LSAW vs ERW vs seamless pipe: which one for your pipeline?
Short answer: the welding process follows the diameter, the wall thickness and the duty — not the price list. Up to about 24″ in thin wall, ERW is economical; above roughly 16″/406 mm in transmission duty, LSAW (JCOE) is the standard product; seamless stays the answer for small diameter and the most severe pressure or temperature service.
The three processes in one table
| ERW | LSAW (JCOE / UOE) | Seamless | |
|---|---|---|---|
| How it is made | Coil formed and welded by electric resistance | Plate formed (J-C-O), welded from both sides with filler, then expanded | Billet pierced and rolled — no weld |
| Typical outside diameter | ½″ – 24″ (up to ~610 mm) | 406.4 – 1422.4 mm | 21.3 – 660 mm |
| Wall thickness | Thin to medium | 6.35 – 52.37 mm | Thick in small diameter |
| Seam | One longitudinal, no filler metal | One longitudinal, welded both sides | None |
| Where it belongs | Water, low-pressure gas, structural, smaller lines | Oil and gas transmission, sour service, submarine lines | High pressure / high temperature, boiler, refinery, casing |
| Relative cost per tonne | Lowest | Middle | Highest for the same wall |
| Watch out for | The weld seam is the weak point; limited wall | Forming and welding discipline — the reason we run 11 × 100% inspection | Diameter and length limits; price |
Three questions decide it
1. How big is the pipe?
Above about 24″ you are out of the ERW range. Above 16″ on a transmission line, LSAW is the normal specification — the plate route is the only economical way to make a 48″ or 56″ pipe with a predictable, tested weld.
2. What pressure and medium?
High-pressure gas transmission, sour service and submarine lines push you to LSAW with PSL2 testing. Water lines and low-pressure networks rarely justify it — ERW is cheaper and perfectly adequate.
3. What temperature?
Steam, hot process lines and high-temperature service are seamless territory: small diameter, heavy wall, no seam to heat treat around. Where the project needs both — a large pipeline and a hot tie-in — the two products meet at the flange.
Standards do not choose the process for you
API 5L / ISO 3183 covers all three processes. PSL1 gives you the basic grade and test regime; PSL2 adds tighter chemistry, tensile and impact requirements, more frequent testing and traceability — which is what oil and gas transmission projects normally specify, whatever the welding process.
That means two mills can quote the same “API 5L X65 PSL2” pipe in different processes and different prices, and both can be compliant. The commercial question is which one your engineering specification actually asks for — and the technical question is whether the process can deliver the diameter, wall and test level you need.
What to put in the enquiry
- Standard and grade: API 5L / ISO 3183, X60 / X65 / X70 / X80 (L415 – L555), PSL1 or PSL2
- Outside diameter and wall thickness (mm), not just the nominal size
- Length, and whether random or fixed lengths
- Coating: bare, FBE, 3LPE, 3LPP or internal lining
- Service conditions: sour (NACE MR0175 / ISO 15156), low temperature, hydrogen or CO₂
- Inspection and documents: third party, MTC EN 10204 3.1, weld and test records
- Destination port and required date — it decides packing and shipping method
Mistakes we see in tenders
“Seamless” written for a 48″ line
Seamless is not made at that diameter — the enquiry either comes back as LSAW or it dies. Ask the question at design stage, not at purchase order stage.
ERW chosen for heavy wall high pressure
The coil route has a wall limit, and the seam is the part your inspector will look at first. If the line is high pressure, the process should follow the duty.
PSL1 quoted for a PSL2 job
The price looks better because the test regime is lighter. On delivery it is a rejection. State PSL2, and the impact test temperature, up front.
Coating left to the last minute
FBE and 3LPE change the handling, the stack height and the delivery time. A coating agreed after the pipe is rolled is a second production step, not a detail.
Questions we answer every week
Is seamless pipe always better than LSAW pipe?
No. For pipelines above roughly 16″/406 mm, LSAW/JCOE is the standard product: plate formed, welded from both sides, expanded and tested 100%, which delivers a round, straight pipe with predictable properties at a diameter seamless cannot reach economically.
At what diameter does ERW stop being the right choice?
Around 24″ (610 mm) in thin to medium wall. Above that, and wherever heavy wall or high internal pressure is involved, LSAW takes over.
Can LSAW pipe be used for sour service?
Yes — with chemistry and heat treatment controlled for hardness, PSL2 testing, and HIC / SSC testing to NACE MR0175 / ISO 15156 agreed before the order. Sour service changes the steel and the inspection plan, so it has to be stated at enquiry stage.
What is JCOE, and why does it matter to the buyer?
J-C-O-E is the forming sequence — the plate is pressed into a “J”, then a “C”, then an “O”, welded, and finally expanded (E). The expansion step is what gives the finished pipe its roundness, straightness and uniform residual stress, which is what pipe-laying equipment and automatic welding crews need.
Send the line parameters — we will confirm the process and quote it
Medium, design pressure, design temperature, diameter × wall, quantity and destination port are enough to start. We reply with the process (LSAW / seamless / ERW), the grade, and a price — normally within one working day.