Core Processes, Applications, and Industry Anti-Warfare for Double-Sided Submerged Arc Welded Straight Seam Steel Pipes

Submerged arc welded steel pipes, as a key product in the modern industrial steel pipe market, demonstrate the deep integration of materials science and welding technology through their diverse manufacturing processes and applications. Double-Sided Submerged Arc Welded Straight Seam Steel Pipes, with their unique structural properties and process advantages, hold an irreplaceable position in applications such as long-distance steel pipe transportation and building support structures. The manufacturing process of this type of steel pipe integrates automated welding technology with precision forming processes. Double-Sided Submerged Arc Welding achieves high weld strength and tightness, making it a key material for ensuring energy transportation safety.

First, an Analysis of the Core Processes of Double-Sided Submerged Arc Welded Straight Seam Steel Pipes.

The manufacturing of double-sided Submerged Arc Welded Straight Seam Steel Pipes begins with the precision machining of high-quality hot-rolled steel plate. The steel plate is first milled to the desired width using a milling machine, followed by multiple progressive press forming steps on a JCOE forming machine to form an open tube billet. The core welding stage utilizes double-sided Submerged Arc Welding: a pre-weld seam is first welded to the inner wall of the tube billet, followed by submerged arc welding of the outer wall to complete the main weld, and finally, a repair weld is performed on the inner wall. This layered welding method achieves weld penetration exceeding 70% of the plate thickness, significantly improving joint strength. During welding, the arc, covered by a flux layer, melts the metal at a high temperature of 1600°C. The resulting slag shield effectively isolates the weld from the atmosphere, preventing defects such as porosity and slag inclusions. Compared to conventional straight seam welded steel pipe, the double-sided submerged arc welding process produces a fine, acicular ferrite structure in the weld area, resulting in over 30% higher impact toughness than conventional welds. Online ultrasonic testing and X-ray inspection ensure that the internal quality of the weld meets international standards such as API 5L and GB/T 9711. Typical products, such as X80-grade steel pipe, boast a yield strength of up to 555 MPa and can withstand transmission pressures exceeding 15 MPa. They are widely used in national-level steel pipeline projects such as the West-East Gas Pipeline.

Second, a comparison of the technical and economic benefits of double-sided submerged arc welded straight seam steel pipe and spirally welded steel pipe.

While double-sided submerged arc spirally welded steel pipe (such as grade L485M in GB/T 9711) offers advantages in continuous production and large diameters, straight seam welded steel pipe offers superior pressure stability and dimensional accuracy. Due to the helical distribution of the weld seams in spiral welded steel pipe, hoop stress decomposition can lead to weak points under high-pressure conditions. In contrast, the longitudinal weld seam of straight seam steel pipe is subjected to stress aligned with the principal stress, resulting in a burst pressure typically 10%-15% higher. Comparative testing on an oil pipeline project revealed that the fatigue life of straight seam welded steel pipe of the same specification reached 2 million cycles, approximately 1.5 times higher than that of spiral pipe. In terms of production cost, the material utilization rate for straight seam steel pipe with a diameter of less than 1420 mm can reach 96%, while spiral pipe suffers from approximately 5% scrap loss due to width limitations. However, in the ultra-large diameter segment (e.g., over 3000mm), spiral welded steel pipe eliminates the need for custom-made, extra-wide steel plates, and its economic advantages are becoming apparent. Notably, straight seam welded steel pipe is more easily automated for expansion. Mechanical expansion can keep roundness deviation within 0.5%D, a key factor in ensuring pipe joint accuracy.

Third, Innovative Processes and Special Applications for Double-Sided Submerged Arc Welded Straight Seam Steel Pipes.

In recent years, straight seam submerged arc welded steel pipe technology has continued to achieve breakthroughs. In the South China Sea submarine steel pipeline project, X65 steel-grade straight seam steel pipe with a double-layer FBE+PP anti-corrosion coating achieved a low-temperature impact energy of over 220J at -40°C by adding 0.06% Nb microalloying elements. In polar steel pipeline construction, X100 steel pipe produced using the TMCP (Thermo-Mechanical Control Process) achieves a 15% reduction in wall thickness while maintaining excellent crack resistance. Pipes for specialized applications, such as nuclear power, require compliance with the Z-direction performance specifications of the RCC-M standard. The straight seam steel pipes used in the containment vessel of a nuclear power plant utilize specially made low-sulfur and phosphorus steel plates (S ≤ 0.002%), combined with a multi-pass narrow-gap welding process, to achieve a cross-sectional reduction in thickness exceeding 75%. In the coal slurry transportation sector, composite straight seam steel pipes lined with a 6mm thick ceramic layer offer eight times greater wear resistance than ordinary steel pipes.

Fourth, Industry Development Trends and Challenges of Double-Sided Submerged Arc Welded Straight Seam Steel Pipes.

With the advancement of intelligent manufacturing, leading domestic companies have digitized the entire straight seam welded steel pipe production process. A manufacturing execution system (MES) implemented at one plant enables real-time monitoring of over 200 parameters, including welding current (fluctuation controlled within ±15A) and input energy (18-22kJ/cm), boosting the product qualification rate to 99.92%. However, high-end pipeline steel still relies on imports. For example, 80% of X90/X100 grade steel plates are sourced from companies such as Nippon Steel. Environmental protection requirements are also driving technological innovation. The application of a new generation of low-smoke flux has reduced dust concentrations in welding workshops from 15mg/m³ to 3mg/m³. 

As demand for hydrogen-powered steel pipe construction grows, the research and development of hydrogen-embrittlement-resistant straight-seam welded steel pipe will become a priority. Currently, domestically produced L415H steel-grade products with a hydrogen-induced cracking (HIC) sensitivity index of ≤2% have been trial-produced. However, in the field of deep-sea steel pipes exceeding 1,500 meters, the challenge of controlling welding residual stress in thick-walled straight-seam steel pipes (≥40mm) remains. From land to sea, and from conventional energy to new energy transmission, double-sided submerged arc welded straight-seam steel pipes continue to demonstrate their core value as the lifeblood of industry. Their technological evolution reflects China's manufacturing transformation from scale expansion to quality improvement and heralds the endless possibilities brought about by the integration of new materials and processes. In the context of carbon neutrality, these high-strength and long-life steel pipes will undoubtedly play an even more critical role in the reconstruction of global energy infrastructure.