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Bubbling in anodizing after repeated pressure cycling

Bubbling in anodizing after repeated pressure cycling

Bubbling in anodizing after repeated pressure cycling

(OP)
Hello All,
   This concerns a pressure case made from 7075 Aluminum and anodized to the following spec: 'MIL-A-8625 Type III, Class 1 including duplex seal on all components, 0.001" buildup/0.02" thick'.  This case is several years old, and has pressure cycled in the ocean to several thousand meters a few hundred times.
   On the contact surfaces exposed to saltwater, that is, the mating surfaces on the high pressure side of the o-ring, it has started to show extensive bubbling.  The bubbles range from one to several millimeters, and they chip off fairly easily, some can be simply rubbed off with a fingertip to expose the bare aluminum.  The exposed aluminum does not look (to the naked eye) to be heavily corroded.
   Is this sort of failure something I should expect to see given the operating envelope for the pressure case?  Can someone help me with a cause of what might be happening here?  From reading similar posts I see that impurities in the aluminum may be the culprit, but those seem to have shown problems earlier than I am seeing here.  Could the pressure cycling be a factor?
   Thanks in advance for your help.

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