SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Mar 24, 2007 18:53:14 GMT
... Do they?
Guys,
I've just returned from a nice ride on my new motorcycle, still running in at present. I went to see someone and arrived just after his boiler let go in a cloud of steam and a spray of soggy insulation.
It's early days so no names, no pack drill and I have little info on the victim loco. However, this thing had last been tested to twice working pressure and this was the first steam-up of the year. The reported gauge pressure was rising through 40 and the safeties were nowhere near blowing.
What happed was that the outer wrapper let go at a couple of rows of stays and appeared to have also blown off the cleeding (cladding??). So, stunned faces all round.
So no complacency out there.
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Post by spurley on Mar 24, 2007 19:04:27 GMT
Hi Steve
Interesting and alarming I agree! My question though would be why was it tested to twice working pressure? The current rules, as far as I am aware, only call for the first hydraulic test, when the boiler is new, to go up to twice and subsequent tests to one and a half times.
The theory here, I think, is to do a 'proof' test first off then once the copper has work hardened in use the one and a half times test is a good indicator of a sound boiler. It's possible that your mate's boiler was damaged by the over pressure test?
I hope no-one was hurt?
Cheers
Brian
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Post by chris vine on Mar 24, 2007 20:31:23 GMT
Hi Brian,
I suppose it could have been stressed (more than necessary) by going to 2X working pressure, but with a factor of safety of say 8 or 10, at 40psi it should be nowhere near a danger level. It will be interesting to find out the facts of what happened.
Chris.
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Post by Tel on Mar 24, 2007 21:14:45 GMT
2x shouldn't do any harm at all - sounds more like a failed pressure gauge to me
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Post by GWRdriver on Mar 24, 2007 21:26:13 GMT
I think it would be very beneficial to honestly and accurately document ths incident, not for what occurred but for what did NOT occur. Admittedly mostly over here, dispite there not being a single incident to support such talk there are many who insist upon includng the terms "bomb", "shrapnel", "missle", and such in their rhetoric when talking about boilers and potential failures. Some of us discourage this kind of language (one never knows who might be listening) and criticize it if we can so I think this is a significant incident because it can be confirmed there was a major structural failure yet no catastrophic (or injurious) result. For instance, it would also be important to record the proximity of attendees to the boiler because this certainly would bear on the fact that there was no personal injury.
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Post by alanstepney on Mar 24, 2007 22:14:33 GMT
I would like to hear more details, and as Harry said, facts are most useful not only to prevent the same thing happening elsewhere, but to allay fears of others who might hear of the occurance, perhaps an exagerated account, but not know enough to debunk rumours.
As some here may know, I have tried to collect information on model boiler failures, and the safety record is superb, as can be seen from the low insurance premiums we have.
Failures of boiler shells are unusual, so this alone makes this an interesting event and one that would be worth investigating.
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Mar 24, 2007 23:05:42 GMT
All,
I have pointed the owner at this thread, more of a courtesy really, but also in the hope that he can provide more detail either directly or through me.
I agree that it is important for the hobby in general that the cause of the failure is known. However, I also feel it important that if the individual is unable to offer more detail then neither will I.
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Tony K
Elder Statesman
Posts: 1,573
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Post by Tony K on Mar 25, 2007 9:03:02 GMT
Steve, the fact that a boiler that has been working at, say, 80 psi and above has blown at only 40 psi is suspicious I think.
We think the boiler regulations are adequate and common sense confirms it. Like the MOT though, the test only says things were OK on the day. For instance, later damage may happen and is not a reflection on the validity of the test.
As you are close to this issue, perhaps you could make a judgement yourself as to what happened and report back. If the owner is embarrassed then perhaps if you get the facts and discuss with Alan (with his record of model boiler failures). I am confident Alan could then decide whether we need to be alerted or told not to worry. We do not ALL need to rake this over and if anonymity will help the owner open up then this would be a good thing.
Someone like Aristotle once said "Every addition to the knowledge of man is an expansion of the power of mankind" - or something. There, that's a bit profound for a Sunday morning when we all lost an hour's sleep.
Kind regards, Tony.
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Post by Laurie_B on Mar 25, 2007 11:53:43 GMT
Spurley/Brian is quite right.The 2X hydraulic pressure test is for new copper boilers which,after all the silver soldering operations tends to be in a somewhat annealled condition.The 2X initial test is to work harden the material to improve its tensile strength.Any subsequent test should be to 1.5X the design pressure,and no more,as this serves no useful purpose and is only over-stressing the boiler components.
Another important aspect of the new model steam boiler regulations is a test of (what the Pressure Safety Systems Regulations call them) the 'protective devices',i.e the safefy valves and the pressure gauge,items which had been somewhat overlooked in the past.
It will be very interesting to find out what the exact cause of this failure was.
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Post by GWRdriver on Mar 25, 2007 16:17:29 GMT
While I agree that repeated pressurization, hot or cold, will work-harden a copper boiler (and not all authorities agree on that) I have never seen nor heard it stated that the purpose of the intial 2X test is for work hardening alone, or at all. But then I've never read or heard any other specific reason for 2X intial testing, only that it shall be done that way.
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John Lee
Part of the e-furniture
Posts: 375
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Post by John Lee on Mar 25, 2007 17:49:02 GMT
I am surpised a copper boiler has burst if tested properly, albeit in a non injuring fashion.
Steel boilers however; cast your minds back to the Victorian days and many deaths
John
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Post by chris vine on Mar 25, 2007 17:54:15 GMT
All boiler "explosions" that I have read about in old Model Engineers have a common theme. That is, before the failure there is always a sentence to the effect that "the locomotive/boat/traction engine had never gone better before"........ Usually because the boiler was running dry and so the engine was running on superheated steam.
It will be interesting to find out more about this.
Incidentally, does anyone know the temperature of steam and water when released from, say, 100psi to atmospheric pressure? That would be another interesting fact. Maybe I will try to use my old steam tables to work it out but don't hold your breath!
Chris.
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Post by havoc on Mar 25, 2007 17:57:23 GMT
Lots of speculation. Until all circumstances are known there is no conclusion to be drawn. Strange that it happened at such a low pressure. Unless the pressure gauge was defective, but then the safeties would also have been defective.
Since all model boilers are overdesigned by a factor 4 at least a 2x working pressure test won't damage a boiler.
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Post by steammadman on Mar 25, 2007 20:46:16 GMT
This boiler incident sounds very suspicious to me,especially as it is supposed to have "let go" at only 40lbs psi. After over 50+ years in model engineering i have only ever known of a boiler "letting go" is when it has been caused by human error, human negligence, human ignorance, or SHEER STUPIDITY. Yes there are other times, when someone has let the water get too low, once when a guy filled his boiler through the safety valve bush, got talking and forgot to to tighten the safety valve in. But both of those come under the heading "STUPIDITY".
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Post by GWRdriver on Mar 25, 2007 22:05:13 GMT
Thank you Steamadman. This post virtually assures us that we will not see a first-hand report of this incident from those involved for fear of harsh judgement. Who could blame them.
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Mar 25, 2007 23:44:46 GMT
Gentlemen,
From my original post:
"What happed was that the outer wrapper let go at a couple of rows of stays and appeared to have also blown off the cleeding (cladding??)"
I omitted to state that the stays were around the fire box about half way up on the right flank. As far as I could determine there was no rupture of the copper structure or a failure at any of the major silver soldered joints although there is now a new bulge where a bulge shouldn't be and yes there was a bit of steam or so I heard.
The "Why" has yet to be determined and if and when I get to know more I will attempt to share it with you. If anything it puts a very good case for getting the stays in there and in there correctly. If the stays are put into holes with insufficient rattle factor then the solder won't wick in because there's simply no room. What you can get is a perfect fillet hiding a classic 'dry joint'. This may be the reason for this failure but please note the phrase 'MAY BE'. Failures of this type of joint can be the result of temperature cycling and stress cracks at the fillet and in reality impossible to spot without a major strip. Once a fillet fails there may then be an avalanche affect on the others. I have no idea of how old this boiler was.
Soldering takes us into the realms of competencies and the dangerous concept that some folk just shouldn't be allowed to do things. Soft and hard soldering is an art form and a skill to acquire usually the hard way of actually doing it and maybe screwing up a couple of times on the way. However, we really don't want to be forced to use certified solderers in the same way steel boiler manufacturing requires certified welders.
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Post by alanstepney on Mar 26, 2007 7:19:03 GMT
As far as I have been able to discover, the last time that a model boiler exploded and injured someone, was back in the late 1920's.
There have been other failures, including one at a northern club in the early 90's, where no-one was hurt, but in that particular case, two guys moving a loco manually, tilted it uncovering the firebox. Carelessness rather than a faulty boiler.
As for skills in building, I have a boiler that I made 40 years ago, and which I am now replacing. The original hasnt failed, and spent many hours doing a lot of hard work. However, the quality of construction is way below what I would accept nowadays, with, as was usual at that time, soft solder caulked seems. It was as good as my abilities then, and obviously sufficient for the task as it worked OK, but I still feel it should be replaced. My point is that a novice, which I then was, can build a boiler which is safe and works OK, provided they follow the basic "words and music". They dont need to be built by a professional to ensure they are safe. In the case of the boiler concerned in this thread, I would dearly love to see a detailed analysis of the boiler to ascertain why it failed, what, if anything, was wrong with the design or constructon, and what can be learned to prevent it happening in the future.
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Post by Shawki Shlemon on Mar 26, 2007 9:03:14 GMT
I have been away for a week ,and I am back catching up with the latest information . Boiler failure ,not exploded boiler is the case . In my humble opinion without knowing the details , I would suspect stays failure due to one or more of the following :- 1) boiler was overheated with low water level . 2) The stays were incorrectly silver soldered and/or not enough protrusion . 3) Not enough stays to support the wrapper . 4) Soft soldered stays . Soft solder is OK for sealing small weeping leaks but not for structural joints. 5) A crack in copper or in silver solder due to thermal shock for some reason or another. 6) Incorrect silver solder used to build the boiler . 7) Incorrect material used for wrapper or stays . 8)Physically damaged and may be not noticed . Generally boilers are built as mentioned above to a safety factor of 8 to 10 , therefore this seems to me suspicious .
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Post by stantheman on Mar 26, 2007 9:03:53 GMT
I am sure there are many club boiler testers, like myself, that would be very interested in reading anything about the boiler mentioned. I echo Alans thoughts about this subject. More details would alleviate concern amongst those of us that undertake this task within our own circle of club mates. Also let us consider how many boilers there are in regular use in the UK alone that give un-failing service, yet have been built by 'novices'. Severe structural failure is rarely heard of which must say something about our dedication to the hobby and safety. Stan.
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Post by Shawki Shlemon on Mar 26, 2007 9:21:47 GMT
Hi Stan I am a boiler inspector myself and likewise I like to know the details . In Australia we have to report any incident to AMBSC in writing .
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