White rust on cooling towers and water treatment systems isn’t an uncommon phenomenon here in Atlanta; our humid, rainy summers are terribly harsh on metals, and many companies that use galvanized steel outside aren’t aware of it’s potential for rusting.  After all, you would expect a galvanized material to resist rusting, not be prone to it.

What Is White Rust?

Also known as white storage stain, white rust is a type of chemical buildup that occurs on galvanized (zinc-coated) surfaces when repeatedly exposed to water without drying properly.  Much like the more common ferrous rust, white rust can lead to the eventual corrosion and breakdown of whatever system is rusting.  This is why some industries also refer to white rust as white corrosion.  It’s important to stay ahead of white rust in your cooling towers; however, if it does take hold, you will need to refurbish the coating to prevent corrosion of the underlying steel.

What Causes White Rust?

Decades ago, before cooling towers were allowed to operate at higher internal pH levels, internal white rust wasn’t really a problem.  However, after consumers began to demand sulfuric acid’s removal from water treatment systems to maintain a neutral pH (7.0), systems were optimized for the more basic (around 9.0) internal water solutions.  Unfortunately, the implications on newly cast and galvanized steel products were not considered.  Under basic, high pH conditions, the unweathered zinc coating tends to oxidize much faster than at a neutral pH.

As mentioned above, the weather here in Atlanta isn’t helpful in keeping white rust at bay.  Unfortunately, humidity causes there to be a constant supply of water in the air, even when it isn’t raining.

Isn’t Galvanization Supposed to Eliminate Rust Issues?
The galvanization process isn’t quite finished after a piece of steel has been dipped in zinc coating.  In fact, it can take up to two years for galvanized steel to become completely protected against unwanted corrosion; this is because the surface of galvanized steel has to be exposed to the atmosphere in order to create an efficient seal (a process called passivation).

Additionally, higher temperatures can increase the potential that a piece of galvanized steel will develop white rust.  In evaporative cooling towers that are constantly exposed to warm, moist, high pH environments, there is an enormous potential for white rust.

How to Avoid White Rust Buildup
Preventative measures against white rust start with your project’s planning stage.  Perform a water test to identify which materials will be best for your equipment’s construction.  When you choose what to construct your machinery with, take everything into consideration, including the likelihood for white rust in your cooling towers and other machinery that uses galvanized steel

You can severely reduce the likelihood of a surface developing white rust by allowing proper ventilation and minimizing exposure to mineral-free water.  If you start to notice a powdery white buildup on your equipment, you need to take a look at the environment and what changes can be made; additionally, you may need to renew the natural passivation with a solution of sodium dichromate and sulfuric acid.

White Rust Treatment in Atlanta
Depending on how much damage has been inflicted to the underlying steel, we may need to apply new zinc coating to the galvanized steel panel.  For more information about our refurbishing services or to schedule a free consultation with our team of white rust experts in Atlanta, reach out to us on our website.