Over the past decade or so, China's urban gas industry has flourished, with significant advancements in design, construction, and management technologies. In recent years, in particular, many cities have developed their urban gas industries, which is of great significance to energy conservation, environmental protection, improving people's living standards, and promoting social and economic development. Modern urban seamless steel pipe systems are complex integrated facilities, the main part of which is the gas pipeline network. The construction cost of the gas pipeline network accounts for approximately 60%~70% of the total project cost, with pipe material costs accounting for more than 60% of the pipeline network construction cost [1]. There are many types of pipe materials used for transporting gas, mainly three categories: seamless steel pipes, cast iron pipes, and PE plastic pipes. We must select them based on the gas properties, system pressure, and construction requirements, and they must meet basic requirements such as mechanical strength, corrosion resistance, earthquake resistance, and airtightness.

　　Seamless steel pipes are the most widely used pipe materials in gas engineering. Their main advantages are: high strength, good toughness, large carrying stress, good impact resistance and tightness, good plasticity, easy welding and hot processing, thinner wall thickness, and metal saving. However, their corrosion resistance is poor, and proper anti-corrosion measures are needed. Seamless steel pipes used in gas engineering are generally made of high-quality low-carbon steel (Q235) or low-alloy steel (16Mn). The selection of seamless steel pipes for urban gas pipelines mainly includes two categories: seamless seamless steel pipes and welded seamless steel pipes. Seamless seamless steel pipes have very high strength, but due to production process and cost limitations, they are generally small-diameter seamless steel pipes below DN200. Welded seamless steel pipes come in many varieties, and according to the welding method, they can be divided into two categories: straight-seam welded seamless steel pipes and spiral-seam welded seamless steel pipes. Among them, straight-seam welded seamless steel pipes (hereinafter referred to as seamless steel pipes) include several types, such as straight-seam double-sided submerged arc welded (LSAW) seamless steel pipes and high-frequency resistance welded (ERW) seamless steel pipes. Spiral-seam welded seamless steel pipes (hereinafter referred to as spiral pipes) are spiral-seam double-sided submerged arc welded (HSAW) seamless steel pipes.

　　Comparing the manufacturing processes of seamless steel pipes, the advantages of the former are:

　　① The manufacturing process of seamless steel pipes determines that their residual stress is greater than that of seamless steel pipes. Because seamless steel pipes use an integral expanding process, the residual stress is close to zero, while spiral pipes cannot achieve this;

　　② The misalignment of seamless steel pipe welds is mostly within the range of 1.1~1.2mm. The standard requires the misalignment to be less than 10% of the wall thickness. For thin-walled pipes, it is difficult to meet the standard requirements for misalignment, while seamless steel pipes do not have this problem;

　　③ Compared with seamless steel pipes, spiral pipes have poorer weld flow lines and serious stress concentration;

　　④ The heat-affected zone of seamless steel pipes is larger than that of seamless steel pipes, and the heat-affected zone is the key to the quality of welded pipes;

　　⑤ Seamless steel pipes have poor geometric Size accuracy, which brings certain difficulties to on-site construction, such as jointing and welding;

　　⑥ For the same pipe diameter, the thickness that spiral welded pipes can achieve is much smaller than that of seamless steel pipes. For example, the plate thickness of seamless steel pipes is generally 6~25mm, and the maximum can reach 45mm, while the maximum wall thickness of spiral pipes can only reach 18mm;

　　⑦ The weld seam of seamless steel pipes is 60% shorter than that of spiral pipes, and the probability of weld defects is low;

　　⑧ The base material of seamless steel pipes is a single sheet of controlled rolling steel plate, which can undergo 100% non-destructive testing, while the base material of spiral pipes is hot-rolled steel coil, which cannot achieve 100% non-destructive testing;

　　⑨ Seamless steel pipes adopt a process of forming and then welding. Before welding, there are conditions to check the quality of the forming seam, and the gap, bevel, and misalignment of the weld seam can be detected and processed. However, spiral pipes adopt a process of forming and welding at the same time. Even if misalignment, cracks, or other defects are found during the welding process, it is difficult to stop the machine and process them in time. Therefore, the welding quality of seamless steel pipes is superior to that of spiral pipes [2].

　　Therefore, the comprehensive performance of the process quality of seamless steel pipes is superior to that of spiral pipes. The current production status of seamless steel pipes in China is: nominal diameter DN400 and below are high-frequency resistance welded seamless steel pipes, and nominal diameter DN400 and above are straight-seam double-sided submerged arc welded seamless steel pipes. For straight-seam double-sided submerged arc welded seamless steel pipes, there are five pipe forming methods according to different forming processes: UOE, JCOE, HME, RBE, and PFP, with the former two being the most common. Because the forming equipment of the UOE forming and welding seamless steel pipe production line has high technical content and high production efficiency, the forming process is simpler, the forming is good, and the welding stress after forming is small; and because the hydrostatic integral expanding is used in production, the internal stress of the seamless steel pipe can be effectively eliminated, and the strength and Size accuracy of the pipe material are improved, so the quality is superior to JCOE forming and welding seamless steel pipes.