ERW Pipe Meaning

What is ERW Pipe?

ERW pipe (short for Electric Resistance Welded Pipe) is also known as straight seam resistance welded steel pipe, commonly called resistance welded pipe or high-frequency straight seam welded pipe.

It is a steel pipe made by rolling hot-rolled or cold-rolled steel strip into shape, using high-frequency current resistance heating to heat the edges of the steel strip to the welding temperature, and then applying pressure through extrusion rollers to form the weld seam. Its weld seam is parallel to the pipe body, therefore it belongs to straight seam welded pipe.

Simply put: ERW = Resistance heating + Pressure welding + No filler metal.

ERW vs. HFW vs. LSAW vs. Seamless Steel Pipe:

Many people confuse ERW, HFW, LSAW, and seamless steel pipe. The table below provides a clear comparison:

Item	ERW	HFW	LSAW	SMLS
Full Name	Electric Resistance Welding	High Frequency Welding	Longitudinal Submerged Arc Welding	Seamless Steel Pipe
Weld Type	Straight seam, no filler metal	Straight seam, no filler metal	Straight seam, with welding wire/flux	No weld seam
Welding Frequency	Low frequency to high frequency (typically <10kHz)	High frequency (100~800kHz)	Low frequency AC	—
Outer Diameter Range	21.3~610 mm	21.3~610 mm	406~1524 mm	6~1200 mm
Wall Thickness Range	1.0~20 mm	1.0~16 mm	6~175 mm	1~200 mm
Applicable Pressure	Medium and Low Pressure	Medium and Low Pressure	High Pressure	Ultra-High Pressure
Typical Standards	ASTM A53, API 5L	API 5L PSL2	API 5L, ASTM A381	ASTM A106, API 5L
Cost	Low	Medium	High	Very High
Applications	Water, Gas, Structural Pipes	Oil and Gas, Structural Pipes	Oil and Gas Trunk Lines, Offshore Platforms	High Temperature and High Pressure Pipelines, Boilers

△ Key Point: HFW is a special high-frequency form of ERW, but with higher weld quality.

ERW Pipe Production Process:

The production process of high-quality ERW steel pipes is strict and highly automated. A typical process is as follows:

1. Raw Material Inspection: Select high-quality hot-rolled or cold-rolled steel strip coils and check their dimensions, chemical composition, and surface quality.
2. Uncoiling: Unwind the steel strip coils and feed them into the production line.

3. Strip Leveling: Eliminates bends and wavy edges of the strip using a multi-roll leveler.
4. End Shearing & Butt Welding: Neatly cuts and temporarily butt-welds the ends of the strip to ensure continuous production.

5. Strip Loop Accumulator: Provides a continuous and stable supply of strip for subsequent forming and welding.
6. Roll Forming: Gradually bends the flat strip into an open tube using multiple forming rollers.

7. High-Frequency Resistance Welding: Utilizes the skin effect and proximity effect of high-frequency current to instantly heat the strip edges to a molten or plastic state, then forges a strong weld (without any filler metal) using extrusion rollers.
8. Inside/Outside Bead Trimming: Removes excess burrs from the inner and outer surfaces of the weld using specialized tools to ensure a smooth inner wall.

9. Online Heat Treatment/Normalizing: Normalizing or tempering the weld area refines the grains, eliminates hardened structures, and makes the weld toughness close to that of the base metal.
10. Sizing & Straightening: Precisely controlling the outer diameter and roundness using a sizing machine, followed by straightening to improve straightness.

11. Non-Destructive Testing + Hydrostatic Testing:
● Ultrasonic Testing (UT) / Eddy Current Testing (ET): Detecting weld defects.
● Hydrostatic Testing (held at standard pressure): Verifying the pipe's sealing performance.

12. Cutting & Final Inspection: Cutting to length, inspecting appearance, dimensions, and mechanical properties before packaging and warehousing.

△ Unlike ordinary submerged arc welding, ERW is pressure welding, which does not add welding wire or flux; therefore, the chemical composition of the weld is the same as that of the base metal.

ERW Pipe Specifications:

Parameters	Typical Range	Limiting Range (Custom Orders)
Outer Diameter (OD)	21.3 mm ~ 610 mm	≤ 660 mm
Wall Thickness (WT)	1.0 mm ~ 16 mm	≤ 20 mm
Length	6 m / 12 m / 18 m	As per customer requirements
Steel Grade (API 5L)	Gr.B, X42, X52, X60, X65, X70	X80 (Less common)
Shape	Round, Square, Rectangular Tube	Irregular Shape

Common Standards for ERW Pipes:

When purchasing ERW welded pipes, the applicable standard must be clearly specified. The following are the most common ERW pipe standards worldwide:

Standard Number	Standard Name	Applicable Scenarios
API 5L PSL1/PSL2	Pipeline Steel Specification	Oil and Gas Transportation (Medium and Low Pressure)
ASTM A53	Seamless and Welded Steel Pipe	Low Pressure Water, Gas, and Steam Piping
ASTM A135	Resistance Welded Steel Pipe	Water, Gas, and Air Transportation
ASTM A500	Round/Square/Rectangular Cold-Formed Welded Structural Pipe	Building and Mechanical Structures
EN 10217	Welded Steel Pipe for Pressure Applications	European Pressure Vessels and Piping
GB/T 3091	Welded Steel Pipe for Low Pressure Fluid Transportation	Water, Gas, Air, and Heating

△ For the oil and gas industry, API 5L PSL2 + HFW + weld heat treatment is a hallmark of high-quality ERW pipe.

Advantages and disadvantages of ERW pipe:

Advantages:

1. No filler metal: Weld composition is consistent with the base metal, free of impurities.
2. Uniform wall thickness: Superior to seamless pipe, no eccentricity issues.
3. High production efficiency: 30-50 meters/minute, suitable for mass production.
4. Low cost: 20-50% cheaper than seamless pipe.
5. Best for small and medium diameters: 21-610mm offers the best economic benefits.
6. Weld can be heat-treated: After normalizing/tempering, toughness can approach that of the base metal (90-100%).

Disadvantages:

1. Sensitive to welding parameters: Improper temperature/pressure control can easily lead to ash spots or incomplete fusion.
2. Difficult with thick-walled pipes: Production is difficult for wall thicknesses > 20mm.
3. Limited for large diameters: Uneconomical for diameters exceeding 610mm; LSAW or SSAW is required.
4. Not suitable for extremely high pressures: Generally ≤20MPa; seamless pipes are safer.
5. Unsuitable for acidic environments: H₂S corrosive environments require special acid-resistant steel grade + HFW.
6. Burrs affect the inner wall: Incomplete removal can affect fluid transport or scratch the pigging tool.

△ERW pipes are suitable for small to medium diameter, low to medium pressure, and cost-sensitive projects; unsuitable for large diameter, high pressure, and highly corrosive environments.

Main Applications of ERW Pipes:

● Oil and Gas Transmission: Medium and low pressure gathering and transmission pipelines, station pipelines (API 5L)
● City Gas and Water Supply: Low pressure buried pipelines (ASTM A53, GB/T 3091)
● Building Structures: Scaffolding, steel structures, pile pipes (ASTM A500)
● Machinery Manufacturing: Drive shafts, cylinders, idler rollers
● Automotive Industry: Drive shafts, shock absorber sleeves
● Agriculture and Engineering: Sprinkler irrigation pipelines, water supply pipes, scaffolding

Frequently Asked Questions (FAQ):

Q1: Are ERW and HFW the same thing?

Not entirely. HFW (High Frequency Welding) is a type of ERW, specifically referring to high-frequency resistance welding with a welding frequency ≥ 100 kHz. HFW welds have a smaller heat-affected zone and higher quality, and are often listed separately in the API 5L standard. All HFW belongs to ERW, but not all ERW is called HFW.

Q2: Which is better, ERW pipe or seamless pipe?

It depends on the application:
High pressure, high temperature, corrosive environment → Seamless pipe (higher price)
Medium and low pressure, structural use, cost-sensitive → ERW pipe (economical)

Q3: Will ERW welds crack?

Qualified ERW pipes (standardized + non-destructive testing + hydrostatic testing) will not crack under rated pressure. After heat treatment, the weld strength can actually reach 90-100% of the base material. Inferior ERW pipes do have a risk of weld cracking.

Q4: How to judge the quality of ERW pipes?

Check the following four items:
Standards: API 5L, ASTM A53, etc.
Non-destructive testing report: UT or ET 100% inspection
Hydrostatic test report
Whether the weld has undergone online heat treatment: High-quality pipes must have this.

Q5: Why do "gray spots" appear on the welds of ERW pipes? 

Gray spots are oxide inclusions in the center of the weld, caused by:

● Welding temperature being too high or too low
● Insufficient extrusion pressure
● Poor cleanliness of the steel strip edges

Gray spots significantly reduce weld toughness and must be detected and removed by UT (Ultimate Test) inspection.

Conclusion: 

ERW pipes are the most cost-effective small-diameter, medium- and low-pressure straight seam welded pipes, suitable for a wide range of applications including water, gas, structural, and mechanical applications; HFW is its high-frequency upgraded version, offering higher weld quality and suitable for oil and gas transportation.

For more details on the general manufacturing process and classifications of ERW tube, please refer to our guide: 

● What is Electric Resistance Welded Tube?
● API 5L Specification (Official)
● ASTM A53 vs A106 vs API 5L – Comparison Guide
● ERW vs Seamless Pipe: Which One to Choose?

● What is HFW Steel Pipe?

● API 5L ERW Line Pipe Standard & Grade