What Is ERW Pipe?
ERW (Electric Resistance Welded) pipe is a type of welded steel pipe manufactured by forming flat steel coil or strip into a cylindrical shape and welding the longitudinal seam using electrical resistance heating. No filler metal is added during welding. The result is a clean, narrow weld seam with mechanical properties close to the base material.
ERW pipe is one of the most widely used pipe types for oil and gas gathering lines, water distribution, structural applications, and moderate-pressure process piping.
ERW Manufacturing Process
- Uncoiling: Steel coil (hot-rolled) is fed into the forming mill
- Forming: Rolls progressively shape the flat strip into a round cross-section
- Welding: High-frequency electric current (typically 100-400 kHz) heats the strip edges to forging temperature; squeeze rolls press them together
- Weld scarfing: External (and sometimes internal) flash is removed
- Sizing: Calibration rolls achieve final OD tolerance
- Testing: Online NDT (ultrasonic) and hydrostatic testing per applicable standard
| Property | ERW Pipe |
|---|---|
| Weld type | Longitudinal, no filler metal |
| Frequency | Low-frequency (LF-ERW, obsolete) or high-frequency (HF-ERW/HFW) |
| Size range | NPS 1/2 to NPS 24 (OD 21.3 to 610 mm) |
| Wall thickness | Up to ~25 mm (typically SCH 10 to SCH 80) |
| Length | Single random (5-7 m) or double random (9-13 m) |
| Specifications | API 5L, ASTM A53 Type E, ASTM A135, EN 10217 |
| Weld joint factor (E) | 0.85 (ASTM A53) to 1.0 (API 5L with full-body UT) |
| Material grades | API 5L Gr. B to X70, ASTM A53 Gr. A/B |
HF-ERW vs LF-ERW
Modern ERW production uses high-frequency (HF) welding, which replaced the older low-frequency (LF) process. LF-ERW pipes, manufactured before the mid-1980s, had a wider HAZ and higher susceptibility to seam failures. Today, HF-ERW (also called HFW) is standard, and API 5L requires it for all ERW production.
Applications
ERW pipe is cost-effective and widely available for:
- Oil and gas gathering lines and flow lines (API 5L grades B through X65)
- Water transmission and distribution
- Fire protection systems (ASTM A795)
- Structural columns and piles (ASTM A500, EN 10219)
- Mechanical tubing (ASTM A513)
- Casing and tubing in shallow wells
For pressures and sizes beyond ERW capabilities, LSAW or seamless pipe is specified. ERW pipe is not typically manufactured above NPS 24 or in heavy wall thicknesses.
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