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    PEX pipe split (hydronic) (4 Posts)

  • Forensic Forensic @ 7:09 PM
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    PEX pipe split (hydronic)

    Has anyone ever seen this type of PEX splitting, see attached photos? hePEX installed in concrete slab, hydronic heating system. Suspect some sort of freeze incident(s) but never seen it like this. Likely pressure tested with water, left to over winter in temps as low as -30F.  
  • Gordy Gordy @ 9:21 PM
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    Not surprising

    If what you think happened actually did. I'll bet Weezbo could share some frozen anomalies.

    Note 100 psi rating at 180* probably a 2:1 safety factor. The power of ice.
  • Zman Zman @ 9:08 AM
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    Freeze

    Pex generally does really well with freezing. The problem you are likely seeing is that if most of run is completely incased and cannot expand, any part that is not completely encased, ends up expanding a disproportionate amount. I bet that part was sitting at the bottom of the slab. Another reason to center the tubes in the slab.
    Carl
  • Mark Eatherton Mark Eatherton @ 7:33 PM
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    I agree...

    In most of the cases where I have been involved, the tubing ends up on the bottom of the slab profile. Even with rebar and or mesh on chairs, it still ends up close to the bottom at points.

    I suspect that in this case, the tube was near the bottom of the slab, and the slab was on XPS insulation. When the tubing finally got to the freeze solid point, the expansion of the fluid in a tube will generate pressures in excess of 20,000 PSI. The insulation gave way when the tube pushed downward due to expanding ice. Had it been more near the top, it would have caused the top of the concrete to spall, showing exactly where the tubing was located.

    I have to ask though, who in their right mind would NOT evacuate the tubing after the pressure test. Technically speaking, it is against code to use compressed air for pressure testing plastic pipe (UMC, USEHC, UPC) due to possibility of a catastrophic failure. We attempted to get the use of compressed air approved for codes, but got resistance from the plastics industry.

    I have seen PVC and CVPC break in a pattern similar to this, but in most cases, by the time they get done doing "jack hammer surgery" to remove PEX from a slab, there's not much left of the tubing to diagnose anyway.

    Honestly can't say I've seen PEX fail in tis mode, but just when you think you've seen everything, you find out you have not seen jack squat…

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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