periodic cross-section pipes.
 
Steel pipes are divided into ordinary carbon steel pipes, carbon structural steel pipes, alloy structural pipes, alloy steel pipes, bearing steel pipes, stainless steel pipes and bimetallic composite pipes based on the material of steel pipes.
 
Steel pipes can be classified into plain pipes and threaded pipes according to the shape of the pipe end. Threaded pipes can be divided into ordinary threaded pipes (pipes for low-pressure transportation such as water and gas, connected by ordinary cylindrical or conical pipe threads) and special threaded pipes (pipes for petroleum and geological drilling, connected by special threads. For some special pipes, the pipe end is usually thickened to compensate for the influence of threads on the strength of the pipe end (internal thickening, external thickening or internal and external thickening) before threading. 
 
According to the ratio of outer diameter to wall thickness, steel pipes are divided into extra-thicken pipes (D/S less than and equal to 10), thick-walled pipes (D/S equal to 10 to 20), and thin pipes (D/S between 20 and 40) and extremely thin-walled tubes (D/S greater than and equal to 40). 
 
Steel pipes can be classified into OCTG pipes such as casing, oil pipes and drill pipes, boiler pipes, mechanical structural pipes, hydraulic support pipes, gas cylinder pipes, geological pipes, chemical pipes such as high-pressure fertilizer pipes, petroleum cracking pipes and pipes for ships.