Submerged arc welded steel pipe is a key product in modern industrial piping. Its diverse manufacturing processes and application scenarios demonstrate the deep integration of materials science and welding technology. Double-Sided Submerged Arc Welded Straight Seam Steel Pipe, with its unique structural properties and process advantages, holds an irreplaceable position in applications such as long-distance pipelines 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 transmission safety.
First, an Analysis of the Core Process of Double-Sided Submerged Arc Welded Straight Seam Steel Pipe
The manufacturing of double-sided Submerged Arc Welded Straight Seam Steel Pipe 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-end 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 air, preventing defects such as porosity and slag inclusions. Compared to conventional straight seam welded pipe, the double-sided submerged arc welding process produces a fine, acicular ferrite structure in the weld area, resulting in impact toughness that is over 30% higher 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, have a yield strength of up to 555 MPa and can withstand transmission pressures exceeding 15 MPa. They are widely used in national 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 spiral welded pipe. While double-sided submerged arc spiral welded steel pipe (such as grade L485M in the GB/T 9711 standard) offers advantages in continuous production and large diameters, straight seam welded pipe excels in pressure stability and dimensional accuracy. Due to the helical distribution of the weld seams in spiral welded pipe, hoop stress decomposition can lead to weak points under high-pressure conditions. In contrast, the longitudinal weld seam of straight seam 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 pipe of the same specification reached 2 million cycles, approximately 1.5 times higher than that of spiral pipe. In terms of production cost, straight seam pipe with a diameter of less than 1420mm can achieve a material utilization rate of 96%, while spiral pipe suffers from approximately 5% scrap loss due to plate width limitations. However, in the ultra-large diameter (e.g., over 3000mm), spiral welded pipe eliminates the need for custom-made, extra-wide steel plates, and its economic advantages begin to become apparent. Notably, straight seam welded pipes are more easily automated for expansion. Mechanical expansion can keep roundness deviation within 0.5%D, a key factor in ensuring accurate pipe jointing.
Third, Innovative Processes and Special Applications for Double-Sided Submerged Arc Welded Straight Seam Steel Pipes
In recent years, straight seam submerged arc welded pipe technology has continued to achieve breakthroughs. In the South China Sea submarine pipeline project, X65 steel-grade straight seam pipes with a double-layer FBE+PP anti-corrosion coating were used. By adding 0.06% Nb as a microalloying element, their low-temperature impact energy at -40°C reached over 220J. In polar pipeline construction, X100 steel-grade pipes produced using the Thermo-Mechanical Control Process (TMCP) achieved a 15% reduction in wall thickness while maintaining excellent crack resistance. Pipes for specialized applications, such as nuclear power plants, require compliance with the Z-direction performance specifications of the RCC-M standard. The straight seam pipes used in the containment vessel of a nuclear power plant utilize specially prepared low-sulfur and phosphorus steel plates (S ≤ 0.002%). Combined with a multi-pass narrow-gap welding process, this achieves a cross-sectional reduction in thickness exceeding 75%. In the coal slurry transportation sector, composite straight seam 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 pipe production process. One factory introduced an MES system that enables real-time monitoring of over 200 parameters, including welding current (fluctuation controlled within ±15A) and line energy (18-22kJ/cm), increasing product qualification rates to 99.92%. However, high-end pipeline steel still relies on imports for raw materials. For example, 80% of X90/X100 grade steel plates must be sourced from companies like Nippon Steel. Environmental protection requirements are also driving technological innovation. The use 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 pipeline construction grows, the research and development of hydrogen-embrittlement-resistant straight seam welded pipes will become a key priority. Currently, domestically produced L415H steel-grade products with a hydrogen-induced cracking (HIC) sensitivity index of ≤2% have been trial-produced. However, for deep-sea pipelines exceeding 1,500 meters, the challenge of controlling weld residual stress in thick-walled straight seam pipes (≥40 mm) remains.
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 lifeblood of industry. Their technological evolution reflects China’s manufacturing transformation from scale expansion to quality improvement and heralds the infinite possibilities presented by the integration of new materials and processes. In the context of carbon neutrality, these high-strength and long-life pipeline products will undoubtedly play an even more critical role in the reconstruction of global energy infrastructure.
Post time: Sep-10-2025