Different test !.
Yes the elements themselves are tested to 1000 psi. This was done last year (a couple were repaired and retested in the Spring).
What we are setting up for now is a much lower pressure test to assure that there is no leakage in the joints with the header made yesterday.
This is certainly a possibility.
With any steam locomotive this can happen in service and it becomes necessary to remove some elements to fix a leaking flue. This is a nuisance rather than a major problem. However it is certainly one reason why we would like to steam test this Fall so that, should this be detected, it is part of the over Winter "fix" list.