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  • Galvanic Corrosion protection, and testing,

    I am reasonable sure some of you are familiar with pipe line protections systems, and testing, so this is why I am asking here,

    ~~~~~~~~~~~~~~~~~~`

    I am in the process of building a project that I need to protect from electrolyse

    I have galvanized steel anchor rods, that will be embedded in concrete footers, and attached to that some guy wires, that will be grounded out for lighting protection and in time will probly end up being bonded to the electrical system, thus there will be a copper to zinc potential of electrolyse, that will occure to some extent,

    so along with the galvanized protection of the anchor points, I will isolate them as well, with (shrink tubing), but that may or may not be enough, so as a final protection I am planing on using Zinc sacrificial anodes as well.

    now in the process of time one will want to check on the anodes and there degrading and the possible corrosion's on the anchor it self,

    and I read to use a copper/copper sulfate reference electrode, which is a "half battery"

    and then take electrical measurements from the various units, anodes, and anchor, to determine the rate of corrosion and the extent, of it,

    OK I understand that to a extent,

    Now If I am understanding it, the copper/copper sulfate provided a know rate of electrical potential, and by reading the voltage for the most part, and some what the milli amps, between the various anodes and anchor to the copper/copper sulfate half battery reference electrode, one can see how effective the units are,

    I guess what I am some what at a loss at is, are not the readings are going to vary to the soils moisture conditions, if it is bone dry, they I would think would be less than a few days after a good couple inch rain,

    http://efotg.nrcs.usda.gov/reference...pgs6-34g-k.pdf

    http://www.cpdesigncenter.com/propanetext.pdf

    so I am still some what at a loss on understanding the "reading" one would be recording

    and would not the placement of the referenced cell potential change the voltage readings, and when the reference cell is used and readings are taken.

    also where is the best location for the reference cell?

    or do the chemicals around the zinc and the copper sulfate create the "battery effect" so the readings are basically the same regardless of the ambient soil conditions?

    If some one could explain this jsut a little clearer to me I would appreciate it, thank you,
    Push sticks/blocks Save Fingers
    ~~~~~~~~~~~~~~~~~~~
    "The true measure of a man is how he treats someone who can do him absolutely no good."
    attributed to Samuel Johnson
    ~~~~~~~~~~~~~~~~~~~
    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

  • #2
    Re: Galvanic Corrosion protection, and testing,

    This is pretty interesting stuff here. As plumbers, we see the effects of electralysis, and often find the reasons for it (I once found it to be a huge ballast on a florescent lamp that was on a water line, actually measured magnetic voltage in the air around it with a regular digital multimeter). But as far as getting into what you're doing, I doubt we'ld be much help. I'ld go on the electricians forum and see if any of them work the dairy farms, as they'ld probably have more info. I am gonna look at those web sites some more though,
    sigpic3:00, I mean 5:00, and work is done. Time to crack a cold one.

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    • #3
      Re: Galvanic Corrosion protection, and testing,

      I think the person who would best be able to help you out is "gofor".
      Buy cheap, buy twice.

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      • #4
        Re: Galvanic Corrosion protection, and testing,

        Thank you for your responses, I will probly figure it out, but with out some hands on experience It is not totally clicking in my mind as of yet,

        when I get the anchors in and the things set up, it will probly make sense to me,
        Push sticks/blocks Save Fingers
        ~~~~~~~~~~~~~~~~~~~
        "The true measure of a man is how he treats someone who can do him absolutely no good."
        attributed to Samuel Johnson
        ~~~~~~~~~~~~~~~~~~~
        PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

        Comment


        • #5
          Re: Galvanic Corrosion protection, and testing,

          After scratching my head for a bit, I think I finally have the answer..... It's ....42
          sigpic

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          • #6
            Re: Galvanic Corrosion protection, and testing,

            Originally posted by NHMaster3015 View Post
            After scratching my head for a bit, I think I finally have the answer..... It's ....42



            sigpic3:00, I mean 5:00, and work is done. Time to crack a cold one.

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            • #7
              Re: Galvanic Corrosion protection, and testing,

              Try looking up cathodic protection systems. I think this may help.
              Mike

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              • #8
                Re: Galvanic Corrosion protection, and testing,

                I'll try to answer some of the questions, but it has been about 15 years since I did CP testing, and no longer have my reference books.

                1st: Rule of thumb: Steel encased in concrete is protected from corrosion except in the presence of chlorides If you will be using salt in the concrete cure, it is best to epoxy coat the anchors. Same if the concrete is exposed to sea water, etc.

                2nd: Moisture will affect the readings, as well as affect the corrosion rate. If it gets bone dry, you in effect have no electrolyte, so no corrosion. The ground does not have to be wet, but should contain some moisture. If taking a reading on dry concrete, place a wet sponge under the Cu/CuSO4 half cell.

                3rd. It is best to get a native reading (anode not connected and soil moist) as a reference reading. With the anode attached, and after it has had a chance to build up the potential (up to 24 hours in some cases), a second reading is taken and the two compared. You are looking for a -300mv shift to indicate good corrosion protection (-350mv is best). If a native reference is not possible, usually a reading of -850mv indicates protection (lots of variables here due to soil conductivity, presence of chemicals, etc) . When the shift is down to 200mv, its time to replace the anode. Earlier if there is slim margin for error.

                4th. The best location for the reference cell is directly over the protected structure as much as possible, and if not, on the opposite side than the anode.

                One of the problems in the setup you are planning, which will require a practicing CP professional, is that initially, if no base steel is exposed, you will getting a reading between the zinc galvanized and the zinc anode (zero potential difference). In essence, the galvanized is an anode plated onto the pipe. After the copper ground is connected, the readings will be between the copper grounding and the galvanizing, which will indicate severe corrosion.

                A second problem is the connection of the guy wire to the anchor. Unless it is a good electrical bond, any readings obtained by connecting to the guy wire may not indicate what is happening with the anchor. You will need an accessible test lead that is bonded to the anchor., or a bonding jumper across the connection.

                If the concrete will extend above ground level, and no chlorides are present, I doubt any additional sacrificial anodes in the ground will be beneficial. If not, then epoxy coated anchors with a test lead and the anode bonded to them would allow you to get accurate readings. If there are no voids in the epoxy coating, tho, you won't be able to get a reading as no current can flow. As the epoxy wears away at the anchor point, current can flow, the anode will start doing its job, and then you can get readings.

                Realize the test connections need to be to the base steel, not any galvanized coating.

                Hope this made sense and is not too confusing. Probably time to ask someone more current in the field.

                Go
                Practicing at practical wood working

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