Complete guide to ERW steel pipes

In the global steel pipe market, ERW steel pipe(Electrical Resistance Welded steel pipe) is the most cost-effective and widely used solution in the construction, infrastructure, and energy transmission sectors.

This guide delves into the manufacturing process, specifications (API, ASTM), and why ERW steel pipe is the preferred alternative to seamless steel pipe in many low-pressure applications.

What is ERW Steel Pipe? A Detailed Explanation of Resistance Welded Steel Pipe

ERW steel pipe is a longitudinally welded steel pipe manufactured by cold-bending flat steel strips (coils) into a cylindrical shape and then welding the edges together using resistance heating. Unlike seamless steel pipe formed from solid round steel, ERW steel pipe originates from rolled steel coils, thus offering higher dimensional accuracy and wall thickness consistency.

However, not all ERW steel pipes are of the same quality. In the modern steel industry, when we talk about high-quality ERW steel pipe, we almost always mean high-frequency welding (HFW) technology.

Key Difference: HFW vs. Traditional ERW

Traditional ERW (Low Frequency): Historically used low-frequency current. This typically results in a wider heat-affected zone (HAZ) and potential weld problems. This technique has been largely phased out in high-standard applications.

High-Frequency Welding/Induction Welding (HFW/HFI): This is the modern standard (typically operating at frequencies of 70-450 kHz). High-frequency current generates intense heat at the edges of the steel strip, instantly forming a solid-state forged weld.

ERW Pipe Manufacturing Process: From Coil to Certificated Pipe

The quality of ERW welded pipe depends not only on the steel grade but also on the precision of the manufacturing process. Unlike extruded seamless welded pipe, ERW welded pipe is manufactured using a continuous, high-speed process, requiring strict control at each stage to ensure weld integrity matches the base material.

Below is our detailed production process for welded pipes conforming to API 5L and ASTM standards:

1. Uncoiling and Forming (Basic)

This process begins with high-quality hot-rolled steel coils. These coils are uncoiled, leveled, and cut to a precise width matching the diameter of the welded pipe.

Cold Forming: Flat steel strip passes through a series of forming rollers. These rollers progressively bend the steel strip into a cylindrical shape (open tube) without heating the material, thus ensuring the steel retains its original mechanical properties.

2. High-Frequency Welding (HFW/HFI)

This is the core of the entire welding process.

No filler material required: Unlike other welding methods, HF welding uses high-frequency current (induction technology) to heat the strip edges to a plastic state.

Forging pressure: Precise pressure is applied through extrusion rollers, fusing the edges together. This creates a solid weld without the need for any filler metal, resulting in a cleaner and stronger bond.

3. Weld Removal (Scraping) – A Key Step

During welding, excess metal is extruded, forming "burrs" or "welds" on the inner and outer surfaces of the pipe.

External Scraping: The external weld is trimmed flush to ensure a smooth surface for subsequent coating or assembly.

Internal Scraping: For fluid transmission or mechanical components, internal welds must be removed.

4. Weld Annealing/Heat Treatment

Rapid heating and cooling during welding can cause the weld area to harden and become brittle. To prevent cracking during installation or bending:

In-line heat treatment: Induction heating (weld annealing/normalizing) is applied to the weld (or the entire pipe) to refine the grain structure.

Result: This restores the ductility and toughness of the weld area, ensuring it has the same mechanical strength as the rest of the pipe.

5. Sizing and Cutting

The pipe is sizing rollers to achieve the precise outer diameter (OD) tolerances required by international standards. Finally, a flying cutter is used to cut the continuous pipe to specific lengths (typically 6 meters, 12 meters, or custom lengths).

6. End Finishing and Hydrostatic Testing

Before packaging, the pipe ends are chamfered (for easier on-site welding) or flat-cut. Each pipe is then subjected to a hydrostatic test, i.e., water is injected under pressure to verify its leak-proof performance and pressure resistance.

Why Choose ERW Pipes?

Compared to seamless steel pipe (SMLS) or submerged arc welded pipe (LSAW/SSAW), ERW pipe offers significant commercial advantages for your projects:

Cost-effectiveness: Due to its simpler manufacturing process and faster production speed, ERW pipe is typically 20-30% cheaper than comparable seamless steel pipe. This can result in substantial budget savings for large projects such as scaffolding or water pipelines.

Stricter tolerances: Because ERW pipe is welded from hot-rolled coils (producing with extremely high precision), its wall thickness is uniform throughout its entire length. Seamless welded pipe often exhibits uneven wall thickness.

Faster lead times: ERW pipe production lines are highly automated and efficient. Suppliers can typically fulfill large-volume orders for standard sizes (e.g., ASTM A53, BS 1387) faster than seamless welded pipe manufacturers.

Surface quality: ERW pipe has a smooth, clean surface, allowing for easy subsequent coating treatments (galvanizing, 3LPE, FBE) without extensive surface preparation.

Below is a comparison of the most commonly used ERW welded pipe standards:

Standard	Primary Application	Key Steel Grades	Mandatory Testing Requirements
API 5L	Oil & Gas Line Pipe	Gr. B, X42, X52, X60	100% NDT（UT/ET）, Hydrostatic Test, Impact Test for higher grades, Full Material Traceability
ASTM A53	General fluid, pressure pipe	Grade A, Grade B	Chemical analysis, Mechanical test, Hydrostatic test
EN 10255 / BS 1387	Water, gas, air (non-critical)	S195T, S235JR	Surface quality, weldability, leak tightness
ASTM A252	Piling, foundation	Grade 1, 2, 3	Yield Strength verification, dimensional tolerance

Key Dimensional Parameters

Parameter	Common Unit	Schedule Range	Notes
Nominal Pipe Size (NPS)	Inch / DN	1/2" – 26"	NPS indicates pipe capacity, not exact OD.
Outer Diameter (OD)	mm / inch	21.3 mm – 660 mm	Used for fitting and connection design.
Wall Thickness (WT)	mm / inch	SCH 10 / SCH 40 / SCH 80	Determines pressure rating.
Length	m	6m / 12m / Custom	Fixed or random lengths are available.

Summary

ERW steel pipes are widely used in engineering projects worldwide. Their core value lies in their strict adherence to international standards (such as API 5L, ASTM A53, EN 10255, ASTM A252), excellent control over outer diameter and wall thickness tolerances, and a complete dimensional system (NPS, OD, WT, Schedule).

Read more : What is ERW steel pipe?