Seamless vs ERW vs LSAW

Quick Answer

Seamless pipes have no weld seam and offer the highest pressure integrity. ERW (Electric Resistance Welded) pipes have a longitudinal high-frequency weld seam and are cost-effective for low-to-medium pressure service. LSAW (Longitudinal Submerged Arc Welded) pipes have a single longitudinal SAW seam and are used for large-diameter, heavy-wall pipeline and structural applications. The selection depends on size, pressure, service criticality, and cost.

Manufacturing Process

Seamless: A solid steel billet is heated and pierced to form a hollow shell, then elongated and sized by rolling. No weld seam exists, eliminating seam-related defects and producing a pipe with uniform circumferential strength.

ERW: A flat steel strip (skelp) is formed into a cylinder and the longitudinal edges are welded by high-frequency electrical resistance heating. The weld seam is heat-treated (normalized) and inspected inline. Modern HFW (high-frequency welded) ERW produces consistently high-quality seams.

LSAW: A steel plate is formed into a cylinder using the U-O-E or JCOE process, and the longitudinal seam is welded from both inside and outside by submerged arc welding. The heavy SAW seam allows large diameters and thick walls.

Comparison Table

Feature	Seamless	ERW (HFW)	LSAW
Weld seam	None	Longitudinal (HF resistance)	Longitudinal (SAW, ID + OD)
Size range	1/8” to 24” NPS	2” to 24” NPS	16” to 60”+ NPS
Wall thickness	Up to Sch. XXS (~60 mm)	Up to ~25 mm	Up to 40-50 mm
Weld joint factor (E)	1.00	0.85-1.00 (per code)	1.00 (with full RT)
Pressure rating	Highest for a given wall	Moderate	High (large diameters)
Dimensional tolerance	Wider OD/WT tolerance	Tighter (formed from strip)	Tight OD; moderate WT
Surface finish	Mill scale (hot finished)	Smoother	Mill scale
NDT requirement	UT per ASTM/API	Full-length seam UT/ET	RT or UT of full seam
Typical specifications	A106, A335, API 5L PSL2	API 5L PSL1/PSL2, A53 Type E	API 5L PSL2
Cost (same size/wall)	Highest	Lowest	Moderate
Lead time	Moderate to long	Short	Moderate

Selection Guide

Application	Recommended Type	Reason
Process piping (refinery, chemical)	Seamless	No seam-related defects; code preference
High-pressure/high-temperature	Seamless	Full E-factor (1.00); no weld concerns
Sour service (NACE MR0175)	Seamless preferred	Seam area susceptible to HIC/SSC
Oil/gas transmission pipeline (<24”)	ERW or seamless	ERW cost-effective; seamless for critical service
Large-diameter pipeline (>24”)	LSAW	Seamless not available in this range
Water transmission	ERW or LSAW	Cost-effective; lower criticality
Structural/piling	ERW or LSAW	Mechanical loads; no pressure containment

Pro Tip

For API 5L line pipe, the PSL (Product Specification Level) matters as much as the pipe type. PSL2 mandates tighter chemistry, mandatory impact testing, and full NDT of the weld seam. ERW pipe manufactured to PSL2 with a weld joint factor of 1.00 (per ASME B31.4/B31.8) can replace seamless in many pipeline applications at significant cost savings.

For a detailed comparison of seamless vs welded pipe types, including DSAW, SSAW (spiral), and HFW manufacturing, refer to the full guide.

Read the full guide to pipe materials