ralt wrote:Hi.
The fellow who supplies us with alloy radiators mentioned in passing many years ago the problems are caused by electric leaks into the water from an external source and any radiator shop can test the water for this problem. He has never suggested to us to use earths, anodes or any such things. Just put it in admire and polish and watch your temp gauge needle in the same old spot.
Yes you can get stray current corrosion. This happens when the thing corroding is acting as a conductor because the return path for the current isn't appropriate. THe current jumps onto the radiator for say......a poorely wired fan?? uses the radiator as a conductor then jumps off somewhere else. The Jump on site is likely to become cathodic protected (sometimes excessively so) and the jump off site becomes the corroding site. This might be a poor explanation as I'm not sure that example would actually occur as again the fan is outside the electrolyte and an alloy radiator is electrically continuous with itself.
An example of where it DOES happen is where you have DC train lines (like Melbourne trams) running along side pipelines. If there is a problem or even partial problem with the earth return for the current the train it will seek the path of least resistance. This can mean is jumps (through soil - which is an electrolyte) from the DC train system onto the pipe at a coating defect (steel/ iron gas / water pipe). Runs down the pipeline (which are generally very well coated and such act like big cables) until it gets to the coating defect nearest the earth return for the train line (or similar) and then jumps off the pipe. Industrially a bond between the two systems would be used to allow the current a return path with out "jumping off" the pipe and causing corrosion at that place. Please remember in this example SOIL IS AN ELECTROLYTE which is true. Air in not an electrolyte/ conductive medium at the sort of voltages we are talking about.
