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Dielectic revisisted

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  • Dielectic revisisted

    We've been having a discussion at work about dielectric unions/nipples and the necessity. The discussion revolves around a job we're on now involving a remodel of chilled and heat lines. The existing lines are all black iron pipe. We've drained and demo'd lines to where we need to tie back on. Being this is the start of the cooling season, we've placed bronze ball valves at the tie in points and refilled the system. The debate is being that this is a closed loop glycol system, do we need a dielectic break when we switch to the copper we are installing? I have read it both ways on whether we do or don't.

    opinions?

  • #2
    Re: Dielectic revisisted

    yes

    IMO Bronze and Steel are "similar" since I don't ever remember seeing a Bronze to steel failure that I could contribute to galvanic corrosion But every galvanic failure I have seen involves copper being joined to a non similar metal (copper to steel being the worst).

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    • #3
      Re: Dielectic revisisted

      Bill:

      So, you're saying that I should place a dielectric union/nipple after the valves I have in place?

      Bronze and iron being "similar" I can see, but is bronze is almost "similar" to copper is it not? Bronze valves are routinely soldered into copper systems all the time without issues.

      I appreciate the input.

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      • #4
        Re: Dielectic revisisted

        A brass fitting, nipple, or valve is an acceptable transition between steel and copper, according to IPC. Even though the inspectors like to see dielectric unions and nipples, they are probably the worst choice, especially the unions.

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        • #5
          Re: Dielectic revisisted

          Originally posted by TMc View Post
          Bill:

          So, you're saying that I should place a dielectric union/nipple after the valves I have in place?

          Bronze and iron being "similar" I can see, but is bronze is almost "similar" to copper is it not? Bronze valves are routinely soldered into copper systems all the time without issues.

          I appreciate the input.
          No, I just meant that steel to copper is the connection to avoid... Bronze copper and bronze-steel are OK IMO

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          • #6
            Re: Dielectic revisisted

            Thanks guys! So far you are confirming what I've been secretly thinking.

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            • #7
              Re: Dielectic revisisted

              Just had this discussion with our state plumbing inspector. He said it's not in the code book. There is nothing in the code book that stops me from going from galvanized water pipe directly to copper. He said it's not a code issue and it's not up to him to say.
              When I got home I looked for it, found nothing.

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              • #8
                Re: Dielectic revisisted

                Just read an interesting article by ASHRAE on galvanic corrosion. They said basically that this type of corrosion needs 4 conditions at least:
                1) an anode
                2) a cathode
                3) a conductive fluid
                4) a current

                Copper is higher on the nobility charts than steel, so copper will be the cathode (will attack the anode), steel will be the anode (will get attacked) and the chilled/heating water will be the conductive fluid. The conductivity of the fluid is what's going to determine how far the corrosion is going to go, but it will happen one way or another, even if it's localized. The way to reduce this is to make sure proper water treatment happens after the install. Dielectric unions are ok, but they don't stop the problem if the conductivity of the water is high (the corrosion will occur across a large area, jumping the plastic spacer and rubber washer). Since certain corrosion inhibitors (like molybdate-based ones) will promote an oxide film across the interior surface of the pipes, it will inhibit the current, thus reducing the corrosion.

                In a nutshell, if you are going to put copper in a steel system, or vice-versa, make sure you have the appropriate water treatment once the system is fired up. Copper to steel connections won't corrode in a dry compressed air system, so really the water is the main factor here that we can control.

                Hope that made some kind of sense and helps!

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                • #9
                  Re: Dielectic revisisted

                  Thanks for that bit of info.......very interesting reading.

                  Our entire systems get flushed with D/I water, so conductivity of the solution should be next to nil.

                  I may have to see if I can locate the entire article, should make for some good bedtime reading.

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                  • #10
                    Re: Dielectic revisisted

                    http://www.ashrae.org/content/ASHRAE...133630_266.pdf
                    SMELLS LIKE $$$$$$ TO ME

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