On carriers your talking about enough heat that can either generate 600 or 1200 PSI steam pressure depending on which system they likely somewhat copied. USN used asbestos on all conventional powered carriers and likely Enterprise and Nimitz as well. I'm not sure what could replace it.
USN hasn’t used asbestos for decades...they just went to a very thick high temp lagging.
One of the toughest days I ever spent on the boat was after overhaul during the first steam plant startup. The all new lagging had to cure, and there was a rather thick atmosphere in the engine room that burned the eyes. Took a few days for that to go away. I still remember that smell though.