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Copper boiler plate flanging, or not?

Why are copper plates in boilers flanged?

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Andrew Tinsley09/08/2020 21:07:00
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Hello Bob,

It seems you are convinced that thick copper plate is better than flanging thinner plate. Well go ahead and do it, I would like to see and hear how you get on. There are quite a few people on the forum that stick to the tried and tested ways of boiler making, me included.

I am all for someone else experimenting and showing how wrong we have been.

Andrew.

duncan webster09/08/2020 21:26:23
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Posted by Paul Kemp on 09/08/2020 20:52:33:

Duncan,

Its a long time since I read it and in truth it has probably been updated since. Did you note anything re FOS and how they specify it is calculated? Nigel's comment re girder stays rang a bell, is it anything to do with the "girder" if permitted must be attached to the wrapper and the crown? I have heard several comments that the design is not accepted in Australia over the years but do not recollect a specific reason, hence my question!

Paul.

It's a long time since I read it as well, but it specifies allowable stresses and how to calculate them for shells and stays, and how to get stay pitch. Very well laid out and understandable. I compared it as far as is possible with BS5500, and it was broadly in agreement, certainly not wildly over cautious. I'd offer to send you a copy, but it is copyright. I could send you my comparison, if you're interested pm me your email.

There are one or 2 issues that would not go down well, stays running full length of the boiler and silver soldered both ends are verboten. This is because differential expansion makes it difficult to get them in and not bowed (been there done that!), and GWR style water columns joining top and bottom gauge fitting are not allowed. It would make a lot of sense to me for SFED and NAME to adopt this, even f only as guidance (ie you can do it different, but you've got to justify it).

 

Edited By duncan webster on 09/08/2020 21:26:55

Paul Kemp09/08/2020 21:51:37
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Duncan,

Thanks, I will send you a PM. I think I have a copy of the code somewhere although I may have given it away. More years ago than I can properly define through NAMES and I think it was Frank Cooper? A number of societies around the country were consulting with the Boiler Liason Group (I think that's what they called themselves anyway, been to sleep since then) on trying to thrash out a British code along the same lines as the Australian. If I remember correctly (and it's entirely possible I don't!) it gained some momentum initially and the 'rules' for copper boilers were pretty well there, it seemed to lose its way with steel boilers and I think because of the disagreements on standards it started to move towards producing a code for copper boilers only. I and quite a few others were not in support of this and because the differences couldn't be resolved maybe it just petered out. RSA were involved as were HSE (when they were still an executive and not a self supporting agency), 7 1/4" Society, SFED etc. I have a vague recollection this was around 1998 before CE and the PED were enacted but again that may be wrong!

Anyway I don't disagree with you and to get some real clarity in combination with the test code (which I think is fit for purpose with the exception of small boilers but not well audited) a code of practice would be a very useful way of doing it. That would allow departures from practice supported by appropriate evidence and a far more pragmatic way of dealing with it than a one size fits all set of hard and fast rules.

Paul.

duncan webster09/08/2020 22:02:15
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There already is a BS for fusion welded externally fired pressure vessels (otherwise known as steel boilers), I think BS EN 12953-3. It would no doubt need adapting to suit things as small as ours, but as it would almost certainly require qualified welders it seems a step too far to include it with copper boilers. There is no system for coded silver solderers as far as I know, and you don't need to worry about corrosion allowances.

Paul Kemp09/08/2020 22:15:53
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True, there are a couple of other references as well but 'miniature' boilers especially in the road steam niche are increasing towards steel, the test code covers steel so to join everything up if we are to have a comstructional code it should also include steel.

Paul.

duncan webster10/08/2020 00:48:24
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Ah but if we did that, over zealous boiler inspectors would start applying stuff relevant only to steel to copper boilers.

Nick Clarke 310/08/2020 10:37:26
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Posted by duncan webster on 09/08/2020 22:02:15:

There already is a BS for fusion welded externally fired pressure vessels (otherwise known as steel boilers), I think BS EN 12953-3. It would no doubt need adapting to suit things as small as ours, but as it would almost certainly require qualified welders it seems a step too far to include it with copper boilers. There is no system for coded silver solderers as far as I know, and you don't need to worry about corrosion allowances.

But with TIG welded copper boilers now commercially available they are certainly included in the references to welded boilers in the current UK code where a coded welder or lab checks are necessary with no reference to the material the boiler is made from.

Martin Connelly10/08/2020 11:14:51
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I have no experience of making boilers and have not read up about them either but I do have a question. Is it a case that with a flanged end plate the inspector can see the area of the soldered joint and also inspect it well enough to pass judgement on it but with a thick plate they will have no idea of the actual area of the soldered joint or the thickness of the plate?

Martin C

JasonB10/08/2020 11:32:13
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Posted by Bob Worsley on 08/08/2020 13:02:34:

............................... There will also be a slight reduction in water space, but just shift the plate to keep the 1/4" or whatever gap between plates, firebox isn't going to notice.

Bob did you miss my earlier post where I did a quick calculation based on a 4.75" traction engine boiler where changing from 10swg to 6mm would reduce the grate area by 15% I would say that would have a very noticable effect on the steaming of a boiler that size which need a lot of work to keep a healthy fire anyway.

Also where did you get this 0.005" you seem so worried about? for a common 55% silver solder the joint can be anywhere between 0.002" and 0.006" with the strongest tensile joint being at the bottom end of that range. Gap can go up a little if using a 40% solder.

duncan webster10/08/2020 11:48:38
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Posted by Nick Clarke 3 on 10/08/2020 10:37:26:
Posted by duncan webster on 09/08/2020 22:02:15:

There already is a BS for fusion welded externally fired pressure vessels (otherwise known as steel boilers), I think BS EN 12953-3. It would no doubt need adapting to suit things as small as ours, but as it would almost certainly require qualified welders it seems a step too far to include it with copper boilers. There is no system for coded silver solderers as far as I know, and you don't need to worry about corrosion allowances.

But with TIG welded copper boilers now commercially available they are certainly included in the references to welded boilers in the current UK code where a coded welder or lab checks are necessary with no reference to the material the boiler is made from.

Good point. I'd forgotten TIG welded copper. Perhaps the divide should be twixt fusion welded ( any metal ) and silver soldered (copper) boilers

Edited By duncan webster on 10/08/2020 11:50:15

Bob Worsley10/08/2020 12:58:38
53 forum posts

Should I apologise for this post? Getting some good comments.

Sorry, yes, did miss that and 15% is significant. Here comes the lack of any hands on experience. Might be flanging after all!

the 5 thou came from all the boiler books and other articles I have been reading. They all seemed to think that 5 thou was critical, so I followed on. My point about SM chips is with hand soldering, not automatic.

Just stir it up even more, is TIG welding of copper for pressure vessels? The above boiler books say that carbon arc heating is simply not on, but what is a TIG torch than similar in temperature to a carbon arc? There is no control over the temperature of the arc.

I don't really understand the problem with girder stays on the top of the firebox either.

JasonB10/08/2020 13:05:28
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Yes TIG boilers are for use under pressure. Some are fully tig welded others may just weld up a rolled boiler barrel and then silver solder the rest or main joints welded and bushes etc soldered in.

I expect most of the books were written before the advent of TIG, current and electrode size can affect the amount of heat going into the job giving some control in the right hands (not mine)

Edited By JasonB on 10/08/2020 13:08:13

Nicholas Wheeler 110/08/2020 13:19:22
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Posted by Bob Worsley on 10/08/2020 12:58:38:Just stir it up even more, is TIG welding of copper for pressure vessels? The above boiler books say that carbon arc heating is simply not on, but what is a TIG torch than similar in temperature to a carbon arc? There is no control over the temperature of the arc.

I don't really understand the problem with girder stays on the top of the firebox either.

A TIG torch surrounds the weld with inert shielding gas.

Paul Kemp10/08/2020 14:35:05
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Acceptable TIG welds on copper for pressure vessels require low arsenic copper. Controlling the temperature of the 'job' is done by the settings on the machine and the wielding of the torch. As Jason said the TIG process per se has come a long way since a lot of the books were written, the most basic variants are AC and DC but getting more advanced you can adjust frequency and other parameters to suit the job in hand.

Paul.

Paul Kemp10/08/2020 14:42:34
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Posted by duncan webster on 10/08/2020 00:48:24:

Ah but if we did that, over zealous boiler inspectors would start applying stuff relevant only to steel to copper boilers.

If they did that they should be struck off! There is already an opportunity for that within the test code. There is also an opportunity within the test code where it requires supporting calculations to be presented for a non published or pre approved design for over zealous inspectors to make up their own requirements because there is not an accepted or referenced underpinning COP or standard!

Paul.

JasonB16/08/2020 13:36:18
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Posted by Bob Worsley In another thread on 16/08/2020 10:50:08:

Anyone building any model from plans gets a collection of sheets of paper, no calculations to be seen about boiler safety. In fact my Thetford Town drawings assume you are going to rivet it, with brazing as a last option if it leaks.

If a line contact joint is considered to be perfectly ok, then why not line joint all the other joints? I would guess that certainly wouldn't be acceptable to any inspector. Why not? It is how a steel boiler is made, never flange them. So there must be a fundamental difference between silver soldering and arc welding. One is done by a trained professional?

There was a comment in an old ME about where do all the models made go to? Must be tens of thousands. And since the boiler is the first thing made with a traction engine, how many are made, leak, and the person gives up, 50%? How many Minnie boiler kits have Reeves sold over the last 50 years?

 

And yes, the boiler does look good, well done. It amazes me just how well the pickle cleans the copper, lovely.

 

And yes, again, these are my opinions.

 

As mentioned byJeff in the other thread the way the throatplate/barrel joint is constructed would be quite different to say the smokebox tubeplate/barrel if the tubeplate were not flanged.

If you look at this basic section through the boiler you can see that the pressure shown in green arrows will push the throatplate against the end of the barrel which will greatly reduce the load on the joint as the end of the barrel adds support light blue arrow. The suggested use of a higher melting point solder will also produce a larger filler thus adding strength to the joint.

Compare that to an unflanged tubeplate where there is just the empty smokebox on the outside so no additional support for tubeplate so joint has to resits all the loads.

minnie joints.jpg

As for steel boilers the weld prep is very important as it gives a far wider joint area that you would get if it were just plate to tube and the fillet will almost double the area. A throatplate to barrel joint would also probably be welded from both sides.

 

Edited By JasonB on 16/08/2020 14:08:42

Paul Kemp16/08/2020 22:56:18
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Bob,

I think you have been reading too many books! You cannot make comparisons between welded steel joint design and silver soldered copper. 2 completely and fundamentally different processes with their own advantages and disadvantages in two completely different materials. I haven't seen the drawings for TT or any constructional advice but I very much doubt there is any serious recommendation to rivet and braze if it leaks. I would think with the age of it the boiler was designed as rivetted and soft solder caulked, the rivets take the stress the solder bungs up the leaks. It's not a method condoned now for new boilers but properly done there is nothing wrong with it and there are still a fair number in service.

There were over 50 Ruston Proctor kits sold by Winson and Modelworks, they came with a ready made and certificated boiler but I haven't seen 50 chuffing round! A lot of part complete models sold are nowhere near the boiler stage, sometimes without motion work completed even so I don't think leaky boilers are the real reason for non completion.

Paul.

Bob Worsley17/08/2020 17:12:53
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Yes, these threads do seem to take on a life of their own!

Jason, you are utterly wrong with your drawing above. The pressure is internal, and this pressure acts on the tubeplate and backhead to blow the ends of the boiler apart, the internal pressure by the firebox front and boiler are irrelevant.

More reading, found some interesting comments in ME 3672 1-14 Jan 1982 p48/49 about throat plate flanges. I read the very old thread about posting photos in the forum, didn't really understand it. Seems very complicated and I refuse to use facebook or any other of these data thieving sites.

Also about longitudinal stays in other copies with writing by Martin Evans about why he thinks they are rubbish and replaces them with a chunk of copper across the smoke box plate and back plate.

I agree that TT with a riveted boiler is 'interesting', Reeves did include a newer drawing with it brazed. These drawings are near 40 years old, bought, never made, sold to me. One thing is clear, just how much better the quality of the castings is then to now. Some of the newer aluminium castings are basically rubbish.

JasonB17/08/2020 17:19:31
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Posted by Bob Worsley on 17/08/2020 17:12:53:

 

Jason, you are utterly wrong with your drawing above. The pressure is internal, and this pressure acts on the tubeplate and backhead to blow the ends of the boiler apart, the internal pressure by the firebox front and boiler are irrelevant.

Sorry Bob but you are obviously not following my drawing.

Here are the same green arrows on the actual minnie drawingare showing the pressure pushing the plates outwards

minnie pressure.jpg

Edited By JasonB on 17/08/2020 17:24:10

Edited By JasonB on 17/08/2020 17:37:03

Nick Clarke 317/08/2020 18:34:42
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Posted by Bob Worsley on 17/08/2020 17:12:53:

Also about longitudinal stays in other copies with writing by Martin Evans about why he thinks they are rubbish and replaces them with a chunk of copper across the smoke box plate and back plate.

I agree that TT with a riveted boiler is 'interesting', Reeves did include a newer drawing with it brazed. These drawings are near 40 years old, bought, never made, sold to me. One thing is clear, just how much better the quality of the castings is then to now. Some of the newer aluminium castings are basically rubbish.

If you have a smokebox tubeplate or backhead the failure mode will be for it to bulge and then 'peel' the flanged silver soldered seam apart. if you can prevent the bulge the silver soldered seam will be in pure shear and I expect the joint will be far stronger under these conditions.

How do you stop the plates bulging? - either with a longitudinal stay or stays or with a stay soldered on - as I believe was done in some traction engines .

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