Zinc Puddling?

Althalus · Oct 29, 2013

One of the managers here just said something rather strange. I'm wondering if he was off base or not.

Imagine a W8x31 column welded to a base plate. During hot dipping a puddle of zinc forms in a corner pocket created at the intersection of the plate, flange, and web. If it dries on there there is a noticeable puddle of zinc sitting there. While it may not be aesthetically pleasing, and it may cost the fabricator a little more, I didn't think it created any service issues.

The manager here said that such a thick layer of zinc could pop off via vibration/impact during shipping. ???

Has anyone heard of this?

Compositepro · Oct 29, 2013

Most coatings shrink after application. This includes paint and zinc galvanizing. Thin coatings can stretch without exceeding the bond strength with the substrate. Overly thick coatings will debond because they are too stiff to stretch and stay the same length as the substrate. So, yes there is some truth to what he said, but I have no personal experience with this exact scenario.

SlideRuleEra · Oct 29, 2013

The excess zinc puddle may come off, but that does not necessarily mean that corrosion protection from the zinc has been lost. During the hot dip process the zinc actually forms a "tightly bonded alloy coating". At least a portion of this alloy would remain and continue to provide corrosion protection.

Even is all the zinc AND all the alloy came off of a small area, the galvanizing surrounding the damaged spot will continue to protect the exposed steel. Read all about it at the American Galvanizers Association website:

http://www.galvanizeit.org/hot-dip-galvanizing/what-is-hot-dip-galvanizing-hdg/

http://www.SlideRuleEra.net