Can galvanized steel pipes be welded?

Galvanized steel pipes, coated with a layer of zinc, offer improved corrosion resistance, extended durability, and an aesthetically pleasing finish. These pipes are commonly used in a range of applications, from transporting low-pressure fluids like gas and heating to supporting infrastructure such as mine tunnels and oil pipelines. But can galvanized steel pipes be welded? Let's explore this in more detail.

Welding Galvanized Steel Pipes:

In general, galvanized steel pipes can indeed be welded. The galvanized layer is typically thin in ordinary galvanized pipes, allowing for standard welding methods such as electric welding or gas shielded welding. Gas shielded welding is particularly useful when grinding is difficult and welding with a galvanized layer is required. For thicker galvanized coatings, argon arc welding is a viable option.

How to Weld Galvanized Steel Pipes:

Given their corrosion resistance, long service life, and cost-effectiveness, galvanized steel pipes are widely used. However, welding these pipes requires attention to proper technique and a few key considerations:

- Pre-Welding Preparation:

The preparation process for welding galvanized steel is similar to that of regular low-carbon steel. Focus should be placed on the groove size and the galvanized layer around the groove. Typically, the groove angle should be 60-65°with a gap of around 1.5 to 2.5 mm. Before welding, it’s crucial to remove the galvanized layer from the groove area to minimize zinc penetration into the weld.

- Welding Process:

Beveling: Use a centralized beveling technique with no blunt edges. A two-layer welding process is preferred to reduce the risk of incomplete penetration.

Zinc Vaporization: When welding the first layer of a multi-layer weld, aim to melt and evaporate the zinc layer, allowing it to escape from the weld. This helps to minimize the amount of liquid zinc in the weld.

Welding Fillet Joints: For fillet welds, allow the zinc layer to vaporize during the first layer of welding. This can be achieved by first advancing the electrode by 5 to 7 mm, then returning to the starting position to continue welding after the zinc has evaporated.

Welding Techniques: For horizontal or vertical welds, it's recommended to use short-slag electrodes like J427, which help reduce the tendency for undercutting. A back-and-forth motion with the electrode can improve weld quality.

- Post-Welding Considerations:

After welding, it's important to remove the remaining galvanized layer from the weld area. Failing to do so can lead to issues such as bubbles, sand holes, poor weld quality, and brittleness in the joint, reducing its overall strength and integrity.

By following these steps, you can effectively weld galvanized steel pipes while maintaining their strength and durability.