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Thread: Corrosion at copper joints. Why??

  1. #1
    DIY Junior Member Plumbing Newbie's Avatar
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    Default Corrosion at copper joints. Why??

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    Hello all,

    I'm looking at a house to buy and in it there's a newer looking water heater with a very new looking pipe fitted to it; still quite shiny but with substantial corrosion at the joints. If it's just from a poor soldering job, I can get that fixed. But I'm concerned there may be something more significant going on like current running through the ground (there are power transmission towers nearby).

    Does anybody have any thoughts? How would I determine what the cause is?

    Many thanks in advance!!

  2. #2
    DIY Senior Member Fubar411's Avatar
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    I'm new, but I'll take a stab at it. Those seem to be the pre-soldered fittings and it looks like someone didn't properly clean/flux those joints. The white stuff is just very slow leaks and the minerals left from evaporation.

    The good news is it looks like the bumbler stopped outside the wall.

  3. #3
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Looks like a drain line coming off the T&P on the HWT going into a PVC line and out the wall.

    I would say that the buildup looks like calcium deposit from slow leaking water. The T&P shouldn't ever trip in an ideal world so you may have a problem. Possibly too much expansion in the water or maybe the house PRV has failed and you are over pressurizing the tank.

    That stuff there is an easy fix and would be 1 hour of work if you hired a professional.

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    DIY Junior Member Plumbing Newbie's Avatar
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    Thanks guys! It's a relief to hear your assessments! I'm glad to hear it's not thought to be of my greater concern -- ground current!

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    In the Trades Gary Swart's Avatar
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    That is the pressure relief line, and there are at least two things besides the corrosion wrong. First of all, it should not go into the wall, and secondly, it should not be PVC. Normally, these pipes are just 3/4" galvanized, although any metal would be OK, and the just go to just above the floor. They can be directed to a floor drain, but not connected solidly. I'd suggest a licensed plumber would be in order here to investigate and correct all of the previously listed problems and potential problems. The current owner of the house should pay for this.

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    Moderator & Master Plumber hj's Avatar
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    quote; First of all, it should not go into the wall, and secondly, it should not be PVC. Normally, these pipes are just 3/4" galvanized, although any metal would be OK, and the just go to just above the floor. They can be directed to a floor drain, but not connected solidly

    I assume you are not a plumber or you would not have made EITHER of those statements.

    1. The drain from a T&P valve MUST discharge at a point where it will NOT cause damage, and that point is often outside the room or building where the heater is located so it OFTEN goes into the wall.
    2. Discharging onto the floor often creates a situation where it COULD cause damage.
    3. The only way to connect to a pipe in the wall is to make a "solid" connection.

    In this area almost ALL heaters have a solid connetion to a pipe in the wall which leads outside the building. This picture is not good enough to tell whether that is a PVC pipe or even if the T&P valve discharge is connected to it.

    As far as this situatation is concerned, since that pipe will seldom have water in it, and it should NEVER be under pressure, about the only way those joints could develop that much calcification would be if they were NOT soldered in the first place and are just stuck together.

  7. #7
    DIY Junior Member vittorio6's Avatar
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    Default copper corrosion

    the surface of pipe seems ok, i mean i don't see any sign of corrosion, when copper corrodes the typical color of the corrosion product is green. copper turn green because copper oxides and other carbonates develop.
    i agree with one of the previous comment that the cause of the white product is due to the flux used during the fabrication of the copper piping.


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    corrosion prevention
    Last edited by vittorio6; 06-04-2010 at 07:08 AM.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Flux is burned off during the soldering process, just as it was for the joints which do not have the residue. And flux does NOT cause that type of "corrosion", it is more likely minerals from the water which were left behind after the water evaporated.

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