ERW vs SMLS Pipe

The ERW vs SMLS pipe manufacturing difference comes down to one factor: the weld seam. ERW (Electric Resistance Welded) pipe is made by forming steel coil into a tube and welding the longitudinal seam using electric resistance heating. SMLS (Seamless) pipe is made by piercing a solid billet with no weld seam. This difference affects pressure rating, cost, delivery time, and allowable service conditions.

The ERW vs SMLS pipe choice is one of the most frequent decisions in piping material selection. Both pipe types can meet the same ASTM and API 5L specifications, but their manufacturing processes create distinct characteristics that make each type better suited for specific applications.

Manufacturing Comparison

Feature	ERW Pipe	SMLS Pipe
Raw material	Hot-rolled steel coil/strip	Solid round steel billet
Forming	Coil unrolled and shaped into tube	Billet heated and pierced
Weld seam	Longitudinal (resistance welded)	None
Weld heat input	Low (no filler metal)	N/A
Wall uniformity	Excellent (±5-8%)	Moderate (±12.5%)
OD tolerance	Tighter	Standard
Surface finish	Smoother	Rougher (hot-finished)
Max. size (typical)	NPS 24	NPS 24
Min. size	NPS 1/2	NPS 1/8
Production speed	High (continuous process)	Lower (batch process)

Performance and Cost

Parameter	ERW Pipe	SMLS Pipe
Weld joint factor (E)	0.85-1.0 (per ASME B31.3)	1.0
Pressure rating	Lower (when E < 1.0)	Higher
Cost	15-30% less than SMLS	Higher
Lead time	Shorter (wider stock)	Longer for special sizes
Sour service (NACE)	Restricted (HAZ concerns)	Preferred
High-temperature use	Limited	Standard (A106, A335)
NDT on weld	UT or eddy current (100%)	Not applicable
Hydrostatic test	Mandatory	Mandatory

When to Use ERW Pipe

ERW pipe is suitable and cost-effective for:

• Moderate-pressure piping systems (utility water, air, low-pressure steam)
• Structural and mechanical applications
• Pipeline applications where ERW meets the design code (API 5L ERW with E = 1.0 after proper examination)
• Projects where budget and delivery schedule are critical
• Line pipe sizes NPS 2 to NPS 24 for non-critical services

When to Use SMLS Pipe

SMLS pipe is required or preferred for:

• High-pressure process piping per ASME B31.3 where E = 1.0 is needed
• Sour service per NACE MR0175/ISO 15156
• High-temperature service (ASTM A335 Cr-Mo alloys)
• Low-temperature service (ASTM A333)
• Small-bore piping (NPS 2 and below)
• Critical services in refineries, offshore platforms, and chemical plants

Pro Tip

Modern ERW pipe with proper heat treatment and full-length ultrasonic testing achieves a weld joint factor E = 1.0 per ASME B31.3. This means ERW can match SMLS pressure ratings for many applications. However, some client specifications and engineering standards still mandate SMLS for specific services regardless of the ERW E-factor. Always check the pipe class specification before assuming ERW is acceptable.

Specification Coverage

Both ERW and SMLS pipe can be supplied to the same specifications, but the product form must be stated:

Specification	ERW Available	SMLS Available
ASTM A53	Type E	Type S
API 5L	ERW (PSL1/PSL2)	SMLS (PSL1/PSL2)
ASTM A106	No	Yes (seamless only)
ASTM A335	No	Yes (seamless only)
ASTM A312	Yes (welded)	Yes

For a detailed comparison of all pipe manufacturing methods, see the complete guide to seamless and welded pipe types.

Read the full guide to pipe types