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Copper pinhole leak and PVC pipe

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  • Copper pinhole leak and PVC pipe

    Got a call from my brother-in-law today about a pinhole water leak found on the bottom of the drain line from the laundry tub and washing machine. I went over to have a look and came back with more than a few questions, mostly about what causes copper pipe to corrode, and how far we need to go to correct his situation. I've read several threads here, notably "(dielectric) unions VS brass fittings" where I learned that "galvanic corrosion only happens when the metals have direct contact AND water in the pipe serving as the electrolyte." [link to post]

    My main questions are about how this pinhole leak could have been caused:

    1. Would a section of PVC pipe isolate one area with a problem caused by joined dissimilar metals (#2 in details below) from another area showing a pinhole in copper pipe (#3 in details below)? Would it be any different if this drain pipe could possibly be lined with water some of the time? It runs pretty flat for approx 16 feet. (i.e. could the connection at the sink drain be the root cause of the pinhole further down the drain line, even though they are separated by PVC?)

    2. The only other non-plastic, non-copper (iron?) piece that can be seen in contact with this drain complex is a single clamp holding a pipe to a wall some 10-12 feet beyond the leak. (see 4b, below) Could this single piece cause the pinhole that is so much further up the way?


    Layout - drain line pinhole leakage problem:

    1. Plastic drainline from washing machine clipped into vertical copper pipe for draining of machine; leads to

    2. Soapstone laundry tub with iron tailpiece connected to copper/brass downpipe and trap/fittings with ~18" horizontal run to 90-degree fitting of PVC pipe. The tailpiece fitting and trap are obviously corroded, with much blue-green precipitate. Washing machine is to the right. To the left of the drain line we see the PVC elbow that leads to ...






    3. Approx 8 feet of PVC, joined to a further length of copper that runs for about 8 feet behind a furnace, ductwork, HWT and powder room. The join is just before the HWT.

    The newly installed HWT is pressed up against the copper drain line. Between the HWT and the powder room is our visible leak on the bottom of the copper drain line;

    obvious blue-green precipitate and a fairly steady drip when the washer empties or the laundry tub is in use. This whole line is very flat with little drop to the whole ~16 feet. This runs behind the powder room to a ...

    4a. Closet area that houses the city supply with meter and the we wall of the powder room as well as a waste stack and drain point for all of the basement plumbing save for the toilet.


    4b. Beyond the stack, the drain from the powder room sink is clamped to the wall with one non-copper/brass fitting, seen about one foot to the left of where the pipe enters the wall


    Another question: Potential for supply-line problems?
    On the supply-side, I've noticed some brass clamps for a grounding point and a saddle valve that are fastened with steel bolts. Some copper clamps fasten this half-inch copper supply to studs using steel screws or nails. One piece of supply line is in contact with ductwork. Could any of these seemingly minor contacts with dissimilar metals cause potential problems in the copper pipe? For instance, this grounding wire is secured with a brass/copper clamp, but steel bols are used to hold the clamp together.



    This is in a home where this was installed perhaps 45 years ago. The home is likely to be sold in the next 18-24 months where new owners will want to redo the basement area that includes the laundry and bath areas. So no large expenditures are in the cards for this, but the leak does need to be corrected. I'm assuming all the non-plastic, non-steel/iron fittings are copper, maybe some are actually brass.

    Thanks for your opinions!
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