With huge pieces of that boiler lagging missing, it's hard to see how it could be restored to operating condition. The 4018 had small holes in its boiler lagging, so there must be more than meets the eye when judging restorability. I imagine new lagging will be fabricated?
Aaron
It's the jacketing and only sheet metal. Lagging is the insulation around the boiler. In the past, it used to be asbestos.
Any well equipped metal shop could fabricate new jacketing, it's not rocket science. I seriously doubt that any of the steam locomotives running around today still have their original boiler jacketing.
Rusty
Rusty is absolutely correct about the sheet metal Jacketing. In fact, UP 844 has even had her Jacketing renewed at least twice during her "excursion career" alone.
The asbestos insulation material was removed from #4014 many, many years ago. The best way to keep a steam locomotive boiler shell in good condition when "out in the weather" on display was/is to IMMEDIATELY remove the Jacket and asbestos lagging. Some places have even gone through the effort to reapply the sheet metal jacketing with appropriate spacers between the sheet metal and boiler so the it APPEARS that everything is "as it was in the old days".
Over the last 30 years or so, obviously asbestos insulation is no longer used on restored & operating steam locomotives. There is much higher "R Factor" fiberglass material now available, and is also MUCH easier to work with.