“Seamless or welded?” is usually the first fork in any line pipe enquiry — and the honest answer is that modern welded pipe has closed most of the historical gap. The right choice today is mostly a function of diameter, service and budget, not blanket rules.
How each type is made
Seamless (SMLS) pipe starts as a solid billet, pierced and rolled into a hollow — no weld seam anywhere in the body. ERW (Electric Resistance Welded) pipe is formed from strip and welded longitudinally without filler metal, then the weld zone is heat-treated. LSAW (Longitudinal Submerged Arc Welded) pipe is formed from heavy plate and welded inside and out — the standard route for large diameters. All three are recognized in API 5L for both PSL 1 and PSL 2 line pipe.
Where each wins
Seamless dominates in:
- Smaller diameters and heavier walls (roughly up to 16”, where mills roll it economically)
- Sour and high-pressure service where buyers prefer no long seam to inspect
- Well environments — casing and tubing are overwhelmingly seamless
ERW is the value choice for:
- Small-to-mid diameters (up to 24”) in standard transmission and distribution service
- Projects where tonnage is large and wall thicknesses are moderate
- Schedules that benefit from ERW’s shorter mill lead times
LSAW takes over where seamless physically cannot go:
- Large diameters — 16” to 84” and beyond, in line pipe and structural service
- Heavy-wall offshore and high-pressure transmission lines
- Piling and structural tubulars rolled from plate
The inspection question
Buyers sometimes treat “welded” as “lower quality.” Under API 5L PSL 2, welded pipe carries mandatory non-destructive examination of the weld seam, hydrostatic testing and toughness requirements — and a modern LSAW double-submerged-arc seam is a thoroughly inspected piece of steel. What matters for your order is that testing is documented and independently witnessed: CSACI shipments carry a Certificate of Conformity, Certificate of Origin and an SGS third-party international inspection certificate, whichever manufacturing route the material took.
A simple decision path
- Over 24” OD? LSAW.
- Sour service, heavy wall or downhole? Seamless first; ERW only with your engineer’s blessing.
- Standard sweet-service transmission up to 24”? Price ERW against seamless — the savings are often 15–30% and entirely legitimate.
- Unsure? Quote both. The comparison costs nothing.
Send your line list — diameters, walls, grade and service — and we will quote the routes that make sense side by side. Request a quotation or browse the API 5L line pipe range.