Good morning
I have a quick (dumb) [D)] question. Do the tubes in the picture carry water or heat?
The reason I ask, is that a long time ago I remember something about the tea kettle style locos had a tendency to blow up and that water in tubes aleviated that problem.
Thanks [:D]
Lee
Heat (hot gases from the firebox). They increase the “heating area” of the boiler. making it more efficient.
Howdy, Lee,
That’s a typical fire-tube boiler, the type originally designed by George Stepehenson and brought close to to perfection by the N&W Roanoke design team. Note the two sizes of tubes - the larger ones are called flues and were intended to contain superheater loops.
The two ‘bugeye’ tubes at the top carried steam from the superheater header (that boxy-looking thing to which they are attached) to the valve chambers above the cylinders.
A very few locomotives were built with either water tube boilers or water tube fireboxes. While ideal for fixed installations or maritime use, water tube boilers proved unable to stand the slam-bang rigors of rail service without frequent (expensive) maintenance. I would guesstimate that well over 99% of the world’s steam locos were of the type seen here.
As for the tendency to explode, there were several common reasons:
Early locomotives were designed mostly by guesswork, and the materials used were not consistent. A steam boiler will yield at its weakest point, so if one spot in the boiler shell was flawed - BLOOIE!!! The lap-riveted longitudinal joints in old boilers were also prone to failure, which is why the design was changed in later years.
One early boiler explosion was caused by an uninformed fireman who tied the safety valve down because it was making too much noise. (He had no idea that it was making noise because he was over-firing the vertical wood-burning boiler.) Safety valve failure, and boiler overpressure, resulted in boiler failures and stringent inspection/test requirements for safety valves.
The most common failure leading to explosion was failure to keep water over the crown sheet (top of the firebox.) If the crown sheet
I have been told the reason boilers explode is not a rise in pressure, but a sudden drop.
The water when heated absorbs a lot of energy. But the increase in pressure in the boiler keeps the water in a liquid state, a condition called super heated, it is liquid but hotter than the boiling point. The throttle lets some of the steam out, lowering the pressure in the boiler slightly, allowing some of the superheated water to turn into steam.
When a portion of the metal boiler fails, it leaks and actually drops the pressure in the boiler quickly.
At the lower pressure the superheated water cannot remain liquid and ALL the water instantly turns to steam and expands tremendously, causing the boiler to explode.
Thanks Dave & Chuck
Very informative replies. I was trying to explain to a non modeling friend how the boilers work. We were looking at a boiler with the smoke box off and he ask me about the tubes. Thankfully I had the correct answers even though I started second guessing myself later.
[:D]
Lee
Superheating as I understand it is actually more a process where the steam in the steampipes is sent thru the firebox a second time. This second heating causes the steam to change from “saturated” or “wet” steam to become superheated or “dry” steam.
Adding superheating to an engine could increase it’s power by IIRC 10-20% with no other modifications.
Thank You.
More often, a boiler will explode because of a rupture in the boiler. The explosion is energized by the fact that you have a large quantity of water suddenly flashing to steam when the water escapes from the pressure vessel into the atmosphere. The expansion rate when water goes from liquid to steam is around 1:1600, where 1 gallon of water will become 1600 gallons of steam. The drop in pressure doesn’t cause the explosion, but once initiated, it adds the energy to it.
Also, your use of the term “superheated” in reference to steam locomotives is misleading. The water in the boiler will convert to steam at a higher temperature because of the pressure in the boiler, so its boiling point is above 212 degrees.
Even with the throttle wide open you cannot lower the pressure in the boiler fast enough to cause that kind of hyper-steaming (I don’t know the real phrase) As is stated earlier, if a flue tube or crown sheet would ever become not covered in water it would almost instantly turn plastic and rupture and allow the boiler to fail. Crown sheet failures would be much more impressive then say a flue tube or stay-bolt failure.
Depending on date, size and location steam loco boilers mostly work at between 120 amd 250 lbs pressure. To get from even the lower pressure to a negative pressure sufficient to cause an implosion without the crew noticing would be quite an achievement. If it were possible through the fast action of a valve or whatever the design would be prohibited. It would, after all,mean that a loco boiler could implode without warning at any time.
Look at it another way. When a tank car is discharged without the lid being opened or relief valves set then the whole body collapses inwards as can be seen in various pics on the web. The visible damage is entirely different from a boiler explosion. Imploded cars do not get launched hundreds of yards… even if the employee that caused them does - by his supervisors boot…
Unfortunately firebox crown failure does not always result in instant death for the footplate crew. I have read several accident reports in which crews died several days later from their burns. This was the principle reason why British loco cabs largely remained open cabs until about 1940-45. The crews prefered putting up with the weather and being able to get out fast - or even to be blown out - rather than the risk of being boiled alive.
[:)]
Sorry, my last class in thermodynamics was over 30 years ago. 
the term superheated means only that a substance has absorbed enough energy to change from one state of matter to the next, it doesn’t matter if we’re talking about water or iron. Now as for a boiler, any uncontrolled venting of the contents of the pressure vessel is called an explosion. In a boiler when you open the throttle the pressure doesn’t drop measurably (at first) but several things happen. First the volume of water in the boiler will suddenly increase. if you watch in the water glass you will see the water level suddenly rise by a half to a whole inch! this is normal and we call it “swell.” As steam is drawn off through the throttle you don’t suddenly run out of steam because the water in the pressure vessel is still water only because it is under pressure. As steam is drawn off additional water converts into steam to take the place of the steam being drawn off. This also is normal and is called “replenishment.” Why doesn’t a boiler explode when steam is drawn off? because when steam is drawn off there is restriction called back pressure from whatever work is being done. In an uncontrolled venting of the pressure vessel there is no back pressure, there is nothing to prevent the contents from converting itself in its entirety from water to steam, to get an idea of how much power we’re talking about here watch a boiler being blown down sometime, and don’t stand too close!. In the case of an explosion, lets use a recent example. about 10 years ago a steam traction engine operating at 40 psi blew up from a thinned and leaky crown sheet. There was a tiny leak of water coming through the crown sheet where it had eroded from old age, the water converted into steam and replenishment began inside the boiler, the leak became a vent and steam began to exit in an uncontrolled manner. it only took a few seconds for the vent to become a tear and the entire contents of the boi
i just finished reading about a boiler explosion which occoured in Watertown, NY on the Rome Watertown & Ogdensburg RR. A locomotive which was in steam was being used to assist in steaming another locomotive which had a cold boiler. The cold locomotive had just had a fire started in it, and a pipe was used to connect one locomotive to the other. apparently an inexperienced worker opened the valve on the locomotive in steam all the way and steam went roaring into the cold boiler. the cold boiler stressed as it tried to expand as the steam and heat roared into it. suddenly, with a ripping sound the steam dome detatched itself and went skywards, followed by the dropping of the crownsheet of the hot locomotive as the water level dropped. two locomotives were destroyed, six men were killed, a wall adjacent to the fiasco was blown in, (injuring several unsuspecting shopmen) and a nearby house was destroyed when the steam dome landed on it.
[quote user=“toot toot”]
the term superheated means only that a substance has absorbed enough energy to change from one state of matter to the next, it doesn’t matter if we’re talking about water or iron. Now as for a boiler, any uncontrolled venting of the contents of the pressure vessel is called an explosion. In a boiler when you open the throttle the pressure doesn’t drop measurably (at first) but several things happen. First the volume of water in the boiler will suddenly increase. if you watch in the water glass you will see the water level suddenly rise by a half to a whole inch! this is normal and we call it “swell.” As steam is drawn off through the throttle you don’t suddenly run out of steam because the water in the pressure vessel is still water only because it is under pressure. As steam is drawn off additional water converts into steam to take the place of the steam being drawn off. This also is normal and is called “replenishment.” Why doesn’t a boiler explode when steam is drawn off? because when steam is drawn off there is restriction called back pressure from whatever work is being done. In an uncontrolled venting of the pressure vessel there is no back pressure, there is nothing to prevent the contents from converting itself in its entirety from water to steam, to get an idea of how much power we’re talking about here watch a boiler being blown down sometime, and don’t stand too close!. In the case of an explosion, lets use a recent example. about 10 years ago a steam traction engine operating at 40 psi blew up from a thinned and leaky crown sheet. There was a tiny leak of water coming through the crown sheet where it had eroded from old age, the water converted into steam and replenishment began inside the boiler, the leak became a vent and steam began to exit in an uncontrolled manner. it only took a few seconds for the vent to become a tear and
Thank You.
[quote user=“TomDiehl”]
[quote user=“toot toot”]
the term superheated means only that a substance has absorbed enough energy to change from one state of matter to the next, it doesn’t matter if we’re talking about water or iron. Now as for a boiler, any uncontrolled venting of the contents of the pressure vessel is called an explosion. In a boiler when you open the throttle the pressure doesn’t drop measurably (at first) but several things happen. First the volume of water in the boiler will suddenly increase. if you watch in the water glass you will see the water level suddenly rise by a half to a whole inch! this is normal and we call it “swell.” As steam is drawn off through the throttle you don’t suddenly run out of steam because the water in the pressure vessel is still water only because it is under pressure. As steam is drawn off additional water converts into steam to take the place of the steam being drawn off. This also is normal and is called “replenishment.” Why doesn’t a boiler explode when steam is drawn off? because when steam is drawn off there is restriction called back pressure from whatever work is being done. In an uncontrolled venting of the pressure vessel there is no back pressure, there is nothing to prevent the contents from converting itself in its entirety from water to steam, to get an idea of how much power we’re talking about here watch a boiler being blown down sometime, and don’t stand too close!. In the case of an explosion, lets use a recent example. about 10 years ago a steam traction engine operating at 40 psi blew up from a thinned and leaky crown sheet. There was a tiny leak of water coming through the crown sheet where it had eroded from old age, the water converted into steam and replenishment began inside the boiler, the leak became a vent and steam began to exit in an uncontrolled manner. it only took a few seconds for t
This psuedo-science is almost as entertaining as Toot-Toot’s screen name. If the volume of water is going to suddenly increse due to the change in temperature, what causes this temperature change in large enough margin to cause this so called “swell?” Still not explained by the Physics of the situation.
As I said, your last sentence is correct, but the question is in how you got there.
lets say that a boiler is operating at 200 psi g. the temperature of water in the boiler is 381.79 * F. open the throttle. steam from the boiler fills the dry pipe and whatever appliance is being run. let’s say its a turbine, since i happen to have one right in front of me. The temperature of the steam measured at the nozzle is 368.41 * F. Difference of 13.38 * F.
i have 22 years in as a steam plant operator. i have run ships, a hospital, a power plant, and a few locomotives. if you want to discuss this further i’d suggest you read Steam Plant Operation by Woodruff and back channel me afterwards.
So how often does this boiler blow up when the temperature drops that much? Boiler temperature and pressure constantly fluctuate during operation and don’t cause the boiler to explode. Loss of containment cause explosions.
So how often does this boiler blow up when the temperature drops that much? Boiler temperature and pressure constantly fluctuate during operation and don’t cause the boiler to explode. Loss of containment cause explosions.
That’s what I said.
Now go back under your bridge.