Storm,
So long as the work load is kept below 71ksi for Grade 5 there is no fatigue life. This works out to about 55% of the UTS. Or about 60% of the yield strength. In other words, assuming a safety margin of 2:1 titanium parts don't have a fatigue limit in marine environments.
Practically speaking the only life span restriction is from galling. So anything with threads could be a problem. Anything that is static should last long enough that it doesn't matter (the U.S. Navy figures 5,000 years fyi).
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