Tom, if the pipe you are dealing with is bare pipe, then it would be pretty expensive to put enough protection on it to do any good. The theory is the same whether using passive or active, pretty much acts as a complete battery circuit with the earth as the electrolyte. On coated pipe with the occasional nick or scrape on it that is where the current flows onto the pipe and back to the bonded on wire that goes back to the anode or rectifier and makes the circuit.TomB wrote:Never heard of protecting steel pipe this way. Its a good example of ignorance from somebody who should know better. I've mentioned in other posts that I have a ski mountain with several miles of steel snowmaking pipe, all of which is corroding. I've always blamed it on iron oxide that is native to the mountain gravel. (If I set a welding magnetic ground down in the sand/gravel it will have stuff stuck to it when I pick it up and I've always though that was iron oxide. Never kn ew the chemistry but assumed that iron oxide plus water leads to a slightly corrosive acid.) But this discussion of using a copper leg as a sacrificial material to slow steel corrosion makes me wonder it that is the case and also if it may be important to me to understand the cause and prevention.
Does anyone have one or more links to technical papers or background web pages on the topic? I will also plan to go and review the Cadwelder web pages.
Tom
Any anodes I used for pipe in earth were always magnesium bagged in a white powder to help give the soil around it a lower resistance to enhance current flow. The only place we ever used zinc was in a tank or other liquid environment
To test you need a copper sulphate half cell and a high impedance meter. You are looking for a negative voltage reading, if memory serves me -850mv up to -1. 5 volts was pretty common and considered protected.
James
