Galvanic Corrosion Explored

Ahh the joy of mixing metals in a closed water loop…:)  While many water coolers have had excellent success with running copper/brass/nickel over the years with plain water, we have seen many examples of where certain conditions result in not so favorable results.  While we often call copper/brass loops a “Similar” metals loop, I think we are also forgetting that “Similar” is not the “Same” and we have a LOT more than just copper and brass in our loops.  Your typical water cooling loop has a mixture of copper, brass, nickel, and tin.  Note, that I think I’m the first example of the “TIN” corrosion by an unintentional experiment I had been carrying out over the last year or so..:)

The manufacturers pretty much all say “use our coolant” which includes corrosion inhibitors, yet we persist in thinking nothing is wrong with this mixing of “Similar” metals.  I’m not a corrosion expert by any means and have typically had the same or similar good success without the use of inhibitors.  I am however becoming more of a believer of corrosion potential as these repeated problems persist and as I have now experienced a recent loss myself.

Last year when doing my fan testing series, I filled up two radiators with water as part of my testing rig templates.  One was a Swiftech MCR120, and one was a Hardware Labs SR1 140.  Upon digging those radiators out in preparation for my radiator testing bench rebuild, I noticed that the MCR was still full of water, but the SR1 140 was empty.  I also noticed what appeared to be water stains on the bottom of the SR1.

Could this be corrosion?  I thought..

Oh my, my SR1 has become a victim of corrosion!!

But I thought the idea was if you run copper/brass loops, corrosion wasn’t possible?

Well…it is..

My SR1 is now a leaking sieve, so I decided to do a little digging in on galvanic corrosion.  I think most people including myself have been thinking about corrosion between copper/brass/nickel, but I don’t think we have been thinking about the solder in radiators.

What is Galvanic Corrosion?

Per Wiki:

Galvanic corrosion is an electrochemical process in which one metalcorrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. The same galvanic reaction is exploited in primary batteries to generate a voltage.

So it’s not all bad..after all Galvanic corrosion is what starts your car in the morning..:)

What is needed for Galvanic Corrosion?

Per the corrosiondoctors.org:

1. Electrochemically dissimilar metals must be present

2. These metals must be in electrical contact, and

3. The metals must be exposed to an electrolyte

Of particular interest to me is #2, I didn’t realize that the metals had to be in electrical contact, but that does explain a few things I’ve been seeing.

Now to make sense of my SR1 loss:

Ok, so in a closed loop of water, while water is initially non-conductive, it only takes a short time in a water loop to become contaminated and conductive.  Once conductive it now satisfies the “Electrolyte” criteria. #3 is done.  The stagnant condition (and not at all typical) probably made this many times amplified.

Also the metals must be in electrical contact.  In my radiator example the soldered connection of the radiator fins is clearly a good metal contact. #2 is satisfied.

And finally they must be dissimilar metals:

According to the corrosiondoctors.org anodic index, it appears a normal copper solder radiator has about a .30 galvanic potential.

Yep, seems to make sense I guess.  How about a few other examples others have shared:

ALUMINUM/COPPPER

Aluminum and Copper in direct contact.  Pn0yb0i gave an example of what running an aluminum/copper block can do after an extremely long 4 year run here.  He was going to reuse the block after cleaning, so I ask him if I could use some of his pictures if I sent him a replacement block sample for free.  He accepted happily and I feel better that he’s got a new block too..:)  Anyhow, here are a couple of photos that he shared and gave me permission to use.

He said he used distilled water plus pentosin and purged every 2 months.

And to compare the anodic index between copper and aluminum.

In general most manufactures have given up on attempting to make aluminum/copper blocks, which has led to eliminating that problem.

However, as water cooling has become “Art” as much as it is performance, there has been a dramatic increase in Nickel plating of blocks.  It is handy not having to deal with tarnished copper and a lot of people like the shiny surface of Nickel plating which in itself has caused problems as well…

Nickel Plating

The hot topic in the forums has been in regard to nickel plating failures.  Manufacturing processes have been improving regarding the plating quality.  Electroless plating is the latest preferred method which is supposed to plate the parts more evenly.

If you look at the anodic index again and compare nickel to copper, you can see it is actually very similar in index meaning their corrosion potential is very small.  In the case of metal corrosion, opposites attract and nickel/copper are very similar.

But….the difference is still there.

We have seen failures on blocks and we have seen failures on fittings.  The one commonality I have seen in all the various forum examples is “stagnant” water.  Just like my radiator example, where you normally see plating fail, is where water sits still.  I believe this stagnant condition is what promotes the #3 electrolyte condition.  The longer the water sits still near metals the more contaminated and electrolyte like it gets.  We typically see plating failures between surfaces such as the GPU block and acrylic or delrin top.  We also see it between CPU nozzle plates and the CPU block bases plated in nickel. In fittings we see the plating failures at the threads…again where the water is stagnant.

The other reason I think the small index still causes problems is simply due to the plating being very thin it just doesn’t take much to show.  Also since copper is the anode to nickel, it works in an undermining process where the copper goes away, and the nickel flakes.  Also as the copper goes away and undermines the nickel, it creates a pocket where that electrolyte enhancement (stagnant water) grows even faster.

I do think a “Perfect Plating Job” could avoid the issue with plastic tops, if there was a perfect nickel plating over the copper block and that was the only metal in direct contact, you will have essentially removed the “electrolyte” variable.  If there is no way for the electrolyte (water) to get between the copper and nickel, then life is peachy.  I just don’t think plating is ever perfect.  Any little microscopic pin hole, scratch, or thread wearing into the plate will expose the copper allowing the reaction to occur.

What is the problem?

• We are mixing metals.
• Some of the mixed metals have direct electrical contact.
• Our water is becoming an electrolyte with stagnant water conditions in some areas.

Sacrificial Anodes

One thing that hasn’t really been explored much in water cooling is the use of sacrificial anodes.  These are used quite regularly for corrosion applications where the idea is to make the electrolytes go after a more active metal instead of the metals you are trying to protect.  The anode need to be in electrical contact with the other metals and will over time corrode and need replacement.  You see them in household water heaters and on ships in saltwater, and bridges along the coast.  Most industries that have some sort of corrosion problem lean toward either or a corrosion inhibitor or some sort of anode to provide that protection.

I don’t see why you couldn’t have some sort of zinc barb insert or something that could be easily replaced though. I’m not quite sure what sort of deposits the zinc would make, but it should theoretically work in preventing corrosion from occurring. I’m not sure???

I could see that as being a possible solution for folks that would rather not run anything than water. That’s what we do for water heaters (inhibitors not possible), why not for water cooling?

Anyhow, not sure if sacrificial anodes would work or not, but I’m really curious to try. It could be a solution for giving plain water loops corrosion protection without the fuss of a coolant with inhibitors.  You would just need to attach a piece of zinc to each of the mixed metals blocks/rads and see what happens.

Conclusion

I don’t think it is possible to completely stop galvanic corrosion from occurring, but we can reduce it by:

• Eliminating direct electrical contact of dissimilar metals (Plastic top/unplated copper base blocks)
• Reduce Electrolytic Conditions – Reduce areas where water is stagnant, flow is your friend.  Regular maintenance and complete cleaning of the block/pieces probably helps too.
• Improve plating processes and increase plating thicknesses.
• Slow the process with corrosion inhibitors in the fluid
• Slow the process using a sacrificial anode in system running plain water.

But I don’t think you will completely stop corrosion.  The idea is to keep it at bay long enough and/or reduce it for the intended service life. Unless you made the entire loop of one metal or kept all the metal parts from touching one another, you will have the potential for galvanic corrosion to occur.

Cheers!

Martin