ERW vs seamless pipe — the difference, the price gap and which specification requires which
Most "seamless" enquiries we receive are for water, structural or fire-fighting lines where ERW pipe is not only acceptable but specified — and 25–60% cheaper. The reverse mistake, ERW where a code demands seamless, is rejected by the inspector. This page draws the line by application and standard.
How each is made
ERW (electric resistance welded): hot-rolled strip is formed into a tube and the longitudinal seam is fused by high-frequency induction without filler metal; the bead is scarfed flush and the seam annealed, then the pipe is sized, cut and tested. Uniform wall, tight OD tolerance, sizes ½"–24", walls 1.5–12 mm. Seamless: a heated solid billet is pierced on a rotary piercer and elongated on a mandrel or plug mill, then sized or cold-drawn. No weld, any wall to 60 mm, some wall eccentricity (±12.5%), sizes ⅛"–24" (larger by forging). Both are carbon steel; the grades differ by standard, not by process.
Side by side
| ERW welded | Seamless | |
|---|---|---|
| Seam | HF weld, heat-treated, NDT-tested | None |
| Wall uniformity | ±10%, very even | ±12.5%, possible eccentricity |
| Wall range | 1.5–12 mm | 2–60 mm (heavy schedules) |
| OD tolerance | ±0.5% (tight) | ±1% |
| Surface | Smooth | Slightly rougher (hot-finished) or bright (cold-drawn) |
| Pressure rating | Code joint factor 0.85–1.0; to ~40 bar general service | Full wall; high pressure |
| Temperature | To ~200 °C general (higher with EN 10217 grades) | To 425–550 °C (A106, P235GH, 16Mo3) |
| Sour / hydrogen service | Limited | Preferred (NACE) |
| Sizes | ½"–24" | ⅛"–24" |
| Price index | 1.00 | 1.25–1.60 |
| Lead time | Stock | Stock for common schedules, 3–6 wk otherwise |
Which standard requires which
| Standard | Process | Typical service |
|---|---|---|
| ASTM A106 | Seamless only | High-temperature steam, refinery, power |
| ASTM A53 | Type E (ERW) or Type S (seamless) | General pressure, water, air — both accepted |
| API 5L | ERW (HFW), SAWL/SAWH or seamless — stated on order | Pipelines; PSL2 sour often seamless |
| EN 10216 | Seamless | Pressure and boiler tubes (PED) |
| EN 10217 | Welded (ERW / SAW) | Pressure tubes, welded — PED accepted |
| EN 10255 | Welded (ERW) | Water, gas, sprinkler, threadable |
| EN 10219 / EN 10210 | Welded cold-formed / hot-finished (seamless or welded) | Structural hollow sections |
| EN 10305-1 / -3 | Seamless cold-drawn / welded cold-sized | Precision, hydraulics, machinery |
| ASME B31.1 / B31.3 | Either, with joint efficiency E (1.0 seamless, 0.85 ERW unless 100% RT) | Power / process piping |
Where ERW is the right (and cheaper) answer
- Building water services, fire sprinklers, compressed air (EN 10255 / A53 E)
- Structural tube: frames, columns, trusses, scaffold, fences (EN 10219)
- Low-pressure gas distribution (EN 10255 heavy)
- Piling and casing at large diameter (spiral SAWH)
- Conduit, handrail, furniture, agricultural lines
Where seamless is required
- Boilers, superheaters, steam lines above 200 °C (A106, EN 10216-2)
- Refinery and petrochemical process piping under ASME B31.3 with A106
- Hydraulic cylinders and high-pressure hydraulic lines (EN 10305-1)
- Sour gas, H₂S service (NACE MR0175)
- Heavy-wall pipe over 12 mm (Sch 80 above 8", Sch 160, XXS)
- Any drawing or spec that states A106, EN 10216, API 5L seamless or "SMLS"
Price gap explained
Seamless costs more because the billet route has lower yield, slower output and tighter chemistry; the gap is smallest on common sizes (2"–6" Sch 40: about 25–35%) and largest on small diameters and heavy walls (50–60%). Both are stocked in Dilovası: see the ERW pipe and seamless pipe pages for the current USD/MT bands.
Can you tell them apart?
On ERW pipe a faint longitudinal line is visible on the ID after scarfing, and the certificate states "welded" (A53 E, HFW); seamless shows no line and a slightly less uniform wall on the cut face; the mill certificate and marking ("SMLS" / "A106") are the proof an inspector accepts. Dual-marked pipe (A53 B / A106 B) is always seamless.
Frequently asked questions
What is the difference between ERW and seamless pipe?
ERW is welded from strip along its length (uniform wall, cheaper, sizes ½"–24", walls to 12 mm); seamless is pierced from a solid billet (no weld, heavy walls, high pressure and temperature, 25–60% dearer). The specification decides which.
Is ERW pipe good for high pressure?
With EN 10217 or A53/API 5L grades and 100% weld NDT it serves to about 40 bar at ambient temperature; boiler, refinery and sour service require seamless under the codes.
Is seamless stronger than ERW?
Not in material terms — the same grade gives the same strength — but the absence of a seam removes the joint factor (0.85 → 1.0) and allows thick walls, so a seamless pipe can carry more pressure at a given size.
Why is A53 sometimes seamless?
A53 covers both Type E (ERW) and Type S (seamless); A106 is seamless only. Dual-marked A53 B / A106 B pipe is seamless.
Which do I need for a fire sprinkler system?
ERW to EN 10255 medium/heavy or A53 Grade B — threaded or grooved; seamless is not required.