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OT galvanic corrosion , dissimilar metals corrosion Question?

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  • OT galvanic corrosion , dissimilar metals corrosion Question?

    Hello Group,

    I have a project @ work that I need some clarification on, the galvanic corrosion process. Background is, the commercial building has all copper domestic waterlines, in the ceilings, walls, and into the building. The building was built 20 yrs ago. It had galvanised nipples used in all water taps (the problem) from the copper to the plumbing fixtures with brass shut-off valves installed to each fixture.
    I understand SOME of the theory of galvanic corrosion, the anode, cathode and an electrolyte (curtsey of Google) to move the weaker metal which causes corrosion.
    What I need to understand is why the galvanized pipe is the one that leaks, and not the copper. Which of these is the weaker metal and what is the final clogged buildup in the pipeline. I'm assuming (yes I know what it makes me) it is the dissolving steel pipe, but I'm just not getting the reason why.
    We are redoing the entire building with brass nipples which I've been told will not have this problem. Still dissimilar metal's (copper,brass) why no problem with this combination?

    Thanks for reading and hopefully some of you smarter than me type will help me feel less assuming

    TX
    Mr fixit for the family
    Chris

  • #2
    I'm going to have to say that the zinc is the sacrifice material in this particular corrosion process. Once it's dissolved the iron is exposed and free to corrode.
    Copper is much more impervious to corrosion. I've seen this before, this is not uncommon.
    I would look for a chart of galvanic reaction where it lists how dissimilar metals will corrode. Copper is higher on the chart than iron.
    This process is usually speed up by introducing a voltage. Being water pipes I'm sure there is a ground wire attached somewhere and perhaps there is some back feeding of current that is helping to speed this process along.

    JL.............
    Last edited by JoeLee; 07-26-2016, 10:45 PM.

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    • #3
      I think the galvanic corrosion would be less in a copper to brass connection because copper is the major ingredient in the recipe for brass. I'm sure someone will educate us both if I'm wrong.
      Jim

      Comment


      • #4
        JL,
        Yes possibly there was, a 480v hot water heater had a voltage leak and not grounded, (Carlon PVC flex connection) that was found a couple of yrs ago. This certainly was a contributor in my opinion.

        TX
        Mr fixit for the family
        Chris

        Comment


        • #5
          That's a good bit of it. Bronze might be even better.

          The copper survives well, everything else corrodes to protect it, in your case the steel fittings.

          Fixes..... Brass or bronze fittings, dielectric unions (if installed correctly). Plumbers seem to like to connect copper to steel, they have to know it's a bad idea, but they still do it all too often. Or they put in a dielectric union, BUT they fry the plastic soldering the union in place, so it goes metal-to-metal and doesn't work.
          CNC machines only go through the motions.

          Ideas expressed may be mine, or from anyone else in the universe.
          Not responsible for clerical errors. Or those made by lay people either.
          Number formats and units may be chosen at random depending on what day it is.
          I reserve the right to use a number system with any integer base without prior notice.
          Generalizations are understood to be "often" true, but not true in every case.

          Comment


          • #6
            My old house had that issue. Copper pipes fitted to a galvanized steel feed pipe. It lasted a good number of years although the corrosion had just about strangled the flow. Finally the steel pipe rotten through and I had to dig it up and replace with plastic plus a ground rod.

            Copper and steel connected together don't play well. It's not that the one gives itself up to save the other. The metals are not built to feel that way after all . It's simply that copper is higher on the galvanic chart than zinc or steel.

            The fix seems pretty simple. Replace the galvanized fittings with brass valves and fittings. Brass is close enough to copper that there's no reaction between the two. After all brass is mostly copper.
            Chilliwack BC, Canada

            Comment


            • #7
              Ok Thanks,
              I found a chart that makes sense and I see the similarities which explains why the brass and copper work together.
              This seals the deal for me to better understand what was happening and why the fix is what it is.

              BC Rider, Isn't something giving up something to cause the blockage?
              TX
              Mr fixit for the family
              Chris

              https://www.google.com/search?q=galv...GfSux6RlU9M%3A
              Last edited by Mr Fixit; 07-26-2016, 11:59 PM.

              Comment


              • #8
                Thirteen years ago we moved into "This Old House" with 90 year old galvanized iron pipes in bad condition.
                I decided to DIY replace the pipes with copper and lead free solder.
                Working and travelling long hours, I broke the job into weekend sections.

                I pre-prepared sections as much as possible before turning off the water valve.
                The old iron pipe at the section was sawn off with oscillating hand saw, then the zinc was polished with emery paper.
                A copper male fitting was slid on then fillet brazed using oxy-acetylene and flux coated 125 fc Cu-Zn +
                ( I pre-wet the surrounding structure and had a pressurized water hose and fire ext available during this)

                By that way if I had a delay or screw up, I could just add a valve temporarily.
                https://app.box.com/s/3upf2azlf1i288kefpjegi01vwmqs5re

                Reading this thread i checked and found there is still one old gal pipe left to do!
                https://app.box.com/s/qni42herfykg5obr5c9dq03o3f9ca6r8

                Anodic indices:
                Copper 0.35 Volt
                Brass 0.4 Volt
                Low carbon steel 0.85 Volt
                Hot dip thick gal 1.20 Volt

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                • #9
                  Just thinking......... the hot water tank at my aunts house has copper and brass fitting connected to galvanized iron pipe and all the connections are well over 50 years old and there are no leaks........ just a little green stuff around the edges of some of the copper fittings. There also is no ground or any type of electrical connections coupled to any of the pipes either.
                  I'm sure that voltage is a major contributing factor.

                  JL.................

                  Comment


                  • #10
                    Hard water (higher mineral content) will act to make water more conductive and thus more current can flow between dissimilar parts. This means faster corrosion. If you can install a water softener, the problem will be less. In addition it's nicer to drink and wash with.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                    Comment


                    • #11
                      With brass, it is also possible that the zinc may corrode out and leave a copper-enriched surface, which obviously would survive well with copper.

                      We had steel to copper connections in the house when we moved in. EVERY time we opened a valve on the sink, we would, after a little travel time, get a shot of rusty water. It took only minutes for the water to get rusty again near the joint.

                      I nearly had to threaten the plumbers with weapons to force them to put in dielectric unions. They did, but slightly fried one. Not badly enough to render it ineffective.
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

                      Comment


                      • #12
                        Originally posted by Mr Fixit View Post
                        ....BC Rider, Isn't something giving up something to cause the blockage?
                        ....
                        Other than having seen the chart I've not really looked into it. But I do know that what was left of the galvanized pipe was plugged full of rust or mineral pustules one after the other so that the 1 inch main was only passing about as much water as you'd get from about a 1/4 or 3/8 pipe. The shower was twice as strong after the new plastic main went in.
                        Chilliwack BC, Canada

                        Comment


                        • #13
                          Water softeners that work by replacing Ca/Mg with Na may actually increase the water conductivity. Water softeners that work by reverse osmosis will reduce conductivity but need to be installed at the
                          mains entrance to the facility to be effective in reducing any galvanic corrosion. Point of use softeners won't help the pipes but may reduce human consumption of metals leached from pipes and fixtures.
                          You know, the faucets "known to the state of California......"
                          Steve

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                          • #14
                            Originally posted by J Tiers View Post
                            With brass, it is also possible that the zinc may corrode out and leave a copper-enriched surface, which obviously would survive well with copper.

                            We had steel to copper connections in the house when we moved in. EVERY time we opened a valve on the sink, we would, after a little travel time, get a shot of rusty water. It took only minutes for the water to get rusty again near the joint.

                            I nearly had to threaten the plumbers with weapons to force them to put in dielectric unions. They did, but slightly fried one. Not badly enough to render it ineffective.
                            The surface would be better described as copper sponge rather than copper-enriched. The brass usually survives in domestic water systems only because potable water is usually not all that corrosive.

                            High-zinc brass in salt water is another matter. I have seen brass screws under the waterline in a new wooden boat turned to sponge copper after only one summer afloat in salt water. Many of them so weak that the heads twisted off when trying to remove them.

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                            • #15
                              Originally posted by Mr Fixit View Post
                              BC Rider, Isn't something giving up something to cause the blockage?
                              TX
                              Mr fixit for the family
                              Chris

                              https://www.google.com/search?q=galv...GfSux6RlU9M%3A
                              Yes, the water gives up dissolved oxygen to combine with the iron and produce rust.

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