boiler design verification

The boiler test codes accept that previously published designs are considered to be proven and safe even though they may never have been subjected to calculated stress loading.

What is the position if one is working on a model that is not a published design, but a replica of an original. All the boiler dimensions are available for full size and it is reasonable to alter the tube numbers and spacing in the model to accommodate suitably sized tubes that match the design of a similar sized boiler of a published design.

My question is how would one go about proving the design is safe and getting the boiler inspector to agree to that ? The B I can reasonably expect one to provide stress calculations to demonstrate this, but these are not easy to do for an individual, and would cost an arm and a leg to get them done commercially because of the liability implications.

Any thoughts please ?

Kind regards

BK.

The calculations are in fact quite straightforward, and are set out in detail in the Australian design code

**LINK**

gives some background. I have compared this with an relevant British Standards (with a bit of interpretation for use of copper). All the stuff about this code being over restrictive is tosh. It is a very well thought out document.

Alternatively, you can adapt the design of a similar sized boiler, but that assumes that the original is OK. Speak to your boiler inspector before you do anything else

There are a couple of spread sheets about that will do a lot of the calculations for you, just enter things like material, barrel dia and pressure then it will give you things like stay spacing, thickness of materials, etc.

The main restriction with the Aussie code is that you are limited to 100psi, not such an issue with copper but a bit limiting for a steel boiler.

I would like to obtain a copy of the AMBSC Book1 and Book3. Has anyone purchased these, and where is the best place to get these from? Thanks.

Steve

Thanks Duncan. I, like Steven have struggled to find a copy of the codes other than by outright purchase, which it may come to. I am happy to try and do the calcs if I could get the information to confirm I am doing it properly and this sounds like it will provide that.

To explain a bit more , The design I have in mind has almost exactly the same dimensions as a standard LBSC boiler in terms of length diameter etc, however LBSC's design has a firebox that fits between the frames and the design I am looking at uses a wide firebox sitting above dropped frames. in principle this type of firebox should be inherently stronger and easier to stay but obviously does not constitute an approved design by virtue of grandfather rights. The LBSC design is also reputed to be difficult to fire because of the narrow firebox and hopefully this wide firebox may help to resolve some of these problems.

I would also like to consider adding a baffle ( brick arch type within the firebox) to improve gas flow, which again would be an alteration to the original.

Jason, - Thanks- I will look for those spreadsheets - in this instance 100psi is OK . Grateful for any links you may have.

My BI is fully on board, but quite understandably has asked me to consider getting independent calculations to confirm the design basis.

I bought my copy, which I think is now out of date. It's not fair to our antipodean friends to just scan it, their charge is to cover the costs of running the scheme, not a big fat profit. If you have a decent (big) public library near you they might have a copy of BS5500, which is for unfired pressure vessels, but contains all you need to know about shell thickness and stay spacing. There is a supplement for aluminium vessels, if you use a bit of judgement this can be interpreted to cover copper. Don't even think of buying it, I've got a copy which was being dumped from work, it must be 3" thick.

I've done the comparison, and written it all up, but I'm loathe to go public in case someone subsequently sues me! I think SFED and NAME should get off the fence and adopt the Australian code. At the moment we don't seem to have a reference-able criterion. The 'various spreasheets' may well be correct, but on what are they based?

There are plenty of wide firebox designs out there, but I wouldn't use LBSC as a basis, well out of date

If looking via a library (in person or on-line access to access British Standards), be aware that BS5500 isn't called that any more. It has been re-designated as PD5500. If you ask for BS5500 you'll either get an outdated version, or nothing.

Thanks Duncan . I'm not using LBSC out of choice but because it is the closest to the dimensions I am looking for. We have already discussed with BI, the need for changing all direct threads to bushes, increases in safety valve dimensions and firebox crown staying, so the original LBSC design is largely changed anyhow.

If I can get a copy of the necessary design calcs I am already sort of 50 % towards creating a new design as I have the original loco boiler drawings from the NRM . so its beginning to look as though getting a copy of the aussie code and doing the calcs for a copy of the original design and dimensions is going to be the simplest way forward.

Its just that both my BI and I would feel happier if we can get some independent verification of the design and calculations without it costing an arm and a leg, which is why we keep coming back to the grandfather rights vested in some of the older designs , poorly designed as they may be.

PS just looked at PD 5500 - £ 1800 a copy - £ 900 if you sign up for membership of BSI !!!!!!!!!!!!!!!!!!!!!

You could try one of the model boiler builders, Paul at Southern boiler works will do design work, not sure of costs though likely still cheaper than going through one of the insurance companies.

The Spreadsheet that I do have is not really mine to share unfortunately.

Most BS documents (including PD5500) can be accessed on-line via major libraries. Printing isn't allowed, but what do you expect for free!

Design verification isn't such a mystery. It's an independent check that a sensible approach has been taken to calculations etc. (of course that is much easier to show if there is an accepted code for the application). Then some of the calculations may be checked. Tip - use a spreadsheet for calculations (much easier to identify mis-typed inputs than if you just use a calculator).

Be aware that PD5500 covers fusion welded, unfired pressure vessels - so whilst some material may be applicable, it isn't an exact match for what you are attempting.

Write up your design methodology and the key calculations very clearly - that reduces the work for whoever is verifying. So making it less onerous if taken on as a favour, or reducing costs if done commercially.

Edited By David Jupp on 23/03/2017 15:22:10

Martin Evans' "Model Locomotive Boilers - their design and construction" chapter 2 takes the reader through the process, equations and calculations for designing a boiler with the appropriate safety factor. Although out of print (but readily available on the 2nd hand market) and slightly dated, the approach and calculations are sound. Most of the existing designs in the UK will have been designed according to the various formulae used in the book so I think it is a pretty safe bet that any calculations based on the book will be acceptable to a UK club inspector.

HTH,

Rod

This page at Camden Books suggests the Martin Evans book is available again.

Another book that has a full section on designing copper boilers is "Model Boilers and Boiler Making by K. H. Harris". I haven't checked lately but from recollection the formula and calculations are very similar to those in Evans book. Again I believe it may be out of print, but copies may be avail;able. I know there is one in our club library here.

John

I am after purchasing a copy. The AMBSC website listed a few suppliers in Australia, and I just wondered if I could buy a copy from somewhere more local. I bought a programming book from America once, and the import fees were almost as much as the book, which was not cheap!

Duncan, where did you buy your copy, may I ask?

Steve

It's a long time ago, but I think I got it from Australia. For some reason I don't think I paid any duty. I'd e-mail whoever sells it and ask if they will sell you a pdf, pay for it via credit card or paypal

As regards the Martin Evan's and KNHarris books, they are the thoughts of their authors, not referenced to any national standard. They may well be right, but would not pass muster. I know this sounds pedantic, but if you're going to go to the trouble of sums, they might as well be using proper criteria.

Many thanks Duncan, I'll contact the seller.

Steve

NAME publish a guide on the calculations to be used. it is the same / very similar to one of the books quoted. (cant remember which one) At the time it was done the SFED wouldn't adopt it but at the joint boiler conference I went to it seemed that might move.

If the joint committee only adopted the Australian rules then all the published designs would need reviewing and reworking so i don't see that happening

Steve

Hi BK,

I dont think it is as problematic as you may fear.

Most experienced club boiler inspectors 'know whats what' in the UK.

If you have a proven track record of building miniature loco boilers then things become much easier.

I would not want the UK amateur builder to be governed by the 'Aussie Code' which is far too prescriptive, and certain anomalies that drive a coach and horses through the code.

It would be of far more assistance if you said what loco you propose building and to what scale, and which bits of the LBSC designs you propose to use.

I have a particular aversion to LBSC's butt joint of barrel to throatplate joint preferring double flanged throatplate because LBSC's design was for use with a sifbronze joint here, and not a silver soldered joint.

Cheers,

Julian

Our club, which started the AMBSC code, has tried to convince the committee to put the codes online, but they reckon they need the revenue from sales.

The trouble with safety committees is that they feel obliged to make things even safer, when there is absolutely no need, and no demonstrated problem. Then there are personal emnities and agendas etc..

AS a professional boiler maker I have studied all 4 parts of the aussie codes in detail, and to be fair they lay down good ground rules, having said that they dont offer anything which is outside of best practise. PM me if you want a breakdown of the salient points.