Antifreeze for galvanized pipe in Hyrdonic system

Paul Dennis

My 30+ year old hot water heating system has both copper and galvanized pipe loops. Since Glycol is not recommended for use with galvanized pipe what is the recommended antifreeze and where can I get information on this?

Aidan (UK)

Glycol and galvanised pipe

I went through this same process for an old heat recovery system with galvanized pipes. I never did find a satisfactory solution, either figuratively or literally.

My understanding is that it is not the glycol, but the corrosion inhibitors (phosphates) that react with the zinc coating. It was suggested to me that I may be able to get straight glycol, without any of the usual inhibitors. Since the system was entirely made of galvanized pipe, there was little need for corrosion inhibitors.

The other solution suggested was that I should use a different anti-freeze chemical. Methyl alcohol used to be used. It's not as effective as glycol and I don't think this would be a good idea for a heating system.

I tried getting some advice from the anti-freeze suppliers in the UK, but I got nowhere. It seemed that they get their business from supplying the standard mixture and couldn't be bothered to attend to my particular problem.

Please let me know if you get any further than I did. I'd be interested to know if there is a solution.

Paul Dennis

Does the inhibitor react with galvanized pipe?

Thank you for the information. I have been using a Dearborn 537 Closed System Inhibitor (borate-nitrite treatment containing an organic corrosion inhibitor and erosion impingement passivator which provides complete corrosion protection for both ferrous & non-ferrous metals - according to the label). I used this inhibitor because there was scaling in the cast iron boiler and it seems to be fine now. I am not aware of any sludge problem caused by the reaction of zinc & the inhibitor. Would the sludge tend to build up in the boiler? I will try to follow up with the supplier to get more information.

Aidan (UK)

inhibitors

I think it's the inhibitors which are usually supplied with the glycol anti-freeze mixtures. The inhibitor is usually potassium di-phosphate (I think, I not 100% certain) which reacts with the zinc and reduces it to sludge. I don't think there's a compatibility problem with zinc and nitrite inhibitors, but I'm no chemist.