An authoritative side-by-side technical comparison of SSAW (Spiral Submerged Arc Welded) and LSAW (Longitudinal Submerged Arc Welded) steel pipe. Manufacturing process differences, diameter ranges, cost analysis, application recommendations, and pros/cons to guide your welded pipe selection.
Both SSAW and LSAW are SAW (Submerged Arc Welding) processes — they use a continuously fed wire electrode beneath a blanket of granular flux that protects the arc and molten weld metal from atmospheric contamination. The fundamental difference is the orientation of the weld seam relative to the pipe axis.
LSAW pipe is manufactured by forming a steel plate into a cylindrical shape and welding a single longitudinal seam (parallel to the pipe axis). The two main forming processes are UOE (U-ing, O-ing, Expansion) and JCOE (J-forming, C-forming, O-forming, Expansion). The plate is first edge-milled, then crimped at both edges, progressively formed into a J-shape, then a C-shape, and finally an O-shape before welding. After welding, the pipe is mechanically expanded (cold expansion) to achieve precise dimensions and relieve welding stresses.
SSAW pipe is manufactured by continuously feeding hot-rolled steel coil (strip) at an angle through a forming mill. As the strip is formed into a cylinder, a continuous spiral weld seam is deposited simultaneously from both the inside and outside. The spiral angle (typically 40-75 degrees relative to the pipe axis) determines the relationship between strip width and pipe diameter. The process is continuous — pipe is cut to length as it exits the forming/welding line.
| Characteristic | SSAW (Spiral Welded) | LSAW (Longitudinal Welded) |
|---|---|---|
| Weld Orientation | Spiral (helical) seam at an angle to pipe axis | Single straight seam parallel to pipe axis |
| Raw Material | Hot-rolled steel coil (strip), up to ~2m wide | Steel plate, cut to size for each pipe OD |
| OD Range | 8" – 120" (219 – 3048 mm) | 16" – 64" (406 – 1626 mm); some mills up to 100" |
| Wall Thickness | 5 – 25 mm (limited by coil thickness) | 6 – 60 mm (plate can be thicker than coil) |
| Length Capability | 6 – 24m (limited by transport, not process) | 6 – 18m (standard); double-jointing possible |
| Production Speed | High — continuous process, 2-8 m/min | Lower — batch process, 3-5 pipes per hour per line |
| Diameter Flexibility | Extremely flexible — change forming angle for different OD from same coil width | Limited — each OD requires dedicated forming tools (or adjustable JCO press) |
| Weld Length per Meter of Pipe | Longer (1/sin(angle) times pipe length) | Exactly one meter of weld per meter of pipe |
| Dimensional Accuracy | Good — within API 5L tolerances | Excellent — cold expansion provides tight OD and ovality control |
| Residual Stress | Moderate — spiral weld geometry creates complex stress pattern | Lower — cold expansion relieves forming and welding stresses |
| Cost per Ton (typical) | Lower — 10-20% less than LSAW for comparable sizes | Higher — more processing steps, slower production |
| Min Order Quantity | Lower — flexible production, smaller runs possible | Higher — typically 50-100 tons minimum |
| API 5L PSL2 Capability | Yes — full PSL2 compliance achievable | Yes — PSL2 with excellent consistency |
| High-Pressure Service | Suitable — widely used in transmission pipelines | Preferred — tighter tolerances, lower residual stress |
| Sour Service (NACE) | Possible — requires strict process control | Better — proven performance, easier NDT of single seam |
| Process Step | SSAW | LSAW (JCOE) |
|---|---|---|
| 1. Material Preparation | Uncoil, level, trim strip edges | UT of plate, edge milling (bevel preparation) |
| 2. Forming | Continuous spiral forming at angle; three-roll bending | Edge crimping -> J-forming -> C-forming -> O-forming (progressive press) |
| 3. Tack Welding | Continuous tack weld (often CO₂ gas-shielded) | Tack weld along longitudinal seam |
| 4. Inside Welding | SAW from inside, continuous | SAW from inside, single pass or multipass |
| 5. Outside Welding | SAW from outside, continuous | SAW from outside, single pass or multipass |
| 6. Expansion | Not standard (optional) | Cold mechanical expansion (0.8-1.5% strain) — standard |
| 7. NDT | 100% UT of full spiral seam length (continuous) | 100% UT + RT of longitudinal seam ends; full-length UT |
| 8. Hydro Testing | Individual pipe hydrostatic test | Individual pipe hydrostatic test |
| 9. End Finishing | Beveling per API 5L / customer spec | Beveling per API 5L / customer spec |
| Application | Recommended Type | Rationale |
|---|---|---|
| High-pressure gas transmission (onshore) | LSAW (preferred) or SSAW | LSAW for X70+, SSAW for X52-X65 where cost is key |
| Offshore / subsea pipelines | LSAW | Tighter tolerances, lower residual stress, CTOD proven |
| Large-diameter water transmission | SSAW | Best cost for diameters 24-120"; AWWA C200 compliant |
| Pipe piling (structural) | SSAW | Cost-effective for large-diameter piling; wall thickness sufficient |
| Sour service pipelines | LSAW | Proven NACE compliance, reliable hardness control |
| Slurry / mining pipelines | SSAW | Cost-effective, large diameters available, acceptable for non-critical fluids |
| Penstock (hydroelectric) | LSAW or SSAW | LSAW for high-head (high pressure); SSAW for low-head large diameter |
| Bridge / high-rise structural columns | LSAW | Tighter straightness and ovality for structural fit-up |
| Process plant piping (low pressure) | SSAW | Cost-effective for large-diameter, low-pressure applications |
| Casing pipes (road boring, tunnel) | SSAW | Economical, wide OD range, continuous length advantage |
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