Hot-Dip Galvanizing Defects: What Are They and How to Treat Them?

Despite the advent of new treatments and protection methodologies, the most used method with the longest duration over time is hot-dip galvanizing. This particular treatment is most recommended for the protection of structural steel, as the treated parts require a low level of maintenance compared to fasteners made from other materials or treatments.

Before sending the material for galvanizing, it is good to check that there are no defects or irregularities on the surface, color stains, oil, grease, paint, or any welding imperfections.

Upon receipt of the treated goods, it is crucial to verify that the galvanization is suitable and does not present defects. In this short article, we will list the main visual defects of non-compliant hot-dip galvanizing:

Rough and Irregular Surface

If the part, before being treated, presents surface irregularities, the galvanizing treatment will accentuate these defects.
The onset of irregularities on the surface could also be caused by the chemical composition of the starting raw material, presenting high percentages of phosphorus or silicon.
Another factor that could have caused these defects is the time the part was left in the galvanizing bath; in this case, the layer of zinc deposited is too thick and therefore presents an irregular surface.

Slag Inclusions

It is possible that small nodules are present on the surface of the treated parts.
These imperfections are due to the agitation of slag at the bottom of the galvanizing bath during the treatment, in this case, the presence of these nodules does not affect the suitability of the part.
If for aesthetic reasons one wanted to remove these small nodules, it is sufficient to file or sand the part until the desired aesthetic effect is achieved.

White Rust

The presence of white or gray-colored spots on the galvanized surface is due to the excessive presence of zinc oxides and hydrates. Exposure to conditions of high humidity during transport or storage causes the appearance of these spots, which fortunately do not compromise the zinc layer, it is possible to remove them by brushing, filing, or sanding. White rust naturally dissolves, leaving the treated parts in non-humid environments.

To conclude, it is good to remember that hot-dip galvanizing must comply with ASTM A 153/EN ISO 1461:2009 standards to be considered compliant.