What Is ERW Pipe? Manufacturing Process, Grades, and Applications

Electric resistance welded (ERW) pipe is the highest-volume welded steel pipe in the world. On gathering systems, distribution networks, and medium-pressure transmission lines, ERW line pipe delivers API 5L mechanical properties at significantly lower cost than seamless alternatives. For EPC engineers and procurement professionals specifying line pipe for projects in Africa, the Middle East, and South America, understanding where ERW fits — and where it does not — is essential for cost-effective pipe selection.

ZC Steel Pipe manufactures ERW welded line pipe to API Specification 5L, 46th Edition in grades Grade B through X70 for distribution, gathering, and transmission projects across Africa, the Middle East, South America, and Southeast Asia. All PSL2 products are supplied with EN 10204 3.1 MTCs and third-party inspection as standard.

What Is ERW Pipe?

ERW pipe is welded steel pipe made by continuously roll-forming a flat strip of hot-rolled steel (skelp) into a cylindrical shape and joining it along a single longitudinal seam using high-frequency electrical resistance — no filler metal is added.

The governing standard for ERW line pipe in oil and gas service is API Specification 5L, 46th Edition, which defines two product specification levels:

• PSL1 — standard quality: minimum yield and tensile, basic chemistry and dimensional requirements
• PSL2 — higher quality: adds maximum yield limits, maximum yield-to-tensile ratio, mandatory Charpy V-notch impact testing, carbon equivalent limits, and non-destructive examination of the weld seam

Within the API 5L grade family, ERW pipe covers Grade B (L245) through X70 (L485). For grades X80 (L555) and above, LSAW manufacturing is the standard in practice because the thicker walls and higher seam toughness demands of those grades are better served by the LSAW process.

ERW Manufacturing Process

Strip Preparation

ERW line pipe begins as a hot-rolled coil (HRC) of steel strip, slit to the precise width needed to form the target pipe OD. Strip width accuracy is critical because it directly controls the finished OD — width tolerances are held to ±0.5 mm on modern slitting lines.

Roll Forming

The slit strip passes through a series of progressive forming rolls that bend it from a flat strip into a cylinder. The sequence moves from roughing rolls through fin-pass rolls that angle the two edges slightly inward, preparing them for the forge weld.

High-Frequency Welding

At the weld station, high-frequency alternating current — typically 100 to 400 kHz — is applied to the strip edges via contact shoes or an induction coil. Two physical effects concentrate the electrical energy precisely at the strip edges:

Skin effect: At high frequencies, current flows along the conductor surface rather than through the bulk. At 400 kHz, current penetrates only a fraction of a millimetre into the steel, concentrating energy at the edge surface.

Proximity effect: When two conductors carry current in opposite directions close to each other, current concentrates on the facing surfaces. As the strip edges converge toward the weld point, proximity effect focuses heat at the exact contact zone.

Together these effects heat the edges to forge-welding temperature — above 1,260 °C (2,300 °F) — in milliseconds. Squeeze rolls then forge the two hot faces together under pressure, expelling the oxide layer as a thin flash of metal. No filler metal is added. The weld is a solid-state forge weld with properties that depend entirely on the base steel chemistry and the thermal cycle.

Seam Finishing and Heat Treatment

After welding, the external weld flash is mechanically scarfed flush with the pipe OD. For pipe with smaller diameters, the internal flash may also be removed.

For API 5L PSL2 ERW pipe, seam heat treatment is mandatory. The weld heat-affected zone (HAZ) must be heated to above the Ac3 temperature — the full austenitisation temperature, typically above 900 °C — then air-cooled. This restores the HAZ grain structure to the same fine-grained condition as the base metal, ensuring the seam meets the same Charpy impact energy and tensile requirements as the pipe body. Without this step, the ERW seam HAZ retains a coarser, harder structure that can fail NACE MR0175 hardness limits or low-temperature Charpy requirements.

For API 5L PSL1 ERW pipe, no seam heat treatment is required by the standard.

Sizing, Testing, and Inspection

After seam treatment, the pipe passes through a rotary sizing mill to achieve final OD and roundness, then:

• Hydrostatic test — every joint is pressure-tested per API 5L Table 26 (Barlow formula at 60% or 75% SMYS)
• Ultrasonic seam inspection — full seam length scanned by automated UT for PSL2 (mandatory)
• Dimensional check — OD, wall thickness, straightness, and end squareness per API 5L Table 10

API 5L ERW Grades and Mechanical Properties

All values from API Specification 5L, 46th Edition (effective November 2018).

PSL1 — Yield and Tensile by Grade

PSL2 — Additional Requirements

API 5L PSL2 adds maximum yield limits and a maximum yield-to-tensile (Y/T) ratio of 0.93 for pipes with OD greater than 323.9 mm (12.750 in), plus mandatory Charpy V-notch impact testing. For ERW pipe at X65 and X70, the M delivery condition (thermomechanically controlled process) is standard.

For the complete PSL1 and PSL2 grade tables including Charpy requirements and delivery conditions, see the API 5L specification tables →

To calculate wall thickness for your operating pressure and grade, use the Pipeline Design Calculator →

Standard Sizes — ERW Line Pipe (ASME B36.10M-2018)

ERW line pipe is commercially produced in NPS 2 through NPS 24. For large-diameter pipe above NPS 24, LSAW or SSAW manufacturing is standard. All dimensions from ASME B36.10M-2018.

Note: For NPS 14 and above, the Standard (STD) wall is constant at 9.52 mm (0.375 in) per ASME B36.10M-2018.

ZC Steel Pipe supplies ERW line pipe in NPS 2" to NPS 24" (Grade B through X70). Wall thickness range: 3.2 mm to 22 mm. Fixed lengths (6 m, 12 m) and double random lengths (DRL, 10.7–13.1 m) are available.

ERW vs Seamless Pipe — When to Choose Each

For a detailed comparison including weldability and cost analysis, see Seamless vs Welded Line Pipe Selection Guide →

Purchase Order Guidance

Minimum Required PO Line Items for ERW Line Pipe

A complete ERW line pipe PO for oil and gas service must specify:

• Standard: API Specification 5L, 46th Edition
• PSL level: PSL1 or PSL2 — never leave blank
• Grade: e.g., X65 (or L450 in metric documentation)
• Delivery condition (PSL2): M, N, or Q — e.g., X65M
• Pipe form: ERW (not just "welded")
• Size: OD (in or mm) × wall thickness (mm) × length (DRL or fixed)
• End finish: plain end (PE) or bevelled end (BE per ASME B16.25, 30° ± 5°)
• Supplementary requirements: Annex H sour service, Charpy test temperature, third-party inspection, EN 10204 3.1 MTC

The Seam Treatment Trap

The most common ERW specification error: ordering PSL1 for service that requires PSL2 seam heat treatment. PSL1 ERW pipe has no mandatory seam treatment — the weld HAZ can be significantly harder than the pipe body. In H2S environments, the hard seam can fail NACE MR0175 hardness limits and initiate hydrogen-induced cracking. In sub-zero service, an untreated seam may fail Charpy requirements. Always specify PSL2 for sour service, temperatures below 0 °C (32 °F), and any service where seam toughness must be certified.

What to Verify on the MTC

Before accepting an ERW pipe consignment, verify on the Mill Test Certificate (MTC):

• PSL level declared in the product designation
• Seam heat treatment type and temperature (PSL2 mandatory)
• Tensile test results — body and weld seam separately (PSL2)
• Charpy impact energy at the specified temperature (PSL2)
• Carbon equivalent (CE_IIW or CE_Pcm) for PSL2
• Hydrostatic test pressure and hold time
• Ultrasonic seam inspection confirmation (PSL2)

For the complete EN 10204 MTC review procedure, see Pipe Mill Test Certificate Guide →