Boiler Explosion

[mike os]

Surprised nobody posted this, which is a good illustration of what can happen - remember this is a very small, relatively low pressure boiler, having said that, they had no idea what the pressure was at - watching it as I type ... idiots.

Nick

what a bunch of total arseholes... some people deserve maiming....

[PTsideshow]

Here are some of the better known books on boiler building. During the computer upgrade the reviews have been misplaced.



Volume 1 and 2


paperback and hard cover





There are a number of others who's scan has also gone missing.

[PTsideshow]

Hi ya,

Could someone/anyone please reply to my question regarding whether a model boiler-engine,etc, could blow regarding my previous question? I do not mean to come across as being arrogant or bossy but I feel it could be pertinant to beginners such as myself and other guys who wish to start in the steam world.

Again,

many kind regards,

Ron.

If all the conditions are met it might be possible. But the commercial ones are designed with abuse to a point in mind. Small fuel/fire box larger water/steam space then the full can convert etc. A home made one, can also have a failure if all the conditions are met.
Again they don't go like in the TV or movies like with the car explosions, a car parked across the street was rear ended by a drunk, We slept through it and the lazy/slow fire. What woke me up was the 200 people on my front lawn making noise!

[DaveH]

Well thank you all, I have certainly learned a lot, and probably so have lots of others.

Your generosity in giving your knowledge and taking the time and effort to write and post it,  is sincerely appreciated.

Dennis thanks for your offer – accepted with thanks.

Ron(Ronkh) are you happy?

 
DaveH   

[GWRdriver]

Ron,
If I sort out your question correctly, it concerns the possibility of a separation of the boiler from the chassis of a model engine in the case of say, a failed crown sheet.  Please correct me if I've gone down the wrong track.  Thew answer is, always "possible", but hightly, greatly, unlikely.  I have only known of one separation of parts upon the occurrence of a model boiler failure.  Some years ago in the UK, the lower edge of a firebox wrapper seperated from the mud ring in a 5" gauge (1"scale) model locomotive while standing in steam.  The resultant release blew the nearest adjacent drive wheel off the end of its axle and of course sent ballast and dirt flying.  There was no serious injury reported but observers and examiners were perplexed at how a release of such relatively small scale could have the force to dislodge a drive wheel, especially when the spoked drive wheel would allow an ample pressure escape route.

So far as a boiler leaving its frame and becoming airborne, no such event has ever been reported in an engineered model although over the decades many crown sheets (or their stays) have failed without catastrophic results.  I specify "engineered" models apart from soldered brass tabletop toys which can blow at any time for a variety of reasons.  The only explanation I can offer as to why no separations have occurred is that model locomotive boilers, even those which strictly adhere to scale detailing, tend to have more relative strength of connection than full size locomotives at the firebox end, while at the same time would have many times less propulsive force acting in the event of a crown failure.  Not very scientific, but that's the opinion I have.

[DaveH]

GWRdriver,

I think, also Ron wants to know if the boiler is tilted say from the horizontal with a low water level, then tilted back it likely to cause a major problem.

DaveH

[GWRdriver]

Thanks Dave.  What will happen will depend upon several variables, among them he amount of water in the boiler, the depth and intensity of the fire, the state of the boiler (heat and pressure reading) before uncovering the crown, the number and size of safety valves, the length of time the crown is uncovered, and then of course the physical condition and design strength of the boiler.  Lets say there is a good fire, the kind normally wanted for continuous running hauling passengers, the boiler is at full operating temperature and pressure and water is low but not in the danger zone if in a level position.  What is most likely to occur if the crown sheet is uncovered and then quickly recovered is a momentary severe over-pressure which should be released by the safeties.  If the crown is left exposed for longer and is allowed to get very hot the safeties probably can't release enough pressure soon enough and the probability is a failure will occur at the weakest point in the area closest to the pressure source.

In the event of such a low water disaster-in-waiting the thing to do is stop the locomotive wherever it is, drop the fire immediately, and walk away (ie, wait) and allow the engine to cool.  At that point whatever damage there will be has been done and under no circumstances should an attempt be made to introduce cold water into a hot boiler, even a tiny amount.  This will produce an extreme over-pressure failure and a ruined boiler.

Of the books listed above my favorite is the KN Harris book, but what I know about model boilers and boiler building (by far not everyhting there is to know) has been learned from several sources including books, magazines, my mentors, trial and error, and just building them.  The photo is of a boiler for a 4.75" gauge (1"scale) tank loco I built for a fellow in Ohio a few years ago.

[DaveH]

GWRdriver,

I have the K N Harris book and the two by Turbal Cain.

So I have no excuses
 
DaveH

[Ronkh]

Thank you DaveH, GWDriver, PTsideshow and all very much indeed for your replies.

There is sooooo much to learn regarding steam. I have quite a few of the books mentioned, and I think it will be a fair while before attempting to make one once I've read and re-read them, plus taking in what has been posted on this site.

Kind regards,

Ron.

[NickG]

I perhaps should have put a few more words around the video I posted. I agree completely with what GWRdriver is saying but I posted it to get across a point. In the UK small model boilers under 1.5 bar-litres (I think, but will check so correct me if I'm wrong), do not need testing or inspecting or anything. So the video is a good example of what can happen, any tom dick or harry could make or buy such a boiler and put it on show infront of thousands of people. It doesn't necessarily have to be an idiot either. When I was about 9 or 10 my grandfather gave me the Mersey model steam engine he bought as a kid, but the boiler had a leak so he soft soldered one end up using a soldering iron heated up in the coal fire, this did the trick and it worked a treat. I was thinking the other day it'll soon be getting to the time where I pass the model on to my children, but then I had 2nd thought - it's made from brass, soft soldered (neither of which are considered good practice now), doesn't have any stays, who knows whether the safety valve works, never been tested etc etc the list goes on. Imagine if I gave it to my children and something happened similar to that video - unlikely I know, but unlikely isn't good enough for me - I think it'll have a new boiler before my sons go anywhere near it. My grandad wasn't an idiot, he was a skilled engineer but maybe just wasn't aware of what could happen? There are other certain parameters that are designed in with such commercial boilers for instance, the meths runs out before it can boil away all of the water but these things can be by passed in the wrong or naive hands. So I posted that video just to try to make people aware of what could happen. With anything over 1.5 bar litres the boilers are subject to all the regulations and inspections etc so I agree such an incident is so unlikely if you did a risk assessment like we do at work, the risk would be very low due to the probability being so low. The consequences remain high though.

Anyway, thanks GWRdriver for the information. It has been useful discussion for a few people I think.

[andyf]

This reminds me of the Sunday 50 years ago when the ballcock float in the toilet sprang a leak and got a bit of water inside. In the old days, they were made as two hemispheres of thin copper sheet joined with solder round the equator. Dad decided it would be easy to fix. Grasping the thing by its attached lever, he held it over the gas hob to boil the water away, waving it around to distribute the heat. All seemed to be going well, with a slow escape of steam from one point on the equator – there must have been a pinhole in the fillet of solder.

However, while rolling the thing around, Dad must have got that point hot enough to melt the solder for a moment, before it re-solidified and sealed the hole. Not realising this, he continued heating what was now a sealed thin copper sphere containing a spoonful of water.

The bang was deafening; it must have been audible a quarter mile away. Happily, there was no damage except to the float, which resembled two tulip petals. Shops didn’t open on Sundays back then, so the family was reduced to taking a bucket of water to the loo for flushing purposes until Dad returned from work on Monday evening with a new-fangled plastic float.

Ever since, I’ve been very respectful of any closed system containing boiling water.

Andy

[DaveH]

Andy,

 

I know I shouldn't laugh but it is funny.

DaveH

[David Jupp]

Further to NickG's post above - Under the Pressure Equipment Directive, steam generators under 2 L volume fall into the 'Sound Engineering Practice' category.  This means that there is no laid down requirement relating to design or manufacture, but it is expected that 'Sound Engineering Practice' (SEP) will be applied.   SEP is not defined, but it might include making use of accepted formulae, standards, guidelines etc.

Ignoring an established good practice would tend to suggest that SEP had not been applied.
It is down to the manufacturer to be able to demonstrate that SEP has been applied.
Note that PED does not cover operation or maintenance.

I recall that some time ago a 'code of practice' or something similar for model steam plant was drawn up by a working party involving the HSE in some way.  If that document is still current it would seem to be 'required reading' - see http://www.hse.gov.uk/pubns/etis12.htm