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Thread: Corrosion in the Kitchen

  1. #1
    DIY Junior Member Couch-Tuber's Avatar
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    Default Corrosion in the Kitchen

    As preferred, sunday night at 8pm we realize there is water coming from under the sink. Ripped out to get into the wall to find a leak underneath - a tiny hole in the copper stack coming out of the slab. The house is 3 1/2 years old. There is green trails across the outside of the pipe. When I cut out the bad area, there is cavitation inside that caused the hole and was working on another. What could cause this?

    I have a circulator pump that runs about 7 hours a day.
    I have heard that an electrical ground the copper plumbing can cause this too.
    Any ideas? My nightmare is this will happen in other parts of the house or even underneath the slab foundation.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default copper

    I assume you mean a water line, and not a stack, which would be a drain line. There can be many causes of the problem, but many of them, such as circulation pump erosion, depend on exactly how the pipe was installed. It could even be caused by contact with the concrete if it was not isolated from it.

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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Default

    Quote Originally Posted by Couch-Tuber View Post
    As preferred, sunday night at 8pm we realize there is water coming from under the sink. Ripped out to get into the wall to find a leak underneath - a tiny hole in the copper stack coming out of the slab. The house is 3 1/2 years old. There is green trails across the outside of the pipe. When I cut out the bad area, there is cavitation inside that caused the hole and was working on another. What could cause this?

    I have a circulator pump that runs about 7 hours a day.
    I have heard that an electrical ground the copper plumbing can cause this too.
    Any ideas? My nightmare is this will happen in other parts of the house or even underneath the slab foundation.
    The green streaks are from from the plumber not properly wiping off all of the flux when he soldered the connections. It's called patina and is basically how copper "rusts".

    The pin hole leak could be caused by LOTS of things....

    Too high of pressure and too much turbulance
    Unreamed pipe ends
    Too high of water temps causing excessive turbulence
    Bad Copper

    Lots of things....

  4. #4
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    Red face Erosion electrolysis flux boric acid or turbulence etc

    Name:  laundry plumbing 1.jpg
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Size:  72.1 KBNot a "stack" then. Here is a picture of a "manifold" in my house (but not the kitchen, this was from the laundry room but similar) Note green flux.

    Where the copper comes up through the slab they form a "manifold" with three pipes jointed (they don't join underground I assume because code disallows a joint beneath the slab foundation. So when the plumber runs out of a length of tubing during construction, he comes up above slab and builds a manifold.) There are several of these manifolds as this is a big house. There are at least 3 that go nowhere above the slab - they just continue back under. Also, the run from the water heaters to the kitchen travels through Arkansas and back to Texas. So it takes 4 minutes to get hot water at the kitchen sink. Great design....hence I need either a recirc pump or a point of use water heater under the sink.

    Here is a picture of the slab before framing, the kitchen sink island position is mid upper left

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    Under the kitchen sink there is a hot and cold set of "manifolds". The cold side leaked. THis is close to the Grundfos/Watts recir thermostatic "crossover" between hot and cold sides. Also, the leak is from the inside out. I found "divots" on the inside of the failed piece of pipe. The divot pattern is not a horseshoe. It is a symetrical sphere with a hole at its center (not to say it is not erosion). There are two of these divots close together. There are a inch or two beyond the 90 degree fittings of the manifold. One of the divots gave way and leaked. I will try to produce a picture and upload it here.

    I have two 50 gal gas fired water heaters in the attic. The Grundfos/Watts recirc pump sits on the second heater. There is a flex copper pipe coming from the steel nipple and runs to the recirc pump (18"). THe flex copper tube has a spot of severe copper corrosion forming right where the pipe bends. Has not eroded through yet. Does this suggest erosion? Or could it actually be electrolysis? hmmmm..

    I tried to pick the brain of the hardware store clerk who professed plumbing expertise. He suggested electrolysis maybe perhaps.

    Based on that discussion I was really thinking it was electrolysis based on the following 1)the recirc pump is not isolated with a dielectric fitting; 2) the shape of the failure point is a round divot which looks symetrical and seems electrolysis would make it so 3) the two failure points I know about are near the recirc pump and its thermostatic coupling thingey.

    So I bought a new flex copper tube (to fix the corroding one attaching the pump) along with two 100% dielectric unions to potentially create a way to isolate the pump dielectrically. The thinking being that the pump may be inducing current. BUT what does I know?

    Electrolysis: here is what copper.org states:

    Electrolysis is an overused and misused term when applied to copper tube. True electrolysis, or electrolytic corrosion, as it is more properly designated with regard to piping, is caused by an imposed (external) stray DC current and virtually ceased to occur with the disappearance of the trolley-car that was powered by high amperage DC current. In many cases, it is also thought that grounding of a building’s electrical system to the copper piping can cause this phenomenon, but there is no statistical data to support this, nor is it recommended that the piping system be used as the main electrical ground for a building or dwelling.

    The clever wording here does not say it is not possible, just less likely than older times.....

    But if the problem is erosion from high velocity, I can't use a recir pump no more. Don't want to risk it.

    If the problem is electrolysis, if the recirc pump was the cause, I can't use the pump. But maybe its not the pump. If there is something using my copper plumbing as a ground, what is the method to isolate where the ground is located? I've had some problems with the electrical already (shorts from too tight staples, miswired outlets shorting out) so I would not put it past them to have grounded into the copper plumbing accidentally...

    Perhaps it is both. I have pictures of the install when the house was built. THere are many green streaks I understand are from too much flux. Will also post those pictures. There is also alot of green "boric acid" solution they sprayed on the lower frame members some of which is on the plumbing. Sheez.

    Sorry for the long post. Final question: Is there a clever way to detect electrolysis with an ohm meter or something? What am I looking for on the meter?

  5. #5
    DIY Junior Member Couch-Tuber's Avatar
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    Default corrosion erosion confusion

    Name:  IMG_2978.jpg
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    best pic I can get for now shows corrosion and hole from inside out on piece I cut out

  6. #6
    Senior Robin Hood Guy Ian Gills's Avatar
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    Who did that bloody soldering?

    It's too shoddy for a DIY'er.

  7. #7
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    M.I.M. LOL

    hey its Texas still growing by leaps and bounds on the cheapest bid.

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