Type M Cu For Hot/Cold Water Lines Question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Robert11, Nov 9, 2008.

  1. Robert11

    Robert11 New Member

    Nov 9, 2008

    Live in a 35 year old house outside of Boston.

    Had a leak in a Copper water pipe that the plumber finally found.

    Unfortunately, I forgot to ask him if it was in a hot or cold line, as this might, perhaps, be meaningful ?

    Anyway, what surprised me was that it was pinhole leak in the middle of a run.
    Not at a joint or fitting, etc. Right in the middle of a line.

    Apparently they used the thinnest Copper they could find when they built the place.

    I used a caliper on it, and found it to be 0.028, which I guess is a grade M. (outside diameter of 5/8 inch)

    But, it still should take the household pressure without any problem, I would think. True ?

    The plumber replaced it with heavier wall stuff of approx. 0.038, which is probablyType L


    a. 35 years ago, was this (Type M) a "very common" Copper gage they used for household hot and cold water lines ?

    b. Is it still allowed, or the Codes prohibits it now all over ?

    c. What might make a pinhole leake in the middle of a clear run ?
    I guess the pinhole can be considered as a corrosion type of breakthrough.

    d. How common is something like this is the thinwall Type M tubing ? What causes ?

    Any thoughts on this would be most appreciated.

  2. nhmaster

    nhmaster Master Plumber

    Jul 30, 2008
    Tech. Instructor
    S. Maine
    IPC and UPC both allow it's use but many states have adopeted an ammendment making illegal except for heating pipes. Most of us use type L.
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    I have not used type "L" copper in a residence, EVER. "M" has always been the standard.
  5. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    You might want to investigate your water chemistry. Also water velocity and flow, like on a pumped recirc line, or a small line feeding a large demand, can cause erosion.
  6. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima WA
    I believe type M is still the standard. There may be some local codes or issues that specify type L.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    The OD on copper like this is the same so any fitting will work (same with pex)...it is only the ID that changes with the wall thickness.
  8. AcidWater

    AcidWater Member

    Oct 14, 2008
    My ~40 year old pipes are failing from pinholes. I just finished struggling with fixing a second pinhole that was caused by yanking the pipes around in the process of putting in a coupling to fix the first pinhole. What a PIA.

    I'm going to replace the whole system with PEX, except for the couple of risers are inside walls.

    Pinholes are usually not found in the hot lines for some reason.
  9. Redwood

    Redwood Master Plumber

    Dec 15, 2007
    Service Plumber
    Multiple pinholes are a case of aggressive water conditions.

    The handle you are using hints at something...
    Have you checked the PH of your water?
    If so what is it?
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