Mr. Austin,

Thanks for posting this, certainly seems to address the question well enough. I linked back to this in the "old wives tale" discussion, but those guys have a different explosion to foam about now.

Great reading! Was the periodical simply titled "The Locomotive," or is that only the article title?

The Locomotive was(maybe still is) the publication produced by the Hartford Steam Boiler Inspection and Insurance Company. Many older issues can be found here:http://archive.org/index.php
Use locomotive in your search. Lots of other good steam information also.

Mike Tillger

The topic of what to do if a crown sheet is uncovered surfaced again last night on Facebook on a traction engine group. A rather lively discussion ensued. Most were of the opinion that under no circumstances should water be injected into the boiler. I took the opposite opinion and pushed back, asking for reasons why they support the "add no water" position. I am not advocating one method over the other, but rather seeking information so as to better understand what would happen in such an incident.

My contention is that if a crown sheet had not yet failed, there is still time to cool it down to prevent a catastrophic failure. Adding water to the boiler slowly starts to cover over the crown sheet, and as the water progresses it begins to cool the sheet, thus restoring strength. This may ultimately result in plate warpage and cracks but would more than likely prevent a catastrophic failure.

A counter argument is that the hot steel would flash such water into steam with such ferociousness that the pressure would increase uncontrollably. But would it? The phase change between liquid and gas consumes a lot of BTUs and the amount of BTUs stored in that sheet at the elevated temperature is not sufficient to transfer enough energy to the water to create that condition. At least this is my theory.

The PRR and others apparently conducted tests where they dry fired boilers and injected water to see what would happen. Does anyone know where these test reports might be found? I would be interested in doing more research into this issue before developing an opinion on the matter, one way or another.

A few years ago, near me, a fertilizer truck caught fire after picking up a load of ammonium nitrate. The local fire services were called and established a perimeter to allow the truck to burn out. I can't remember why the driver went back, it was either to get his wallet or was going to try to disconnect his truck. They managed to find a few pieces to shove in the coffin:
https://www.ktbs.com/news/texarkana/fertilizer-truck-explodes-1-dead-creates-massive-crater-arkansas-officials-say/article_4dc572ba-5093-11e9-a255-0b650d4c6efe.html

Trying to shove water into a boiler that may have ran dry is the same thing. You're going after a out of control situation that may or may not be fixing to explode at some random time. Is the crownsheet already drooping? Firebox stuffed full of wood? Does the injector work? Does the safety valve work? Is there even water to inject? That the soft plug hasn't popped already should scare the crap out of anyone because it shows the maintenance may be poor. Your time is best spent evacuating the area and establishing a perimeter. The 'fact' that people have 'saved' boilers by running in and doing "whatever" is the same way people get killed doing stupid stuff all the time-because 'most' of the time, you get away with it. It also tends to sound like a lot like a way to 'hide' the mistake.

Obviously prevention is the best cure, but what would you do if you found a box labeled 'grenades' with a few pins laying next to it? It's too late now, run away!!!

In the late 1970’s, I heard a first-hand account of an incident of adding water to a dry, hot boiler on the Rockton & Rion Railway in SC. The person telling the tale had worked (and was still working) at the quarries and lived just across the street from the engine shop at Anderson Quarry.

He said one of their firemen was assigned the task of coming in on Sunday night to fire up an 0-4-0T so it’d be ready to go Monday morning. The worker carefully prepared a bed of kerosene-soaked wood and coal, turned on the shop air to the blower, and lit the fire. About the time the fire was going really well, it occurred to him he hadn’t checked the boiler water level, and it was apparently dry. He frantically connected a water hose to the boiler and turned on the hose. This was soon followed by a loud KA-WHOOM! and the engine house filled with steam. The man telling this story said he heard the noise, ran out onto his front porch and looked over to see steam billowing out of every crack on the engine house. By the time he got to the shop the fireman staggered out, apparently uninjured, and told what had happened.

When they finally got the fire out and the boiler cooled down, presumably the next day, they found that most if not all the tubes had pulled out of the flue sheet(s). I don’t know if the engine was repaired afterwards or not.

It turned out the fireman was either drunk or suffering the effects of a Saturday night drinking spree at the time of the incident, and his railroading career on the R&R came to an unfortunate end.

My main problem with the idea that adding water to a boiler that is on the verge of a low-water crown failure will either cause or accelerate an explosion is that every person I've heard defend the idea uses or relies second-hand anecdotal evidence to back it up. Give me documented cases where we know what happened, especially in the final moments. Most never survived to tell, sadly.

I generally believe the solution to a low-water situation is to immediately begin adding water and then work to reduce the amount of heat going into the boiler. If the crown has been uncovered for sufficient time that a crown failure is imminent, and water could affect the sheets integrity, it's probably too late to do anything except kiss your rear goodbye anyways.

There's too many industry professionals and railroads I know and respect that also take this stand, and accept the "add water" approach, to dismiss it- I can't say the same for everyone that takes the old wife's tale to heart.

I don't claim to be an authority (I'm a graduate of OJT University), but I lived through a low water situation:

In early 2001, I was on the Ferrovias Guatemala steam crew, and we took a doubleheaded passenger train from Guatemala City to the Caribbean, 212 miles each way, leaving our second engine at the half way point of Zacapa. On our return trip we were on duty for FORTY HOURS straight because we had to go back to Guatemala City for fuel instead of being able to rest somewhere in between. Westbound, the line is mostly uphill after El Rancho, and our two engines and tank cars had to stop constantly to repair any number of defects, using only the crudest of methods. Last time we got under way the whole crew was riding the first engine, leaving the engineer and me with no company on the second one.

The frantic whistling of the first engine woke me up just as we started over the famous Puente Belize trestle 240 feet above the city cemetery. It is our custom to wake the dead whenever we cross it. The first thing I saw was the canyon below us --- I could just as easy have tumbled out the window !!! I knew I had been out of it for some time when I saw 60 pounds on the steam gauge. I was WIDE AWAKE when I saw the empty water glass !!! I got real damn busy THEN. Couldn't bounce the water in the glass, Try cocks showed NADA.

I did NOT start the water going then. First, I figured I better look inside the firebox to see if the crown sheet was glowing cherry red above the water line. In my infinite wisdom, I figured that if the soft plug hadn't let go, there must still be enough water to keep it cool. (We had just changed the fusible plug, I knew it wasn't covered with scale.) Everything looked OK, and the tiny idle fire told me I'd been snoozing since the last stop. THEN I started my injector. Next I tried to wake the engineer up, and he pointed at the empty glass and told me it was FULL. I became quite insistent at that point, pushed him aside and started his injector, too.

While I was cussing him out, I bumped up my fire. By then we had gotten to the west bridge abutment, the grade resumed, water rushed to the back end of the boiler and started bouncing in the glass. Everything was back to normal when we tied up a few minutes later.

Of course, since most railroad bridges are level, we had water in the glass until we started across it, and it surged toward the front, draining the glass right when I came to. We weren't really out of water, I just scared myself nearly to death is all. I was 50 years old when I hired out, with no grey hairs or bald spots. The next morning when I was getting ready for the last day of the charter, I noticed that my hair had started to turn grey overnight.

You guys can fire an engine however you want to, but I still think that adding water is a bad idea if the plates have already overheated. I'd kill the fire and JUMP if it was me in that situation.

Eisenhoffer/Leidenfrost crops up in DNB, too.

This is the same 'steam blanketing' effect that limits superheater heat transfer at low mass flow. It is the effect that makes pan-blackened fish such a delight.

The point is that the steam film is superheated, but the pressure energy added by superheat is comparatively not that great compared with the latent heat of vaporization, so that as the pressure against the film rises, the tendency for it to 'collapse' far enough for water to be in direct heat-transfer contact with the metal greatly increases.

The effect of this collapse can be dramatically seen in the "experiment" where small drops of water skitter around in a hot pan, levitated on the steam film. Once they heat up enough, they touch the surface, and you'll notice they very quickly disappear in a POOF of evolved steam, rather than starting to boil levitated until gone.

Now, the issue with "whether or not to add water" can be very much as Sammy King indicated: if the sheets don't show visible heat, or bagging of some sort, it might be possible to bring the water level up. But it may not be possible for the rising water level to lower the crosn temperature rise enough to prevent sagging or damage before failure occurs -- ISTR a calculation showing that an actual uncovered crown would be heated to softening temperature in seconds if the fire is not reduced.

Now, another consideration comes up here. As Porta noted, the boiling water is not like level water in a pot: it is foaming up like boiling milk above and around the heat-transfer surfaces. This implies that even at low water, there is still some foam tending to cool the crown from 'quilibrium' temperature, and the foam should be more mobile than sloshing liquid water. As usual, I listen carefully to Sammy's recommendation in the matter.

A different concern comes up, though. I don't know whether the postulated explanation for the explosion of the Allegheny in 1947 was fully correct, but they implied that the water welling up from the thermic syphons was, instead of keeping the crown cool as the manufacturer claimed, actually thermal-cycling much of the crown in unpredictable patterns. I suspect using an injector to raise water level in the legs would produce similar instability as it rises at the curved edges of the crown, and then across the evolving steam film if it is overheated. That seems to be really too much of a crapshoot for me to recommend as a practice...

I was trained by old heads, and have stayed out of trouble by doing like they told me. I don't fire an engine based on "old wives tales".

It often happens, maybe on a quick stop, or more often when topping over a summit, that the water will momentarily uncover the crown sheet and the glass will be empty. You have a little bit of time before the sheet gets hot, this time will be less if your fire is bumped up. 15 seconds, I think you're safe to add water. 30 seconds, maybe yes and maybe no.

Another thing the old timers taught me was to start your injector before topping over a summit, so you're free to bump your fire back as soon as you start downhill (oil firing --- you coal scoopers must have your own methods). The empty water glass phenomenon usually happens in the same places every trip, so BE READY.

More than 30 seconds of empty water glass, you might want to start looking for a place to bail out. If you're in a deep cut or a tunnel, going over a bridge, or on the side of a cliff, your only option is to scramble back over the tender and get down on the rear sill, hiding behind the tank. That way you'll most likely live long enough to clean out your locker and go hunt for a new job...

In addition to anything you can do to slow the heat input, what about opening the blowdowns? It seems anything you can do to remove hot water and reduce the pressure should help....

Sometimes we lay an engine up for the winter by killing the fire and opening the blowdowns and every other valve on the boiler, letting it blow dry. Granted that doing this might help prevent an explosion, but they would have to call another crew to bring another locomotive out to tow you back to the shop. You'd most likely be charged with a road failure.

On the other hand, if you kill the fire and leave things alone, there's a reasonable chance that after cooling down, you'd reach a point where it was safe to add water and you would still have enough steam left to work the injector. You could refill the boiler, light off, and make it back to your terminal. Then you'd only have to explain a train delay.

I'm not one to push my luck when it comes to trains. It's asking for trouble, and you might just receive what you've asked for....

Opening the blowdown on an already low water boiler would just remove any doubt as to whether there is enough water or not. I doubt that the blowdown would be able to remove all of the water from the boiler before the crownsheet ruptured.

The question here seems to be this. Add water and there is a chance that it will cool the crown sheet and save the locomotive. Don't add water and there is no chance of saving the locomotive. Either way you can still run away from the locomotive. It only takes seconds to turn on the injector.

"Removing hot water" does NOT lower the steam pressure significantly. Think about how a fireless cooker works. All that happens when you open the blowdowns is relieve some of the pressure that is keeping "the water from changing phase to steam" and while the massive bubbling may raise the effective water level "swell" it is also accelerating the water mass in the shell radially outward, not at all what you want.

It might be instructive to work through the series of events that caused the massive staybolt fiesta on PRR turbine 6200 when there was excessive steam demand at starting...

There was a similar scam involving drop plugs "relieving excess pressure" in overheated-crown situations. A child of six can see that there won't be enough mass flow through the 'legal' number of plugs, whether drop or not, and indeed if you read the fine print in the Nathan ads instead of looking at the pretty picture with the nice level water and the cute little puffs of venting steam, you will find how many plugs would be needed to get reasonable pressure drop. Of course they fail to mention where all that live steam goes when all those drop plugs let go... not quite as bad as the LMS Fury in terms of pressure, but it makes it up in volume...

What you'd need is enough fast-acting relief-valve area to let the evolving steam push the water mass out fast enough, low and away from the cab enough, that the failing crown does not produce a rocket effect and massive steam release right where the cab is. I don't think there is any chance of this without explosive bolts at the front of the convection section... [note: /s]