Having Diesels as the dominate engines of my railroad career, the intricacies of steam engines is out of my depth. Simple explanations
I got to see what happens when a soft plug in a crown sheet lets go. The water level was not a problem. The plug just failed from age and doused the (oil burner) fire.
And yet today, a good portion of the electric power generated on this planet is produced in thermal power stations using high pressure steam. Coal-fired power stations, petroleum, nuclear, geothermal, and waste incineration plants usually use steam turbines to turn the generators. I guess boilers have become more reliable since steam locomotion was the norm.
Stationary boilers are not subject to the stresses that moving boilers in railroad service are subjected to, additionally they aren't subject to the varying water conditions that railroad boilers are in getting water of differing quality at every water stop. Throw on top of that the varying financial conditions that affect railroad inspections and maintenance between inspections mandated by the various laws that apply to railroad locomotives. Probably the biggest thing is that 21st Century metallurgy is head and shoulders better than 1920's & 30's metallurgy in designing and ensuring metals meet the needs of the application. Like everything else in the human panorama, the more we learn about something, the better we can have the technology fit the purpose. The metal required for high pressure, pressure vessels is not the run of the mill ferrous product.
