My engineering abilities are fuzzy at best, but I would think that, if and when the boiler was filled clear into the dome, the boiler pressure would rise to the point that it was in equilibrim with the pressure that the injector could muster, and water would simply stop flowing before anything broke.

Just a strong hunch...

Mike

Here's a couple entries from The Traveling Engineers' Examination Book, Revised 1940, unfortunately, no publisher information. This 300 page book is entirely in question and answer format, meant as a training aid for firemen, to prepare them for the engineer's exam.

308. What would be result if fire box sheets became overheated?

A. They would be weakened and forced off of staybolts and explosion would occur.

309. Would it be advisable to put water into boiler after sheets had become bare and red hot?

A. No. Fire should be killed at once.


Note that it doesn't just say the sheets are uncovered, but bare and red hot. It does not elaborate as to the likely result of that action, but much of this section deals with minimizing temperature differences, explaining that the uneven contraction causes leaks.

Further along is this discussion.

390. Suppose that with water glass is in good working order, immediately after closing throttle water disappeared from water glass, what should be done?

A. would open throttle and endeavor to raise water until both injectors would put enough water in boiler to make it entirely safe to close throttle. If unable to raise water level to lower gauge cock, would smother fire or put it out entirely, if necessary keeping both injectors working.

So, it would appear the authors are advocating determining the condition of the sheets before adding water, but if they are not red and deformed, adding water and taking action to bring the water level up over the firebox is the proper course of action.

Bob, it's commpn practice on some tourist and museum operations to bank the fire, cap the stack, and run the injejctors to fill the boiler completely at the end of the day if you are running again the next day. The injector "breaks", stops feeding water, when it receives water through the steam line. No damage done. the hot water gradually cools, drops below the dome, and is generally visible in the glass the next morning.

Never tried this with a FWH. Seems it may be possible that the feed pump could get damaged by trying to work water, like any recip steam engine.

dave

The Locomotive: Engine Failures by Marshall Monroe Kirkman, Cropley Phillips Co. 1910: Chapter IV, "The Boiler":

We now have a plausible explanation for this pervasive belief, and one that makes much more sense than "It gives the crew an excuse to run away..."

As has been discussed, these are working men out in the field, not scientists. If they had reliable information or even first hand knowledge of the crown sheet in a small boiler breaking due to cold water, they're not going to "well, this is a larger boiler and a thicker crown sheet, so maybe we should do the math?" They're going to say "Add water? Ah, hell no!"

I had asked the question before about why this belief is so widespread and so oft repeated. There must be some basis for it someplace? If its just the crown sheet melting due to heat, then why add the myth about adding water? Why not simply say "If you expose the crown sheet, it gets soft and the engine blows up!" If adding water would be good, why have so many people put so much effort into telling us not to? What did they gain?

I've got to wonder if there wasn't some grain of truth, either failures in small heating boilers and/or something related to the BLEVE situation. Why simply make this up out of whole cloth?

I recall that the Royal Hudson had boiler damage caused by a feed water pump being left on too long. The damage was fairly serious, but I don't know specifics. I also never did quite understand how this happened, why it didn't work water and how it could over pressurize the boiler when that was the source of power.

Here is an excerpt from the Locomotive Fireman's Magazine, Vol. 26, Jan. 1899, Pg. 452-453. I know this is a pretty early era to take technical examples from, but I think it's worth some consideration. It doesn't really answer the big question of "should I turn the water on or run," but it does cite the fact that someone did turn on the water in their particular situation.



If you want to check out the source, here is a link: http://books.google.com/books/reader?id=jnUWAAAAYAAJ&num=19&printsec=frontcover&output=reader&pg=GBS.PA452

- Chaz Robitaille

I have heard one first-hand (well, virtually first-hand) report of a similar incident on the Rockton & Rion Railroad in South Carolina in the late 1950's or early 1960's. This railroad is the current site of the South Carolina Railroad Museum and was famous for operating steam locomotives through the late 1960's.

Back around 1978 I visited the end of the line at Anderson Quarry (where Winnsboro "Blue Granite" was mined) and met one of the last workers at the site. Most of the railroad's maintenance facilities were located there, including the engine house, which was still fully equipped at that time with a wheel lathe, drop table, all sorts of other machine tools, and a stack of new 2 inch boiler tubes intended for former Atlantic Coast Line 2-8-0 #712.

This worker was ~65 years old and lived in a house constructed of granite block (like virtually every structure nearby) that overlooked the quarry and enginehouse. He told me a story of a similar incident that happened with one of their 0-4-0T's I'd guess in the early 60's.

One of their worker's jobs was to come in on Sunday night and build a fire in the 0-4-0T so it'd be ready to go on Sunday morning. Well, apparently this fireman/hostler had been hitting the bottle pretty heavily all weekend and showed up for work Sunday night still drunk. He proceeded to lay the preparations for a fire in the firebox of the 0-4-0T which was parked in the engine house. He got everything arranged, supplied the blower with house air and lit the fire. About 15 minutes later, when the fire was pretty much roaring, he remembered to check the site glass and realized there was no water showing. If fact, the boiler was completely dry (apparently because the engine had just been shopped) and he'd forgotten to fill it. He quickly connected a ~2" hose to one of the blowdowns and ran outside and turned on the water full blast. There was a huge "BOOM!!!" and the enginehouse filled with steam.

The man telling the story was sitting in his living room at the time, and rushed outside to see a huge cloud of steam gushing out of the eaves and doors of the engine house. He figured a boiler had exploded and the fireman was dead. He rushed down and found the guy unharmed, but completely dazed. The locomotive appeared to be intact, but when they examined it later he claimed that all the firetubes had popped out of the front and rear sheets and were lying loose in the bottom of the boiler. I'm sure firebox damage was done too but I can't recall what he said about that (if anything). This fireman was apparently one of the railroad owner's best workers but he told him he couldn't afford incidents like this and fired him on the spot.

Admittedly this is a significantly different incident from adding water to a hot, pressurized boiler with LOW water, but it shows what can happen under these conditions.

I have been following this thread off and on since Brendan told me he was going to start it. I have seen several damaged crown sheets over the years including #1278’s at Gettysburg four days after the incident. As was noted before, the button head crown stays were certainly an important reason why the crown sheet didn’t completely fail, but that wasn’t the only reason. Ironically, because of numerous stress corrosion cracks, the sheet opened up several places in front of the button heads after being overheated. This not only blew steam into the firebox, but water as well. This put out the fire and the water being drawn through the openings effectively cooled the sheet and helped prevent further damage. I have seen "quilting" in crown sheets caused by overheating that didn’t fail because water washed over it either from feed water devices or from the engine entering a grade. Next to no cracking occurred, but the leaking bolts would turn the firebox into a shower

Boiler plate is made from low carbon steel (less than .35% carbon) and is ductile for a reason. It is more forgiving of sudden temperature changes unlike medium and high carbon steels. Sure, your boiler made from 4140 will be strong, that is until you put water in it and light a fire. It simply won’t withstand uneven stresses and sudden temperature changes without failing.

It was not uncommon for crown sheets to be exposed for short periods of time. This typically happened on long boilered engines when they topped a grade and the water rushed to the front of the boiler. The water would then wash back over the sheet with no ill effect. The N&W actually lowered the crown sheets by several inches on the first A class engines when tests showed it was impossible to keep it covered on the downhill side without working water on the uphill side. Circulators and especially siphons were shown in controlled tests to keep water “spewing” on a crown sheet even when the water was several inches below the sheet. Talk about “cold water” hitting the steel? The siphon gets its water from the lowest part of the boiler when the crown is uncovered. These devices saved many a crew with next to no damage to the firebox.

The ICC investigated all locomotive boiler explosions back in the steam era. (Most were crown sheet failures) and every time, the cause of the explosion was stated as “overheated crown sheet”. Not once is any mention made of water causing the failure.

There have been several suggestions made as to what to do instead of killing the fire and/or turning on feed water devices. Opening the blow down will only make the water level lower and will do very little to drop the pressure since water doesn’t compress. Checking to see if water comes out of the bottom water glass valve won’t tell you if you are ok or not because it is typically below the lowest part of the crown sheet. You will be spam long before you could tell. Overheating a crown sheet with a banked fire is next to impossible because there isn’t enough heat being produced to soften the sheet. You will instead get some leaking bolts.

Certainly we all know that low water should never happen. That doesn’t mean you shouldn’t know what to do if it does. At Strasburg, we have just finished completely revamping our training and testing program for engine and train crews. If I board a locomotive and I can’t get water to bob in the glass, both injectors are going on and THEN I’m dumping the fire.
That is our policy and it is based on two facts;
1- Low carbon steel heated red hot will not shatter when quenched in water.
2 - The ICC investigations always said the same thing, "falure was caused by OVER HEATED crown sheet".

Rick

[i][/iOpening the blow down will only make the water level lower and will do very little to drop the pressure since water doesn’t compress[i][/i]]

I was curious why no one pointed this out sooner. With water in the boiler under pressure opening the blowdown will only increase the production of more vapor as the slight pressure drop lowers the boiling point which produces more steam.

What is Maximum Allowable Working Pressure definition?
Answer:

The Maximum Allowable Working Pressure (MAWP) is used to rate components, steam drums, piping, tubes, boilers and any other pressure vessel in a hydraulic system.

The reason this is so important can be seen easily in steam systems. The temperature that a fluid boils increases as pressure increases and decreases if pressure decreases.

What this means is if you are running a boiler at 200 psi the water will boil around 387 degrees F. If it is creating steam this is the minimum temperature. If the boiler cracks and the pressure drops to atmospheric pressure, water would boil at 212 degrees F. This creates superheating or heating passed the boiling point. This will create Flash steam and cause an explosion.

The MAWP rating is to decrease the chances of this happening.

Lowering temperature by quenching the fire or if possible adding water will lower pressure. I wonder how many will stick their heads in the firedoor to see of the carbon had been burnt off the crownsheet?
Question: Does the superheating taking place locally at a rupture caused by a leak in an overheated sheet cause the damage to increase?

So, thus far:
*The two training textbooks I presented give contradictory information--one says to turn on the injectors for an exposed crownsheet; one says to NOT touch them.....
*The PRR "Mythbusters"-style test of 1868 gave inconsistent results--one didn't blow, one did. (Man, score one for the PRR in testing everything, eh?)
*We've had evidence/examples presented of crownsheets failing without what was supposed to be the inevitable boiler somersaulting forward into the next county that we've been trained to believe will happen, and on boilers that apparently/supposedly did not have the vaunted CP "safety" design that supposedly prevented 1278's boiler somersaulting or otherwise more catastrophically failing in the Gettysburg RR incident.

Right now, I STILL don't know what to think. Sheesh.

To which I'll add... Many low pressure heating boilers (<10PSI) were, and still are, cast iron. Those are definitely known to crack from the thermal stress of adding water to a dry, overheated boiler. Back in steam days these were a lot more common than they are today (practically any building larger than a cabin was heated with steam) and I'm sure had their own lore, which could easily be confused with power boilers. Hey, a boiler is a boiler, right?

Brings to mind a bit of accepted wisdom drilled into the heads of boys of my generation... Never, NEVER add water to an overheated car engine, or you'll crack the block.