I've only been exposed to this in oil & gas, but there is a problem that non-destructive testing of drill stems does not test for all failure modes

Edit: i.e. NDT'd pieces are not immune from failure (but other factors such as age and in-service time/rotations/re-thread/re-collar runs etc. can provide additional context to NDT results and should correlate more or less with actual failure patterns).

In a single-use part, non-destructive testing mightn't be a complete picture of how the part will perform.