Re: DIELECTRIC UNIONS
Posted by Aros on November 29, 1998 at 03:20:29:
In response to Re: DIELECTRIC UNIONS

: How about if we start with the premise that di-electric unions are largely ineffective and go from there. The electrolysis is a reaction between to different metals in the presence of water. the reaction result in the more noble metal (copper) damaging the less noble one, (steel). This is the same principal behind the Mag rod in a water heater, except there the reaction is between steel, (the more noble in this case), and magnesium. In this case the magnesium sacrifices itself to protect any exposed steel areas by means of the electrolysis. Since the active medium in these cases is the water, the reaction will occur point to point and bridge the di-elctric union. I tell customers that if they install a copper water service to a house with steel piping, or replace a section of steel with copper, (with or without DE unions), they will hasten the demise of the steel system.
: : TERRY:
: : I HAVE A COUPLE OF QUESTIONS. WHEN YOU JOIN GALVANIZED AND COPPER PIPES TOGETHER, DO YOU NEED TO USE A DIELECTRIC UNION? IF YOU DO NOT, WILL IT CREATE A REACTION OR CORROSION? WILL THIS CORROSION TAKE PLACE AT THE SPOT OF THE UNION OR AT SOME OTHER PLACE? LET'S SAY THAT A LEAK DEVELOPED AWAY FROM THE SPOT OF THE UNION, COULD ONE SAY THAT THE LEAK OCCURED BECAUSE THERE WAS NO DIELECTRIC UNION INSTALLED OR THE LEAK HAPPENED FROM OTHER CAUSES?

If you join copper and galvanized pipe together, the corrosion will occur at that joint only. A die
electric union will prevent this from happening. However consider that most houses are grounded electrically through the plumbing. Using a die electric union could actually leave your house
ungrounded if located in the right spot. What I prefer to do is to use a brass nipple at least 6"
in length with two brass couplings between the copper and the galvanized. No corrosion takes place and the ground is maintained. -Aros



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