Second opinion identical to Borek's.
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Has someone here first-hand experience with sacrificial anodes aka cathodic protection?
My trials told "very little efficient if any".
My opinion until I change it is that the theory about potentials, corrosion and cells works with batteries made of very pure metals but fails with construction alloys as these contain already corrosion couples before building any explicit cell of them.
Also, even pure magnesium has a bad reputation of corroding without any sort of couple or cell.
Sure, Mg is commonly used to protect steel. But so are radioactive lightning rods despite zero evidence suggests they are better.