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I know that electrolysis damages copper plumbing. What is it and how can the plumbing be protected from it?
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Electrolysis does not damage copper plumbing. If you combine iron and copper plumbing directly, electrolysis from the dissimilar metals will cause the iron to rust. You should connect the two with a dielectric union that keeps the two from touching directly.
*To talk about electrolysis is to discuss what a battery is. A battery is a sourse of electrons and the electrons are stored in the metal which makes up the battery itself. From basic chemistry we can explain how a battery works or rather why a battery works. When two dissimilar metals are made to come in contact with on another through a junction, in the case of a battery this is called the electrolyte, one metal will give up electrons more easily than the other. The metal that gives up it's electrons is said to get oxidized and, at the same time, the metal that receives these electrons is said to get reduced. In chemistry, this phenomenon has been observed in all metels and they have been ranked according to their ability to give and receive electrons. The ranking is called the elecromotive series. In the case of your plumbing, the two metals we're hooking up are iron (in the galvanized pipe) and copper in the copper pipe. The electrolyte, which allows the electrons to make a complete circuit, is the water inside the pipe itself. In essence, when you thread the two pipes together and fill them with water your making a big battery. Iron gives up it's electrons more easily than does copper, so iron gets oxidized from elemental iron(0) to say iron (2+ or 3+) and forms various oxides in the process. At the same time the electrons from the iron are taken up by the copper and, if there are any positively charged copper spieces around, they get reduced to elemental copper. Now this battery isn't very efficient but over the long haul, enough electron exchange takes place such that the iron pipe will form significant amounts of rust(oxides of iron)and the pipe will eventually form a leak. To stop this, we deliberatly break the electrical connection between the two metals by inserting a small piece of non-conducting material. This break is called the dielectric union and it's just a special fitting that is half copper and half iron with a piece of plastic fitted between the two. When it's threaded onto the ends of the two pipes they are hooked together physically but not allowed to touch each other electrically.If you have a voltmeter in the house take a lemon, grapefruit, or orange and stick a short piece of copper wire into one side and shove a nail into the other end. When you connect the voltmeter between the nail and copper wire, you will see that there is a significant current of electricity between the two. It's a crude battery and will generate a current for as long as the two metals are in contact with each other through the electrolyte, which is the juice inside the lemon. If you allow these two to be connected for two or three hours and then remove the wire and nail, you can see that the nail is coated with a dark layer of oxide and the copper wire will remain untouched.
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Hey Steve C.
Just wanted to commend (and thank) you on a great explanation of electrolysis! I really enjoyed it!
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An additional comment is that if one uses a dielectric union between a copper and iron pipe, the downstream pipe can no longer be considered grounded for such things as case grounding a washing machine or such. To re-establish continuity, a length of copper grounding wire should be strapped across the union.
*Interestingly, the nitwit who renovated this house about thirty years ago soldered galvanized directly to copper; today there are no signs of leaks. Our water is fairly pH neutral and soft; a battery won't work with pure water (water is hard to ionize) and maybe that's why we've gotten by. This arrangement is not recommended, and even a dielectric union is not meant to be concealed in a wall.Now, doesn't Barry's grounding strap put the poster right back where she started, negating the dielectric (insulative) union?
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Whew! What a relief. I just got out of that Jo-Jo thread. And I was just thinking today about how this newsgroup is a relief from all the klap-trap in the world. Then i clicked on that thing. Anyway, plumbing. Somewhere I got the idea that a brass fitting between copper and galvanized prevents the electrolysis. True or false?
CLG
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Well all I know, is that the next time my truck battery goes dead, I'll just jump it with a lemon ;)
*A truckload of lemons, sure! What's a contractor without a lemon?
*Pete,I'm not even close to a "Diehard" lemon battery expert, but I would think you'll need a matrix of a gross of lemons ...12 in series, by the twelve series groups, connected in parallel...That should do it.And if it doesn't, as they say, when you've got lemons, make lemonade.Jack : )
*No way! A starter can easily draw 50-100 amps in brief surges, I don't think a lemon can do more than milliamps.... For starting, peak amps is probably more important than sustainable current, hence the problem of starting a car in the cold.Prove me wrong AJ! It will take some of your time away from this board, but...
*Sort-of true. The code allows (or used to allow) brass fittings between galvanized and copper. Although it doesn't stop the electrical contact, and the electrolytic corrosion will still happen, it apparently doesn't cause distruction right at the threaded areas and is "sort-of" okay to do. Locate them wher you can inspect and repair them later though.By the way, the zinc on galvanized iron helps protect the iron by the same mechanism mentioned on the detailed post by Steve C. The zinc tends to protect the iron by losing its electrons before the iron's. Even when the zinc coating (which acts as a sacraficial anode) is already broken on the pipe or galvanized roofing. Sometimes the excess electrons are deposited on the surface and are called "white rust".Putting a ground strap accross a dialectric union makes little sence. Although they may be required by code. There are some (like myself) that are concerned that tieing all the steel rebar, copper pipe, galvanized iron pipe, and aluminum roofing together as part of the electrical ground system will cause problems down the road. Maybe the electronics industry will (if they haven't already) develop some kind of inexpensive component that will allow large amounts electricty to pass for ground protection, but will block small amounts of electricity as in corrosion.Also, the PH of the liquid (electrolyte) affects electrolytic corrosion. Distilled water would have little or no problems, acid rain or salt water causes more problems. Heat also aggrevates the problem.A good referance on electrolytic corrosion I've found was a book on electrical systems for boats. Apparently the different kinds of brass (or stainless steels) will react with each other to some extent.
*How about a roll of lead flashing in a igloo of leamonaide?Don't drink it later...
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I know that electrolysis damages copper plumbing. What is it and how can the plumbing be protected from it?