Introduction
If you are sourcing steel pipes for a construction project, water pipeline, or oil gas projects, you have likely encountered the term ERW Pipe.
As a factory supplier with years of experience on the production floor, we hear the same questions every day: “Is ERW as strong as seamless?” “What is the difference between MS and ERW?”, and “How do I know I’m buying quality?”
In the crowded steel market, terminology can be confusing. Our goal today isn’t just to sell you pipe; it’s to help you understand what you are buying.
By understanding the manufacturing process, standards, and applications of ERW steel pipes, you can save your project from high costs without compromising on quality.
What is ERW steel pipe?
ERW stands for Electric Resistance Welded. Unlike seamless pipes which are extruded from a solid billet of steel, ERW pipes originate as a flat sheet of steel (coil).
Here is how it happens on our production line:
Uncoiling: We take a coil of steel (Hot-Rolled or Cold-Rolled) and unspool it.
Forming: The flat steel strip passes through a series of rollers. These rollers gradually curve the steel into a cylindrical shape.
Welding: This is the magic moment. High-frequency electrical current is passed through the edges of the cylinder. The resistance to this current generates heat, melting the edges together without the use of any filler material.
Bead Trimming: The welding process leaves a “flash” or bead of excess metal on the inside and outside. We use carbide tools to trim this flush while the steel is still hot, creating a smooth surface.
Sizing and Cutting: The pipe passes through sizing rolls to ensure the exact diameter and is then cut to the required length (usually 6m or 12m).
Key Takeaway: Because ERW pipes are made from rolled sheets, they possess excellent wall thickness consistency, which is often superior to seamless pipes.
What are ERW pipes, GP pipes, GI pipes, MS pipes & Tubes?
This is the number one source of confusion for our clients. Many buyers use these terms interchangeably, but they refer to different aspects of the pipe: Manufacturing Process vs. Material vs. Surface Treatment.
Let’s break down the “Alphabet Soup” of the steel pipe industry.
- MS Pipes (Mild Steel Pipes)
“MS” refers to the Material.
Mild Steel contains a low amount of carbon (usually 0.05% to 0.25%). It is easy to weld, cut, and form.
Relation to ERW: Most ERW pipes are made from MS coils. So, an ERW pipe is technically an MS pipe, but “MS” tells you what it is made of, while “ERW” tells you how it was made. - GP Pipes (Galvanized Plain Pipes)
“GP” refers to the Raw Material used.
GP pipes are made from steel coils that were already galvanized (zinc-coated) before they were formed into pipes.
Visual Check: The weld line usually has a zinc spray applied over it because the welding process burns the original zinc off at the seam. These are typically used for thinner, lighter applications like greenhouses. - GI Pipes (Galvanized Iron/Steel Pipes)
“GI” refers to the Surface Treatment.
Usually, this refers to “Hot Dip Galvanized” pipes. We take a finished black ERW pipe and dip the entire thing into a bath of molten zinc.
Benefit: This coats the entire pipe, inside and out, offering maximum corrosion protection.
Summary Table for Quick Comparison
| Term | Full Name | Focus | Key Characteristic | Common Use |
| ERW | Electric Resistance Welded | The Process | Manufactured by rolling and welding a strip. | General construction, piling, fencing. |
| MS | Mild Steel | The Material | Low carbon content (<0.25%), ductile and easy to weld. | Structural frameworks, fabrication. |
| GP | Galvanized Plain | Pre-Coated | Made from pre-galvanized sheets; lighter zinc coating. | Greenhouses, electrical conduit. |
| GI | Galvanized Iron | Post-Coated | Hot-dipped in zinc after welding; heavy zinc coating. | Water transmission, harsh environments. |
ERW Steel Pipe Application
Why do we produce so much ERW pipe? Because it is the workhorse of the modern industrial world. Its versatility allows it to be used across various sectors.
- Oil and Gas (Onshore)
While deep-sea, high-pressure lines often use seamless pipes, ERW pipes (specifically High-Frequency Induction or HFI pipes) are standard for onshore transportation of oil and natural gas. Strict adherence to API 5L standards ensures safety. - Structural & Construction
If you see a round steel column supporting a roof, or scaffolding at a building site, it is likely ERW pipe.
Uses: Piling, structural support columns, bridge supports, and fencing.
Why? The concentricity (even roundness) of ERW pipes makes them easy to fit and connect. - Water and Agriculture
ERW pipes are the backbone of watersupply systems and irrigation. - Potable Water: GI (Galvanized) ERW pipes prevent rust from entering the water supply.
- Irrigation: Large diameter ERW pipes move vast amounts of water for farming.
- Automotive & Machinery
Because ERW pipes have precise dimensional tolerances, they are used in shock absorbers, exhaust pipes, and roll cages.
ERW Steel Pipe vs. Seamless Steel Pipe
As a supplier, we sell both, but we believe in recommending the right pipe for the job. Customers often overspend on Seamless pipes when ERW would suffice.
The Manufacturing Difference
- Seamless pipes : A solid billet is heated and pierced through the center. It has no weld seam.
- ERW pipes : A flat plate is rolled and welded. It has a longitudinal seam.
Performance Comparison
| Feature | ERW Steel Pipe | Seamless Steel Pipe |
| Cost | Lower. Production is faster and automated. | Higher. Process is complex and energy-intensive. |
| Wall Thickness | Consistent. Made from rolled sheets which are very uniform. | Variable. The piercing process can cause slight eccentricity. |
| Pressure Rating | Low to Medium High pressure. | Ultra-High pressure and critical temperature. |
| Surface Finish | Smooth and clean. | Often has a rougher scale finish. |
| Availability | Readily available in standard sizes. | Large diameters or very thick walls require long lead times. |
The “Weak Seam” Myth:
Decades ago, the weld seam was the weak point. However, modern factories (like ours) use HFI (High-Frequency Induction) welding and post-weld heat treatment (Annealing). This normalizes the grain structure of the weld, making the seam often stronger than the parent metal.
Verdict: If you are building a skyscraper, transporting water, or running low-pressure gas, choose ERW. If you are running a high-pressure boiler or deep-sea oil rig, choose Seamless.
ERW Pipe Standards
When you send us an inquiry, specifying the standard ensures you get exactly what you need. Here are the most common standards we manufacture to:
ASTM Standards (American)
ASTM A53: The most common standard for steel pipe used in mechanical and low-pressure fluid applications. It covers both seamless and welded (ERW) pipe.
ASTM A252: The standard for welded and seamless steel pipe piles (used in construction piling).
ASTM A500: Standard for cold-formed welded and seamless carbon steel structural tubing in rounds and shapes.
API Standards (Oil & Gas)
API 5L: The global standard for Line Pipe used in conveying gas, water, and oil. Grades range from Grade B to X70 (referring to yield strength).
BS / EN Standards (British/European)
BS 1387 / EN 10255: Very common for water and gas pipes, suitable for screwing and threading.
How to Choose ERW Pipe and Supplier
Choosing the right partner is just as important as choosing the right grade. With thousands of suppliers in China, India, and Vietnam, how do you filter the good from the bad?
- Check the Welding Line Quality
Ask your supplier about their heat treatment. A quality ERW pipe must undergo Seam Annealing. This process heats the weld area after welding to remove internal stresses. If a supplier skips this, the pipe may crack during bending or flattening. - Dimensional Tolerances
Ask for their “Wall Thickness Tolerance.”
Good factory: +/- 5% or better.
Poor factory: +/- 10% or more (this can affect your project weight and structural integrity). - Necessary Testing (The NDT Factor)
Never buy ERW pipe without Non-Destructive Testing (NDT). A reputable factory will perform:
Hydrostatic Test: Filling the pipe with water under pressure to check for leaks.
Ultrasonic / Eddy Current Test: An online scanning system that detects invisible internal defects in the weld seam. - Surface Condition
For “Black” pipes, ask if they apply a protective varnish. Without it, the pipes will rust during ocean transit. For Galvanized pipes, ask for the “Zinc Coating Mass” (e.g., 200g/m² vs 500g/m²). This determines how long the pipe lasts before rusting. - Third-Party Inspection
A confident supplier will always accept inspection by SGS, BV, or Lloyds. If a supplier hesitates when you mention Third-Party Inspection, consider it a red flag.
Conclusion
ERW Steel Pipe is a triumph of modern manufacturing—combining strength, precision, and affordability. Whether you are distinguishing between GI and MS, or deciding between ASTM A53 and API 5L, understanding these details empowers you to make smarter purchasing decisions.
At our factory, we don’t just roll steel; we provide solutions. We ensure that every inch of pipe leaving our facility has passed rigorous Eddy Current testing and Hydrostatic checks, ensuring that the “cost-effective” choice doesn’t become a “high-maintenance” problem later.
Are you looking for a quote on high-quality ERW pipes?
Whether you need standard construction pipes or high-grade API line pipes, contact our engineering team today. Let’s build something strong together.
Please contact us if you have any questions.
