Robert11 wrote:
....
a. 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.

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

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

d. Is it still allowed, or the Code prohibits it now all over ?

Any thoughts on this would be most appreciated.
....

Probably was pit from manufacturing process that took that long to
finally break through. While not common, it's not unheard of for a new
section to have a leak initially.

Corrosion pitting is a combination of material and water chemistry. One
possibility is as someone else noted a touching piece of other metal
such as a truss bracket, etc. that can rub or be an electrolysis potential.

M was (and is) pretty common simply for cost -- it takes less Cu to make
thinner wall (obviously) so many contractors used it--particularly
houses built "on spec" rather than on contract where there wasn't a
specific buyer to satisfy or look over the materials.

I know of nothing in the Code that would proscribe it...nor should there
be, really. Even in your case it's been 35 years which ain't too bad
annoying as it is...

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