Question about steam engines

1) There was NO "blow up"!

2) Even with 3 or 4 4" diameter safety valves, there is no way ANY "boiler explosion" could be prevented, should the boiler "run out of water". The safety valves are only an audible warning to the Fireman that he has exceeded the designed maximum pressure for THAT locomotive. The Fireman must then adjust his firing rate and feed water input rate accordingly.

3) A boiler of that sizes takes a long time to "run out of steam", thus if the throttle is open it will keep moving.

The 1225's boiler did not blow up. In fact, the engine is in the midst of an extensive overhaul right now. She had a couple of flues let go in 2009, but that is an entirely different scenario than an explosion.

If a boiler does blow, it is not due to excess pressure. That is what the safety valve is for, to limit the pressure to the rated pressure of the boiler. A low water event in a boiler results in an explosion because the steel in the crown sheet has no water behind it to absorb the heat, so it gets soft and pulls away from the staybolts. In other words, it starts to melt.

The analogy here is a pan of water on the stove. As long as that pan has water in it, you can turn the heat up as high as you want and all it does is boil the water. If the pan runs dry, what happens? It melts!

...and what happens when it melts is that all that water in boiler comes in contact with the hot air of the fire, and tries to all turn into steam all at once. One square foot of water becomes something like 1700 sq. ft. of steam, so if you have a boiler full of water that all becomes steam in an instant, it creates an explosion that can be amazingly powerful!!

During the 91 convention a problem developed with the 1225 during the doubleheader to Hinton. A crack in one of it's thermic syphons developed and made firing the locomotive very difficult.

From Montgomery on the 765 handled the train pretty much by herself for the rest of the trip. I'm a little biased towards the 765 but that feat showed why she is one of the best out there!!

I believe this is what he was thinking of:

http://www.ntsb.gov/Publictn/1996/SIR9605.pdf

It was in the 12-hundreds anyway...

Opps!  My link has worn-out I guess.  Anyway I'm thinking he was referring to the 1995 incident with the Gettysburg 1278.

Jon

Your are partly correct, Stix.

It is the release of the pressure that causes all the water to flash to steam. At 200 psi, water boils at 388 degrees F. If that pressure is suddenly released due to a crown sheet failure, the water is way above 212 degrees F, which is the temperature where water boils at atmospheric pressure. With the sudden release of pressure, all of the water instantly flashes to steam, and that's when things come apart.

And there was the C&O Allegheny #1642 that had a crown sheet failure down in Hinton back on June 10 1953.

This is what you're seeing if you've ever seen a blowdown in action. The blowdown isn't releasing steam from the boiler--it's releasing 300+ degree water into the atmosphere, where it is instantly exploding into steam.

Excellent explanation!

That 300 degree water, blasting out of the very bottom of the boiler, is also carrying a lot of scale and sludge with it.

Thanks Rich and everyone for the explanation. I did a little research today and the one I was thinking of was the crown sheet failure at gettysburg( Can't remember the engine number ) It showed a diagram of what happened and like you guys said the crown sheet was so soft it sagged inward .
Rich they mentioned the boiler and gauges hadn't been cleaned properly so the fireman had no way of telling how much water was actually in the boiler.
A lot more to a steam engine than people think.
David

That's what tri-cocks are for, to verify the water glass is correct or in case it gets clogged or broken.

Rusty

There was also no working light in the cab to read the gauges, and they were pulling a dinner train at dusk.

Jon

There were so many FRA defects on that Gettysburg locomotive, you simply wouldn't believe it! Even the injector wasn't putting water into the boiler, so when they "topped the hill", even as little as their hill was, the water "sloshed" forward, exposing the crown sheet and the rest is history. The ONLY reason that the whole boiler didn't actually blow up, was the fact that it was a Canadian locomotive, which were/are designed to have the crown stay bolts "pull through" and thus put out the fire, while relieving most of the pressure. However, the fire was then blown into the cab and all that steam and hot coals burned the crew members. They did live, though.

 Basic Thermodynamics.

A BTU is defined as the amount of heat require to raise 1 lb of water 1 degree Farenheit

1 lb of 50 degree water to a boiler would require 162 BTU of heat to Reach Boiling point at 1 Atm pressure (14.7lbs/square inch) open vessel at sea level.

Latent heat of vaporization for water. (970 BTU per Pound)  Is the amount of heat required to take one pound of water at boiling point (212 degree F)  to one pound of steam still at (212 degree F) in an open vessel, 1 Atm pressure.  A lot more heat energy here.

Put this in a containment vessel the energy no longer has the ability to change volume, So both temperature and pressure change. Suddenly breach the containment and volume  re-enters the picture.  At one Atm pressure normal expansion of water (liquid) to steam(gas) is about 1760 times as has been mentioned. That would be done by the Latent heat of vaporiztion 970 BTU's per pound.  The pressure containment vessel allows for a lot more energy to be packed into the one pound of steam, as Rich mentioned. With Super heaters, I'm guessing easily 600 to 700 degree dry steam is available. ??Approaching double the amount of energy per pound of steam???  So the rapid expansion on failure could easily double the 1760X.

Jack I think the engineer on the Gettysburg tragedy died about 6 months later of his injuries. The two fireman from the report bailed quickly but the engineer stopped the train before exiting. 

Very hot water 140 degree F can do human damage. The steam released from a breached vessel is much hotter and unfortunately those exposed also breath this very hot gas.

NTSB report on the Gettysburg tragedy

Simplified report on the failure.

The locomotive is part of Jerry Jacobson's Age of Steam collection, Sugarcreek, Ohio. 

For those international participants, I can change this to Joules/Calories, grams and degree C (Celcius) if you request.  Some browsers do this automaticly.  Done in a true American spirit of insane measuring systems that cost us millions if not billions every year.         

When locomotive boiler explosions have occurred, they have left no doubt.  The normal result is that the entire cab, and anyone in it, is blown off of the boiler, along with the smoke box door, appliances, boiler jacketing and insulation.  What you typically see remaining is a "naked" boiler sitting on the frame and drive wheels (or on the ground) some distance from where the explosion occurred.

"Back in the day" there were thousands of cases where an engine crew decided to not take water (usually to make a run for a better location to take siding for a Regular Train) and later unplanned delays left them without even a bobble in the water glass, running for the next tank on very low water and sudden religious conversions.  In almost all cases, the boiler did NOT explode, because there is still a little bit of water left below the water glass.  

You can find the investigation and report about 1642 on the web.  Very interesting reading.

I read the full NTSB report and it said the engineer was still in rehab 9 months after the accident .So going by that he didn't die.

David

In 1978 I was helping to remodel some homes here in Roanoke that were right next to the N&W yards. Up in the attic of one of them I found a book titled "The Care and Maintenance of the Baldwin 4-6-0 Locomotive" and I think the copy write was 1910.
The guy who owned the homes said I could have it. I thumbed thru it but didn't understand most of it. I know it's still at my mom's in her attic LOL
maybe when I'm over there I need to get it and read it.

David

Now that would be a very cool book to have!  Nice find.

Rich wrote:

"If a boiler does blow, it is not due to excess pressure. That is what the safety valve is for, to limit the pressure to the rated pressure of the boiler. A low water event in a boiler results in an explosion because the steel in the crown sheet has no water behind it to absorb the heat, so it gets soft and pulls away from the staybolts. In other words, it starts to melt.

The analogy here is a pan of water on the stove. As long as that pan has water in it, you can turn the heat up as high as you want and all it does is boil the water. If the pan runs dry, what happens? It melts!"

And later on, added:

"It is the release of the pressure that causes all the water to flash to steam. At 200 psi, water boils at 388 degrees F. If that pressure is suddenly released due to a crown sheet failure, the water is way above 212 degrees F, which is the temperature where water boils at atmospheric pressure. With the sudden release of pressure, all of the water instantly flashes to steam, and that's when things come apart."

Wouldn’t it be great if school teachers (grade, high, college) would explain physics principles as clearly as Rich did?

Alex

I didn't know that schools EVEN teach basic science & physics anymore. I remember back in the 1950s, High School Science was a lot of fun.

Jack, my sister who retires in a few month tells me the top 10% of high school kids are doing well.  There is some light at the end of the tunnel, yet.  My four kids at college also did very well.  I was impressed.        

Here's a video of a lot of cab shots of 1278 acouple years before her crownsheet failure.

Thank you, Alex. Some say I missed my calling. I don't know. I sure didn't do all that well in school as a student!

Where is the video?

The last explosion of an "in service" steam locomotive was N&W Y-6 2-8-8-2 #2153 at Wytheville, Va. on N&W's Bristol Line in December 1955.

The water was nine inches below the top of the crown sheet; the boiler did not leave the frame because there was only 130 pounds of steam.  The cast frame of the high-pressure engine was broken right behind the cylinders.  The engineer, fireman and a student brakeman were killed. 

I can refer you to an article entitled "Big Bang No Theory" that appeared in TRAINS a few years back; it was reprinted in the BULLETIN of the National Board of Boiler and Pressure Vessel Inspectors shortly thereafter.

EdKing

Does anyone know what was done with the Gettysburg locomotive after the explosion?  I rode behind it many times over the years.

Everything you need to know:

http://www.ageofsteamroundhouse.com/loco1278.html

Jon 

The internet is an amazing thing. there's no limit to what you can find.
N&W 2153 after the crown sheet failure.

David

It is amazing what pressure can do.

How close to a gas is superheated steam.  Is it possible to have steam get so hot it does turn to a pure gas.

Huh?

A couple of things come to mind???

(1.) Super heated steam is an attempt at eliminating any saturation or existing liquid in the steam (already a gas). The more energy present the more that energy becomes mechanical energy via the controlled(edit) explosion(expansion) in the cylender/piston.  

(2.) Can you get it hot enough to seperate Water (steam) into Hydrogen and Oxygen? I would say no not in the confines of the pressure vessel discussed here. I could be wrong on this.   

According to this Wikipedia article, water breaks down to hydrogen and oxygen through thermolysis (thermal decomposition) at 2500 degrees C (4532 degrees F). 

Andy

I always thought that the "gas" coming out of the teapot was steam, which you really can't see until it condenses into visible vapor.

And we did that at Three Mile Island nuclear plant, near Harrisburg, Pa in the 1970s  We were really lucky.