Steam & Excursion > Steam Locomotive question.

Many years ago, I read an article concening the bursting of steam locomotive boilers when the crown sheet failed. IIRC, it stated that each gallon of the superheated water in the boiler expanded 1600 times when the pressure was suddenly released by the crown sheet failure.

Thinking about this last night, I got to wondering just how many gallons of water a locomotive boiler contained when filled to the level considered proper for safe operation. Realizing that locomotive boilers came in many different sizes, how about the 4449? Or the 3751? Maybe even a Big Boy?

Does anyone know?

Appreciate any information anyone might have.

Yardclerk

yardclerk Wrote:
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> Many years ago, I read an article concening the
> bursting of steam locomotive boilers when the
> crown sheet failed. IIRC, it stated that each
> gallon of the superheated water in the boiler
> expanded 1600 times when the pressure was suddenly
> released by the crown sheet failure.
>
> Thinking about this last night, I got to wondering
> just how many gallons of water a locomotive boiler
> contained when filled to the level considered
> proper for safe operation. Realizing that
> locomotive boilers came in many different sizes,
> how about the 4449? Or the 3751? Maybe even a
> Big Boy?
>
> Does anyone know?
>
> Appreciate any information anyone might have.
>
> Yardclerk

The Following is from "The 4-10-2: Three Barrels of Steam" p.110

"The force of a boiler explosion is dependent upon the size of the rupture, boiler pressure at the time of the explosion, and the amount of water in the boiler. As an example: an average boiler having 500 cubic feet area below the crown sheet and steam space of 150 cubic feet, with a pressure of 200 PSI. At the instant of explosion there would be an energy release of approximately 700,000 horsepower. A boiler the size of those built into the Southern Pacific Class and Overland Class locomotives would release close to 1,000,000 horsepower at the instant of explosion."

If you take the full weight of the engine, and subtract the dry weight of it, you'll get about how much water it has. Now the full weight of an SP 4-10-2 is 445,000 pounds, and its dry weight is 395,700 pounds. The weight of 1 gallon of water is 8.33 pounds. So if you take the difference of those 2 weights, its 49,300 pounds. Divide that by 8.33 and you have the amount of water in the boiler, which is 5918 gallons of water. That should be right.

I don't have any more info than this, but the steam inside locomotive boilers is not superheated, it’s saturated. It is only superheated after it has passed through the throttle and then through the superheater units. The only way I can think of that it could be superheated is between the time all the water evaporates off the crown sheet and the crown sheet failing. I'm guessing that SP 4449 and ATSF 3751 would have about the same amount of energy released at the time of explosion.

The largest engine that I know of that exploded was Cheasapeake and Ohio 2-6-6-6 1642. When the engine "disintegrated" the boiler separated from the frame and the backhead landed 639 feet ahead of the point of explosion. When you consider the size of these engines, that much metal flying through the air for that distance is almost incomprehensable. What is more incomprehesable is why the engineer and fireman were working the engine with a medium throttle to the point of explosion even though lineside observers could hear the low water alarm sounding for some distance away. An examination of the boiler later showed the water level was almost 7" below the crownsheet when the explosion occurred. The force of the explosion twisted the rrails into pretzel shapes for hundreds of feet. Superintendenta believed between 1500-2000 feet of tracks would have to be replaced. The final report concluded that the cold water pump had quit, and that the injector was found in the closed position. Why the crew did not stop and dump the fire was the only unanswered question.
Material contained herein was found in Huddleston's book "The Allegheny-Lima's Finest"

> I don't have any more info than this, but the
> steam inside locomotive boilers is not
> superheated, it’s saturated. It is only
> superheated after it has passed through the
> throttle and then through the superheater units.

That is correct.

> The only way I can think of that it could be
> superheated is between the time all the water
> evaporates off the crown sheet and the crown sheet
> failing.
>

Superheated steam cannot exist in the presence of water, so no superheated steam can exist in a boiler until the last drop evaporates. Once the boiler is rended and pressure is released, the water in the boiler at a temperature of, say 381 degrees at 200 psi, would turn to steam virtually instantly due to the release in pressure and would, in a sense, be superheated, or more correctly wiredrawn in this case.

Steam2k Wrote:

> As an example: an average boiler
> having 500 cubic feet area below the crown sheet
> and steam space of 150 cubic feet, with a pressure
> of 200 PSI. At the instant of explosion there
> would be an energy release of approximately
> 700,000 horsepower. A boiler the size of those
> built into the Southern Pacific Class and Overland
> Class locomotives would release close to 1,000,000
> horsepower at the instant of explosion."
>

As an additional comment, a boiler explosion on a UP 9000 class occurred at Upland, Kansas, near Marysville in the late 1940's. The boiler from that locomotive became airborn and landed approximately 1/2 mile from where the explosion occurred. Boiler explosions do indeed release an emormous amount of energy.

I'd say it's a safe bet the water in the boiler doesn't all evaporate instantly-- evaporation always takes heat, and there isn't any source for that much heat. A good chunk of it evaporates, and that steam sprays the rest around the landscape.

FWIW, we ought to be able to estimate the water space in a given boiler, with all the known dimensions.

Can any of you recall the incident in which a U.P. 4-8-4 blew up in Denver Union Station sometime in the 1940's?

tolland Wrote:
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> As an additional comment, a boiler explosion on a
> UP 9000 class occurred at Upland, Kansas, near
> Marysville in the late 1940's. The boiler from
> that locomotive became airborn and landed
> approximately 1/2 mile from where the explosion
> occurred. Boiler explosions do indeed release an
> emormous amount of energy.

This subject came up some time back, probably about a year ago. One of the unfortunate circumstances of such an event is that typically the boiler would land on the tracks ahead and since the crew is no longer, the train would continue on and collide with it adding to the mess. Just a cheery thought. Keep them crownsheets under water guys...

timz Wrote:
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> I'd say it's a safe bet the water in the boiler
> doesn't all evaporate instantly-- evaporation
> always takes heat, and there isn't any source for
> that much heat. A good chunk of it evaporates, and
> that steam sprays the rest around the landscape.
>
> FWIW, we ought to be able to estimate the water
> space in a given boiler, with all the known
> dimensions.

Remember that prior to this supposed failure/explosion that the steam/water in the boiler was under pressure. When the failure occurs, the remaining water wants to flash to steam pretty darned quick with the sudden loss of pressure. I think we're talking about seconds here.

> The Following is from "The 4-10-2: Three Barrels
> of Steam" p.110
>
> At the instant of explosion there
> would be an energy release of approximately
> 700,000 horsepower. A boiler the size of those
> built into the Southern Pacific Class and Overland
> Class locomotives would release close to 1,000,000
> horsepower at the instant of explosion."
>
>
There is a dimension problem here. Horsepower is power, not energy. Power over some period of time is energy. Is there an assumed duration for this release?

Doug Wrote:
-------------------------------------------------------
> > The Following is from "The 4-10-2: Three
> Barrels
> > of Steam" p.110
> >
> > At the instant of explosion there
> > would be an energy release of approximately
> > 700,000 horsepower. A boiler the size of
> those
> > built into the Southern Pacific Class and
> Overland
> > Class locomotives would release close to
> 1,000,000
> > horsepower at the instant of explosion."
> >
> >
> There is a dimension problem here. Horsepower is
> power, not energy. Power over some period of time
> is energy. Is there an assumed duration for this
> release?


My best guess is "at the instant of explosion"

MTMEngineer Wrote:
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> > > I don't have any more info than this, but
> the
> > steam inside locomotive boilers is not
> > superheated, it’s saturated. It is only
> > superheated after it has passed through the
> > throttle and then through the superheater
> units.
>
> That is correct.
>
> > The only way I can think of that it could be
> > superheated is between the time all the
> water
> > evaporates off the crown sheet and the crown
> sheet
> > failing.
> >
>
> Superheated steam cannot exist in the presence of
> water, so no superheated steam can exist in a
> boiler until the last drop evaporates. Once the
> boiler is rended and pressure is released, the
> water in the boiler at a temperature of, say 381
> degrees at 200 psi, would turn to steam virtually
> instantly due to the release in pressure and
> would, in a sense, be superheated, or more
> correctly wiredrawn in this case.
>


Ah, that makes sense. I forgot that superheating means that all the water has phased changed into a gas.

Duration of explosion -

On old hogger once told me "You might hear the Ka, but you won't hear the Boom."

Finderskeepers Wrote:
-------------------------------------------------------

> Material contained herein was found in
> Huddleston's book "The Allegheny-Lima's Finest"

The 1642 incident, ICC report No. 3250 (6/9/1953), and many other reports on steam era wrecks can be found online here:

DOT INVESTIGATIONS OF RAILROAD ACCIDENTS 1911 - 1966
http://dotlibrary2.specialcollection.net/scripts/ws.dll?websearch&site=dot_railroads


An excerpt from the 1642 report, dated 7/6/1953:

The force of the explosion tore the boiler from the frame and cylinder connections and it was thrown upward and forward. The boiler struck on its front end on the rails of the eastbound track approximately 440 feet ahead of the point of the explosion, then rebounded. The back head, struck the track 639 feet ahead of the point of explosion where the boiler came to rest on its right side in reversed position with front end, on the adjacent westbound track and firebox on the switching track. The smoke box front was blown off and several super-heater units were blown out. The cab was blown 133 feet to rear and 58 feet to right of the point of explosion where it fell at the water edge of New River. Grates, grate bars, throttle lever, and other parts were scattered for distances up to approximately 772 feet from point of accident, some falling in New River, Many appurtenances were badly damaged and some parts could not be located. The track rails at point of explosion were indented by the trailing truck wheels and the two rear pairs of driving wheels and the westbound track was moved approximately 5-1/4. feet to the left. At the point where the front end of the boiler struck the track rails were broken and badly bent and a large hole was torn in the road bed. Where the back head of the boiler struck, the westbound track was moved 3 feet to the left. The locomotive running gear with tender attached came to rest with front end alongside the front end of the boiler with only trailing truck wheels derailed. All tender truck wheels were derailed and the front truck was off center. The tank was skewed, to the left with left front corner leaning approximately 10 degrees to the left. Nine cars were derailed and bunched, five were at approximately 90-degree angles with the rails four of which were on their sides.

The engineer, fireman, and head brakeman were killed. The engineer's body was found at the water's edge of New River, approximately 75 feet to rear of the cab. The fireman's body was found in the cab, and the brakeman's body was found in a ditch on the left side of the tracks near the point of the explosion.

To read the full report, visit the link above.

Enjoy,

* JB *
Agent at a very snowy Clicquot

Anybody remember Ed King's fine article a few years ago in "Trains"? It was on the subject of boiler explosions, and he explained in detail what happens in a second or two. I believe it was in this article he mentioned the fact that more men had walked on the surface of the moon, than had survived locomotive boiler explosions.