ERW Pipe — What It Is, Types, Specifications & Applications

ERW pipe — electric resistance welded pipe — is the most widely manufactured form of steel pipe in the world. It is the pipe that runs beneath your city streets carrying gas and water, the gathering lines on onshore oil fields, and the casing strings in thousands of wells. Understanding what ERW means, how it is made, and when it is and isn't the right choice is fundamental knowledge for anyone procuring or specifying steel pipe.

ZC Steel Pipe manufactures ERW pipe to API 5L (PSL1 and PSL2) and ASTM A53 standards, supplying line pipe and casing projects across Africa, the Middle East, and South America. Our ERW capabilities cover OD 21.3 mm to 508 mm (NPS ½ to NPS 20) in grades from Grade B through X80.

1. What Does ERW Mean?

The "resistance" in ERW refers to the physics of the process: the electrical resistance at the joint interface generates the heat needed for welding. Because no filler metal is added, the weld zone has the same composition as the parent steel, and modern high-frequency ERW (HF-ERW) produces a weld that meets the same pressure and mechanical requirements as the pipe body itself.

2. How ERW Pipe Is Made

The ERW manufacturing process follows a consistent sequence regardless of pipe size:

1. Steel coil (skelp) preparation — Hot-rolled or cold-rolled coil is uncoiled, leveled, and edge-trimmed to the precise width needed for the target OD.

2. Cold forming — The strip passes through a series of forming rolls that progressively bend it into a circular cross-section. No heating is applied at this stage.

3. High-frequency welding — As the tube approaches the welding station, its edges are brought together under pressure. High-frequency current (typically 350–450 kHz) is applied, heating the edges to forging temperature in milliseconds. The squeeze rolls force the molten edges together, expelling oxides and creating a solid-state forge weld.

4. Weld bead removal — The internal and external weld flash (upset material) is cut away to restore a smooth OD and ID profile.

5. Sizing and straightening — The pipe passes through sizing rolls to achieve final diameter tolerances and is straightened.

6. Heat treatment (when required) — For API 5L PSL2 and some ASTM standards, the weld seam or entire pipe body is normalized to relieve residual stresses and restore toughness in the HAZ.

7. Non-destructive testing — Full-body ultrasonic testing (UT) of the weld seam is standard for API 5L PSL2; hydrostatic testing is standard for all grades.

8. Cut to length — Pipe is cut to random or specified lengths, beveled at pipe ends, and marked per the applicable standard.

3. ERW vs HFW — Are They the Same?

Technically, HFW (High-Frequency Welded) is a subset of ERW. Older ERW pipe used low-frequency (LF-ERW, 60 Hz) current, which produced inconsistent heat distribution and weld quality problems — particularly susceptibility to "hook cracks" in the weld HAZ under sour service. Modern ERW pipe uses high-frequency current exclusively and is more correctly called HF-ERW or simply HFW.

4. Standards Covering ERW Pipe

5. ERW Pipe Specifications & Grades

API 5L ERW (Line Pipe)

API 5L is the primary standard for ERW pipe in oil and gas service. It defines two product specification levels:

API 5L ERW Grade Mechanical Properties

6. ERW vs Seamless Pipe

7. ERW vs LSAW vs SSAW

For a detailed comparison of all three welded pipe types, see our guide: Welded Steel Pipe — ERW, LSAW & SSAW Types, Specs & Selection Guide →

8. Size Range & Dimensions

ERW pipe dimensions conform to ASME B36.10M for carbon steel pipe. Commercially available sizes concentrate in NPS ½ through NPS 20, with OD tolerances typically ±0.75% of the specified OD (tighter than seamless). Wall thickness tolerance is ±10% for most sizes.

9. Applications

Oil & Gas Gathering Pipelines

API 5L ERW pipe (PSL1 and PSL2) is the standard for onshore gathering lines collecting crude oil and gas from wellheads to processing facilities. Operating pressures are typically moderate (500–2,000 psi), making ERW's cost advantage significant over seamless on large-diameter projects.

Natural Gas Distribution

Municipal and industrial gas distribution networks — including the buried mains feeding residential and commercial consumers — predominantly use ASTM A53 Type E (ERW) and API 5L Grade B ERW pipe. The consistent OD dimensions of ERW simplify fitting connections and joint sealing.

Water Transmission

ERW pipe (ASTM A53 Grade B, often galvanized) is used for water mains, fire protection systems (per NFPA 13), and irrigation infrastructure. The tight OD tolerances of ERW facilitate mechanical couplings and grooved-end connections common in fire suppression systems.

Oil Country Tubular Goods (OCTG)

API 5CT ERW casing (grades K55 and J55) is used for surface casing and intermediate casing in wells where elevated corrosion resistance and strength are not primary concerns. ERW OCTG is significantly less expensive than premium seamless grades and is appropriate for many onshore well programs.

Structural & Mechanical

ASTM A500 ERW pipe and hollow structural sections (HSS) are used for columns, trusses, conveyor frames, and mechanical components across construction and manufacturing. The tight tolerances and smooth surface finish of ERW are advantages in fabrication and coating applications.

10. Frequently Asked Questions