magnesium sacrificial anode getting eaten like candy

I'd take the faceplate off this installation & put it on one of the others & see if the behavior transfers.

regards Bob

Jim:

The anodes being used up rapidly are telling you that you have a serious corrosion problem that needs to be taken care of before you have the larger expenses of leaks and repairs. The water conditions may have been different. Possibly you have lots more oxygen than normal, but it's hard to tell.

You might want to look at a Corps of Engineers Public Works Technical Bulletin titled "Boiler Water Treatment: Lessons Learned"

Pittsburgh Pete

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Thanks Bob. He's going to take the Aluminum off at least and see what the rods look like after 2 weeks.

Thanks for the link Pete! I'll take a look and see what I can learn from their experiences. I DO believe he's got a serious problem but where it's coming from & why has got me stumped. He did have some leaks and he's already fixed them once.

Nice disclaimer!

Jim

It may not be the boiler consuming the electrodes, but something else, to which the boiler is simply acting as a conductor. Without a doubt the boiler is well-grounded, and it may be difficult to un-ground it, altho it can be done, by using plastic plumbing as a conductive break, altho you have to be careful on the hot-water side. I would imagine this would include electrical ground wires as well. Once the boiler is conductively isolated, observe the rate of Mg consumption. Alternatively, high consumption implies a voltage, and you could measure the voltage between the Mg and the boiler, and between the Mg and

---------------------------- Mr. P.V.'d formerly Droll Troll

IIRC, The Magnesium is slightly more positive than the Aluminum. They are both reactive materials, Mg being 12 and Al being 13. Since the two metals are used, there are currents being generated by the dissimilar metals. You actually have three or more metals with the iron or steel vessel.

Iron, Fe - lies between them on the chemical chart and is less reactive (by a long shot) from Aluminum. So looking at the Electrochemical Potential Series :

Vo/V values : Iron = -0.04 Magnesium = -2.37 Aluminum = -1.66

Cast iron = -0.18

So normally there is -2.33 difference between the Mg and Iron and the ionic metal migrates from the Magnesium to the Iron, but goes into solution.

When the Al is added, the difference is -1.62 to the Iron (Al goes into solution or salts), and -0.71 between Aluminum and the Magnesium.

So in this case, Mg is giving to the Iron and giving to the Al. Al is giving also.

This information comes from the "Handbook of Physics" [ AIP press ] ISBN

Martin

Jim wrote: