Boiler repairs question

Looking for the "ball park" time that would be needed by an experienced steam era shop to replace the steam dome ona Shay boiler, given they had all the parts and equipment needed? Was this a "few hours" kind of job, a few days, a week? What would be the mechanical reasons for replacing a steam dome ( other than roll over damage). Do they wear out, rust through, better designes came out over time? My questions come from trying to put a Uintah roster together, and in at least one case, it seems that the engine recieved as many as four different steam domes over time. Also, were steam domes "jacketed" like a boiler, or is what you see on the outside, the actual wall of the dome? Thanks.