In the late 19th century, The Pennsy tried to intentionally blow up a boiler by spraying cold water on a red-hot crown sheet.
Nothing happened.
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In the late 19th century, The Pennsy tried to intentionally blow up a boiler by spraying cold water on a red-hot crown sheet.
Nothing happened.
Geeze, after reading these messages, to think I actually fired one of these tourist RR teakettles for a one time afternoon! Wow , I said "how hard can this be, what can possibly go wrong" (babe in the woods attitude or stupid)!!
traindavid posted:I think the fallacy of that test is the cold water. The boiler water is superheated (above 212) when it hits the overheated crown sheet, and requires much fewer caloric units to cause it to flash into steam. But, I'm not an engineer! Just talked to a lot of them.
How does water that is already over the boiling point "flash to steam" upon hitting a hot crown sheet? Besides, since it's under pressure, by definition it can't "flash to steam."
Normal, 1 atmosphere pressure. 1 gram water takes 1 calorie, heat, to raise the temperature 1 degree C, (Celsius)
Change of state (Vaporization), 1 gram (liquid) water, at 100 degrees C, to 1 gram of steam (gas) at 100 degrees, 540 calories per gram.
540 times the energy is involve in the change of state. liquid to a gas. Super heating by increasing pressure adds energy to both the change of state and temperature increase.
The discussion continues about saturate steam. Steam with a lot of liquid water still mixed as a solution. Super heater tubes allow for the steam to be in effect, dried out, more energy added to the gas, by further changing the remaining liquid, part of the saturated solution, to gas.
Interesting machine as it evolved. Those super heater tubes would not have a lot of visible liquid in them.
Water under 200 PSI boils at ~387 degrees. The water around the firebox and in the front part of the boiler can be at 380 degrees and be liquid....
Chain of events... crown sheet uncovered, crown sheet (which is the very top of the firebox for those unsure) gets soft from the 2500 degree fire below it. Metal on crown sheet starts to bow and being soft, starts pulling away from the stays. The 200 psi(or higher depending on design and working pressure) exerts thousands of pounds of force on the soft metal bowing it even farther away from the staybolts until the metal ruptures into a large tear. The intial burst of steam blows into the firebox, out through the bottom of the firebox and some through the firedoor. Those in the cab never notice this burst of steam, because a second later, water that surrounded the firebox, at 380 degrees, INSTANTLY turns to steam. This massive flash of water to steam cannot be contained by even the 1/2 inch sheets of steel and usually the exit of the force of the steam is through the firebox. The resulting thrust (equal and opposite reaction) lifts the whole boiler up and off the running gear/frame. Some times large pieces of boiler sheet are ripped off and thrown large distances. I used to have a picture of a SP engine that blew up in a roundhouse after class repairs. It destroyed most of the roundhouse and threw a 3 ton piece of steel 1/4 mile from the roundhouse.
traindavid posted:My assumption (danger, assumption here!) is that the hot water, at an elevated temerature only needs to be raise a few degrees to become steam
This is where your assumption fails: Water in a boiler under pressure is already above boiling point--often by hundreds of degrees. The reason it doesn't turn to steam is because it's under pressure--even if it sloshes onto an exposed crown sheet.
steam fan posted:Water under 200 PSI boils at ~387 degrees. The water around the firebox and in the front part of the boiler can be at 380 degrees and be liquid....
Exactly - when an dry, overheated furnace or crown sheet fails, suddenly water that's liquid under pressure finds itself at closer to atmospheric pressure and flashes to steam; so the whole pressure/temp/volume thingy corrects itself with disastrous results. Here's a fire-tube boiler explosion aftermath showing the collapsed furnace sheeting and exposed tubes. These are the incidents that send entire package boilers flying through walls, as can be seen.
The flash of steam is because of the reduction of pressure as the boiler is exploding. Water is a liquid at 200PSI and 387 degrees but reduce that pressure even a little and 387 degree water turns to steam and expands. That stored energy has to go somewhere as the pressure lowers.
traindavid posted:One thing not mentioned here is the results of the instant heating to boiling point of the water that sloshes onto a very hot crown sheet; this is what initially raises the boiler pressure far beyond its design pressure.
This is an old wives tale and is not true.
Rich, You realize you are telling me that Santa doesn't exist?
OK, but I still say "My American Flyer is better than your Lionel!"
steam fan posted:Water under 200 PSI boils at ~387 degrees. The water around the firebox and in the front part of the boiler can be at 380 degrees and be liquid....
Chain of events... crown sheet uncovered, crown sheet (which is the very top of the firebox for those unsure) gets soft from the 2500 degree fire below it. Metal on crown sheet starts to bow and being soft, starts pulling away from the stays. The 200 psi(or higher depending on design and working pressure) exerts thousands of pounds of force on the soft metal bowing it even farther away from the staybolts until the metal ruptures into a large tear. The intial burst of steam blows into the firebox, out through the bottom of the firebox and some through the firedoor. Those in the cab never notice this burst of steam, because a second later, water that surrounded the firebox, at 380 degrees, INSTANTLY turns to steam. This massive flash of water to steam cannot be contained by even the 1/2 inch sheets of steel and usually the exit of the force of the steam is through the firebox. The resulting thrust (equal and opposite reaction) lifts the whole boiler up and off the running gear/frame. Some times large pieces of boiler sheet are ripped off and thrown large distances. I used to have a picture of a SP engine that blew up in a roundhouse after class repairs. It destroyed most of the roundhouse and threw a 3 ton piece of steel 1/4 mile from the roundhouse.
Was that not at the San Antonio roundhouse?
Whena boiler fails, is it not a boiling liquid vapor explosion?
Kelly Anderson posted:steam fan posted:I used to have a picture of a SP engine that blew up in a roundhouse after class repairs. It destroyed most of the roundhouse and threw a 3 ton piece of steel 1/4 mile from the roundhouse.
That was not a low water event, but an over pressure event. A new employee was assigned to set the pops without training or supervision. The investigation uncovered that the steam to the pressure gauge had been shut off at the boiler, the pops were screwed down until the springs were solid, and that some crown bars had been torn in half. Tensile testing on other, intact crown bars showed that the boiler pressure may have reached 600 PSI.
Well, I guess on the bright side (if you can call it that, considering) proved the designers built in a good safety margin in that boiler, though what a way to find out it was valid.
This is a great thread and helps me understand why the guy operating the train is called an "engineer" and not a pilot or driver etc. Seems to me that a good engineer in the day would have to know a fair amount about thermodynamics either by training or experience. That had to be a tough job keeping an engine running efficiently while at the same time being mindful that you could blow it up if you make a mistake.
This has certainly been an interesting and educational post.
The picture on the original post shows a picture with the boiler tubes pushed out the front of the engine. Was this caused by something other than crown sheet failure or were the tubes pushed forward by the explosion?
If the crew knew the crown sheet was dry how long would they have to get away?
Was there any way to extinguish the fire if they suddenly realized they were dangerously low on water?
Douglas
rrman posted:Well, I guess on the bright side (if you can call it that, considering) proved the designers built in a good safety margin in that boiler, though what a way to find out it was valid.
The CFR states that the boiler is to be built with a safety factor of 4 (as in, it should be able to withstand a pressure four times its maximum allowable working pressure).
Scott T Johnson posted:Seems to me that a good engineer in the day would have to know a fair amount about thermodynamics either by training or experience.
If you ever get a chance to look at any of the old steam locomotive textbooks, they look more like math books.
smd4 posted:The CFR states that the boiler is to be built with a safety factor of 4 (as in, it should be able to withstand a pressure four times its maximum allowable working pressure).
To have a Safety Factor of 4, the tensile strength of the steel is divide by four prior to doing the calculations. The tensile strength is where the metal actually fails under tension. Therefore, the theoretical bursting pressure would be four times the Maximum Allowable Working Pressure. I wouldn't hydro test a boiler built with a safety factor of 4 to 4x its MAWP with the expectation that it wouldn't burst... there are a lot of variables that are impossible to account for, which is why there is a healthy Safety Factor involved in boiler design. I know this may seem a bit pedantic, but it is a very important distinction to make.
This does not take into account the yield strength of the steel - the point where the steel begins to stretch before it breaks - which is why hydro testing is typically done to 150% of MAWP. I can't speak to the FRA regs on this particular point, but hydro testing a commercial power boiler at too high of a pressure is grounds for condemnation.
On a coal burner, dumping a bunch of coal on the fire bed will also cool it down.
I believe you can tip the grates far enough with the grate levers to dump the fire into the ashpan.
I was under the impression you hydro to 125% MAWP.... at 70 degrees.
CFR says water temp for hydro has to be between 70 and 120 F and at 25% over MAWP.
Dumping a fire by shaking the grates might take some time.
125% is correct for a locomotive boiler under FRA. My brain had reverted back to ASME Section 1 that is (or perhaps was - I believe there were considerations for revision and I'll readily admit I'm not current) calling for up to 150%.
All of this just cements further in my mind that what I always thought was true. "If you don't belong in the cab, you shouldn't try to get there." I always try to stay out of the way.
smd4 posted:CFR says water temp for hydro has to be between 70 and 120 F and at 25% over MAWP.
Dumping a fire by shaking the grates might take some time.
I'm pretty sure you can crank them wide open with the shaker bar... Some engines have openings of 7 inches or so between grates when moved to the full open position.
steam fan posted:I believe you can tip the grates far enough with the grate levers to dump the fire into the ashpan.
It's a little more than tipping the grates, the fire isn't going to just fall out. You've got to shake the grates vigorously to get everything to dump out and do it for each grate.
On the locomotive I'm used to (Frisco 1630,) that's placing the shaker bar on each grate stud, swinging it left and right with gusto until the grate is empty. Repeat for each of the five other grates.
Rusty
traindavid posted:Nowadays we put major emphasis on book learning, back then experience was the more prevalent teacher.
Yes, experience was important. But the hundreds, if not thousands, of books, periodicals, magazines and treatises written about locomotive running and management give lie to your statement.
smd4 posted:traindavid posted:Nowadays we put major emphasis on book learning, back then experience was the more prevalent teacher.Yes, experience was important. But the hundreds, if not thousands, of books, periodicals, magazines and treatises written about locomotive running and management give lie to your statement.
Huh? There's no question that "hands on experience" is a much better teacher than articles about running a locomotive. I know quite a few guys that could perfect marks in the written test but couldn't run a sewing machine. (come to think about it I'm not sure I could run a sewing machine)
I guess when I think of running a steam engine I think of all the engineers that lived on our street when I was a kid including my dad. Later I got to work withsome of then when I started as a brakeman ...There were just ordinary folks. Most didn't make it through high school but they took pride in their job as enginemen.
You're right. No one read anything back then.
Interesting thread
Gregg posted:Huh? There's no question that "hands on experience" is a much better teacher than articles about running a locomotive.
I didn't say experience wasn't a better teacher. Only that published material was far more prevalent and utilized than trandavid seems to think.
"The practice of applying to books for information concerning their work, is rapidly spreading among engineers and mechanics of this school-spangled country..."
--Angus Sinclair, Locomotive Engine Running and Management, Jan. 1, 1885
"There is a silly prejudice in some quarters against engineers applying to books for information respecting their engines. Engineers are numerous who boast noisily that all their knowledge is derived from actual experience, and they despise the theorists who study books, drawings, or models in acquiring particulars concerning the construction or operation of the locomotive parts. Such men have nothing to boast of. They never learn much, because ignorant egotism keeps them blind. They keep the ranks of the mere stopper and starter well filled."
--Angus Sinclair, 1899
Steve, my statement didn't say that there weren't books published, nor knowledge known, but that the average engineman learned from experience; it was knowledge handed down, mostly by on-the-job training. Some of the folks read those books, probably most backshop managers too. Many of us fail to know how many folks were employed in building, servicing, rebuilding and running all those steam engines. My hometown had a roundhouse, and a backshop and three shifts working around the clock keeping the locomotives running. Today, although the rail line is still as busy, and the crews still change there, there are no buildings left, save the two-stall "mallet shed" (which is empty with no tracks running to it). The turntable is there, mostly to turn helper engines, but all the locomotive servicing is done far, far away now. The town is a ghost of its former self.
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