Pinprick hole in copper pipe

[algrant]

About 6 months ago we had our lead rising main replaced with copper. Yesterday it developed a small leak from mid-way along a section of pipe. On cutting it out I found the pipe showed no signs of having been abraded on the outside; instead there was a pinprick-sized hole, and inside the pipe there was a small (3mm) cluster of green stuff (presumably, copper oxide).

I have never encountered this before. Would it be due to a flaw in the pipe, or is there something (e.g. some other metal) which can lodge on the inside of a pipe and rot it?

[Andy Dingley]

Pinholes are often caused by uncleaned flux residues. Any sign of that on the outside?

Copper oxide is either red or black, for cuprous or cupric oxides (I forget which is which). However most other copper salts are blue or green, so it could be almost anything.

Nor I.

It would be a rare flaw that left a pinhole in copper pipe - they do happen, but they normally cause splits. It _might_ be an inclusion, that then gave rise to corrosion.

This could certainly happen, but I'd be surprised that such a contaminant could sit there without getting washed out.

Any chance that the hole came first, then the crystals formed around it?

[Dave Plowman (News)]

I once had a similar hole in a Wicks end feed elbow. But IIRC these are cast, rather than drawn as tube tends to be.

I'd guess at an impurity in the copper alloy.

[Andrew Gabriel]

ISTR a batch of very low quality copper pipes around the early 1970's with this problem, due to contamination with iron or carbon or something. Service live turned out to be about 10 years before they were leaking all over the place.

[algrant]

No... and this was a few feet from the nearest soldered joint on that pipe, though there was one on another pipe nearby.

Could be. Do you think anyone (plumbers' training college?) would like a look at it? If not, I might just send it to my local university materials science department on spec.

[Ian_m]

I thought there was a whole batch of duff copper pipe from a couple of years ago that is now springing pin-hole leaks. Due to carbon granules in the copper I think.

I think also the supplier/manufacturer is/was providing compensation, as I am sure when my brother was in the plumbing trade a lot of his work was existing pipe replacement, all paid for by the pipe manufacturer.