Boiler explosions?

[jgallaway81]

I actually spent the time to ready the full NTSB/FRA reports on the Gettysburg explosion, and another factor stuck out there.

The engine in question was Canadian in origin, and they used corrugated crown sheets. According to the report, the idea was that the crown sheet failure would be progressive in such a firebox, theoretically allowing part of the steam pressure to vent into the firebox at a semi-controlled rate. Theoretically this would extinguish the fire, and lower the boiler pressure, preventing a full, catastrophic failure.

Based on the reports, the Gettysburg disaster was pure incompetence, all the way around. Safety first!... if you can't verify ALL safety appliances on the engine are working correctly, DUMP the fire NOW.


Also, I am surprised that any road would suggest venting steam pressure on a boiler that is in danger/process of having of crown sheet failure. As the steam vents, the pressure is reduced, causing liquid water to vaporize into more steam. Therefore venting steam pressure could accelerate a boiler explosion.

What needs to be addressed, is how long does it take for the firebox sheets to cool enough after a fire has been dumped, for a catastrophic explosion to be impossible? IE, how many seconds after the fire is dumped can the steam pressure still cause the soften steel to rupture, before the steel cools enough to gain back sufficient integrity. I realize this would depend on a) boiler pressure at the time b) temperature of the fire... idle/banked/full draft.

[T26MtnGrl]

My grandfather was the engineer of this train, He had just got off before the explosion. That is all i know of this picture

[Eliphaz]

Wow, how interesting, thanks for sharing. I guess that's the ragged edge of the blown out crownsheet circled in red.

[Eliphaz]

...
Also, I am surprised that any road would suggest venting steam pressure on a boiler that is in danger/process of having of crown sheet failure. As the steam vents, the pressure is reduced, causing liquid water to vaporize into more steam. Therefore venting steam pressure could accelerate a boiler explosion.

a word about this - reducing the pressure as rapidly as possible by venting steam is the right course of action, but it does have to be done cautiously.
As the pressure drops water will certainly continue to boil into the steam space, that is well and good, evaporating water takes away alot of heat with it - but that should not normally result in increasing pressure unless the rate of renewed boiling is such that the level of the water is lifted enough to bring it in contact with red hot metal, which might cause flash boiling to an extent great enough to exceed the leakage and/or venting rate. That's the concern, and is also the reason NOT to add water, in the event that the water has gone out of the glass.

What needs to be addressed, is how long does it take for the firebox sheets to cool enough after a fire has been dumped, for a catastrophic explosion to be impossible? IE, how many seconds after the fire is dumped can the steam pressure still cause the soften steel to rupture, before the steel cools enough to gain back sufficient integrity. I realize this would depend on a) boiler pressure at the time b) temperature of the fire... idle/banked/full draft.

The recommended practice requires that once the water level has fallen out of the glass, the boiler may not be returned to service until it has been inspected for integrity.

[johnthefireman]

There's a report by the UK Rail Accident Investigation Board at http://www.raib.gov.uk/cms_resources.cf ... rklees.pdf concerning an incident on a heritage railway where the firebox of a steam locomotive was damaged due to low water level in the boiler. It makes interesting reading.

[scottychaos]

C&O 1642:
http://digital.denverlibrary.org/cdm/si ... 8060/rec/2

after the explosion:
http://digital.denverlibrary.org/cdm/si ... 8114/rec/4

Scot

[mikado-2-8-2]

One thing no one has mentioned in the C&O explosion that these were the last yeas of steam operation. C&O was converting to diesels and was downsizing steam maintenance & repair crews as fast as possible. The steam locomotives that were left were not being serviced or maintained very well. I think the company thinking was to keep them functional at the least possible cost as they are going to be piles of scrap metal soon.

[GSC]

Good point, Mikado.

Responding to a 2-year-old answer to something I posted:

All three of our operating steam locomotives had fusible plugs, vintage 1887, 1925, and 1927.

As far as venting, it was to be done slowly and carefully - we weren't to open up the blowdown valves and run away. We were well aware of generating more steam as the pressure was vented. The idea was to cool the metal (dump the fire) and carefully bring the pressure down.

[Steffen]

Most people think on venting the steam off to prevent explosions, but the most important thing is: Dumb the fire!
The boiler is damaged, give a hell on guessing about the ashbox, dump the fire, open the bottom doors and drop it out into the open.
Then open the blower a little, which will cause draught and the draft will drag cooler air thru the flues, and the boiler will start cooling down... now you can simple leave it, and wait until it has all settled...

[ACeInTheHole]

Wow. Thats just scary...to blow a locomotive that size to pieces.. It must have been a vicious explosion. I cant even imagine it..

[GSC]

People don't realize the power of compressed steam. And get a little leak and it all wants to come out - now!

When I was little, my mother put my infant sister's glass baby bottles in a bottle boiler - an open rack affair that held six bottles in a pan of boiling water to sanitize them, filled with milk and capped. Mom fell asleep and two of the bottles let go. In this case, the plastic caps launched vertically and put nice dents into the plaster ceiling. Bullets fired from baby bottles! Thankfully, the weakest link was the plastic cap, and not the glass!

Unlike compressed air, steam keeps expanding until it reduces itself to atmospheric pressure of 14.7 psi (at sea level).

[2nd trick op]

With regard to safety devices, the last order, and probably more of the NKP's famous Berkshires reportedly had a device referred to as a "Nathan low-water alarm". (Some voice in the back of my head is suggesting that the same firm also manufactured "safety plugs".) Can anyone provide a little more information on the origins of that equipment?

[Eliphaz]

...

Unlike compressed air, steam keeps expanding until it reduces itself to atmospheric pressure of 14.7 psi (at sea level).

not exactly. compressed air and other compressed cylinder gasses also contain very large amounts of stored energy which can expand disastrously.
the difference is that a boiler contains a reservoir of saturated liquid water ready to boil and replenish the supply of escaping expanding gas.