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RRMN: ROFL!! Yes, I can understand that. It's always good to consider "your" boiler as a bomb, safe when handled properly, but !!! I've had a few cab rides and even (very short) throttle time, but I'm always keeping an eye on the glass. Most of my boiler experience has been boats and cars. Even the live steam models can be dangerous, although usually the safety factor is way overbuilt on them. Usually, I say! Actually, I think the fireman's job is more work than the engineers, more so on solid fueled kettles.
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.

Last edited by Mike CT
Steve, as I've said, I'm not an engineer, and with dyslexia, I gave up on complex math, although Mike has posted the formulae. 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--although it will still take some heat to do it; the cold water, OTOH has to be raised to the temperature to boil--say the boiler pressure is high enough that the water has to be at 220 to boil, the cold water is at (assuming "cold" at 60 degrees, that's 160 degrees difference, requiring much more caloric energy to reach the flash point. Chris also points out the difference between saturated steam and superheated steam, which is a lot drier and holds more expansive energy. These old steam engines are a fairly complex machine, oftentimes on the leading edge of available technology.

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.

SAMUT PRAKAN Boiler explosion 3

Last edited by Firewood
Steam fan points out what I was trying to say, that once the boiler pressure drops a little bit, the remaining superheated water flashes over to steam. I was told that the introduction of some of that water onto an overheated crownsheet can start the catastrophic failure, but that could be just railroad lore. No matter how it happens, low water can ruin your whole day.
Thinking about Steamfan's explanation explains why the Gettysburg failure didn't result in a catapulting of the boiler off the frame. The Canadian style button head stays apparently kept the crown sheet from opening full up, so the pressure drop was less and more of a "contained release."; albiet still a disaster. Given the stresses the boiler was put under during that event, has anyone suggested that the boiler could be rebuilt? Although the shell is intact, I'm wondering if the event may have compromised some of the joints. I know, I'm getting quite a bit afar from the original subject. And yes, I'm willing to accept that my assumption on water flashing on the crownsheet, though I've held it for years, could be wrong!
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?

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).

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.

Last edited by WindupGuy
I will admit I didn't read that carefully enough myself, although wondering what would cause that failure, being a very substanial portion of the boiler. Was this a failure of tube swedging, crack in the front tube sheet, or a failure of the barrel joint at the front course? Does anyone have easy access to the accident report? And what measures were taken afterwards to designs? Oh, and in answer to Douglas' question on the fire, with an oil burner, you just shut down the oil, with coal, hmm, close the dampers and somehow wet the fire (although I wouldn't stay in the cab myself! Oh, on oil burners there's usually a fuel shut off "quick release" valve on the tank top.
Pennytrains and Scott J. both alluded to something that was very true "back in the day" (and some say is still true today). Some Engineers were much better than others. Some seemed to be able to "feel" what their locomotive needed for maximum efficiency (cut-off, throttle setting, communications with the fireman) and were a joy to work with, whereas other were ones one tried to avoid working with. Some were more knowledgeable about their charges than others too. Nowadays we put major emphasis on book learning, back then experience was the more prevalent teacher.
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.

Last edited by smd4
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.

 

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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