The major U.S. builders told their customers that the life expectancy of a properly cared for steam locomotive was about 30 years .This was based on a lot of variables like type of fuel ,water quality and climate and of course how the locomotive was employed .The keystone of the locomoive's life was the condition of the boiler barrel .Railroads in the U.S.were capable of very extensive repair and alteration .Engines like the ones we are familiar with on the C&TS and the D&S are probably on their second or third firebox ,a major repair . Lots of real old engines were still running up to the end of steam ,many pushing 50+ years . This old power was fully depreciated so the railroads paid no taxes on them , so it made financial sense to not replace them till dieselization . I theorize that since many of the later engines were not depreciated ,roads like the SP were anxious to get them off the tax rolls ,so sold them first to the scrapper . That may be why Earl's #2248 and dozens of other small, old engines found their way to parks while only one cab-forward and two 4-8-4s did. Baldwin once put out a magazine that often touted stories and photos of their locomotives that were very old still running around the world . The most memorable was the repair of an 1875 4-4-0 deep in Brazil's Amazonia.,after being out of service for years . I think the engine is on display in Manaus .