ERW vs Seamless Pipe: Key Differences

Quick Answer

ERW pipe costs 20-40% less than seamless and is available off the shelf in most sizes up to NPS 24. Seamless pipe has no weld seam, carries a joint efficiency factor of 1.0 in ASME B31.3 calculations, and is mandatory for sour service, high-pressure, and high-temperature piping.

Both ERW and seamless pipes can be manufactured to the same material specifications (ASTM A53, API 5L). The difference lies in how they are made and where the engineering code allows each type.

Comparison Table

Feature	ERW Pipe	Seamless Pipe
Weld seam	Longitudinal (HF resistance weld)	None
Manufacturing	Formed from steel coil/strip	Pierced from solid billet
Filler metal	None (pressure weld)	N/A
Joint factor (E)	0.85-1.0 per ASME B31.3	1.0
Size range	NPS 1/2 to NPS 24	NPS 1/8 to NPS 24
Max wall	~25 mm	Up to SCH XXS
Surface finish	Smoother	Rougher (hot-finished)
Dimensional tolerance	Tighter OD/wall	Wider tolerance (±12.5% wall)
Cost	Base	+20-40%
Lead time	Short (stock items)	Longer
NACE MR0175 sour service	Restricted (HAZ concerns)	Preferred
Typical specs	ASTM A53 Type E, API 5L	ASTM A106, ASTM A53 Type S, API 5L

When ERW Is the Right Choice

ERW pipe suits applications where the weld joint factor in the design code does not create a wall thickness penalty that negates the cost advantage:

• Utility services: water, air, low-pressure steam
• Oil and gas gathering systems at moderate pressures
• Structural and mechanical applications
• Fire protection (ASTM A795, A53)
• Fence posts and bollards (ASTM A500)

When Seamless Is Required

Engineering specifications and codes mandate seamless in these cases:

• Design pressure requires E = 1.0 (no weld reduction)
• Sour (H2S) environments per NACE MR0175
• Temperatures above 427°C (ASTM A335 chrome-moly grades)
• Lethal service per ASME B31.3 Chapter VIII
• Small-bore piping (NPS 1.5 and below) where seamless is default

Pro Tip

For NPS 2 to NPS 8 carbon steel in non-sour, moderate-pressure service, ERW pipe per API 5L PSL2 with full-body UT inspection achieves a weld joint factor of 1.0. This can eliminate the cost premium of seamless without compromising design integrity.

Cost Impact on Projects

On a typical oil and gas project, piping materials represent 20-30% of total material cost. Switching from seamless to ERW where permitted by the pipe class specification can reduce the pipe procurement budget by 15-25%. The decision should be documented in the project’s material selection report and approved by the piping engineer.

Read the full guide to pipe types