What Is LSAW Pipe?
LSAW (Longitudinal Submerged Arc Welded) pipe is a large-diameter welded pipe with a single straight seam running along its length. It is the standard pipe type for long-distance oil and gas transmission pipelines, water mains, and structural piling when diameters exceed what seamless or ERW can supply.
The “submerged arc” refers to the welding method: an electric arc burns beneath a blanket of granular flux, shielding the molten weld pool from atmospheric contamination. This produces a high-quality, deep-penetration weld with excellent mechanical properties.
| Property | LSAW Pipe |
|---|---|
| Weld type | Longitudinal, submerged arc (SAW) |
| Weld passes | 2 (ID + OD) or 1 + ID tack weld |
| Size range | NPS 16 to NPS 60 (OD 406 to 1524 mm) |
| Wall thickness | 6 mm to 40+ mm |
| Length | 6 m to 18 m (typically 12 m) |
| Primary spec | API 5L PSL1 / PSL2 |
| Material grades | API 5L Gr. B to X80 (up to X100 for special projects) |
| Forming methods | UOE, JCOE, or roll-bend |
| NDT | UT + RT on seam, full-body UT, hydrostatic test |
LSAW Manufacturing Methods
Three main forming methods exist:
UOE Process: Steel plate is pressed into a U-shape, then into an O-shape, seam-welded (inside and outside), and mechanically expanded (E). This is the most common method for high-grade pipeline pipe (X65-X80).
JCOE Process: The plate is incrementally formed by a series of J-presses (edges first, then center), welded, and expanded. JCOE mills have lower capital cost than UOE but slower throughput.
Roll-Bend: The plate is progressively rolled into a cylinder. Used for thicker walls and smaller production runs.
All methods require two-pass SAW welding: one internal pass and one external pass, each producing a weld reinforcement (cap). The weld is inspected by ultrasonic and radiographic testing.
Applications
- Cross-country oil and gas transmission pipelines
- High-pressure water transmission mains
- Offshore platform structural members
- Penstocks for hydroelectric plants
- Large-diameter piling pipes for foundations
For a comparison of LSAW with other large-diameter welded pipe types, see LSAW vs DSAW vs SSAW.
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