The New And Improved Unofficial R65 Forum V2
Technical Discussion => Misc. Technical Discussion => Topic started by: Dizerens5 on October 25, 2009, 04:38:49 PM
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It’s clear, those who contribute to this forum know all about technical matters, so can I ask anyone expert in old-fashioned industrial engineering to help me out?
For many years I’ve been mystified by this: whenever you read an eyewitness account of the sinking of a steamship, somewhere it seems there will be a mention of the boilers exploding. Think Titanic!
I just don’t understand. Unless my recall of school physics lessons is totally wrong, the effect of dumping a working boiler into cold water would be to cause a quick drop in internal temperature, condensation of the steam and of course - a fall in pressure, exactly what you don’t need for an explosion. So what is all this boiler-explosion business? Boilers did sometimes explode, but as far as I know because of manufacturing fault or metallurgical failure, or because a fireman had locked the safety valves (strangely there could be a good reason for such an apparently suicidal procedure). Not because they went into cold water. That sometimes did happen with steam powered trains, occasionally trains derailed on a bridge or causeway and went into the water, but the engine’s boiler did not explode, in fact the locomotive was often raised and put back into service. See the famous Tay Bridge disaster in Scotland.
Any ideas?
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A possible explanation, would be a metal failure due to rapid cooling, thereby releasing the pressure inside .
With the mass of a boiler one part could be cooled rapidly, and the rest of it could still be at operating temperature .
Just a quick thought !!!
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A steam locomotive boiler worked at around 200 - 250 pounds pressure. Maybe a ship's boiler used a higher pressure, I don't know.
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i worked in the scrap metal game for many yrs & the scrap that we sent to the steel/copper/alloy melters HAD to be water free. If water gets into the furnace there is a chance it will explode, the scrap gets super heated before it goes into the furnace. This is just a thought but a boiler is like a furnace??? like with all that heat, so if water enters the super hot area it may go bang???....iam sure iam 100% wrong but it was just a thought :-/
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Think stress fracture of the boiler or any of the pipes and fittings attached. Once a crack starts it will propigate releasing the steam in an "explosion".
Many boilers have "exploded" because the water level got too low to cover the uper part of the fire box - the steel overheated and softened, buldged and finally cracked. The resulting release of live steam could rip the boiler from its mounting and flip it end over end. there would not be enough time for cold sea water to quench the steam inside the boiler. It can take several hours to raise a boiler to working pressure - you can't cool it very fast.
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As a Qualified Marine engineer ill give you my two penneth.
Modern boilers for turbines operate at extreme pressures (up to 3000psi) using "superheated "steam which is a different animal to the "wet" steam used by reciprocating steam engines.Either way the result of a ship was sinking is its likely the ancillary equipment would fail first as its usually at the bottom of the engine room, feed pumps would fail causing a massive overheat even if the fuel system had been shut down at the same time and any pipe carrying steam could fail if it was subjected to rapid cooling.
If cold water entered the fire chamber the thermal stress would cause failure.
The result would be a rapid decompression of the boiler not an explosion as such but pretty violent.
BTW superheated steam is like a laser it would cut you in half if you were unfortunate enough to get in the way of it.
Lou
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Thanks everyone. I did have a suspicion that there may have been some kind of violent steam release rather than an actual explosion.
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All of the above, plus you have to remember that it's the press report that we're reading. People who write these reports aren't necessarily the most technically savvy folks around. Consider the reports like "today, a drilling rig caught fire in the Gulf of Mexico and 10,000 gallons of oil was released." In the first place, it's probably not a drilling rig, it's a production platform, and secondly, I've yet to meet the first oilman who meters oil in gallons instead of barrels. (In case you're curious, there are 42 imperial gallons to the barrel.)
Here's an interesting article on the paddlewheeler "Sultana" where a boiler "exploded" resulting in the single greatest maritime disaster in US history.
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Boiler Explosion:
Boiler springs a leak. Causing a sharp drop in pressure. The superheated water "flashes" causing a very rapid rise in pressure. The already compromised boiler fails in spectacular fashion. KABLAMMO! This is why in the USA, all boilers have ten (?)year certificates. At the end the boiler myst be torn down and rebuilt and re-certified becuase they are esentially bombs held in check. This goes even for the live steam model engines.
BTW - The Aloha 737 was a variation on this theme: A longish crack developed in a joint in the ceiling of the fuselage. The air-cycle machines in the pressurization ("packs") compensate for the increased demand for air caused by the leak by increasing the flow of air to the fuselage. Along walks a flight attendant who, due the rapid flow of air out the crack in ceiling, is sucked up and (very temporarily) plugs the leak (insert flight attendant joke here). The increased flow suddenly has nowhere to go and the resulting "flash" of pressure destroys the already compromised fuselage, creating the convertible 737. http://www.aloha.net/~icarus/
Another in a long line of "Boiler" explosions.
Enjoy your next flight please and remember to keep those seat belts fastened!
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Did you read the end? One of the passengers had seen a crack in the plane whilst she was boarding, but proceeded onto the plane anyway and didn't tell anybody. Well, maybe lots of airplanes have cracks in them.
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Did you read the end? One of the passengers had seen a crack in the plane whilst she was boarding, but proceeded onto the plane anyway and didn't tell anybody. Well, maybe lots of airplanes have cracks in them.
Stupid is what stupid does......i wouldn't have got on it,I used to have a "thing" about Pratt and Whitney engines i cringed every time i got on a plane with them on every one p*ssed oil out like theres no tomorrow
It was a PW that blew up on take off from Manchester killing half the passengers. The engineer in me always felt uncomfortable with situations like that when clearly there was a problem with that engine design(it was the long cigar shaped one) it was popular on mid size planes in the 80,s.
Lou
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<snip>
BTW superheated steam is like a laser it would cut you in half if you were unfortunate enough to get in the way of it.
Lou
When you had to go into the boiler room on a US Navy ship that had a boiler casulty, you used a broom to clear the space in front of you just in case the steam was blowing across your path. You stopped if the broom suddenly "sawed" off. Kind of like sweeping for mines.
Great fun for $115 dollars a week! (1979)
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Did you read the end? One of the passengers had seen a crack in the plane whilst she was boarding, but proceeded onto the plane anyway and didn't tell anybody. Well, maybe lots of airplanes have cracks in them.
Stupid is what stupid does......i wouldn't have got on it,I used to have a "thing" about Pratt and Whitney engines i cringed every time i got on a plane with them on every one p*ssed oil out like theres no tomorrow
It was a PW that blew up on take off from Manchester killing half the passengers. The engineer in me always felt uncomfortable with situations like that when clearly there was a problem with that engine design(it was the long cigar shaped one) it was popular on mid size planes in the 80,s.
Lou
Finally a subject I know something about !!
The Pratt & whitney JT8D series engines, were one of the most reliable turbine engines ever made .
The oil leakage, was from the accessory drive gearbox case half seams, they just couldn't get that part right, until they re-engineered the parts, for the JT8D-200 series engines, only used on the McDonnell Douglas MD-80 series aircraft .
That uncontained engine failure that happened in Manchester, was a completely avoidable incident .
When the accident investigation report was released, it was very clear, that the engine should have been replaced, after the first pilot write-up .
The particular series engine on that Boeing 737-200 aircraft, was a JT8D-15, it had the notorious reputation, for combustion chamber flame propagation, or interconnect tubes between the combustion chambers cracking and failing, taking large sections of the combustion chamber with it .
This engine had to be borescoped every 500-750 hours of operation, depending on how many hours the particular engine had accumulated .
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Thanks for the technical input there Bob i used to fly an awful lot in the eighties when i worked for BP at that time i was working on marine steam turbines ect. You must admit that watching oil running out of the cover plates and the back of a engine (any engine)on takeoff is pretty disconcerting as i recall most of the long haul stuff was usually RR.]
I only experienced one turbine failure, that was a small turbine driving a crude oil discharge pump the turbine was about the size of a V8 block the drive shaft snapped and the speed regulator was damaged by debris. The result was like a scene from a war zone the, blades exited the casing and when straight through the checker plate on the walkway above(1/2 thick steel) it looked like it had been hit by a 50cal Gatling from a AC130 fortunately there was no one in that part of the engine room when it blew.
Lou
(just another day at the office on less than 115 bucks a week)
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I was working mostly on McDonnell Douglas DC-9-10/30 and MD-80 series aircraft, and with an aft fuselage mounted engine, passengers couldn't see the leakage .
When the airline I worked for (Midway Airlines) , bought the assets of bankrupt Air Florida, we got Boeing 737's, and the engines are in plain view of passengers, so passenger reports of oil leakage, became fairly common with the 737's .
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Great fun for $115 dollars a week! (1979)
You made $115 a week? I didn't make $115 in a month! (1969)
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When the airline I worked for (Midway Airlines) , bought the assets of bankrupt Air Florida, we got Boeing 737's, and the engines are in plain view of passengers, so passenger reports of oil leakage, became fairly common with the 737's .
Wasnt just me then!!!!!
Lou
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I was on a 747 flying eastbound from hawaii to guam in the 70's and number 3 engine caught on fire and burned all the way back to hawaii.
It was quite a interesting flight watching flaming engine debris fly by your window for 40 minutes.
We landed safely and used the evac slides and ran like deer.
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Holes in the Huey airframe were often repaired with Olive Drab "100 knot tape". Every crew chief had a roll. Lotta roof holes in the "Death from Above" business. Floor holes not so annoying.
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I was on a 747 flying eastbound from hawaii to guam
Man! That is definitely taking the long route!
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Is it not the steam tubes in a boiler which carry the pressure, not the big cylinder we normally think of as the "boiler?"
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In a modern utility/Power boiler- The tubes carry the high-pressure water/steam, but the boiler itself has fans blowing into it and sucking out of it (at mine, the air moves around 60mph through the boiler).
Ideally, you 'balance' the fans so that the 'sucking' fans run a big harder than the 'blowing' fans - this puts the boiler at a slight negative pressure (think in inches of water, tenths of a psi) - this keeps the 'fire' from leaking out.
In a coal fired boiler, the explosion works like this:
Coal is pulverized (made into powder) before being blow into the running boiler (the boiler is started on natural gas or fuel oil). If, for some reason, the fire goes out- and you dont stop blowing in coal dust- you create a large build-up of ultra-flammable coal dust. If you stop the fans (loss of electric power?) and subsequently restart a burner (with oil, nat gas or just a spark) it could ignite the coal dust and cause a large explosion.
Another way to blow up a boiler :)
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As I understand it, Herr Diesel had intended to run his first engines on coal dust. Fairbanks Morse made "semi diesels" for stationary use in WWII. Gotta Google that. I don't think the compression ratio was high enough for self starting, they had to "preheat" a combustion chamber but without the use of glow plugs.
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In the 1930s the French railways built a coal-burning locomotive with a high pressure boiler, could be brought to pressure from cold in about 20 minutes. Fuel was powdered coal. Try "Velox boiler" in a search engine. I believe it worked ok but failed due to very high maintenance cost caused by all the accessories including as Johnster says, all kinds of kit for starting up, restarting, blowing and idling.
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And today they are in charge of what--- 64 nuclear plants?