ERW stands for Electric Resistance Welding longitudinal seam pipe; LSAW refers to Submerged Arc Welding longitudinal seam pipe; both are longitudinal seam pipes, but they differ in welding techniques and applications, thus cannot be solely representative of longitudinal seam pipes. Another commonly used type is SSAW spiral seam pipe.
Seamless High-Frequency (ERW) pipes are further categorized into two types based on the welding method: induction welding and contact welding. Made from hot-rolled wide coils, these pipes undergo processes such as pre-bending, continuous shaping, welding, heat treatment, sizing, straightening, and cutting. Compared to spiral pipes, ERW pipes offer advantages like shorter weld seams, high dimensional accuracy, even wall thickness, good surface quality, and high pressure resistance. However, their limitations include the ability to produce only small and medium-sized thin-walled pipes, with the risk of gray spots, incomplete fusion, and groove-like corrosion defects at the weld joints. Currently, they are widely used in fields such as city gas and refined oil transportation.
The Longitudinal Submerged Arc Welding (LSAW) process involves using a single sheet of medium to thick plate, which is pressed (coiled) into shape within a mold or forming machine. It is then produced through double-sided submerged arc welding and diameter enlargement. The finished product offers a wide range of specifications, with excellent toughness, plasticity, uniformity, and density in the weld seams. It boasts advantages such as large pipe diameter, thick wall, high-pressure resistance, low-temperature resistance, and strong anti-corrosion properties. In the construction of high-strength, high-toughness, and high-quality long-distance oil and gas pipelines, most of the required steel pipes are large-diameter thick-walled LSAW pipes. According to API standards, in large-scale oil and gas transmission pipelines, LSAW is the applicable pipe type when passing through Class 1 and Class 2 areas such as cold regions, underwater, and densely populated urban areas. It can be further categorized based on the forming method into UOE/JCOE/HME.
SSAW (Spiral Submerged Arc Welding) involves a forming angle (adjustable) between the forward direction of the coiled pipe and the centerline of the shaped pipe, welding as it forms, creating a helical weld seam. Its advantages include the ability to produce pipes of various diameters from the same specification, a wide range of raw material adaptability, the ability to avoid the main stress, and better load-bearing conditions. However, it has drawbacks such as poor geometric dimensions, longer weld seam lengths compared to straight seam pipes, and a higher likelihood of welding defects like cracks, gas holes, slag inclusions, and misalignment. The welding stress is in a tensile state. Generally, the design specifications for long-distance oil and gas pipelines only allow the use of SAW in Class 3 and 4 areas. Abroad, after improving this process, the raw material has been changed to steel plates, separating the forming and welding processes, followed by pre-welding and fine welding, and then cold expansion of the diameter, resulting in welding quality comparable to UOE pipes. Currently, this process is not available domestically and represents a direction for domestic factory improvement. The "West-to-East Gas Transmission" project still uses traditional production methods, with only the pipe ends expanded. The United States, Japan, and Germany generally reject SAW for main pipelines; Canada and Italy use it partially, Russia uses it minimally, and all have established very strict supplementary conditions. Due to historical reasons, most domestic main pipelines still use SAW.
1. Welded pipe refers to the common "submerged arc welded steel pipe," denoted as "SC" in electrical engineering.
2. Conduit pipe, also known as wire conduit, is thinner and represented by the letter "T." It is only used for wiring purposes.
3. ERW pipes are "high-frequency resistance-welded steel pipes," differing from the welding process of ordinary welded pipes. The welds are formed by melting the base material of the steel strip, resulting in higher mechanical strength compared to general welded pipes.
