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Mysterious cracks in no hub cast iron pipe

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  • #16
    Re: Mysterious cracks in no hub cast iron pipe

    Plumb4life:

    Unless and untill someone is willing to go through the time and expense of sending a piece or several pieces of failed cast to a testing agency any info you get here is going to be surmise, and best guesses.

    Just a couple days ago on a different thread an image was posted of the top of a cast wye or combo (laying flat) where the top had completely corroded away. With a sewer backup, "stuff" exited. Now, why the failure at the top of the combo that see's relatively little moisture compared to the bottom, and not a failure at the bottom?

    I once had to tie into a cast iron line that carried the waste away from a bar that served soda pop. The bottom of that cast was as thin as paper. I think the reason is obvious in that case. What's more acidic than coca cola?

    I think it's likely there are several failure modes for cast iron. The failure mode you are interested in may be specific to your type of installation. In any event, I don't think you're going to be able to change the environmental characteristics of either the air or water where you live. So, changing the material might be the way to go. Remember that PVC grows or shrinks 6" in a hundred feet for a hundred degree delta T. So support it frequently but keep it loose.

    I personally harbor a suspician that there is something corrosive in the air, and that once an actual hole has developed it propogates. Rick is also correct, as usual, that rust creates pressure. A chemical engineer once mentioned that the oxidation process creates larger molecules, which necessarily take more space.
    Time flies like an arrow.

    Fruit flies like a banana.

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    • #17
      Re: Mysterious cracks in no hub cast iron pipe

      I got a call back on a repair job once regarding cracked cast iron. I had replaced a 4 foot horizontal section that was exposed at ceiling level in a garage. It was a 2" cast iron pipe serving a bathroom sink. The home was unoccupied and in the process of being sold. The sink was seeing use very infrequently. The home was about 30 years old. The large crack on the bottom of the pipe extended it's whole 4' length and was big enough to put your pinky finger in.

      A week later I get a call from the homeowner saying that it was still leaking in the garage. So I went back and checked it out. I found that the next section of 2" cast iron beyond my repair had cracked in the same way as the one I originally replaced. Again the crack was big enough to put your pinky in.

      So it appears to me that this is something that can happen suddenly - I bet that if you were in the room you would have heard the pipe pop open in this instance. I have seen a lot of cracked cast iron pipe over the years but had thought that it was a slow process with the crack becoming larger over a long period of time.

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      • #18
        Re: Mysterious cracks in no hub cast iron pipe

        A possible cause for a cracked stack is settling. If pipe is not properly supported and run to allow for movement in both the pipe and the building (especially wood frame structures) there can be problems.

        In an old home I owned years ago, I had a stack in the basement crack. About a 5 foot split. It was old pipe (1905) and the walls were not uniform as they are today as they did not use the same process as today. Also the house had settled as could be evidenced in many other areas like door jambs, floors, etc. which supported the settling theory. Cut out the bad pipe and replaced with no-hub and a couple bands and good to go.
        ---------------
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        • #19
          Re: Mysterious cracks in no hub cast iron pipe

          we just the other day removed some service weight 8" iron on the horizontal the pipe was not leaking we were replacing due to a remodel. after it was on a pile for a few hours. 2 big cracks showed up, i have seen it spring the crack after it dries out.

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          • #20
            Re: Mysterious cracks in no hub cast iron pipe

            Thanks for the recent replies! This problem does not go away, it just occours in more areas all the time. I will use PVC DWV plastic where ever I can to resolve the issue.

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            • #21
              Re: Mysterious cracks in no hub cast iron pipe

              Originally posted by ranman View Post
              we just the other day removed some service weight 8" iron on the horizontal the pipe was not leaking we were replacing due to a remodel. after it was on a pile for a few hours. 2 big cracks showed up, i have seen it spring the crack after it dries out.

              That is interesting. Thanks for sharing. Too be clear, the pipe was not cracked. You placed it in a pile, sometime later it cracked. Then after the pipe dried, the crack "sprung"?
              Time flies like an arrow.

              Fruit flies like a banana.

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