Type of cracking
Guys
I am only just looking at this thread, and I note the comments on cracks and corrosion. Be aware that there are essentially two types of cracks associated with corrosion. 1: fatigue initiated by the stress concentrations caused by corrosion pitting, and 2: stress corrosion cracking (SCC) caused by the combination of a corrosive environment, a residual stress and an alloy which is susceptible to stress-corrosion.
167 hours seems far too short for fatigue, even if corrosion was extant prior to service. I would be very suspicious of SCC and this is an alloy selection issue.
Regards
Blakmax