1. **Which is better, ERW or EFW?**
* There's no single "better" option; it depends entirely on the application requirements. ERW (Electric Resistance Welded) is generally better for cost-effectiveness, higher production speeds, and thinner to medium wall thicknesses in standard sizes for lower pressure applications (like water, gas, structural). EFW (Electric Fusion Welded), often referring to processes like SAW (Submerged Arc Welding), is better for very large diameters, very thick walls, and high-pressure/high-integrity applications (like oil & gas transmission pipelines, critical structures) where the deeper penetration fusion weld is necessary. Choose ERW for standard, cost-sensitive projects and EFW for heavy-duty, high-pressure critical applications.
2. **Is ERW steel strong?**
* Yes, ERW steel pipes are strong and widely used in structural and pressure applications. Their strength comes from the base material (the steel coil/plate used) meeting specific grades (like A500 for structural, A53/ASTM 135 for pressure), and the weld itself, when properly made and inspected, achieves strength comparable to the base metal. While not as strong as seamless pipe in very high-pressure/high-stress scenarios, ERW pipe offers excellent strength for a vast range of uses.
3. **What are the benefits of ERW pipes?**
* **Cost-Effective:** Significantly cheaper than seamless pipes due to efficient, high-speed production from coil.
* **High Production Rate:** Continuous manufacturing process allows for large volumes quickly.
* **Consistent Quality & Dimensional Accuracy:** Precise control over diameter, wall thickness, and roundness.
* **Availability in Larger Diameters:** More readily available in larger diameters (compared to seamless) at reasonable costs.
* **Good Weld Integrity (Modern Mills):** Advanced high-frequency welding and inspection ensure reliable weld strength.
* **Smooth Surface Finish:** Generally has a smoother internal and external surface than seamless pipe.
4. **Is ERW pipe galvanized?**
* ERW refers specifically to the **welding process** (Electric Resistance Welding). An ERW pipe **can be** galvanized (coated with zinc for corrosion protection), but it is **not inherently galvanized**. Galvanizing is a separate post-manufacturing process. You can find ERW pipes that are bare (black) steel, galvanized, painted, or coated with other materials depending on the intended use and customer specification.
5. **What are the disadvantages of ERW pipes?**
* **Weld Line Risk:** The weld seam is a potential point of weakness if manufacturing defects occur (like lack of fusion, inclusions) or if corrosion starts there. Requires strict quality control and inspection (NDT).
* **Heat Affected Zone (HAZ):** The welding process creates a HAZ near the weld, where the material properties (strength, toughness) can be slightly different from the base metal.
* **Not for Extreme Conditions:** Generally not recommended for the most critical, ultra-high-pressure, high-temperature, or severe cyclic service applications where seamless pipe is preferred due to its homogeneous structure.
* **Potential for Lamination Defects:** Originating from the steel coil, though this affects other welded pipe types too.
* **Surface Imperfections:** Minor surface flaws like weld bead roll marks or discoloration along the weld line might occur, which are usually cosmetic but sometimes need removal.
