Seamless, ERW (Electric Resistance Welded), and large-diameter welded (LSAW/SSAW) pipe differ in how they’re manufactured — and that manufacturing route decides pressure rating, size availability, cost, and which applications each is suited for.
Manufacturing Process
- Seamless: A solid round steel billet is pierced and hot-extruded/rolled into a hollow tube with no weld seam anywhere along its length or circumference.
- ERW (Electric Resistance Welded): Flat steel strip/coil is formed into a cylinder and the longitudinal edge is fused using high-frequency electric resistance heating, under pressure, without filler metal.
- LSAW / SSAW (large-diameter welded): Steel plate is formed and the seam is welded using submerged arc welding (SAW) — longitudinally (LSAW) or spirally (SSAW/HSAW) — typically used for larger diameters than ERW mills can produce economically.
Side-by-Side Comparison
| Factor | Seamless | ERW | LSAW / SSAW |
|---|---|---|---|
| Weld Seam | None | One longitudinal seam | One longitudinal or spiral seam |
| Typical Size Range | 1/8″ to 24″ NB (mill-dependent) | 1/2″ to 24″ NB | 16″ NB and above, up to very large diameters |
| Pressure/Temp Service | Preferred for high-pressure, high-temperature & critical service | Good for low-to-medium pressure; seam strength depends on weld quality control | Engineered for high-pressure long-distance transmission when properly qualified |
| Relative Cost | Highest (more material, slower process) | Lowest for small-to-mid sizes | Most economical route for large diameters |
| Wall Thickness Uniformity | Slightly more eccentricity (process-inherent) | Very consistent OD and wall thickness | Consistent; plate thickness is controlled before forming |
| Common Standards | ASTM A106, A312, A333, API 5L (seamless) | ASTM A53 (Type E), IS 1239, API 5L (welded) | API 5L PSL1/PSL2, IS 3589 |
| Typical Applications | Boiler & steam lines, high-pressure process piping, refinery/power plant piping | Water lines, structural tube, low-pressure fluid transfer, fencing/scaffolding | Cross-country oil & gas pipelines, water transmission mains |
Which Should You Choose?
If the application involves high pressure, high temperature, or a code that mandates seamless construction (many boiler and refinery specs do), seamless is the only correct choice — there’s no substitute. For general fluid transfer, structural, and lower-pressure service where the specification allows it, ERW delivers equivalent performance at meaningfully lower cost and is the more economical, widely available option across most NB sizes. For large-diameter transmission pipeline work, LSAW/SSAW is the standard and often the only commercially viable route, since seamless mills rarely produce economically above 24″ NB.
Always confirm the governing project specification before substituting one manufacturing route for another — many codes (ASME Section I boiler code, for example) explicitly require seamless construction regardless of cost. Seamless Steel Industries stocks and supplies both seamless and ERW/welded pipe across CS, MS, SS and alloy grades — let us know your service conditions and we’ll recommend the right construction type.