As an important product in the field of modern industrial pipelines, the diversity of its manufacturing process and application scenarios reflects the deep integration of material science and welding technology. Among them, double-sided submerged arc welded straight seam steel pipes, with their unique structural performance and process advantages, occupy an irreplaceable position in the fields of long-distance transmission pipelines, building support structures, etc. The manufacturing process of this steel pipe combines automated welding technology with precision forming technology. Through double-sided submerged arc welding, high strength and high sealing of the weld are achieved, becoming a key material to ensure the safety of energy transportation.

First, the core process analysis of double-sided submerged arc welded straight seam steel pipes
The manufacture of double-sided submerged arc welded straight seam steel pipes begins with the precision processing of high-quality hot-rolled steel plates. First, the steel plate is processed into the required width by a milling machine, and then it is formed by multiple progressive presses on a JCOE-forming machine to form an open tube blank. The double-sided submerged arc welding process is used in the core welding stage: first, a weld is pre-welded on the inner wall of the tube blank, then the main weld is completed by submerged arc welding on the outer wall, and finally the inner wall is repaired. This layered welding method can make the weld penetration reach more than 70% of the plate thickness, significantly improving the joint strength. During the welding process, the arc covered by the flux layer melts the metal at a high temperature of 1600℃, and the slag protective layer formed can effectively isolate the air and avoid pores and slag inclusion defects. Compared with ordinary straight seam welded steel pipes, the double-sided submerged arc welding process forms a fine acicular ferrite structure in the weld area, and its impact toughness is more than 30% higher than that of conventional welds. Through online ultrasonic flaw detection and X-ray detection, it can be ensured that the internal quality of the weld meets international standards such as API 5L or GB/T 9711. Typical products such as X80 grade steel pipes have yield strength of up to 555MPa and can withstand a transmission pressure of more than 15MPa. They are widely used in national pipeline projects such as the West-East Gas Transmission Project.

Second, technical and economic comparison with spiral welded steel pipes
Although double-sided submerged arc spiral welded steel pipes (such as L485M steel grade of GB/T 9711 standard) have advantages in continuous production and large diameter, straight seam welded steel pipes are superior in pressure stability and dimensional accuracy. Because the welds of spiral welded steel pipes are distributed in spiral lines, the decomposition of circumferential stress under high-pressure conditions may cause weak points, while the longitudinal weld stress direction of straight seam pipes is consistent with the main stress, and the bursting pressure is usually 10%-15% higher. A comparative test of an oil pipeline project showed that the fatigue life of straight seam welded steel pipes of the same specification reached 2 million cycles, which is about 1.5 times higher than that of spiral pipes. From the perspective of production cost, the material utilization rate of straight seam pipes with a diameter of less than 1420mm can reach 96%, while spiral pipes have about 5% scrap loss due to plate width restrictions. However, in the field of ultra-large diameters (such as above 3000mm), spiral welded steel pipes do not need to be customized ultra-wide steel plates, and their economic advantages begin to emerge. It is worth noting that straight seam welded steel pipes make it easier to realize the automated diameter expansion process. Through mechanical diameter expansion, the roundness deviation can be controlled within 0.5%D, which is the key to ensuring the accuracy of pipeline docking.

Third, innovative processes and special application scenarios
In recent years, straight seam submerged arc welded pipe technology has continued to break through: in the South China Sea submarine pipeline project, the X65 steel grade straight seam pipe with double-layer FBE+PP anti-corrosion coating is added with 0.06%Nb micro-alloying elements to make the low-temperature impact energy of -40℃ reach more than 220J. In the construction of polar pipelines, the X100 steel grade steel pipe produced by TMCP (thermomechanical control process) can reduce the wall thickness by 15% while maintaining excellent crack resistance. Special fields such as nuclear power pipes are required to meet the Z-direction performance indicators in the RCC-M standard.

Fourth, industry development trends and challenges
With the advancement of intelligent manufacturing, leading domestic companies have realized the full process digitalization of straight seam welded steel pipe production. The MES system introduced by a factory can monitor more than 200 parameters such as welding current (fluctuation controlled at ±15A) and line energy (18-22kJ/cm) in real-time, which increases the product qualification rate to 99.92%. However, on the raw material side, high-end pipeline steel still relies on imports. For example, 80% of X90/X100 grade steel plates need to be purchased from Nippon Steel and other companies. Environmental protection requirements also drive technological innovation. The application of a new generation of low-smoke flux has reduced the dust concentration in the welding workshop from 15mg/m³ to 3mg/m³. In the future, with the growing demand for hydrogen energy pipeline construction, the research and development of hydrogen embrittlement-resistant straight seam welded steel pipes will become a focus. At present, L415H steel-grade products with a hydrogen-induced cracking (HIC) sensitivity index of ≤2% have been trial-produced in China. However, in the field of deep-sea pipelines above 1,500 meters, the problem of welding residual stress control of thick-walled straight seam pipes (≥40mm) still needs to be solved. From land to sea, from conventional energy to new energy transmission, double-sided submerged arc welded straight seam steel pipes continue to demonstrate their core value as the blood of industry. The trajectory of its technological evolution not only reflects the transformation of China’s manufacturing from scale expansion to quality improvement but also heralds the infinite possibilities brought by the integration of new materials and new processes. In the context of carbon neutrality, this kind of pipeline product with both high strength and long life will surely play a more critical role in the reconstruction of global energy infrastructure.