Some may not be entirely clear on this. Below, we’ll take a closer look at how they differ.
ERW (Electric Resistance Welded) pipe is a longitudinally welded pipe formed by high-frequency resistance welding, while LSAW (Longitudinally Submerged Arc Welded) pipe is a longitudinally welded pipe manufactured using submerged arc welding technology. Although both are classified as longitudinally welded pipes, they differ in manufacturing processes and application scenarios, and therefore cannot be simply equated.
In addition to ERW and LSAW, another common type of longitudinally welded pipe is SSAW (Spiral Submerged Arc Welded) pipe, also known as spiral welded pipe. Longitudinal high-frequency welded pipes can be further divided into induction welding and contact welding based on the welding method. This type of pipe is typically manufactured using hot-rolled wide coils as raw material, undergoing a series of processes including pre-bending, continuous forming, welding, heat treatment, sizing, straightening, and cutting. Compared to spiral welded pipes, longitudinal high-frequency welded pipes offer advantages such as shorter weld seams, high dimensional accuracy, uniform wall thickness, excellent surface quality, and strong pressure-bearing capacity. However, this type of pipe has a smaller production scale and can only produce small- to medium-diameter thin-walled pipes. It is also prone to issues such as gray spots, lack of fusion, and groove corrosion at the weld seam. Currently, longitudinal high-frequency welded pipes are mainly used in urban gas transmission and the transportation of crude oil and refined oil products.
Longitudinal submerged arc welded pipes use individual medium-thick steel plates as raw material, which are formed by pressing through molds or forming machines, and then welded using double-sided submerged arc welding. These pipes have a wide range of specifications, with good weld toughness and plasticity, and offer advantages such as large diameter, thick wall thickness, high pressure resistance, low-temperature resistance, and strong corrosion resistance. In the construction of long-distance oil and gas pipelines requiring high strength, high toughness, and high quality, large-diameter thick-walled longitudinal submerged arc welded pipes are typically required. According to API standards, in large-scale oil and gas transmission pipelines passing through Class 1 and Class 2 areas such as alpine regions, seabeds, or densely populated urban areas, longitudinal submerged arc welded pipes are the only designated pipe type permitted. Based on forming methods, longitudinal submerged arc welded pipes can be further classified into UOE, JCOE, and HME types.
Spiral submerged arc welded pipes are formed during the coiling process, where the forward direction of the pipe forms a certain forming angle with the centerline of the pipe being formed, with welding taking place simultaneously, resulting in a spiral weld seam. The advantages of this type of pipe include the ability to produce various diameters from the same specification, a wide range of raw material adaptability, and the ability to avoid primary stress along the weld, resulting in favorable stress conditions. However, spiral submerged arc welded pipes have poorer geometric dimensional accuracy, longer weld seams, and are prone to welding defects such as cracks, porosity, slag inclusions, and weld misalignment. The welding stress is primarily tensile stress. In design specifications for long-distance oil and gas pipelines, spiral submerged arc welded pipes are typically limited to Class 3 or Class 4 areas.
Although spiral submerged arc welded pipes are still used in some areas, in foreign countries—particularly the United States, Japan, and Germany—this process is generally considered unsuitable for trunk line construction, as the welding quality is believed to be difficult to meet high standards. Canada and Italy use spiral submerged arc welded pipes to a certain extent, while Russia uses them in limited quantities, all under very strict supplementary conditions. Due to historical reasons, many domestic trunk line projects still use spiral submerged arc welded pipes, despite the fact that some improvement measures have been proposed.
