Introduction to Longitudinal Submerged Arc Welded Pipes (LSAW)
In the modern industrial system, a type of steel pipe—known for its exceptional pressure-bearing capacity and reliable weld quality—quietly underpins the operation of global energy and infrastructure systems. This is the longitudinal submerged arc welded pipe. It is not an ordinary welded pipe; rather, thanks to its unique forming and welding processes, it has become the solution of choice for high-pressure, large-diameter transportation applications.
I. What Are LSAW Steel Pipes?
LSAW stands for Longitudinal Submerged Arc Welding. Unlike spiral submerged arc welded steel pipes (SSAW) or electric resistance welded steel pipes (ERW), LSAW steel pipes are manufactured from a single sheet of medium-to-heavy-gauge steel plate. The plate is formed into a tubular shape through pressure forming, and then a single straight weld seam is welded on both the inner and outer surfaces using submerged arc welding. This "form-first, weld-later" process provides inherent advantages in terms of pipe diameter, wall thickness, and material uniformity.
The range of specifications is extremely broad, typically covering diameters from 406 mm to 1,422 mm, with wall thicknesses of up to 50 mm or more and individual pipe lengths of up to 12.8 meters. The products comply with major international standards such as API 5L, ISO 3183, and GB/T 9711, and are capable of meeting a wide range of stringent requirements, from general water conveyance to the transport of acidic media.
II. Core Manufacturing Process for LSAW Pipes
The production of LSAW pipes begins with rigorous non-destructive testing of steel plates and precision edge milling to ensure accurate weld groove angles. Subsequently, the steel plates are progressively bent and pressed into open pipe blanks using UOE or JCOE forming equipment. After pre-welding and alignment of the seams, high-current submerged arc welding is used to weld both the inner and outer surfaces—this process, protected by flux, produces welds with deep penetration and dense crystallization. After welding is complete, the steel pipes undergo mechanical expansion to relieve forming stresses and ensure roundness. They are then subjected to non-destructive testing (such as ultrasonic and X-ray inspections) and hydrostatic pressure testing to verify the pressure-sealing integrity of each pipe individually. Finally, after end processing and protective coating application, the pipes are ready for shipment.
III. Logic Behind Material Selection for LSAW Pipes
The maximum performance of LSAW pipes depends largely on the selected steel grade. In addition to common carbon steels (such as ASTM A53B), modern long-distance transmission pipelines tend to favor microalloyed high-strength low-alloy steel (HSLA), such as grades X60 through X80. These steels achieve a fine-grained microstructure through controlled rolling and cooling processes, which enhances strength while maintaining good low-temperature toughness.
For corrosive media (such as oil and gas fields containing H₂S), acid-resistant steel (such as X65MS) is typically selected. In offshore engineering or cryogenic environments, however, nickel-based alloy steels or duplex stainless steels (such as 2205) may be used to balance strength and pitting corrosion resistance. The choice of material directly determines the safety margin of the pipeline over its design life.
IV. Advantages of LSAW Compared to ERW and SSAW
Within the family of welded pipes, LSAW occupies a unique niche due to its process characteristics:
Compared to ERW (electric resistance welding): ERW pipes are limited by the width of hot-rolled coil, typically have thinner walls (generally ≤25.4 mm), and feature a weld seam in a hot-extruded state, resulting in complex residual stresses. LSAW pipes have a higher maximum wall thickness, and since the weld is remelted via submerged arc welding, its microstructure is closer to that of the base material, resulting in significantly better resistance to stress corrosion than ERW pipes.
Compared to SSAW (Spiral Submerged Arc Welding): SSAW pipes are formed continuously and at a lower cost, making them suitable for large-diameter, thin-walled pipes. However, they have long weld seams and are subject to significant internal forming stresses. LSAW pipes feature only straight weld seams, which are short in length, making it easier to ensure thorough non-destructive testing coverage. Their geometric dimensional accuracy—particularly ovality—is far superior to that of spiral-welded pipes, and they are more convenient for on-site butt welding.
Therefore, for deep-sea pipelines, high-pressure long-distance natural gas transmission, cryogenic environments, and seismic zones, LSAW pipes are often the preferred pipe type specified by design institutes.
LSAW pipes are currently widely used in onshore oil and gas long-distance transmission lines, deep-sea subsea manifold systems, and municipal high-pressure pipeline networks around the world, serving as core equipment for transnational energy arteries and marine engineering projects. Looking ahead, in response to the demands of hydrogen transportation and carbon capture, utilization, and storage (CCUS), the materials' resistance to hydrogen embrittlement and crack-stopping toughness are being continuously optimized. At the same time, through the integration of fiber-optic sensing and digital twin technologies, pipelines are evolving from "passive pressure-bearing" to “active sensing,” providing reliable support for the global energy transition and smart infrastructure.
Tags: LSAW, longitudinal submerged-arc welded pipe, UOE/JCOE forming, submerged-arc welding process, high-strength low-alloy steel (HSLA), ERW/SSAW comparison,
