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Dielelectric corrosion-problem?

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  • #16
    Re: Dielelectric corrosion-problem?

    I use a 6" brass nipple whenever possible, I will always use a brass nipple, never a dielectric, I have seen them fail.

    Ben, the nipples rick are talking about have a plastic inside coating and have a lip of plastic on the top, just covering the edge of the nipple, where the washer seats down to prevent a leak, these nipples also help with energy savings supposedly.
    sigpic

    Robert

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    • #17
      Re: Dielelectric corrosion-problem?

      Originally posted by gear junkie View Post
      How does the inner plastic lining prevent corrosion? The metals are still touching each other. From the comments of the general public, the majority of you are saying a brass fitting can be substituted for a dielectric union? Is this right?

      In theory the plastic liner seperates the water or "electrolyte" from the two metals.
      It works, once in a great while, (well...no...it doesn't really) I use a brass "heater tee" on the inlet side with a vacuum breaker and then a brass fitting for the hot outlet for good measure on water heaters...despite MFG suggestion.

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      • #18
        Re: Dielelectric corrosion-problem?

        OK now when Mr electrician comes in and starts to BOND everything (as required by the electrical codes), what does that do the dielectric connections? or to the pipe? or to his connections?
        Push sticks/blocks Save Fingers
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        • #19
          Re: Dielelectric corrosion-problem?

          I am not an electrician, hell, I can't even spell it right, (my wife is on the treadmill, so I can't ask her) but I know one thing for sure, when I buy ground clamps at the supply house, they have to be brass
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          Robert

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          • #20
            Re: Dielelectric corrosion-problem?

            The purpose of the dielectric unions are to isolate the water heater from the rest of the piping and most importantly the electrical ground grid. The speed of corrosion is directly related to the amount of surface area of the anode to the cathode in the electrolyte. The larger the cathode in relation to the anode, the faster the corrosion rate (loss of metal).

            Dielectrics were very necessary back when most piping was metal, and the electric ground grid was hooked to the plumbing. The iron or steel in the water heater was the anode, and the cathode was the entire copper electric grid ground. Add to this that the corrosion rate doubles for every 10 degree temp rise over 140 degrees (that means the rate was 2 times more at 150 and 4 times greater at 160, and 32 times at 180 required for commercial dish washers), water heaters that had any cracks in the glass lining didn't last long. I saw copper lined water heaters in a place in upstate NY eaten through in as little as 6 months, and they had 3 anodes in them! (Very aggressive water didn't help the situation)

            With the use of pex, PVC, etc (non metallics), it is no longer the problem it once was. Now the main source of galvanic corrosion is the copper pipe connection being cathodic to any exposed steel in the tank. Sacrificial anodes in the tank will usually protect it fairly well.

            And.BHD, you are absolutely correct. When an electrician bonds to the tank, he has just rendered the dielectric useless, because he has just shorted the protective insulation. They are still necessary in gas heaters in locations with metal piping going into the ground, and yes they can work on electric heaters if not over-tightened, breaking the porcelain insulator, and the electric bond is made to the element fixture, not the tank.

            (I worked 15 years on a corrosion survey/mitigation team dealing with military base infrastructures. We covered cathodic protection (water lines, water towers/tanks, buried piping whether sewer, fuel, gas, HTHW, fuel tank farms, etc), boiler plant and heating system water treatment, structural corrosion on buildings, missile launch gantries, etc, and also used nuclear radiography to measure corrosion loss in pipes. both above and below ground.) I am not a plumber, but I have corrosion evaluted every part of a water distribution system from the pumps at the source, throught the treatment plants, up the water towers, through the steam and boiler systems, throught the facilities, to the sewer plant and to the sewer outlet. I have nothing but utmost respect for those of you who know how to put it all together, maintain it and make it work right!!

            Go
            Last edited by Gofor; 07-15-2007, 09:03 PM.
            Practicing at practical wood working

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            • #21
              Re: Dielelectric corrosion-problem?

              Note to self: Keep Gofor on list of contacts for viable tech info.

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              • #22
                Re: Dielelectric corrosion-problem?

                I'll second that , good post .

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                • #23
                  Re: Dielelectric corrosion-problem?

                  Hmmm, I think I am now a pro in galvanic reaction way to much chemistry for me
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                  Robert

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                  • #24
                    Re: Dielelectric corrosion-problem?

                    In my area, brass to galvanised is not good. I only use dielectrics when I can't use a stainless nipple or fitting between.

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                    • #25
                      Re: Dielelectric corrosion-problem?

                      Originally posted by Bogart View Post
                      In my area, brass to galvanised is not good. I only use dielectrics when I can't use a stainless nipple or fitting between.
                      every shut off valve or angle stop we put in are brass. almost every home piped from the 70's and earlier are gal. steel pipes. the angle stops eventually eat away the gal. nipples.

                      don't know how you install new angle stops on gal. pipe, but i only use brass nipples as the gal. nipples made now are junk. i only use gal. nipples on gas. not on water anymore.

                      rick.
                      phoebe it is

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                      • #26
                        Re: Dielelectric corrosion-problem?

                        Originally posted by PLUMBER RICK View Post
                        every shut off valve or angle stop we put in are brass. almost every home piped from the 70's and earlier are gal. steel pipes. the angle stops eventually eat away the gal. nipples.

                        don't know how you install new angle stops on gal. pipe, but i only use brass nipples as the gal. nipples made now are junk. i only use gal. nipples on gas. not on water anymore.

                        rick.

                        I SECOND THAT, BRASS ONLY ON WATER, GALV ONLY ON GAS (DON'T GET PROUD DADDY)

                        Last edited by westcoastplumber; 07-16-2007, 04:20 PM.
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                        Robert

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                        • #27
                          Re: Dielelectric corrosion-problem?

                          Originally posted by westcoastplumber View Post
                          I SECOND THAT, BRASS ONLY ON WATER, GALV ONLY ON GAS (DON'T GET PROUD DADDY)

                          Um...ok...been meaning to bring this up...doesn't anyone use Black mallable for gas?
                          It's all we use here...aside from CSST, or copper on LP.

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                          • #28
                            Re: Dielelectric corrosion-problem?

                            Originally posted by DuckButter View Post
                            Um...ok...been meaning to bring this up...doesn't anyone use Black mallable for gas?
                            It's all we use here...aside from CSST, or copper on LP.
                            My guess is most of the guys who are using gal nipples for gas are doing it because they only carry gal nipple trays. With a service truck it is easier to just carry a gal nipple tray for water and gas. Our trucks carried Brass, Black and Gal trays up to 1" and Gal only for 1 1/4", 1 1/2" and 2" (but we had big trucks).

                            Mark
                            "Somewhere a Village is Missing Twelve Idiots!" - Casey Anthony

                            I never lost a cent on the jobs I didn't get!

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                            • #29
                              Re: Dielelectric corrosion-problem?

                              oh boy!
                              We don't use galvy period!
                              We all carry 1/2", 3/4" and some 1" BM nipple trays on our trucks.
                              The only time I see galvy is on old 1-1/2" or 2" residential drains connecting to CI, and it's usually when I'm ripping it out on remodels.

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                              • #30
                                Re: Dielelectric corrosion-problem?

                                Ducky, you can use black on gas on exterior? here, black is optional inside, but galvy is required outside because of rust, etc. I carry galv and brass only, nipples and fittings, like I have said before, galv is cleaner looking then black
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                                Robert

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