Mixing metals

Discussion in 'Materials' started by Runhammar, Apr 8, 2021.

  1. Runhammar
    Joined: Jul 2020
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    Location: Stockholm

    Runhammar Junior Member

    Hi all
    I am installing a water based (?) heater on my boat, have used it before and like it. It pumps kerosene heated mixture of water and anti-freeze/anti corrosion (glycole) through radiators. Now I plan to extend it through a stanless steel water heater and make it heat my water.
    This is when I start getting concerned about the ”mixing” of metals... The spiral i side the heater is copper. Radiators and some connectors are aluminium and the tank is, as i wrote, stanless steel. Admittedly the metals don’t touch eachother, but still; will the water mixture connect them and cause corrosion, or does the glycole stop this?

    kindly
    Per
     
  2. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    If you are using a commercial automotive antifreeze solution and respect the recommended change intervals (2-3 years) you will be fine. Just don't use pure glycol mixed with water.
     
  3. Runhammar
    Joined: Jul 2020
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    Location: Stockholm

    Runhammar Junior Member

    Ok, good. Just to make sure: you do mean a glycol mixture, albeit commercially mixed? You do not mean the alcohol stuff for the windshield wipers...? I am quite sure you do, but need to be fool proof.
    So, I get a couple of litres of the same stuff (we call glycol) that we use for winterizing engines. And change it at intervals...
     
  4. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    Yes, the stuff you use for car engines. They contain things that are specifically put there to inhibit dissimilar metal corrosion (modern engines are a big mix of metals) and that's why you have to change it every few years, those chemicals get used up. The car manufacturers even have specific mixtures for specific engine models, and those last longer, but the "universal" ones are only good for two. Buy a brand one, and change it regularly.
     
  5. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    If you don't create an electrolyte there won't be any electrical connection. Use distilled water for best results.
     
  6. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    He can't, look at his location, he would have to purge and recharge the whole hydronic system every time he goes sailing. If it's cold enough to use the heating, it will probably freeze at night.
    Distilled water is not that good anyway, that's why engine manufacturers insist on using the antifreeze solutions even in places where it never freezes.
     
  7. Runhammar
    Joined: Jul 2020
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    Location: Stockholm

    Runhammar Junior Member

    Well, yes and no. We sail from may to october and no risk of freezing temperatures, or at least low risk, managable.
    When we take our boats up we all winterize our engines the first few days because then frost may come any night. so yes, destilled water could be fine, and I could empty the system every fall. But Ill go with antifreeze and have one less thing to consider in october. Exemp to change at stated intervals, but that is a lot less panicky.
    Issue solved. Thank you! On to the next few hundred...
     

  8. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    I wasn't suggesting just distilled water. When mixing with antifreeze, distilled water would work the best to prevent corrosion. The other thing you want to do is isolate the system from ground. The three things you need to have galvanic corrosion is two disparate metals close enough to each other to trade electrons, an electrolyte to provide a pathway and a connection to ground to complete the circuit.

    A sacrificial anode partially relieves the demand by the noble metal (the cathode) and also helps replace the electrons stripped away by the cathodic metal. The less noble metal them becomes the cathode to the sacrificial anode even while it is the anode to the more noble cathodic metal.

    So, you can isolate the two metals from each other by coating one or the other or both, remove any electrical pathway by taking away the electrolytic or you can devise a way to feed electrons back to the anodic metal.

    There are active cathodic protection systems that feed electrons into the galvanic system the way a sacrificial anode does, but they require monitoring and dynamic adjustment.
     
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