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Pex. Hottest Temp

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Birdman, Dec 21, 2009.

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  1. Birdman

    Birdman New Member

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    What is the degradation temp for Pex? I know it says on it... 200 at 80 PSI. Does this mean it can go to 250 at 40 PSI and still hold up? At what temp( and or psi) does it cause damage? Has anyone done an experiment to find out? OR have a guess?

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  2. shoeboxlen

    shoeboxlen Member

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    personally I love pex for its ease of use and all but with hot stuff I would rather go with coper and black pipe and know it will be safe. even if the water is 180 in the pex 20 degrees seems to close from operating temp to failure temp god forbid over heat and then you have a mess...... just my thought. I am not anti pex in fact I just went out and bought the crimping cool kit last week to do some plumbing. since its still pretty new I just feel safer with the tried and true methods.
  3. sgschwend

    sgschwend New Member

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    Good question, or was it 200 at 100 psi? As a single data point I can tell you it can do 200 at 30 psi.

    I do have one high temperature pex line that runs from the boiler output to my storage. It would have been a real hassle to connect it any other way.
  4. trailhound68

    trailhound68 New Member

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    I did an experiment, but not purpose. I can tell you that my 1" PEX 150' round trip has seen about 260 deg or more.
    We were making steam when I left a draft door open AND my automatic fill was plugged. That was my first season, this my fifth on that PEX.
    Interesting though, as a result of the high temps, when the heating season was over the tubes shrank in length and put so much tension on my fittings I had to disconnctt them and add extensions. Still no problems to speak of and no more shrinkage!
  5. 2.beans

    2.beans Minister of Fire

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    ive had copper unsweat itself and the pex stayed connected. it did shrink the pex though. i had to add to it to put the copper back together. this was after a power outage before i had battery back up.
  6. rowerwet

    rowerwet Minister of Fire

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    does the pex shrink in diameter as well as length?
  7. DannMarr

    DannMarr New Member

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    There is another type of pex that has an aluminum liner inside, I believe it's for stronger/hotter applications. I saw it on the counter at an HVAC supply house. Do a search on it.
  8. loggie

    loggie New Member

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    There is a pex that is made for hydronic solar panels I have seen that is yellow and has a 230 deg rating but it is $
  9. sgschwend

    sgschwend New Member

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    Cross linking increases the melting temperature of polyethylene. The patent document for the radiation technique list the melting temperature in the: 320-374 F.
  10. 2.beans

    2.beans Minister of Fire

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    it didnt seem to, but im sure it didnt do it any good.
  11. Gooserider

    Gooserider Mod Emeritus

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    Not sure of the exact number, but it is a pressure / temperature relationship - the higher the pressure the lower the failure temp and vice versa...

    My feeling, and I believe some codes say the same thing, is that it is best to avoid using PEX of any sort for near-boiler piping... To me the logical transition point is the storage tank if one is using storage, otherwise the far side of the distribution manifold... Copper or iron to that point, PEX after. Also if using a discrete dump loop, make that out of copper or iron, at least until after the radiation portion...

    Gooserider
  12. sgschwend

    sgschwend New Member

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    Another way to look at it: To improve reliability a common practice is to use the material below the specified performance limits.

    This is a good rule of thumb, but there will always be unique situations that may work the the users advantage (using pex to different specifications for example). In that case one approach is to test the material in that specific application. For example boiler outputs have pressure relief valves set at 30 psi, that should limit the maximum pressure to 30 psi. Pex however is specified for something like 100 psi and 200F. With a lower maximum pressure the maximum temperature should be higher. And at 200 we are only around one half of the melting temperature.

    let me see if I can find a pex phase diagram

    Not a phase diagram but interest:
    [​IMG]

    the way you read this is you derate the working pressure. For example at 200 F the derating is 50% (which printed on the pipe is something like 100 psi, I have seen 80 psi too).
  13. Gooserider

    Gooserider Mod Emeritus

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    Interesting chart, but I believe there is also a caution that should go with it - namely not to extrapolate the curves beyond where they end - I believe that if you go much further you hit the catastrophic failure point in a hurry...

    Another interesting chart that might be relevant - from Pexheat.com, the technical data on their "Everhot" brand barrier PEX-b tubing...

    Pressure Temperature
    79psi (0.55Mpa) 200°F (93°C)
    100psi (0.69Mpa) 180°F (82°C)
    145psi (1.0Mpa) 73°F (23°C)

    Note how while the tubing rating drops 45 PSI going from room temp to 180°F, that is a more than 100°F change, it drops another 20psi with the next 20°F increase, which suggests that you have a rapidly accelerating curve...

    Gooserider
  14. sgschwend

    sgschwend New Member

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    G, yep those to data sets don't match very well. The only other data point I found was the melting temperature which was higher than the graph would project. I hope you can see why I mentioned the practice of testing the settings.

    I was hoping we could see how tough Pex is, it is just not as tough as copper and steel, even though it is tougher than some solders.
  15. Gooserider

    Gooserider Mod Emeritus

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    I agree the numbers don't quite match, but the ballpark concept seems pretty good... A drop from 145psi to 79psi is IMHO close enough to a 50% derate to be within the potential "noise" difference between that of the toolboxes "typical" (and hopefully conservative) numbers and a manufacturer's specific product test data...

    I went looking at the Engineering toolbox myself, and think I found the same derating chart that you did - but I think the table above it is more interesting... Especially the bottom line on manufacturing data and especially note 1, which I have bolded for emphasis... My take is that you are as safe as can reasonably be expected under 200°F as long as you don't exceed the safe working pressures specified. OTOH, while you might get away with running hotter, it is not recommended or supported - and you shouldn't put bets on it... (Note that they say the same thing about the stuff on the bottom end as well - PEX shouldn't be subjected to freezing, but if it does happen it has better odds of recovering w/o long term damage than copper or steel...)

    Gooserider

  16. sgschwend

    sgschwend New Member

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    That reminds me I did see a graph earlier that showed the loss of strength over time. It was kinda cool, I made me feel like it was what note #1 was all about. The engineering tool box has typical data, it suggest looking at manufacturer's data. Have you ever found any of that?

    here is the link:
    http://www.polyprocessing.com/pdf/technical/Crosslinked Polyethylene with OR-1000 System.pdf

    Attached Files:

  17. Gooserider

    Gooserider Mod Emeritus

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    Interesting, though not sure if it's totally on point, as they were discussing chemical tanks, not hydronic tubing, but it is potentially of value in that it shows that there is some breakdown over time - although it looks like a VERY long time before there would be enough to matter, assuming there is no sudden knee on the curve.

    As to manufacturers data - that little chart that I posted a couple messages up did come off a spec sheet...

    Gooserider
  18. sgschwend

    sgschwend New Member

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    I found a supplier named "GIACOMINI" here is there link:
    http://www.constructor.md/FL/427-R996_2.pdf

    They publish a 5:1 reduction in lifetime, when using the pipe above 80 C. They also said the "softening" temperature is 130C.

    I have also included a phase diagram taken from a research paper working on medical joints made for cross linked high density polyethylene. I will look for a pex pipe version. The diagrams should be simular, and when I look at it I can't see any reason not to use the material as long as it stays in the solid phase, however pressure value for pipe is one atmosphere, which put us all the way to the left side.

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  19. Gooserider

    Gooserider Mod Emeritus

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    Interesting link - found a table w/ durability for temp and pressure... What happens if we translate it to English measure? Hmmm... looks like if one was running at over 87 psi and 176°F there would be some serious lifespan problems - but while we might barely get into that temp range during normal operation, our working pressures are far less than that - maybe about 1/4th on average. However it does give a bit more support and encouragement to the idea of it being a good thing to design for the lowest possible operating temperatures - as if we needed another reason...

    They say softening at 130°C (234°F) which is well over boiling, and consistent with our other data - including the phase diagram you found as best I can tell...

    Gooserider
  20. sgschwend

    sgschwend New Member

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    Sorry I was thinking we were looking at the Wirsbo documents when I wrote this. It is a well written 131 pager.

    http://www.uponor-usa.com/~/media/Files/Technical Documents/PDAM_P1_3 08.aspx?sc_lang=en



    Softening temperature would be 268F which is the same as 131C, you forgot to add the 32 back in.

    I agree high temps are going to make lifespan problems.

    It also mentioned something about surviving an overshoot temperatures. That is helpful in our case.

    Another thing that caught my eye was the note under the strength/temperature table saying:
    Determine pressure ratings at different
    temperatures by using a linear relationship
    between the standard-grade ratings.
    See Table 6-1 for temperature and
    pressure ratings

    I don't know exactly was intended, we need to remember that English is not there main language. My guess is that the phase diagram information would hold, but the lifetime based on the other information would be greatly reduced (in a non linear way), warranty is based on table values in a not to exceed way but short term temperature or pressure overshoots are acceptable.
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