Key considerations when welding galvanized steel pipes

Galvanized steel pipes are widely used due to their excellent corrosion resistance, long service life, and relatively low cost. As their application becomes more common in construction, piping, and equipment support, it’s important to handle them correctly—especially during welding. Careless welding practices can cause serious issues. So, what should you pay attention to when welding galvanized steel pipes?

1. Always Remove the Galvanized Coating at the Weld Area

Before welding, the galvanized layer at the joint must be thoroughly ground off. Failing to do so can lead to defects such as porosity, slag inclusions, incomplete fusion, and brittle welds, which compromise the strength and integrity of the structure.

2. Understand the Properties of Galvanized Steel Pipes

Galvanized steel pipes are typically made by coating low-carbon steel with a layer of zinc, usually about 20 microns thick.

Zinc melts at 419°C and boils at around 908°C.

During welding, zinc melts and floats on the weld pool surface or collects at the weld root.

Zinc can penetrate the weld metal along grain boundaries, causing liquid metal embrittlement.

Zinc and iron also form brittle intermetallic compounds, reducing weld ductility and increasing the risk of cracking, especially in fillet welds and T-joints.

Additionally, the zinc layer oxidizes and evaporates under arc heat, producing white fumes and steam, which can cause weld porosity. Zinc oxide (ZnO) formed during this process has a high melting point (~1800°C), and if welding parameters are insufficient, slag inclusions may occur. The fumes can also irritate the respiratory system, posing a health hazard. For these reasons, it is essential to grind off the galvanized layer before welding.

3. Welding Process Control

Welding preparation is similar to that of regular low-carbon steel, but with additional focus on groove size and zinc layer removal:

Recommended groove angle: 60–65°

Joint gap: 1.5–2.5 mm for better penetration

It's best to remove the galvanized coating in and around the groove before welding

In practice, a narrow groove with no blunt edge is often used

A two-pass weld process (root and cover pass) is recommended to minimize welding defects

Choose welding electrodes based on the base metal. For galvanized low-carbon steel, J422 is commonly used for its ease of operation.

4. Proper Welding Techniques

For multi-pass welding, it’s crucial to vaporize and remove the zinc in the first layer to reduce the amount left in the weld:

When doing fillet welds, preheat the area by moving the electrode 5–7 mm forward, allowing the zinc to evaporate, then return to the start point and continue welding.

For horizontal and vertical welding, using short slag electrodes like J427 can reduce the risk of undercutting.

Use a back-and-forth weaving technique to help produce defect-free welds.

Summary

Welding galvanized steel pipes requires attention to detail and proper preparation. Key steps include:

Removing the zinc coating in the weld area

Controlling welding parameters

Selecting the right electrode

Using proven techniques to reduce weld defects

By following these guidelines, you can ensure strong, reliable welds and avoid the common pitfalls associated with welding galvanized materials.