How long will black iron last passing through bricks without proper sleeving?

New house has fairly new black iron pipes that pass into a dual hearth brick fireplace, both 1/2" schedule 40.

One passed from outside and the pipe is painted with primer on the outside portion.

The second one passes from inside into the ash dump and through the ash dump (both are converted with gas inserts). Bricks at outside don't get wet at where the gas enters.

I think the lifetime should be around 20-40 years but not the 60+ years for black iron if painted or in good environment