Boiler Explosions (not just a lot of hot air)

[gabe]

I was taking water from my water cooler about 5 minutes ago and it led me to think of boiler explosions and water-injected boilers.

Question #1

My understanding of the system is: water is stored in the tender and fed into the injector, which in turn injects it in the boiler. Hypothetically speaking, if the tender runs out of water and—for whatever reason—there is no water to fill the tender, does the fireman have to just drop the fire to avoid a boiler explosion?

In the past, I always thought the steam engine would simply gradually lose power. However, it occurred to me now that the water line would dip below the firebox, causing the metal to be compromised, and the boiler would explode—hence, I think if a steamer were running low on water, the fireman would have to drop the fire to avoid a boiler explosion?

Question #2:

Speaking of boiler explosions, is it just me or did boiler explosions seem more common on larger locomotives? I know of instances where the water line dipped below the firebox in smaller locomotives, and there was no explosion—though the boiler was finished. But, in larger locomotives: finito. Is this my imagination, or is there a reason for this (higher psi maybe?)

Question #3:

God forbid a boiler explosion on one of today's steamers. I really hope every excursion railroad is careful about this and knows that the future of steam excursions rests in their hands. One explosion = no more steam excursions. Darn lawyers [;)]. Do current excursion locomotives carry any modern or advanced equipment to avoid a boiler explosion/detect a drop in water in the boiler?

Question #4

Is it possible for an engineer to rapidly “drop,” for lack of a better term, his boiler pressure? If he suddenly realizes his water is too low, does he have an emergency recourse?

Gabe

[chad thomas]

Good questions Gabe. Again, I'm no expert but I do know that if the crown sheet is exposed and heats up when water does again hit it , well say bye bye.
I think boiler explosions were more dramatic on bigger locos because of greater pressure being allowed to build up before catastrophic failure of the pressure vessel. I have read about the great distances a locomotive can be launched. I used to have a book on train disasters that had many photographs of boiler explosions. Some real wild stuff.
I would be interested in hearing what the old heads have to say about this.

[arbfbe]

Rule 1: Do not run low on water. Make sure the gauges (water glasses) are working properly and the injectors are working. There are two, normally only one is used, the other is a back up or used for short periods when the main one cannot keep up.

Rule 2: If rule 1 is violated, drop the fire, now, not later.

Rule 3: Keep the steam pressure you have, if you reduce it quickly the water boils faster lowering the level in the boiler even more exposing even more firebox and tubes. Do not apply cold water if the crown sheet is exposed.

Rule 4: Stop the train and get clear of the locomotive.

[kenneo]

Actually, most so-called boiler explosions are crown sheet ruptures. Excessive uncooled heat has caused the crown sheet to soften to the point where the boiler pressure forces the top of the firebox (crown sheet) to collapse down into the firebox and vent the boiler out through the firebox and taking the fire right along with it. Unfortunately for all involved, this includes the cab of the locomotive. The engine crew may never know what happened. For a certainty, they won't know it when it does happen.

If coal fired, you will have to drop the fire onto the ties. This causes Mudchicken fits, but lets you live to hear his fits. I prefer to listen. But Mudchicken is going to have to replace everything for several hundred feet, and like I said, he won't be happy.

If oil fired, simply turn off the oil. It won't take long for the fire to go out. You can aid the process by closing off all combustion air going into the firebox. Close the throttle and stop the train. Keep the pressure up as arbfbe said. Let the pops handle the situation.

And be patient. The Dispatcher is going to have to call out a tow for you and he is not going to be very happy. About as happy as Mudchicken. You just shut his railroad down for about 8 hours and took a locomotive out of service for at least two months or perhaps forever.

Hopefully, you got to the situation prior to the crown sheet being exposed. Remember also, that you can have several inches of water over the crown sheet and still have it exposed if the boiler pressure is permitted to drop - water will be making steam faster than liquid can flow in to replace the vanished liquid.

If you ran a water plug that you were supposed to fill up at, you won't be working for a steam operation ever again. They may be impressed by your action in saving lives and machinery, but the fact you permitted this to happen in the first place ... well.

[Anonymous]

There was an incident with a locomotive boiler explosion about 10 years ago in Pennsylvania. Here is the NTSB report on the incident if anyone is interested.

http://www.ntsb.gov/Publictn/1996/sir9605.pdf#search='NTSB%20report%20on%20steam%20locomotive%20boiler%20explosion'

[railroad65]

Didn't a excursion locomotive explode a few years back, mid 90's???

Railroad65

[Anonymous]

QUOTE: Originally posted by railroad65

Didn't a excursion locomotive explode a few years back, mid 90's???

Railroad65

Yeah, on the Gettysburg Railroad, near Gardners, Pennsylvania. Take a look at the link I posted in my previous post. It goes to the NTSB report on that explosion.

[jeaton]

I am not sure, but I thought the FRA revamped and tightened up the Reg's on steam locomotives, maybe because of that accident.

Jay

[Anonymous]

QUOTE: Originally posted by jeaton

I am not sure, but I thought the FRA revamped and tightened up the Reg's on steam locomotives, maybe because of that accident.

Jay

Yeah, they tightened up the rules.

[jeaton]

Getting back to Gabe-We can assume that the crown sheet on the water cooler was covered?

Jay

[Anonymous]

The incident at the Gettysburg was actually a RELATIVELY minor boiler explosion. (locomotive stayed on the track, boiler did not go airborne, no one was killed) As the NTSB report points out, what prevented a full fledged explosion from happening was the Canadian boiler design of alternating straight thread and button head crown stays. (see p22 of the report) In effect what happened was more of a controlled release rather than an explosion.

Regardless, the reason why the water level dropped so low in the first place was due to crew negligence and a false reading on the water glass due to scale blockage. This incident would have been avoided if the locomotive had been properly maintained and the crew had known what they were doing. In this case you cannot solely blame the firemen (there were 2)because the engineer is ultimately responsible for the water level on a steam locomotive.

Brennan

[Anonymous]

Yes, the Gettysburg Steam engine blew out it's saftey plugs because there was insufficient water in the boiler.

Last month I visited the battlefield and they had a Tourist poster featuring a F unit and a small "For sale" sign on the entire railroad.

Most of the recent "Lawyer'ing" versus steam engines stemmed from this accident.

[Anonymous]

Actually, the locomotive at Gettysburg was not equipped with fuseable plugs. What happened was a crown sheet failure. Read the report for the full story. (not as dry as you might think)

Brennan

[Overmod]

A little additional hot air:

#1. Keep in mind that the tender doesn't need to be "empty" to break flow to the injector or feedwater-heater lines. Likewise, grade can affect the working water level in the boiler (at least one class of locomotive, the NC&StL Dixie, had a plaque in the cab indicating the 'right' water level for working a grade). As indicated by previous replies, it isn't the tender water that matters, it's the boiler water. And it's the crown sheet that usually fails -- this sees by far the most heat from the fire, and for a variety of reasons isn't tolerant of overheating even for relatively short periods or over relatively small areas. Supposedly, thermic syphons a la Nicholson help keep water over the crown sheet when working low water, but in at least one explosion, 2-6-6-6 #1642 in 1953

http://www.chessieshop.com/gallery/showphoto.pl?id=39899

the Nicholson syphons kept pumping water over the crown sheet, but did so in an irregular pattern, leading to thermal cycling and quench cracking which may have accelerated the catastrophic failure when it started.

Yeah, the 'right' thing to do is drop most of the fire as soon as you recognize there's a problem with low water. Probably wise (especially with '40s-style weird nickel-alloy construction) to leave some heat going through the boiler structure to let it cool down and equalize instead of 'shocking' with a quick dump and open firedoor. (Also leave some heat in cold weather!)

More on this point in #4, but venting boiler pressure in ways available from the cab isn't going to help you much (and only if you've already dumped the fire). Remember that there is a large mass of overcritical water sitting in the boiler below effective crown level. If you start relieving the pressure, this will obediently start flashing to steam, giving a nice mass flow at 1500 to 1800 times volumetric expansion, until the heat in All That Water drops down to allow the pressure to fall. Meanwhile, the mass flow is being effectively throttled through whatever opening you used to vent the steam -- not likely to drop you far enough fast enough to unload the crown sheet as I think you were hoping.

arfbfe has got one of his points a bit backward (otherwise he's 'right on'; this isn't a criticism of him): very often, if you reduce pressure, you will see the water level in the gauge RISE, not fall, because the flashing on reduced pressure occurs throughout the volume of water in the boiler, not just at the heated points, and this produces lots of bubbles all through the water, which pushes the level higher. Yes, this effect tends to let water flow back over the crown sheet, and may give you a bit more time, but (as noted above) you'll also be providing more of an opportunity for thermal cycling of the crown-sheet metal, which I think should be avoided to the greatest extent possible. Something the engineer and fireman should both remember is that this rise in level on reduced pressure is NOT the same thing as having a proper water level -- it may be hard to remember this point in the kind of emergency atmosphere that having low water problems may produce for the engine crew!

#2 -- much more overcritical water in the larger locomotives, leading to more of a rocket effect through the developing point of failure. Higher pressure, as you indicate. Larger crown sheet leads to greater 'fragility' (and perhaps to larger area through which the evolving steam can jet). And (as in picture above) -- more rocket effect, the higher or further the boiler may go before it hits the ground or stops moving... just as with SUVs, you roll things a few times and fling them in the air, and they may be in poorer condition than if you just fenderbend 'em ;-}

#3 -- to my knowledge, there aren't any special (modern) monitoring devices or controls for low-water on modern excursion engines, although I'd be interested to know details of any. There was a variety of 'patent' devices for boiler water level and quality available back in the day, but the cost and technical tinker required to get many of these things to run effectively is probably beyond the interest or capability of most excursion lines. Hard to beat a Nathan and a pair of ears connected to an intelligent brain...

Of course, stationary boiler practice has had automated level control for many years. It's so much easier when you're sitting still and level and have access to 120VAC electricity... ;-}

I don't know what the current stage of legal opinion on the subject of safety systems is, but there is a point at which automated firing and water controls begin to cause problems, by making their operators complacent or by requiring counterintuitive or (perhaps dangerously) different-from-routine procedures under unusual conditions. On a working locomotive, where terrain and effective trailing load may vary wildly, or where speed may have to be cut to zero without warning at any time, the kind of system that would make a meaningful contribution to disaster avoidance *in the absence of intelligent active oversight* would be expensive and redundant; moreover, it would have to be carefully designed not to hamper normal working -- which would probably make it MUCH more complex and expensive...

#4 -- the "correct" answer is, of course, that an engineer should NEVER be "suddenly aware" that his water level is low. But reducing pressure isn't the first thing he should consider, since you aren't going to 'take the load off' quickly. (And if you did, you might introduce stress in the crown which might induce it to fail where just leaving it under pressure in the absence of firing wouldn't.) One thing to remember is that there's a limited supply of water in the boiler, and anything that vents steam is removing some of that supply. If you're reasonably certain you haven't had the crown exposed badly, you might consider a small controlled venting of steam to make the average water level rise, but (as previously noted) you're NOT going to be in the cab to turn the steam flow off again, and you don't want to drop either the water level or the effective pressure too fast.

As an intermediate stage to the 'catastrophe' theories above, might I suggest the following sequence if low water in the tender is 'suddenly' recognized or detected:

1) Determine whether the engine can be safely worked to a water source.

2) If not, get the engine to a location where service is easy (or the track won't be blocked) and it's safe to drop some of the fire.

3) Drop enough of the fire that you can maintain reasonable working gauge pressure for the pumps and auxiliaries -- I think this is often something like 50psi or so. If you take on water, you can then use the stoker or oil jets to recover.

4) Call somebody like your local fire department, who can often come out quickly with a truck that has a water tank (and can navigate offroad, as if to a brush fire, to get close enough to where you actually are. Only a few hundred gallons should be sufficient to allow you to work the train to where you'd intended to take water.

5) Keep the firedoor closed (and the speed and conditions right for a quick exit!) if you think there's a problem with any part of the boiler; even a little steam in the cab, or in your lungs, is dangerous. If you do see steam, DON'T BREATHE IT, even if there doesn't seem to be a lot or it's "low" pressure -- cover your nose and mouth with a cloth and get the h-ll out of Dodge as soon as you can once you have taken care that the train will stop (e.g., set the air). (High-pressure or superheated steam is invisible, and I won't go into how you detect its lethal presence, but if you get THAT anywhere in a locomotive cab, it's probably well too far along to help you much...)

[jchnhtfd]

Overmod -- sounds to me as though you have some practical experience with this kind of catastrophe? Hope not... but a superb explanation.

One thing for the rest of us to remember -- clearly -- is sort of buried up there, though: if you let the pressure off the boiler, boiling will occur throughout the boiler, not just at the top of the water. And enough water will boil until the water temperature is dropped to whatever pressure is maintained -- in the case of a crown sheet or substantail tube failure, atmospheric. Which will be most of the water. His bottom line advice -- if things look like they're getting out of hand, kill the fire, keep the firedoor closed, set the air, and get the h_ll out of Dodge -- is right on!

One might add that in modern haz-mat and fire work, there is a closely related catastrophe which is, if anything, worse and more spectacular: a BLEVE (Boiling Liquid Expanding Vapour Explosion). It has all the benefits of a boiler explosion, plus the resulting vapour cloud isn't steam, it's explosive.

My recollection is that the SP cab-forwards were peculiarly subject to boiler explosions, as the crown sheet was, of course, on the 'uphill' end of the engine and there were real difficulties in keeping enough water in there to keep it covered when working wide open.

[dldance]

The Uintah Railroad's #50 was a 2-6-6-2T articulated narrow gauge engine built by Baldwin for use on 7.5% grade and 66 degree curves. Baldwin built a special section of track to test the 66 degree curve capability, but had no way to test it on 7.5% grades. The first run of #50 up Baxter pass was uneventful and proved that #50 was a powerful, flexible performer.

However, its first trip down from the top of Baxter pass was much more exciting. As the engine transitioned from lesser grades to the 7.5% grade, the engineer and fireman both noticed the water guage showing less and less water until it showed the crown sheet might be uncovered. In the words of the engineer, they opened the feedwater pumps to force as much water into the boiler as possible, while at the same time he dumped steam to lower boiler pressure. That allowed sufficient water into the boiler to show on the glass. He limped the engine to the yard at the bottom of the grade and quit the railroad.

(I know that this is at odds with your recommendations, Overmod, but he had a full water tank t work with.)

The engine was immidiately embargoed. The railroad's own shops and Baldwin staff started with a drawing of the engine and drew a 7.5% grade line across the boiler and firebox. They determined that the crownsheet had not been uncovered - even though it looked that way on the glass.

The railroad shops then lowered the crown sheet by "several inches" and added a new steam dome near the rear of the boiler. Uintah's undelivered #51 was so modified at the factory by Baldwin. Both engines ran well through their remaining Uintah career and then the Sumpter railroad in Oregon, finishing life in Central America.

dd

[vsmith]

Question #1

My understanding of the system is: water is stored in the tender and fed into the injector, which in turn injects it in the boiler. Hypothetically speaking, if the tender runs out of water and—for whatever reason—there is no water to fill the tender, does the fireman have to just drop the fire to avoid a boiler explosion?

If the tender was suddenly found to be out of water and there wasnt a hole in the tank, the train crew would get fired. Even assuming a water line breakage, if their is sufficient water in the boiler continue for a short distance, the loco could be brought onto a siding and its fire quenched there. Dumping the fire was a big to-do, and was no gaurentee that it wouldnt blow because steel tends to stay hot once it gets hot

In the past, I always thought the steam engine would simply gradually lose power. However, it occurred to me now that the water line would dip below the firebox, causing the metal to be compromised, and the boiler would explode—hence, I think if a steamer were running low on water, the fireman would have to drop the fire to avoid a boiler explosion?

What your describing, the technical name I dont remember, is when the crown sheet is exposed due to low water, gets super heated, then either was water sloshed back onto it or the metal fatigues and fails resulting in a quick trip to heaven for the crew, there is nothing in the performance of the engine to indicate this as long as their is sufficient boiler pressure, the engine will perform normally, right up to the big kabloo-ee!

Question #2:

Speaking of boiler explosions, is it just me or did boiler explosions seem more common on larger locomotives? I know of instances where the water line dipped below the firebox in smaller locomotives, and there was no explosion—though the boiler was finished. But, in larger locomotives: finito. Is this my imagination, or is there a reason for this (higher psi maybe?)

smaller engine less pressure, less area of heating, small locos did blow up often quite regularley on the poorer maintained lines, its just they didnt make the frontpage news doing so. Also for alot of engines were pushed constantly to work, with low maintainence not helping, tube failures were most common and most didnt blow the loco off the track, just generally ruined everyones day, especially the boiler shop guys who now had to dissaemble the whole kit-n-kaboodle and find the fault

Question #3:

God forbid a boiler explosion on one of today's steamers. I really hope every excursion railroad is careful about this and knows that the future of steam excursions rests in their hands. One explosion = no more steam excursions. Darn lawyers [;)]. Do current excursion locomotives carry any modern or advanced equipment to avoid a boiler explosion/detect a drop in water in the boiler?

Grand Canyon RR, both locos have some modern requirements designed to prevent just this, perhaps the biggest is requireing 2 (two) water tubes, one for the engineer and one for the fireman, I beleive this will be standard for new certifications on stean engines

Question #4

Is it possible for an engineer to rapidly “drop,” for lack of a better term, his boiler pressure? If he suddenly realizes his water is too low, does he have an emergency recourse?

there are blow off valves that can be opened for this although they are ment to vent off steam at the end of operation, when the loco is done for the day. The fireman opens the cinder grate under the firebox and "dumps" the fire ruining Mudchickens day and the engineer opens the blow off safety valves and a massive torrent of steam blows off the sides or under the loco ruin the days of the railfans on the ROW who are now poached like an egg. The engineer will set the brakes to emergency and more often than not jump once the engine has slowed enough to do so, leaving it to come eventually to a stop

[vsmith]

One other thing

If a boiler did experience a crown sheet exposure , even for just a short time, its boiler was considered compromised and would have to be rebuilt, and the engineer and fireman would be in deep poop.[:0]

[Anonymous]

There was a story in TRAINS a few years back about explosions and their causes. I think the name of it was "Big Bang - No Theory".

As I recall, the story was reprinted in the National Board Bulletin, the magazine of the National Board of Boiler and Pressure Vessel Inspectors. If you're interested, maybe you could get a reprint from either source.

Old Timer

[nanaimo73]

Big bang-no theory is in the April 1995 Trains.

[selector]

I am not being sarcastic, nor critical, but I have some dificulty believing that a Cab Forward would have its crown sheet compromised on a 2% grade mainly because of the grade itself! If we suppose that its total boiler length was approx. 35', then 2% over that length is merely 8 1/2", hardly a catastrophic change in level. Am I missing something...what do I not understand?

Again, I am interested in this subject, and just want to understand.

[Hugh Jampton]

QUOTE: Originally posted by selector

I am not being sarcastic, nor critical, but I have some dificulty believing that a Cab Forward would have its crown sheet compromised on a 2% grade mainly because of the grade itself! If we suppose that its total boiler length was approx. 35', then 2% over that length is merely 8 1/2", hardly a catastrophic change in level. Am I missing something...what do I not understand?

Again, I am interested in this subject, and just want to understand.

Have a look at Figs. 2 & 3 in this document

QUOTE: Originally posted by jason1

There was an incident with a locomotive boiler explosion about 10 years ago in Pennsylvania. Here is the NTSB report on the incident if anyone is interested.

http://www.ntsb.gov/Publictn/1996/sir9605.pdf#search='NTSB%20report%20on%20steam%20locomotive%20boiler%20explosion'

It shows that the crownsheet is towards the top of the boiler (and hence near the surface of the water), so an 8.5" change in water level is significant. On our preserved Pacifics the water glass tube is only about 6" long and at half glass on level track the water is about a foot above the crownsheet.

btw,, a 35' boiler sounds a bit short for a Cab forwrd, I'd say they were a lot longer than that, given that they were big articulated locos. Perhaps someone can provide the actual boiler length (barrel + firebox)

[nanaimo73]

Did it make a difference if the locomotive had a Belpaire firebox ?

[gabe]

Wow,

Thanks everybody for a wonderful education, especially Overmod—not to dimini***he significance of other contributors.

Just a few comments:

(1) In case there is someone associated with this operation, I am not going to name it and enrage them. But, once I was in a stopped light Mikado that was in a siding for the night with its fire lit for an excursion on the following day. They had a 12-year old watching it for the night. Granted, there might be 100 reasons why this is perfectly acceptable and causes no need for concern that my limited technical knowledge can't comprehend. But, like I say, I am a lawyer, and my first instinct is to look for liability. Overmod's "intelligent" fireman doesn't seem to be always available. Not to knock the 12-year old either, and I am sure he knows more about steam than me; but that scared the hell out of me.

(2) Dropping the fire does happen occasionally. I remember reading a story about the mechanism that greases the driving rods failed on a Hiawatha (at 100mph!). The driving rod froze and literally lifted the Pacific off the ground with each revolution. Remarkably, the locomotive stayed on the tracks, but the first thing the engineer did was dump the fire.

Thanks everyone,

Great discussion.

Gabe

[lonewoof]

Nanaimo brings up a point I've been wondering about: what is the difference between a Belpaire firebox and the ordinary kind? I know it is distinguishable from the outside by the "shoulders" at the top, but what are they caused by?

[selector]

Got it, Hugh, and thanks. It all makes sense....scary sense.

[gmpullman]

Didn't the "Standard Railroad Of The World" adopt the Belpaire firebox to get away from using flexible radial stay bolts? I've never studied the the actual engineering aspects of the Belpaire but I believe the advantage was to avoid the use of the leaky staybolt caps and resulting maintenance hassles that the more common conical connection boiler had? All of this discussion is fascinating and the one thing that has to be considered in locomotive boiler design is that the firebox necessitated using FLAT sheets. Like the crushing egg theory, a cylindrical enclosure is able to withstand much greater pressure than a flat surface... hence the staybolt.

[jockellis]

G'day, Y'all,
I always heard that firemen started to get indigestion when the water level got down to half full. They knew the consequences of an empty tank. What I don't understand is why it took management until nearly the end of steam operations to realize how much simpler life was when they coupled a tank car behind the tender and pumped water forward to the tender. It meant that the train did not have to stop at every water tower to give firemen indigestion relief. Some of the later steamers went through 10,000 gallons in about an hour.
Jock Ellis
Cumming, GA US of A

[gabe]

QUOTE: Originally posted by jockellis

G'day, Y'all,
I always heard that firemen started to get indigestion when the water level got down to half full. They knew the consequences of an empty tank. What I don't understand is why it took management until nearly the end of steam operations to realize how much simpler life was when they coupled a tank car behind the tender and pumped water forward to the tender. It meant that the train did not have to stop at every water tower to give firemen indigestion relief. Some of the later steamers went through 10,000 gallons in about an hour.
Jock Ellis
Cumming, GA US of A

Mr. Ellis,

I am far from an expert in such matters, but my bet would be the reason it took so long for railroads to do this is the lack of power of early steam locomotives.

A tank full of water is a lot of weight--probably several times more than your average reveune loaded car of the time. When you were dealing with underpowered steam locomotives to begin with, one could understand the reluctance to reduce the revenue tons a locomotive would be capable of carrying by attaching the such a heavy car.

As super-power steam came on the scene, a tank load of water represented a lower percentage of the locomotive's revenue pulling capabilities and made it more acceptable.

That is just my bet, good question.

Gabe

[Modelcar]

....As a youngster I rode my bike about 4 plus miles to see the results of a boiler explosion on the B&O on the S&C branch {Somerset, Co., Pennsylvania near Listie. Time frame was about 1943....The remaining parts of the sizeable locomotive were the frame, steam cylinders, wheels and rods....and not much else...! The cab and boiler were non existent. In remembering I believe it was still on the rails.