Quick answer: choose by diameter, pressure, and what you can inspect
The three welded-pipe processes are not interchangeable — they cover different diameter and wall-thickness ranges, different pressure classes, and different inspection expectations. In one line: ERW for smaller-diameter, lower-to-medium-pressure water, gas, and structural pipe; SSAW (spiral SAW) for large-diameter, lower-to-medium-pressure water, piling, and gas; LSAW (longitudinal SAW) for large-diameter, thick-wall, high-pressure oil and gas trunk lines. Pick the process that matches your diameter, pressure, and NDT requirement, then specify the standard and inspection level — that combination, not “welded pipe” alone, is what protects you on a big order.
The three processes at a glance
| ERW (HFW) | LSAW (JCOE / UOE) | SSAW (spiral SAW) | |
|---|---|---|---|
| How the seam is welded | High-frequency resistance, no filler | Submerged arc, longitudinal, with filler | Submerged arc, spiral, with filler (ID + OD) |
| Typical OD range | ~6–660 mm (up to ~26″) | ~406–1626 mm (16–64″) | ~219–3000 mm+ (8–120″) |
| Wall thickness | Thin to medium | Medium to very thick (up to ~50 mm+) | Medium |
| Weld length per meter | Shortest (1 longitudinal seam) | Short (1 longitudinal seam) | Longest (spiral seam, ~1.5–3× pipe length) |
| Pressure class | Low to medium | High | Medium |
| Dimensional accuracy | Good | Best (tight straightness/ovality) | Good (more ovality variation) |
| Relative cost | Lowest (small/medium OD) | Highest (critical service) | Economical for large OD |
| Typical standards | API 5L, ASTM A53, A500, A795, EN 10219 | API 5L, DNV, CSA Z245, IS 3589 | API 5L, ASTM A252, EN 10217, SY/T 5037 |
For the standards behind oil and gas linepipe specifically, our API 5L pipe buying guide covers PSL1 vs PSL2 and what to confirm before order, and our A36 / A53 / A106 comparison covers carbon-pipe grade selection.
ERW: economical for distribution and structural
ERW pipe is roll-formed from coil and welded along a single longitudinal seam by high-frequency current — no filler metal, no flux. Modern HFW (high-frequency welded) ERW is a clean, reliable process; the old reputation of low-frequency ERW came from pre-1970s mills and does not apply to current product.
Where it fits:
- City water and gas distribution mains (ASTM A53, A795; API 5L up to about X70 for lower-stress lines).
- Structural tubing and piling of smaller diameter (ASTM A500, A252 for smaller piling).
- Conduit, fencing, agricultural, and mechanical tubing.
Buyer checks: confirm the weld seam has been normalized (induction) to erase the brittle weld zone, require UT or eddy-current of the seam, and for pressure service require a hydrotest. If you are sourcing for corrosive or high-purity service, note that ERW is carbon steel — for stainless process pipe, our ASTM A312 stainless pipe guide is the relevant spec.
SSAW: large diameter from narrow strip
SSAW forms coil into a spiral and welds both the inside and outside seam by submerged arc. Its big advantage is that large-diameter pipe can be made from relatively narrow strip, so it is economical for big OD that ERW cannot reach and LSAW cannot match on cost for non-critical service.
Where it fits:
- Water transmission and large-diameter municipal mains.
- Piling pipe (ASTM A252) for harbors, bridges, and retaining walls.
- Low- and medium-pressure gas and oil gathering where the design code permits spiral weld.
- Penstocks, outfalls, and structural piles needing large OD at moderate wall.
Buyer checks: because the spiral seam is long, full-length weld inspection matters — require 100% UT of the seam plus radiography on the weld ends and any tie-ins, and check ovality/straightness against the standard. Some end-users restrict SSAW for high-pressure gas due to the longer weld path; confirm your design code and end-user spec allow it before committing.
LSAW: thick wall, high pressure, critical service
LSAW starts from plate (not coil), formed by JCOE or UOE pressing into a cylinder, then welded with a single longitudinal submerged-arc seam, often with an inside and outside pass. Because it uses plate, it can reach the thick walls and tight dimensional accuracy that high-pressure trunk lines demand.
Where it fits:
- Long-distance, high-pressure oil and gas transmission (API 5L up to X80, PSL2).
- Offshore and subsea pipelines (often to DNV or API 5L supplementary requirements).
- Penstocks and large-diameter thick-wall structural and pressure applications.
Buyer checks: this is the most inspected of the three — expect full-body UT, 100% radiography of the longitudinal seam (or a defined percentage per the standard), hydraulic test, and full traceability with EN 10204 3.1 or 3.2 MTC. For sour service, add NACE MR0175 / ISO 15156 and HIC/SWC testing.
Selection by application
- Long-distance high-pressure gas/oil trunk line: LSAW, API 5L PSL2, full NDT.
- City gas/water distribution, structural tubing: ERW, A53 / A500 / API 5L PSL1.
- Large-diameter water transmission, penstock: SSAW or LSAW by pressure class.
- Piling (A252): SSAW for large OD, ERW/LSAW for smaller or higher-load piles.
- Process and corrosive service: seamless or welded stainless per A312 — carbon welded pipe is not the right answer here.
What to specify on your purchase order
- Standard and grade: API 5L PSL1/PSL2 + grade (e.g. X52, X65), or ASTM A53 / A500 / A252 / A795, or EN 10217 / 10219.
- Weld process: ERW / LSAW / SSAW — name it, do not leave it to the supplier.
- OD, wall thickness, and tolerance class; length and bevel/end finish.
- NDT level: seam UT (100% for LSAW/SSAW critical service), radiography scope, hydrotest pressure.
- Coating: bare, FBE, 3LPE/3LPP, coal-tar enamel, or cement lining for water — state the standard (e.g. DIN 30670 for 3LPE).
- Mill Test Certificate EN 10204 3.1 (or 3.2 for pressure/cross-border) — see our MTC reading guide.
- For linepipe: chemistry limits (CEV / Pcm), CVN toughness at design temperature, and NACE testing if sour.
- Calculate landed weight and container/pack planning up front — our steel weight calculation guide has the pipe formula.
Common mistakes buyers make
- Quoting “welded pipe” without naming the process. Three suppliers can return ERW, SSAW, and LSAW for the same RFQ — and they are not the same product.
- Using SSAW for high-pressure gas where the end-user or design code restricts spiral weld. Always check the code first.
- Accepting ERW without seam normalization for pressure service. The as-welded seam is brittle; induction normalizing is standard on quality ERW.
- Under-specifying NDT on large-OD pipe. A long spiral or thick longitudinal seam needs defined UT and radiography — “tested” is not a specification.
- No pre-shipment inspection on a large pipe order. At pipe volumes, dimensional and coating defects are expensive to discover at site. See our pre-shipment inspection checklist and import documents checklist.
Bottom line
ERW, SSAW, and LSAW each own a clear slice of the welded-pipe market by diameter, wall, and pressure class. Name the process on the PO, lock the standard and NDT level, require the right MTC, and inspect before shipment. Do that and the pipe you receive will match the service it was designed for — instead of being the cheapest option a supplier could fit into an under-specified order.