Can galvanised malleable cast iron fittings be welded?

I. Can galvanised malleable cast iron fittings be welded?

Galvanised malleable cast iron fittings can indeed be welded, but attention must be paid to the effects of the zinc coating. Galvanised steel pipe fittings are characterised by a zinc coating on their surface. This zinc layer can adversely affect weld quality during direct welding. Unlike standard steel pipe welding, welding galvanised steel pipes requires particular care. Prior to welding, the zinc layer must be removed to prevent the generation of toxic gases, and specified welding methods must be employed.

II. Effects of Galvanising on Welding

2.1 Zinc Layer Evaporation

During welding, zinc evaporation may induce defects such as weld spatter, porosity, and inclusions, thereby compromising weld quality. To prevent this, the zinc layer must be removed prior to welding.

2.2 Poor Mutual Fusion

During welding, the differing chemical compositions of the zinc coating and steel result in poor mutual fusion. This creates an unstable weld zone prone to cracking and insufficient weld strength. Specific welding techniques must be employed to resolve this issue.

III. Correct Welding Methods for Galvanised Malleable Iron Fittings

3.1 Zinc Layer Removal

Prior to welding, the zinc layer must be removed. Methods include mechanical abrasion, oxyacetylene flame treatment, or mechanical zinc removal equipment. Mechanical methods suit small-scale welding, while oxyacetylene flame treatment is appropriate for large-scale operations.

3.2 Selection of Suitable Welding Materials

To prevent zinc evaporation and burn-through, suitable welding consumables must be selected. Copper and copper alloy welding wires are generally recommended.

3.3 Employing TIG Welding

TIG welding is a slow, high-temperature process delivering superior weld quality. During TIG welding, arc length must be carefully controlled to minimise zinc evaporation and achieve optimal weld integrity.

IV. Conclusion

In summary, galvanised malleable iron fittings can be welded, but attention must be paid to the impact of the zinc coating on the welding process. During welding, the zinc layer must be removed, and suitable welding materials and methods must be selected. This approach ensures both welding quality and satisfactory results.