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 Posted: Fri Oct 8th, 2004 06:20 am
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bottecchia
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When I replaced most of my home's old galvanized steel pipe with new copper, I followed advice given to me with respect to the installation of dielectric junctions wherever the steel and copper were getting connected to each other. These gizmos keep the steel and copper from having direct contact with each other, thereby (supposedly) preventing dielectric corrosion activity from eating up the steel.



Last week I got a new hot water heater. The installation instructions didn't mention use of dielectric junctions when attaching copper tubing to the steel tank's inlet and outlet nipples. In the flex-pipe instructions, the steel-braided flex line is attached to the WH nipple on one end, and attached via a brass compression fitting to the copper house pipe on the other. So, the steel and copper remain in electrical contact even though they don't actually touch. But, in the solid-pipe instructions, the copper fitting is screwed directly onto the WH nipple. The nipples are plastic-lined (with 'heat traps' also), but this doesn't prevent the steel and copper from direct contact. So, now I'm a bit confused about the use/need for dielectric junctions to begin with. If they are needed elsewhere, why not at the WH tank junction? If they aren't needed at the tank junction, why are they needed elsewhere? Does the presence of a WH anode somehow only save the tank's steel, or does it protect all steel throughout the house's water system? Or, does it protect only steel in direct electrical connection to the water heater? Or something else?



If copper-steel connections are OK at a WH, could I use a copper nipple instead of a brass one when installing the suggested brass-body ball valve at the drain port.



My thanks to anyone able to clear up my confusion.

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 Posted: Fri Oct 8th, 2004 05:48 pm
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elenano
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There are answers to your riddles. First, the formula for electrolysis is that two dissimilar metals be physically connected in water.



So it doesn't matter if steel is connected to copper as long as it's dry. There are washers inside both stainless steel and copper flex lines that are key to preventing electrolysis. Indeed, if the rubber washers inside a copper flex line or dielectric union break down from long exposure to hot water, that's when leaks and corrosion begin.



As to screwing a copper fitting directly onto a plastic-lined nipple, if the plastic insert is of the type that forms a lip on the end -- as opposed to some that end flush with the steel, then again, no steel and copper will be connected in water.



However, if water is able to somehow get between the insert and the steel, the nipple will rapidly corrode. I saw this on a bunch of commercial water heaters in San Diego a couple of years ago. It was ugly -- the resulting leak damages not only the nipple, but the water heater. But I also know a plumber who always screws a plain brass union onto a plastic-lined nipple and it always works. Execution may be everything....



In any case, the water heater anode does not protect anything beyond the interior of the water heater. We've seen unlined galvanized nipples that were badly corroded even though the water heater had a functioning anode with plenty of sacrificial metal left on it.



Nipples aren't made from copper. It's a soft metal. You could use a brass nipple at the water heater, and in fact, a lot of plumbers do. We don't like that because the brass can potentially react with the water heater tank steel and damage the latter. It's worth noting that when water heater manufacturers supply nipples, they are invariably plastic-lined steel, not brass. The steel won't react with the tank and the plastic lining prevents electrolysis.



Randy

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 Posted: Mon Dec 21st, 2009 03:06 am
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FrankClay
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This thread posted five years ago turned out really helpful as I'm in this exact situation . Good thing this forum board was the first to pop out on Google during my search.

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