Boiler design

[RRMBKParticipant @rrmbk]

If someone looked to make a boiler in 3 1/2 gauge for a specific locomotive that is not currently a published design how does one go about getting it proven ? I.e. who can certify the shell calculations to comply with NAME or southern Fed ?

If the design were to use a published design but extended or shortened the boiler barrel & tubes by say 30mm what would the situation be then. ?

I am contemplating an unusual model, although the full size boiler was as used on many similar full size locos but 10% shorter.

As far as I can tell there are no published model designs to match this boiler but there are some that are the right diameter but slightly longer or shorter.

At this stage I would prefer not to discuss what the prototype is.

[RRMBKParticipant @rrmbk]

Design verification

[David JuppParticipant @davidjupp51506]

Well the stress calculations for a cylindrical shell are independent of length, so small changes to length should not cause any problems.

I'm sure others will be along to advise on getting any changes accepted (my experience is with PED for commercial items). I'd suggest speaking to the boiler inspector would be a sensible first step.

[Bob YouldonParticipant @bobyouldon45599]

Good afternoon RR

I think your first port of call would be a chat with your club boiler testers for an opinion, it is they who'll give a clearer answer upon looking at your proposal and submitted drawings. What you are suggesting isn't unheard of and avoids many of the pit falls of self design. If you're a member of a UK based club then have a look at the 2012 edition Boiler Test Code BTC 2012, the "Green book"

I trust the foregoing will be of some assistance.

Bob Youldon

[Nigel BennettParticipant @nigelbennett69913]

I'm a boiler inspector for our club. If somebody came to me with a "new" boiler design, but he could say that it was (say) Martin Evans' "Conway" boiler but 2 inches longer in the barrel, and 2 inches longer in the firebox, but he'd used exactly the same stay SPACING and the same boiler plate thicknesses, I'd have no qualms about passing off the design, and approving the manufacture of it at the various stages.

I'm sure your club Boiler Inspectors would be similarly accommodating.

[Brian HParticipant @brianh50089]

Where can one obtain a copy of this standard?

[Andy AshParticipant @andyash24902]

I can't remember where I got it from, but you should be able to find it here;

**LINK**

[RRMBKParticipant @rrmbk]

Hi All thanks for the info.

I had already spoken with the inspector(s) at my club and there views were much the same . I was considering however making the boiler exactly as per the size and shape of the original but obviously different tube dimensions and layout. It was if I decided to go down this route that although I can do the calcs, the inspectors advised It would be best to provide independent verification for these and so I wondered who might do this?

Kind regards

[David JuppParticipant @davidjupp51506]

Verification options – one extreme would be to involve a notified body. You could have an independent Engineer review your calculation, which might give the Inspector more confidence.

Either of the above might appear moderately expensive.

Could another club member perhaps review your calculations, or carry them out independently to see if results match? That might have potential to be less expensive.

Even Notified Body design verification doesn't necessarily redo every calculation – it's as much about checking that a sensible approach has been used. I.E. that you've used appropriate formulae, followed relevant codes, that kind of thing.

[duncan webster 1Participant @duncanwebster1]

Posted by RRMBK on 02/12/2016 10:58:17:the inspectors advised It would be best to provide independent verification for these and so I wondered who might do this?

Kind regards

Isn't that what boiler inspectors are for? For basic design formulae, stay spacing etc you can't do much better than the Australian Boiler Code. Pay particular attention to the backhead and smokebox above the firebox/tubes area.

[David JuppParticipant @davidjupp51506]

My experience with commercial pressure equipment is that Inspectors and Design Verification Engineers have different skill sets. There is no absolute requirement for Inspectors to be comfortable with reviewing design calculations, though some may be.

[Brian HParticipant @brianh50089]

Quote "There is no absolute requirement for Inspectors to be comfortable with reviewing design calculations, though some may be."

I don't see how a boiler inspector could certify a boiler is he wasn't able to assure himself that the design was safe.

[David JuppParticipant @davidjupp51506]

Quite simple – Inspectors verify correct construction to an already proven design, and assess current condition against accepted norms or limits (e.g. extent of corrosion). To do this does not require the inspector to be familiar with the detail of the design calculations that somebody else did.

The Inspector can call upon others with appropriate skills to do analysis or calculations – that is often what happens in industry.

Basically an Inspector need not be a Stress Analyst or a Design Engineer (though some may be).

[RRMBKParticipant @rrmbk]

Duncan , Brian, David.

Your posts have got to the heart of the matter. I have done the necessary design calcs in the distant past, but its something I would be very rusty on now . Similarly I have every faith and confidence in the boiler inspectors I am talking with but i feel it unfair to ask them to verify calculations for what is essentially an an unproven design. These people are after all mainly unpaid volunteers who already take on a huge responsibility to allow us all to enjoy our pastime.

Brian & Duncan " I don't see how a boiler inspector could certify a boiler is he wasn't able to assure himself that the design was safe"

Whilst I agree in principle with what you are saying, I think most inspectors base assurance of the safety of a design, as being the fact that it is a historic published design which has stood the test of time.

I suggest that LBSC is unlikely to have had boiler stress calculations done and independently approved for all of his designs but they work well enough if properly made.

I have had some involvement of Notified Bodies in the workplace and the experience wasn't particularly convincing and was painfully expensive.

I agree with David that the hoop stress should not alter with length and so modifying a current design is probably the best way to go.

I do have copies of the UK and Australian codes and both of these are very helpful publications. Follow these properly and there is no doubt one will have a safe pressure vessel.

unfortunately some numpty in a London underwriters office will know nothing about them and will rely solely on someones proof signature.

Hey ho – onward and downward to the pits of Valhalla!

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