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  • #16
    Re: (dielectric) unions VS brass fittings

    Dielectric is one form. Arranging metals and alloys with similar potentials is another.

    Comment


    • #17
      Re: (dielectric) unions VS brass fittings

      i forgot to mention that the pic i posted of the HWT has brass nipples under the dieclectric unions.

      only the union is corroding.

      Vince

      Comment


      • #18
        Re: (dielectric) unions VS brass fittings

        Originally posted by Vince the Plumber View Post
        wouldn't the presence of a liquid complete the curcuit anyways? this is way we ground the domestic water right? i could be wrong though.

        i came across this today.

        i don't know if this will help.

        Vince
        honestly that pic looks like something was leaking and doesnt appear to be electrolosys

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        • #19
          Re: (dielectric) unions VS brass fittings

          Originally posted by Chemeng View Post
          Dr. House....uummm... exactly what part of my posting is wrong?
          okay, not to get technical, this is just plumbing, when steel and copper r seperated by brass this helps to prevent electrolosys

          Comment


          • #20
            Re: (dielectric) unions VS brass fittings

            Okay, dielectric unions are suppose to be the right way of connecting copper to steel but as known by all they become leak prone rusty pieces of crap. Had to cut one out just the other day on a boiler water make up valve. Now I believe it is or was in the UPC code book as an alternative say in a wall with out an access panel an 8 inch brass nipple was accepted instead of a dielectric coupling. This was in San Diego some years ago. In servicing 14 schools by myself I use both methods, depending on future accessibility.
            Last edited by plumb4life; 02-03-2009, 10:42 PM.

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            • #21
              Re: (dielectric) unions VS brass fittings

              i have seen DEU's that were installed when a HWH/HWT was installed brand new.

              by the time the tank needed to be replaced, the DEU was no good. it couldn't and shouldn't be reused. at least i wouldn't reuse it.

              i don't really understand the need for the DEU.

              the domestic water pipe is grounded. the HWH/HWT is grounded.

              what exactly is the reasoning for these.

              Vince

              Comment


              • #22
                Re: (dielectric) unions VS brass fittings

                I see your point, Vince: but the powers that be ; The old timers sitting around the round table that decide what the code shall be voted that way........... doesn't always make sense does it?
                Last edited by plumb4life; 02-01-2009, 07:41 PM.

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                • #23
                  Re: (dielectric) unions VS brass fittings

                  the dissimilar metals when screwed together creates a small electrical charge the eats away at the copper.... this is a very generic explanation

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                  • #24
                    Re: (dielectric) unions VS brass fittings

                    but why is it necessary to insist on a union?

                    it almost sounds like to me somebodies getting kickbacks.

                    from my perspective, it doesn't make any vinsense.

                    Vince

                    why not a cheap C X NPT coupling, if it absolutely necessary to have such a seperation?

                    why?,..........why?!!,...........i ask you!!!?i'm ex-bushed!!!!

                    i think for the benifit of my customers, i'll stick to brass. at least i know it's not going to fail.

                    i'd guarantee the brass for 1 year before i'd guarentee the DEU.

                    Comment


                    • #25
                      Re: (dielectric) unions VS brass fittings

                      Vinnie, I'm gonna' fly up there to the Big White, turn your home's heat up to 50 degrees and make you sweat if you don't let this thread die.

                      J.C.

                      Comment


                      • #26
                        Re: (dielectric) unions VS brass fittings

                        im loving this thread its what made me join this board... it doesnt have to be a union, it can be something brass or even a waterway nipple, just something to seperate the steel and copper

                        Comment


                        • #27
                          Re: (dielectric) unions VS brass fittings

                          Every time i take apart a DEU it is full of corrosion,and you gota dig out the gasket
                          When i unscrew a cop male off a old tank ,its clean and no corrossion....
                          Makes a guy wonder

                          Comment


                          • #28
                            Re: (dielectric) unions VS brass fittings

                            Tyman,
                            the nipple is just a nipple. I screw it into a npt x sweat copper union.

                            Comment


                            • #29
                              Re: (dielectric) unions VS brass fittings

                              I was adding waterlines to a home today for a couple of humidifiers, and I noticed that the house was piped almost* completely in copper, and the electrical was grounded onto it with what looked to be a galvanized steel grounding clamp.



                              *the main coming into the building was black poly, which seems like it defeats the purpose of grounding to the copper line.
                              No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

                              Comment


                              • #30
                                Zinc-galvanized unions versus brass nipples (zinc wins)

                                Originally posted by Vince the Plumber View Post
                                i have seen DEU's that were installed when a HWH/HWT was installed brand new. By the time the tank needed to be replaced, the DEU was no good....

                                What exactly is the reasoning for these?
                                Vince, I've joined to make a first post because I know how this works. I'd like you all to read and understand this old page from copper.org's plumbing information, http://www.copper.org/applications/p..._corrosion.pdf.

                                But I'll also summarize. First note that the problem we SHOULD be talking about is galvanic corrosion-- "electrolysis" is different, resulting from externally imposed DC current. (You're totally right, the HWH is grounded AND the pipe is grounded-- there ain't no external DC current.) Galvanic corrosion is self-induced between the different metals, in contact with each other and also in contact with an electrolyte. Saltwater is a great electrolyte and distilled is not an electrolyte at all. "Tap water" is a weak electrolyte, it will support the corrosion process, but only over a period of months/years.

                                Under these conditions The "less noble" metal will corrode. That pdf shows a table of metals which are widely used in pipes. The "least noble" metals are: #1- Zinc; #2- Galvanized Steel/Iron; #3- Aluminum; #4- Steel, and #5 Iron.

                                From the "most noble" end, it's #1- Monel; #2- Copper Alloys other than Brass; #3- Bronzes; #4- Copper; and #5- Tin. (I'm leaving out a bunch of metal in the middle of the list which aren't relevant to HWH connections.)

                                When you use a Galvanized union, you're protecting both the copper pipe and any steel which is exposed within the tank. So of course, if any galvanic corrosion occurs, the part which looks the most horrible and messed-up is the galvanized union. From either the tank steel or the piping copper, the galvanized union part of the union loses the corrosion contest.

                                Now compare that with the Brass Nipple scenario: Brass is only slightly less prone to galvanic corrosion than your copper pipes, so there's a tiny bit of protection (for the pipes) when you do this. But steel is vastly less "noble" than both of them, so what gets sacrificed if metal-to-metal contact develops between brass and your steel tank? The tank.

                                You guys who see the "awesome looking" Brass nipples in competition with "look like heck" Galvanized unions might just not be looking in the right place-- if galvanic corrosion has occurred in among the metals in this connection, it's mostly occurred on the other side of the brass, hidden inside the steel tank: There wasn't any "less noble" union which would try to sacrifice itself before the steel when a metal-to-metal contact developed. (And of course, this is why anode rods are made of aluminum and magnesium and sometimes zinc: just like the zinc-galvanized union, the anode sacrifices itself to protect the steel.)

                                But the anode rod(s) aren't close enough to the piping to handle the joint between dissimilar pipe metals. So I think it's best to use the galvanized unions. But they do require maintenance inspections, with possible replacement, before they've sacrificed themselves into a low-flow rusted out mess. Kind of like the anode rods themselves, and the tank drain-- checking 'em once every year or two can save big money in the long term.

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