How to Repair Weld Seam Corrosion in ERW Tube Mills (Without Re-Galvanizing)

🟩 Introduction

If you’ve been running an ERW tube mill for a while, this probably sounds familiar.

The pipes come out looking clean. Surface looks good. Everything seems fine—until you take a closer look at the weld seam.

That’s usually where the trouble begins.

No matter how good the galvanized strip is, the welding process itself changes things. The zinc layer at the seam doesn’t stay intact. And once that protection is gone, the risk of rust goes up quickly.

Left untreated, it’s only a matter of time before corrosion shows up—and spreads.

In this article, we’ll go through what’s really happening at the weld seam, why some common solutions don’t work as well as expected, and a more practical way many factories are now using to deal with it.

🟩 Why Weld Seam Corrosion Happens

Let's break it down in a straightforward way.

Galvanized steel resists corrosion because of its zinc coating. That layer acts as a barrier between the steel and the environment.

But welding changes the situation.

The heat involved in the process is high enough to damage—or completely burn off—that zinc layer along the seam.

So in the end, you're not dealing with a fully protected pipe anymore.
You've got a pipe with one exposed line running along its length.

And that line becomes the weak spot.

Moisture, oxygen, even small contaminants in the air will start attacking that area first. Once corrosion starts there, it doesn't stay in one place.

👉 That's also why many overseas buyers pay special attention to weld seams during inspection.

🟩 Why Re-Galvanizing Isn't Always Practical

A common idea is simple: just galvanize the pipe again.

On paper, that makes sense. In real production, it's not always the best option.

Re-galvanizing brings a few challenges:

• Extra cost that adds up quickly
• Slower production due to additional processing
• More handling, transport, and coordination

And more importantly, it's not targeted.

In most cases, the issue is only at the weld seam—not the entire pipe. Reprocessing everything just to fix a narrow line isn't always efficient.

🟩 A More Practical Solution: Zinc Spray Coating

This is where zinc spray coating comes into play.

Instead of reworking the whole pipe, you focus only on the area that actually needs protection—the weld seam.

The basic idea is quite straightforward:

• Zinc wire is melted using an electric arc
• The molten zinc is broken into fine particles by compressed air
• These particles are sprayed onto the seam, forming a new coating

What you get is a restored protective layer, applied exactly where it’s needed.

👉 In many setups, this can even be integrated directly into the production line.

🟩 Why More Tube Mills Are Using It

This method isn’t new, but it’s getting a lot more attention lately.

The reason is simple—it solves a very specific problem without complicating the whole process.

Factories that switch to zinc spraying often notice:

• Fewer complaints from customers
• More consistent coating quality
• Lower rejection rates
• Better cost control over time

Another advantage is flexibility.

You can adjust parameters based on your needs:

• Coating thickness
• Spray speed
• Zinc consumption

So instead of over-processing, you’re applying just enough protection where it matters.

🟩 Where Zinc Spray Coating Is Used

Although it’s widely used in tube mills, this approach isn’t limited to one industry.

You’ll also see it in:

• Steel pipe production
• Oil and gas pipelines
• Structural steel components
• Outdoor steel structures exposed to weather

Basically, anywhere corrosion protection is critical, this method can be useful.

🟩 How to Choose the Right Setup

If you’re considering zinc spray equipment, a few practical factors are worth looking at.

1. Production Speed
Faster lines need more stable and consistent spraying performance.

2. Coating Thickness
Usually falls somewhere between 10–100 microns, depending on requirements.

3. Level of Automation
Manual systems are more flexible; inline systems are better for consistency.

4. Wire Specification
Most commonly, 1.6 mm or 2.0 mm zinc wire is used.

In the end, the “right” setup depends more on your production conditions than on the equipment itself.

🟩 Common Mistakes to Avoid

From what we’ve seen in real factories, a few issues come up repeatedly:

• Overlooking weld seam protection altogether
• Using low-quality or unstable spray systems
• Uneven coating application
• Poor matching between spray speed and line speed

Any of these can reduce the effectiveness of the process.

🟩 So, What’s the Best Approach?

If your goal is to improve pipe quality without driving costs too high, zinc spray coating is a practical option worth considering.

It doesn’t require a complete overhaul of your process.

Instead, it focuses on a known weak point—and fixes it in a direct, efficient way.

Sometimes, solving one small problem properly makes a bigger difference than changing everything else.