The authoritative public forum
  for Metal Finishing since 1989
-----

Did Electrification of Galvanized Roofing Panels ruin them?

My plant experienced an event whereby the galvanized roof (8 years old) and wall panels became electrified with 480 V for almost 5 minutes. It became so hot that an aluminum bar welded to the side of the structure some 60 feet away. Immediately after the event a white powder appeared on the underside of the roof panels. Within 12 months we got an inordinate amount of rusting, especially for such a young structure. Could the heat of the event affected the zinc plating turning it white? Would this also result in the premature failure of the roof panels that had lasted up to 30 years before?

What happens when such an event happens?

Rick Wilson
owner/operator - Brewton, Alabama, USA
July 13, 2011

---

July 15, 2011

Not quite enough detail to be definitive, but it sounds like you burnt the zinc off, yes.
Firstly galvanized roofing isn't electroplated. Plated means something else. Typically roofing steel is galvanized not plated.

480V is a high voltage, but at what current?
For 5 minutes? Surely a fuse would blow or a circuit breaker trip?
But anyway, if there was heat to "weld" aluminium, then that's more heat that required to melt zinc and heat it to oxidizing temperatures.
The white dust sure sounds like zinc oxide, and if so you turned all your metallic zinc, that was there to protect the steel, into zinc oxide, a compound no longer capable of protecting steel. So the steel will rust.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK