We currently have a closed water system that feeds two white-metal bearings and a two labyrinth seal on a gas booster fan. The water is currently held in a galvanized steel tank and during the winter months we have put ethylene glycol (antifreeze) into the water to make a water glycol mix to stop the water freezing up as this is a vital part of the operating plant. We have been experiencing problems with the galvanized steel tank corroding and I personally have found out that the glycol reacts with the zinc coating of the galvanized steel. However, I don't know the actual reason why the reaction takes place. This is needed as I have the task of redesigning the water system.
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Brian Dalder Forum Moderator 177 Posts
Re: Galvanized steel may not be the best material of construction19 October 2010 at 1:29pmA couple thoughts come to mind. First, when using an ethylene glycol based heat transfer fluid, one must always use a heat transfer fluid that contains a corrosion inhibitor. Uninhibited ethylene glycol heat transfer fluids can decompose into various organic acids such as glycolic, glyoxylic, formic, carbonic, and oxalic acids. The decomposition is accelerated by high temperatures and these acids can be quite corrosive to many materials. Second, according to Dow Chemical (a manufacturer of ethylene glycol based heat transfer fluids), galvanized steel is not recommended for use with ethylene glycol heat transfer fluids, even if they are inhibited and especially if the temperature goes above 120 degrees F. The zinc coating of galvanized steel is designed to protect against atmospheric corrosion. At slightly elevated temperatures, zinc becomes cathodic to iron or steel reversing the galvanic series. Thus, the iron or steel will protect the zinc by corroding. In addition, phosphates in the inhibitor will react with the zinc, precipitating an insoluble material that can foul the system and encourage under-deposit corrosion. It would seem that galvanized steel is not a good material of construction choice for your application.