Re: Out of service Steam *LINK*

That’s how it used to be under the old rule, and was the cause for railroads sending in "out of service" reports every month for decades on some engines, just to keeps them alive in the eyes of the FRA.
With the current rule, every engine gets a new form 4 every 15 years or 1472 in service days, whichever comes first. With a new form 4, the engine is a new engine in the eyes of the FRA regardless of whether it was running one month before, and went into the shop for a quick turnaround 1472 day inspection, or hasn’t turned a wheel in 50 years.
BTW subsequent 1472 day inspections are much less troublesome and expensive than initial ones in that form 4 wise, an ultrasonic thickness survey is the main tool, used to determine if any sheet in the boiler has wasted to less than the minimum thickness required for that boiler as noted in the previous form 4. If there is no thickness problem, then the boiler is inspected for any broken stays or braces, or any cracks, new tubes are installed, a new form 4 made out with current thicknesses filled in , and the engine is ready to go.