Most of today's railroads go berserk if locomotive availability (fleet average) falls under 93%.
By coincidence, I was reading some old copies of Railway Mechanical Engineer and proceedings from the Master Boilermakers Association annual meets (amazing what you can find on eBay sometimes) and much attention and discussion was given the subject of boiler washing for several years in a row.
Consensus (or as close to that as one can expect from an auditorium full of people from dozens of different US and Candian railroads) was that by the early-to-mid-1940's, most railroads were washing boilers by means of what was called the cooldown method, but despite that name, it was much different from what's been described here.
Basically, the fire was killed, the injectors put on and left to run until they broke, at which time the boiler was full and the pressure would be down to 40 pounds or less. A hot water line from the shop was hooked to a boiler check and a discharge line hooked to a blowoff cock and both were opened until no pressure showed on the gauge.
At that point, the water was turned off, the plugs were pulled and washing began, using hot water and various tools. When completed, the plugs were put back in, the relief valve opened,
a hot water/steam line from the house was hooked to the blowoff cock, and a mix of hot water and steam was used to fill the boiler. When the boiler was full, the relief was closed, the boiler blown down until the water was in the middle of the glass, and steam was put in through the house line until the glass was full again and 50 psi was on the gauge. Then the fire was lit, the house lines disconnected, and the engine was moved out of the house.
Oh, yeah....this whole process took about 3 1/2 to 4 hours on a large 2-8-4, 4-8-4, or 2-10-4 and they all said there was no damage to sheets or staybolts from this method and highly recommended it. Boiler metal temperature didn't get much below 190 degrees.
The articles didn't say, but it must have taken a whole army of men to do this, not to mention a good house steam plant.
