Boiler Design

[Phil H 1Participant @philh1]

I am interested to know whether there any boiler design codes or recommended design practices in existence. I understand that there is a boiler test code but what about the design?

For example, I have heard of recommendations to use bushes for longitudinal horizontal stays rather than screwing the plates and the crown stay design seems to cause discussion. Other examples include the use of high melt soft soldered screwed stays versus silver soldered stays. What about the spacing and wall thickness of plates and tubes etc….

Where are the designs (the sums) recorded for existing engines? What did Martin Evans et al use to prepare their bolier designs?

By the way, my main interest is 3 1/2" gauge copper boilers. I am not interested in steel boilers for large engines.

PhilH

[Phil H 1Participant @philh1]

[Dennis WAParticipant @denniswa]

Phil…In my opinion for a 3 1/2" gauge copper boiler you will find the Australian code contains all the design information you need. You need part 1  – see http://www.smex.net.au/Store/Store_AALS-Codes.php

Dennis

 

Edited By Dennis WA on 05/10/2012 19:42:26

[duncan webster 1Participant @duncanwebster1]

I agree, Australian code is very good, but avoid use of leaded bronze for silver soldered bushes

[Phil H 1Participant @philh1]

Thanks guys, I assume there is no UK equivalent and that a design prepared to these codes will be accepted in the UK?

PhilH

[Dennis WAParticipant @denniswa]

I understand that the Australian code is accepted in many countries and has the additional benefit that it was prepared by a panel that includes professional engineers and experienced boiler makers (who may even have been qualified boilermakers).

I would believe that a copper boiler designed to this code should satisfy any UK club inspector – however bear in mind that the advisable route to follow in any country is to make contact with the boiler inspector of a local live steam club. Discuss your project with him, show him your calculations and choice of material and importantly take the advice offered.

The most important point I can offer is make sure those offering advice have actually built some boilers personally. Be very wary of "Armchair boiler experts".

I hope a UK boiler inspector will post comment on this.

Dennis

 

 

 

 

 

Edited By Dennis WA on 06/10/2012 21:01:01

Edited By Dennis WA on 06/10/2012 21:01:46

[Sub MandrelParticipant @submandrel]

I thought that both the Northern Assocition of Model Engineers and the Southern Federation had their own codes?

As an armchair expert (never having made a loco boiler) my understanding is that the Aussie rules favour boilers built like a brick outhouse?

Neil

[Phil H 1Participant @philh1]

Neil,

I have heard of the 'Blue Book' and I believe that it is due to be re-issued very soon. My understanding is that the next issue is an attempt to align Northern and Southern Federations but I also believe that it is a test code rather than a design code.

I am now a member of a local club so I will be seeking further advice. So far, they have been exceptionally helpful.

I have previously been on the receiving end of some unusual advice including issues such as material purchase and traceability.

PhilH

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

(1) Hi Neil ,

One of my one time colleagues once worked out that if Concord had been built strictly to all of the design codes then in use in industry it would have weighed 9600 Tons , would never have got off the ground and would have run out of fuel after 75 yards during a taxi run . He also conjectured that the engines required would be so powerfiul that most of North Bristol would have been flattened by the noise alone .

Codes are described by the more knowledgeable as either :

(a) A way of ensuring that designs are safe or more truly that company concerned is unlikely to get sued .

(b) As a way of preserving mediocrity in all design work .

(2) Model boiler codes :

In case of model boilers it is true that a simple design code is probably best that can be done to ensure safe designs but I have always had grave misgivings about any codes being interpreted in a tick box manner by people without any real understanding .

(3) Club boiler inspectors :

(a) There may be some well informed club boiler inspectors .

(b) I have never met one .

(4) Armchair experts .

There are two types of armchair expert :

(a) There is the usual windbag so commonly to be found in clubs and on discussion sites .

(b) People who , with a good background knowledge of a subject , can make a comprehensive assessment of a problem presented to them and find a solution just by thinking it through .

Regards ,

Michael Williams .

Edited By MICHAEL WILLIAMS on 07/10/2012 10:21:40

[Phil H 1Participant @philh1]

Michael,

Thanks for your input.

I agree that the box ticking mentality is not helpful. I have experienced design engineers paralysed because they can't find the answer in the code. I christened them 'slaves to the code'.

However, I am amazed at the apparent lack of something – even a design basis or set of example calculations. Surely I don't have to start from scratch?

PhilH

[GoCreateParticipant @gocreate]

Hi Phil

If it's acceptable to your boiler inspector I can do an FEA design check of your design, if it helps.

See my photo's

Don't wait to long as I won't have the facility indefinitely.

Nigel

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Phil ,

The whole subject of model boiler design and testing is both vexing and riddled with paradoxes :

(1) Design of something equivalent to a model boiler as an industrial product for sale would only be entrusted to a very well educated , specially trained and experienced engineer .

(2) Design of model boilers for ME type published designs has usually been carried out by people like Martin Evans and LBSC – both of which ( and many more similar ) had practically no technical knowledge at all .

(3) Large numbers of completely satisfactory boilers have never really been designed at all – they have just been copies or very conservative developments of satisfactory designs that have gone before .

Up to about twenty years ago (3) served the hobby well – common sense , conservative design practices , accumulated knowledge and a few simple sums were all that was ever needed .

There is a well known principle in engineering that ' Learning x danger = a constant ' .

Sadly numerous people in recent years have used this principle to lay down rules for how boilers should be designed and tested . The difficulty is that these ever more complex rules can only be interpreted properly by a 'real' engineer and so you end up with either boilers being designed properly like in industry as (1) above or the rules get interpreted by the 'club expert' and the resulting design is very likely less safe than one designed by experience as (3) .

If the present trend towards ever more complex codes continues then the inevitable result will be that one day hobbyists will be effectively barred from designing and building boilers altogether .

Regards ,

Michael Williams .

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

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Edited By MICHAEL WILLIAMS on 09/10/2012 17:10:37

[nigel jones 5Participant @nigeljones5]

Ive just designed, welded and had tested and certifid my own boiler, albeit in steel, but the principals are the same. There is no build code, indeed the blue book stresses that it is not a code to build to. There are however easily availible and well proven formulae (I cant spell!) which if demonstrated to have been correctly applied are generally accepted at club level. The easy approach is to find a proven design, make the changes you need, calculate all stresses etc and then run through all of this with your hopefully friendly boiler inspecter. If youve covered all your bases and can demonstrate this there should be no problem. A note of caution, if you decide to design your own from scratch try to do it on CAD or similar and on 1:1 scale – its a lot more difficult to get right than you would think! There are various books on build techniques but to be honest if you have to go t the book then your probably not quite ready. PM me if you have any specific questions as I have made 3 1/2" boilers aswell.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

I'm afraid there is a world of difference between designing a boiler and getting it past a boiler inspector and designing a boiler that is actually any good . As for checking stress calculations in any meaningful way I doubt whether the average club boiler inspector would even know where to begin .

[AndyPParticipant @andyp13730]

I would hope that any club boiler inspector who could not check stress calculations would admit as much, the only two inspectors I know can do the calcs.

What would be useful is if somebody could point to a publication that holds the necessary formulae and procedure for design – I'll start with these but something even more authoritative would be nice.

SInce I suspect we (the UK) are never going to produce anything quite so matter of fact and plain useful and usable as the Australian code how about the Northern/Southern groups agreeing that a copper boiler built to that code is acceptable here. Well I can dream can't I?

Andy

[Phil H 1Participant @philh1]

Nigel,

Thanks for the offer of the FEA but I suspect that I might need to revisit this issue more than once over the next few years.

Michael,

I agree that we need to avoid complex codes. The last thing that I want to see is the home builder being prevented from building his own boiler. If that happened, model locomotives would not be of any interest to me.

I am looking for very simple style guide that is easy to verify with no more than a calculator – similar to the information provided by Andy in his link.

I stand to be shot down here but I believe that if we resort to FEA (no offence Nigel) then a simple 3 1/2" or 5" copper boiler design has gone too far. In my area of design – things like FEA are not generally accepted unless the software is verified etc etc. Even simple spreadsheets need a set of typed demonstrations to show what is hidden in the cells.

PhilH

[GoCreateParticipant @gocreate]

Hi Phil

No offence taken, FEA is not really for the amateur environment. A simple method that can be used by the armature would be the way to go.

If a simple method could be devised then FEA could be used to help prove it, once verified no further FEA would be needed by the user. Just a thought.

When I was doing those FEA's in my photo's I did think about devising some simple formula myself and using the FEA to prove the ideas, I think, for me anyway, this would be an interesting exercise. Other interests and work make this a low priority though.

Looking forward to hearing your progress.

Nigel

[Paul LousickParticipant @paullousick59116]

As a previous reader has said that the Australian code favours boilers built like brick outhouses.

The Australian Miniature Boiler Safety Committe Code Part 2 is for steel boilers having a working pressure not exceeding 700 kPA and 50 litre capacity. (separate code for copper boilers).

Boilers built under this code are overdesigned for safety because they can be built by the hobbyist and can be inspected by boiler inspectors appointed by registerred clubs.

I have a design for a 6" traction engine which is certified for use in ther UK but does not comply with the Australian code. The Aus code has more requirements, thicker steel for the boiler barrel and tube plates and more inspection ports.

Paul.

[Martin KyteParticipant @martinkyte99762]

Have you talked to SMEE?

[Phil H 1Participant @philh1]

Thanks guys. I think my next step will to speak to my club (perhaps they have a few ideas too). Depending on the result from that discussion I might go ahead and order the Aussie code for reference.

PhilH

[Sub MandrelParticipant @submandrel]

.. but we can all go out and buy pressure cookers and cappuccino machines made of metals and with construction methods we would never be allowed to use for model boilers…

Neil

[julian atkinsParticipant @julianatkins58923]

the alan stepney website contains invaluble info, and martin evan's model locomotive construction book contains the info/formulae applied to ME designs. KN Harris's book does likewise. an ability to quite same is essential for any 'new' design or variation of a proven design for a silver soldered copper miniature loco boiler. ive got 4 locos 3.5"g and 5"g which have boilers that arent to any published design. and quite a few of the published designs are very 'iffy' IMHO!

cheers,

julian

Edited By julian atkins on 12/10/2012 00:21:06

[Donhe7Participant @donhe7]

Posted by Stub Mandrel on 11/10/2012 21:55:27:

.. but we can all go out and buy pressure cookers and cappuccino machines made of metals and with construction methods we would never be allowed to use for model boilers…

Neil

I might suggest, that this could be because we cannot produce a certificate which says that model was safe to use in the home environment (or similar situation) …………

donhe7

Edited By Donhe7 on 12/10/2012 01:58:04

[Phil H 1Participant @philh1]

Julian,

I will have a go at finding the references that you mentioned. I will be building a very simple boiler quite soon (for Northumbrian) and I wish to make some very minor mods (slightly reduce the boiler barrel diameter by 1/4" because of the tube I have and move a couple of the bushes). These changes are clearly not going to challenge the integrity of the original design but I was then left with the question… 'where is the original design?' Yes – I have a drawing from the ME but where are is the 'design' i.e., the work through of the sums to demonstrate that everything is fine.

I am definitely not one of the model engineers who wish to put stringent, new codes which are only possible to apply to commercial manufacturers. Quite the opposite. I was simply looking for the very simple 'qualified' formulae, recognised strengths and safety factors for these very simple fabrications.

PhilH

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