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Joined: Mar 2005
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I think there are some misconceptions here. Galvanization does not inhibit corrosion, it only inhibits corrosion of the steel- the zinc coating starts corroding the moment it hits the ground. Though the zinc-oxide forms a coating that slows the reaction, a typical zinc galvanized coating will be gone in 7-15 years, and the bare steel below will rust to nothing extremely quickly. Thicker zinc coatings would last longer, as might new zinc-aluminum alloys, which also hold some promise. The stainless steel rods discussed above are not solid CRES, but merely have a CRES sheating around a standard steel core. And hold up up rather well. The standard copper-clad ground rods still see some corrosion of the steel core, but also hold up very well. Driving a bare uncoated piece of steel in the ground is a very bad idea. Good report here: http://www.transorbelectrical.com/pq/technical/Electrode_Life_Rempe.pdfGalvanized steel rod: “Most of the galvanizing had been lost. Rusting of the steel was greatest near the surface of the ground. Pitting was worst here and near the tip.
”Stainless-clad steel rod: “The cladding was free of corrosion, but at the tip the steel core had corroded to a point about 1 inch inside the cladding.
”Copper-clad steel rod: “The copper cladding was virtually free of corrosion, but the steel core had corroded at the tip to a point 2 inches inside the cladding.”
The study concluded, “Magnesium, aluminum, zinc, mild steel, and galvanized steel rods did not have the desired corrosion resistance.” There was a concern about the copper clad rod causing galvanic corrosion to coupled mild steel. The amount of galvanic corrosion caused by coupling copper and steel will vary depending on their ratio. Since the ratio of steel to copper in most grounding systems is usually large, the amount of steel corrosion is negligible. Additionally, there are often other sources of copper in the ground, which can add to galvanic corrosion concerns. Two studies have now been examined that clearly show the corrosion difference, and therefore expected life, between galvanized and copperbonded rods.
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Joined: Jan 2005
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Steve ... be careful of your knowledge.
The study I based my comments upon used solid stainless, in both rod and plate form, in Southern Nevada and Southern California. In this study, even after only five years, very little was left of the electrodes.
As I mentioned, there's a lot that is not yet known. I suspect we'll find that there is no such thing as a 'good everywhere, all the time' material.
I also suspect that a lot of what we "know" about ground rods, etc., is based more upon 'logic' than actual experimentation ..... not to mention outdated theories and assumptions.
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Joined: Mar 2005
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There are a lot of different "stainless" steels, too. Technically, they're referred to as CRES, corrosion resistant steel, and underground is a very harsh environment for any ferrous alloy.
One thing they have in common, though, is that they're all going to corrode slower than ordinary carbon steel. I would not be surprised to see some grades of CRES rust out before a copper clad rod, but I'd expect every single one to outlast a piece of rebar.
Can you post some more information about the studies you're referring to?
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Joined: Jan 2005
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Alas, I cannot ... at this time. The %$&^ study is still on-going, and no official report has been issued as yet - though that has not stopped the participants from going on the seminar circuit.
I am also quite interested in the specifics; the assertion that even plain, low quality steel out-performed the stainless has me more than a bit curious.
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Posts: 28
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