Boiler explosions were rare during the twentieth century, but it seems that a handful or so did manage to occur right up to the near the end of steam. I read about one on the AT&SF with a large road engine on a freight train with a diesel yard switcher coupled ahead of it. The switcher was facing forward with its cab next to the head end of the steamer. They were slowly pulling out of a siding when the crown sheet let go.
At that moment, the rear four-wheel engine truck was passing over a concrete end abutment of a small bridge / culvert. The thrust of escaping steam skyrocketed the boiler into the air and the counterforce pushed the rear engine truck about 3 feet below its track position, bending the rails and crushing the concrete abutment in the process. The steam also went through the tubes and burst out the front of the smokebox, and blew the engineer, fireman, and all the window glass out of the diesel cab.
I don’t believe I have any reference to this accident in my collection of magazines or books, but I recall reading an article about it in a book at the library many years ago. I would think that this event would be fairly well known and documented. I would guess that it happened in the 1940s
The last freight service explosion in the US was N&W Y-6 2153 at Wytheville, Va. in December, 1955. The engine was having steam trouble. The boiler pressure was down to 145 (out of 300, you know) when it blew. The boiler did not leave the frame, but it broke the HP cast bed frame behind the cylinders like it was a matchstick. One witness said it broke the rail under each of the HP engine drivers, but it’s not evident in the photos.
When the pressure is higher, the force is usually enough to break the boiler/firebox loose from the frame and catapult it into the air.
But in answer to your question, if the boiler has water in it at a temperature higher than the boiling point (and your 250 degrees is sufficient) it will all turn to steam at once when the pressure is released, with the usual results.
I beleive that right after this that virtually every exist operating steam engine was embargoded till they could be inspected and certified safe to operate. Steam had been pretty much been forgoten about by the FRA as they were no longer in revenue service for a while now. Previously they had been maintained by highly trained and skilled mechanics in large shops that now no longer existed. They found several engines operating that should not have been. They later issued strict and stringent guidelines for inspections and certifications that we still have today. [2c] AS always ENJOY
Wandering a bit off topic, here-while I have often heard of crownsheet failure caused explosions, what about the front/rear tube end sheets? I seem to recall that UP 844 suffered from something like that a few years ago (maybe I’m way wrong there, I don’t recall any details). Or would there ever be failure of a boiler flue? Any cases (since Best Friend) of a boiler simply rupturing (as a primary failure, not as a result of damage from an accident)?
GNRICK is right, a boiler explosion occurs when the water level gets too low, the crown gets exposed, gets super-heated, and the water in the boiler instantly flashes to steam. Remember that expansion of steam is what moves the pistions in the cylinders. Expand that much water into steam in the boiler and it has to go someplace - BOOM!! There is no way the boiler can contain that much pressure.
So it isn’t really a crown sheet failure, so much as a low water level. Yes the crown sheet fails, in that it gets pretty much blown apart along with most of the rest of the locomotive.
The low water condition is something that had to be very much kept in mind when operating on grades as the water gauge doesn’t necessarily give an accurate reading when on any significant incline.
The failure on the Gettysburg was due to a number of things. Some was maintenence-related, some was just operator error. I don’t recall the details, but do recall they were of that nature. Our Master Mechanic (Who was also a steam guy at a past job) was friends with an employee up there and another of our guys worked up there on occasion, so we got the story pretty much first-hand at the time.
The shortline railroad community is small and pretty tight. It’s sometimes like living in a small town spread over a large area, if that makes sense. Everyone knows everyone else, or knows someone who knows someone.
[}:)][}:)][8D][8D][8D] Don’t forget to include the heat from the firebox. At what temp does coal turn from a solid to a gas for combustion to take place???
The crown sheet was above the firebox & was subject to a variety of stresses…heat from the fire, expansion from the heat & contraction after the fire was dumped. Having water over the crown sheet protected the metal from those stresses. Failure to keep water over the crown sheet allowed I believe the “staybolts” to loosen or fail. When you have that much hot water under underpressure, it doesn’t take much of a hole to start a catistrofic event.
Are there not now plugs that can be installed that when the sheet goes dry they melt and vent the steam on the flame to extingui***he fire. The water does not “flash over” as the preasure does not vent suddenly but in a controlled manner? [?] As always ENJOY
Fusible plugs have been around steam locomotion for many years. I have
several ads for different makes in my copy of the “1941 Locomotive
Cyclopedia”-a great resource. In the case of GN 2581, investigation
showed that the water level at the time of the explosion was 12 inches
below the top of the crown sheet-an extremely low level. There is no
mention in the report whether the engine was equipped with fusible
plugs. It was equipped with both a GN-standard water column, which
included a Talmage water glass and 3 Prime gage cocks on the right
side of the boiler and a second Talmage water glass on the left side.
The openings into these safety devices were found to be clean and open.
The locomotive was also equipped with a Nathan low-water alarm.
It was demolished in the accident and was therefore not able to be tested for
function. Why GN may not have included fusible plugs in the design, I
cannot say.
Fusible Plugs: Someone please “expand” on them a bit…I’m wondering if a boiler has a problem and attains a psi too high and fusible plugs are in place and “blow”…Why doesn’t that really cause an explosion since the opening will lower the boiler press pretty quick and…?? cause an explosion because of lower boiler press…??
A fusible plug is a thing that screws into the boiler. It has a hole through it that is filled with lead. If it gets too hot the lead melts and the pressure is released.
Fusible plugs, also known as boiler drop plugs, consist of a hard ‘plug’ in
a threaded flange that screws into the crown sheet, as mentioned. The plug
itself is held in place by the fusible metal-an alloy that melts at a lower
temperature than the crown sheet. When the crown sheet temperature
reaches a calculated level, the fusible metal melts and the drop plug drops
into the firebox. The aperture is small enougn to not allow a too rapid drop
in boiler pressure, thus preventing catastrophic expansion, much like
the safety valves do. The steam vents into the firebox, cooling it and
extinguishing the fire. While this does prevent the catastrophic boiler
explosion, it is still damaging to the boiler. The crew that gets into this
predicament will at least live long enough to be chewed out by the
Master Mechanic, and probably the Road Foreman of Engines as well,
but that is better than the alternative.
Kinda but you’ve gotta think about what it makes to contain 225psi as compaired to 15psi. The higher pressure boilers were huge and thick, lots and lots of steel, and they can usually contain more water. More water equals more explosive force, and more steel equals a lot more shrapnel flying through the air. The reason a steam engine boiler explosion is so much more spectacular than say a water heater is mostly because of size. A water heater has a tiny fraction of the water and metal of say a 4-8-4 Northern.
More than a thrill if the firebox door was open at the time it blew. Here’s a link to the NTSB report on the Gettysburg incident. Page 17 has a cool (or disturbing) photo of the buckled crown sheet.
These are two seperate appliances. If a boiler reaches a preasure above a safe operating point the “safety valve” will open untill the preasure is reduced. There are other types that need to be reset manually and others that must be replaced thou I am unaware of these types being used on locomotives. Fusable plugs are designed to withstand preasures well above the limits of the safety valves. What they will not tolerate is the temperature of a “dry” crown sheet. They allow a controlled release of preasure. The operative word here is “controlled” as opposed to a catastrophic release of preasure. These systems and more are mandatory on todays modern " automated" stationary boiler systems. [2c] As always ENJOY