The upper photomicrograph was taken near the edge ...
Now look at the explanation.
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This is a Muntz metal water pipe which failed after 25 years
in service. What type of failure is it ? Look at both
frames before deciding. Each one is at 500X. The upper photomicrograph was taken near the edge ... |
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The lower one was taken in the interior of the pipe wall. Now look at the explanation. |
| This is dezincification, which
occurs by selective leaching of zinc (from the lemon yellow beta phase)
by corrosive water. Copper remains behind as a spongy mass
because it is reprecupitated as metallic copper after the disappearance
of the zinc. The pipe failed first at the threaded joints because
of the reduction in wall thickness by the cutting of the threads.
Manufacturers persist in using this alloy in cheap lathe-turned parts
(faucet-washer screws and toilet valve components especially) because
of its superior machinability. |
| The fifth specimen is an example of chemically
induced cracking. |