ERW, LSAW and HSAW are the three welded pipe processes that dominate water, oil and gas transmission lines. This guide explains how the three processes differ, where each is the right call, and how to pick the right one for water mains, crude oil trunk lines and gas transmission.
Welded steel pipe for water, oil and gas transmission is produced by three fundamentally different processes: Electric Resistance Welded (ERW), Longitudinal Submerged Arc Welded (LSAW, also called DSAW), and Helical (spiral) Submerged Arc Welded (HSAW, also called SSAW). The choice between the three is driven by diameter, pressure, line length and the project code. Picking the wrong process leads to higher cost, longer delivery, or in the worst case, weld defects under service.
ERW: Electric Resistance Welded
ERW pipe is produced by forming steel strip into a tube and welding the longitudinal seam using the electrical resistance of the steel to heat generated at the seam. Modern ERW pipe uses high-frequency induction (HF-ERW) and the weld is heat-treated in-line to give a normalized weld zone with mechanical properties matching the base metal. ERW is the most economical process and dominates the small to medium diameter range (NPS 2 to NPS 24) for water mains, oil and gas gathering, and structural applications. The weld is fully radiographed and hydrostatically tested before shipment.
LSAW: Longitudinal Submerged Arc Welded
LSAW pipe is produced by forming steel plate (not strip) into a U-shape then an O-shape, and welding the longitudinal seam with submerged arc welding (SAW) from both inside and outside. The result is a heavy-duty pipe with very thick walls (up to 50 mm or more) and very large diameters (NPS 24 to NPS 60). LSAW is the dominant process for high-pressure gas and oil trunk lines, for offshore pipelines, and for any project requiring API 5L PSL2 pipe above NPS 24. The thicker walls and the double-submerged-arc weld give excellent toughness and dimensional accuracy.
HSAW: Helical Submerged Arc Welded
HSAW (also called SSAW) pipe is produced by helically forming steel strip into a tube at an angle to the strip axis, then welding the spiral seam with submerged arc welding. HSAW can produce very large diameters (up to NPS 100 or more) from narrower strip, which means the mill can supply large diameter pipe without the heavy plate mills required for LSAW. HSAW is widely used for water transmission mains, low-pressure oil pipelines, piling, and structural applications where the high pressure and toughness of LSAW are not required. The spiral seam has a different stress distribution than the longitudinal seam of LSAW, which limits HSAW's use in high-pressure service.
Which Process to Specify for Which Project
For water mains and gathering systems up to NPS 24, default to ERW pipe per API 5L. For crude oil and gas trunk lines above NPS 24 at design pressures above about 600 psi, default to LSAW per API 5L PSL2. For large-diameter water mains and low-pressure oil lines where cost matters more than high-pressure capability, HSAW per API 5L or AWWA C200 is the right choice. Confirm the project specification (ASME B31.4 for oil, B31.8 for gas, or AWWA C200 for water) for the exact qualification requirements, including Charpy impact testing, NACE compliance for sour service, and the hydrostatic test pressure.
What to Specify on the Line Pipe RFQ
State the standard (API 5L, AWWA C200, or EN 10219), the product specification level (PSL1 or PSL2), the grade (A25, A, B, X42, X52, X65, X70 etc.), the manufacturing process (ERW, LSAW, HSAW), the diameter and wall thickness, the pipe length (random or double random), and the supplementary requirements (Charpy, NACE, hydrostatic test pressure). For high-pressure gas trunk lines, default to LSAW PSL2 with NACE if sour service; for water and gathering, default to ERW or HSAW depending on diameter. Confirm the mill test certificate per EN 10204 3.1 shows the actual chemistry and mechanical properties.
Related Resources from Baobin Steel
- Carbon steel pipe catalog – ERW, LSAW and HSAW options
- Mild steel overview – grades and standards
- Request a quote – send your line class for welded pipe pricing