The photomicrograph at left was made at the point of failure at 100X ...
Think about this example before seeing the explanation.
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Here are two cross sections of a Muntz metal heat exchanger
tube which failed in service. Water was circulated through the
tubing to cool air, compressed to 100 pounds per square inch, that was
flowing past the outside of the tube. The pipe collapsed
because the corrosion weakened it and because the air pressure outside
the tube was greater than the water pressure inside the tube. The photomicrograph at left was made at the point of failure at 100X ... |
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... and the second photomicrograph was taken at a remote
location where the pipe was still round, also at 100X. Think about this example before seeing the explanation. |
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The coarse microstructure at the point of failure is
indicative of overheating, while the dezincification at the remote part
of the heat exchanger occurred on the outside of the pipe. The
external dezincification removes blame from the water ... and the
coarsening of the microstructure at the point of failure strongly hints
that the air was not simply corrosive, but too hot as well. The seventh specimen is a failure combining corrosion with fatigue. |