Galvanized Repair Gone Wrong!
The easiest way to understand the protective characteristics of Galvanized coatings is with an example of a failed coating. The attached picture shows a steel bridge support just 9 months after the piling and its galvanized coating were repaired and returned to service. There is significant pitting in the region where the Galvanite™ coating meets the pre-existing galvanized coating above the repair weld.
Rules of Thumb for Everyone – Defeating Corrosion
There are three rules of thumb that everyone should know to defeat corrosion on galvanized surfaces:
- Corrosion is always occurring. When the Zinc coating is fresh, even, and thick, corrosion is eating the Zinc coating slowly and uniformly over the entire galvanized surface,
- Corrosion always occurs at the weakest point in the protective system (usually a scratch or area of abrasion)
- To stop corrosion at the weakest point, the weakest point has to become the strongest, most protected point in the system.
So, let’s look at our project picture. In this case, corrosion is occurring in the “feathering” region between the old and new protective coatings just above the repair weld. Following our rules of thumb, this must be the weakest point in the protective coating. In this particular case, this area also sees substantial salt water wave action at high tide. This adds abrasive forces to the corrosive forces in this region of the support.
Finally, let’s look at a close-up of the Galvanite™ coating and apply our rules of thumb.
The area of the weld seam looks extremely well protected. This is how a steel surface repaired with Galvanite™ should look 9 months after repair. The coating is even and seamless. Now examine the broken coating and pitted steel just above the weld seam repair. This type of pitting is most often caused by insufficient feathering of the new Galvanite™ coating into the old coating – TOO MUCH HEAT, NOT ENOUGH SOLDER! This is the most common oversight in repairing galvanized steel coatings. If the old and the new coatings don’t join in sufficient thickness to form a seamless barrier (skin), corrosion will occur right where they meet.
In order to repair this area and prevent it from becoming the weak link again, this weakest area must be made the strongest, most protected portion of the piling. Use Kapp Alloy’s Galvanizing Repair Instructions to reapply a thicker, more resilient Galvanite™ coating to the damaged area. Start in the damaged area and work up and down the support from there. Pay particular attention to the Galvanite™ thickness in the damaged area and where the new coating feathers into the old coating. DO NOT OVERHEAT the parts. Keep the flame and the Galvanite™ rod moving throughout the process.
If you wish to apply another coat of Galvanite™, let the area cool. Then apply another coat starting again in the area of the pitting. Sufficient coating thickness and adequate feathering between coatings should build up a substantial barrier to further corrosion in this area. Make this weak area the strongest, most protected area to defeat corrosion throughout the piling.
Kapp Alloy manufactures Galvanizing repair solder as both:
GalvRepair™ - The original Tin-Zinc-Lead Galvanized surface repair solder. Just like the original Galvanized metal, it metallurgically bonds to the Steel for a seamless, protective barrier. GalvRepair™ exceeds performance standards as specified by ASTM standard A780-92 for repair of Galvanized coatings.
Please Note: GalvRepair™ contains 50% Lead. For Galvanizing repairs requiring a Lead-Free alloy, please see the information for Kapp Galvanite™
Galvanite™ - Tin-Zinc-Copper solder is the new Lead-free formulation designed specifically for high quality repairs to Galvanized Steel surfaces. This solder is simple, effective, and easy to use in both manufacturing and field applications. Just like the original Galvanized metal, Galvanite™ metallurgically bonds to the Steel, for a seamless protective barrier that outlasts Zinc rich paints and sprays.
Galvanite™ exceeds performance standards as specified by ASTM standard A780-92 for repair of Galvanized parts