Copper boiler plate flanging, or not?

[Bob WorsleyParticipant @bobworsley31976]

Back, just replied to another post about a Minnie boiler, the throat plate to boiler joint doesn't have a flange, just a simple 1.5mm thick solder joint. In MY, emphasise MY, book that is simply unacceptable.

Duncan's comment about getting hung up on the 5 thou gap is simply wrong. I am an electronics engineer, and have had to cope with surface mount components, and a 5 thou gap simply means the item fails later on. Tin solder is awful stuff, I have to hand solder, fine if you have got the gear to flow solder the 98% tin 2% silver solder. But even that fails after a few years. I have been seriously burnt by lead free solder, I won't use it.

There is lots of comment about expansion, yes, but why is a solid tube plate different to a flanged one? The solder is easily able to cope with the stresses created, as is the copper sheet, not a problem. It all comes back to not really knowing just how much solder is in the joint. 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.

I will buy a little boiler and make it.

As said there have been thousands of boilers made, but where are they? Going back to the 40's and models were made everywhere, but do you see them? The exhibitions all seem to have new models. Beginnings to wonder if all the thousands have actually been turned into static models, or simply scrapped. Seems like making boilers from steel, up to 2" scale, just having to scrap the thing after 100 steamings because you have no idea of its condition.

Boiler bangs are not a problem, keep it that way!

[Phil H1Participant @philh196021]

Bob,

You don't seem to want to accept any of the answers given here but before you waste money on materials for the very thick plates (because I think they will be quite expensive) why not have a word with whoever is going to inspect and test your boiler.

Phil H

[SillyOldDufferModerator @sillyoldduffer]

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

…

Duncan's comment about getting hung up on the 5 thou gap is simply wrong. I am an electronics engineer…

Many differences between soldering boilers and electronics. Applying boiler methods to electronics would be a disaster, and soldering a boiler electronic style is an expensive way of failing.

Electronics are soft-soldered with a mild built-in flux, the joints have to be clean, and components shouldn't be overheated. Provided electric joints are secure, they don't need to be mechanically strong.

Boilers are made by hard-soldering. Older low-pressure boilers were soft-soldered, but the practice hasn't been accepted for decades. Hard-soldering's done at high temperature with an aggressive flux. Joint strength is important and it depends on the solder flowing by capillary action between the metals being joined. A gap is needed to ensure full penetration, but I'm sure Duncan is right – don't get hung up on 5 thou.

Beware of cross-over engineering. Tales of woe involving high-Tin solder and SMD are irrelevant to boiler construction – they're different problems requiring different techniques.

Dave

[Nick Clarke 3Participant @nickclarke3]

Posted by Bob Worsley on 09/07/2020 19:57:17:

Just been given a large pile of MEs, and quickly scanning my way through them.

One from the 1980's I think had an article by Keith Wilson about how great silfos is to soldering up boilers.

Then I have just read Wardle's article in 1st Feb 1980 about a couple of silfos boilers that literally fell to pieces after about 1000 hours of steaming. I found that incredibly frightening.

The solder had been attacked by the sulpher in the coal causing it to turn to black mush. This is one of the reasons I hesitate about ME flanging plates, that the 5 thou gap might be 50 thou and I do have a bucket full of silfos (used to solder coax cables in the days before fibreoptics) and was tempted to use it. I still look at the reverse curve on a loco firebox and think, without rivets, how do you keep those pieces of copper at a 5 thou distance. Note, not more than 5 thou, or less than 5 thou, but at 5 thou. If bits of the gap are 5 thou then what percentage?

Yes, I worry, but my professional engineering was like that too, eliminate by design known possible failures.

I have many volumes of ME going back in a few cases more than 100 years, BUT……….

What was then was then, and with any magazine article you don't always get to read the correction a month or so later. IIRC Keith Wilson replied in a letter to one instance where he had recommended the use of Silfos agreeing it was not suitable. Another example was J. Austen-Walton's boiler design for 'Twin Sisters' which had no flanged or extra thick plates and was described as dangerous about 10 years later in the same magazine as published the original design. Simplex's boiler was not accepted as safe under the Australian Boiler code due to being designed with too small a factor of safety, and Highlander's boiler went through a redesign a couple of issues after the original was published.

Basically, just because an editor in the past accepted the article for publication does not mean that following that path today is right. Our boilers today are safer than they have ever been, but that is only because we make them according to what is felt to be safe today by today's experts, ie experienced boilermakers and silversolderer's today and of course your boiler inspector first and foremost.

[Clive Brown 1Participant @clivebrown1]

Posted by Nick Clarke 3 on 08/08/2020 14:01:57:

Simplex's boiler was not accepted as safe under the Australian Boiler code due to being designed with too small a factor of safety,

Slight digression, but IIRC, the Simplex design was questioned in Australia because the firebox crown stays weren't fastened to the outer wrapper. A very conservative stance in my view, (but that's colonials for you! ).However, probably hundreds of boilers have been made to the original design over the decades with no problems that I've heard of..

[Nick Clarke 3Participant @nickclarke3]

Posted by Clive Brown 1 on 08/08/2020 14:23:29:

Posted by Nick Clarke 3 on 08/08/2020 14:01:57:

Simplex's boiler was not accepted as safe under the Australian Boiler code due to being designed with too small a factor of safety,

Slight digression, but IIRC, the Simplex design was questioned in Australia because the firebox crown stays weren't fastened to the outer wrapper. A very conservative stance in my view, (but that's colonials for you! ).However, probably hundreds of boilers have been made to the original design over the decades with no problems that I've heard of..

Whilst agreeing that many boilers have been built to Simplex's design (and indeed to many others that are now not considered safe) in a letter in Model Engineer vol 143, edition 3558 Reg. V.Wood commented on behalf of the AMBSC that they had never considered the Simplex boiler design unsafe because of the crown stay design, but rather because of the inadequate factor of safety.

[Bob WorsleyParticipant @bobworsley31976]

My point about the 5 thou is that it is important. Bend a leg on a chip with lots of legs and it will work on the conductive flux, for a while. Crossover engineering could be really good, can't think of an example at the moment of course!

My point about Simplex was simply that it used a thick throat plate, not flanged, which I found interesting. What is the too small factor of safety?

I do have a bucket load of Silfos, was used to solder coax cables, but I won't be using it.

For 30 years I have sold items all around the world, and they were required to be good, however defined, even though the buyer had not a clue about what was inside. I take the same attitude with model engineering, it has to be good. This discussion is much better than none.

I can't find the magazine with Keith Wilson Silfossing a huge boiler to check later issues.

Cost is obviously of importance, but I am currently selling off stuff I am no longer interested in, Meccano, valves, test equipment etc so I do have money to spend, more so no doubt than most people.

[Paul KempParticipant @paulkemp46892]

Bob,

I am not sure the size of your bank balance is of great interest to many and I am positive a large bank balance does not always equall sound reasoning or a sound appreciation of engineering principles. I suggest you spend some of it and add a copy of the Australian Boiler Construction Code to you library, it's not a document I fully agree with but it is well written and sets some common national standard. I was involved very much on the periphery when a British version was being considered but that seemed to quickly lose momentum, particularly with extending it to steel boilers.

The non issue with the Minnie boiler in another post I tried to reply to but due to the vagaries of this forum it logged me out instead of posting it and I can't be bothered to type it out again!

As an aside I have heard more than once the simplex boiler was not compliant with the Australian code but do not recollect a definitive reason why not. Does anyone have a definitive explanation as to why it does not comply? Too low FOS may be due to many reasons, plate thickness, joint design, stay size and spacing or type etc. Where exactly does it fall down?

Paul.

[Howard LewisParticipant @howardlewis46836]

As a non boiler maker, but with some very small experience of oxy acetylene welding, I would have thought that you would only have problems of burning the metal if the flame is not kept moving.

I have repaired an exhaust pipe, where even a brazing flame caused the thin corroded metal to melt, but succeeded in brazing and welding new steel to make a lobster back on the the corroded pipe, which was gas tight. It was not pretty but no one was going to crawl under an old bus to examine!

I would have thought that the original reason for flanging was to provide metal for the plates to be rivetted to the boiler shell.

In our smaller sizes, with lower pressures, the flange allows braze or silver solder to fill the joint and small gaps by capilliary action, to provide a seal, and by virtue of the length of joint, provide the necessary shear strength.

I saw a steel tube plate being flanged in Meiningen, the oxy acetylene several torches were ENORMOUS, and boots of the chap standing on the plate, directing operations were smoking! But they produced a flange some 150 mm wide.

Howard

[Bodger BrianParticipant @bodgerbrian]

Posted by Bob Worsley on 09/08/2020 16:22:33:

My point about the 5 thou is that it is important. Bend a leg on a chip with lots of legs and it will work on the conductive flux, for a while

I design PCBs in my day job. Even on a fine pitch device, 5 thou is nothing. I don’t have any datasheets to hand but off the top of my head but I think that is normally less than the manufacturer’s tolerance for leg position. If it isn’t, a properly designed footprint will allow for it. Even if you’re talking about 5 thou off the surface of the PCB, a correctly applied solder joint will cope with it.

Brian

[Nigel BennettParticipant @nigelbennett69913]

Posted by Paul Kemp on

As an aside I have heard more than once the simplex boiler was not compliant with the Australian code but do not recollect a definitive reason why not. Does anyone have a definitive explanation as to why it does not comply? Too low FOS may be due to many reasons, plate thickness, joint design, stay size and spacing or type etc. Where exactly does it fall down?

Paul.

It’s the crown stays; the Australians don’t allow girder stays. Despite their use in full size boilers, particularly road steam and portable engines, they insist on rod stays between firebox crown and outer wrapper.

[Clive Brown 1Participant @clivebrown1]

Posted by Nick Clarke 3 on 08/08/2020 14:39:30:

Whilst agreeing that many boilers have been built to Simplex's design (and indeed to many others that are now not considered safe) in a letter in Model Engineer vol 143, edition 3558 Reg. V.Wood commented on behalf of the AMBSC that they had never considered the Simplex boiler design unsafe because of the crown stay design, but rather because of the inadequate factor of safety.

I've just re-read that letter and find it rather confused. Although the points above are present, there is no justification whatsoever for the claim about the factor of safety of the Simplex boiler design.. The letter then goes on to critisize the use of girder crown stays, with broad comparisons to other boilers, and recommends crown stays attached to the outer wrapper, as used by a commercial boiler maker down under.

The implication is that girder stays are unsafe, although this rather contradicts his earlier assertion. This was the reason for my earlier post.

[duncan webster 1Participant @duncanwebster1]

I've read the AMBSC code, can't find anything banning girder stays.

[Paul KempParticipant @paulkemp46892]

Nigel,

Thanks for that. As I said in my post I do think the Australian Code is a good document that gives some harmony to the nation's small boilers but I do think parts of it are well OTT. Like yourself it would seem, I don't see anything wrong with girder stays, anything but uncommon in full size. With a round top boiler the curved surface needs no additional support and the flat surface of the crown is ably supported by the girders. When you consider full sized unstayed crowns like the Marshall pressed Maltese cross and Fowlers "corregations" girders are eminently safe. Even rod stays will not prevent quilting of the crown but decent girders offer far more support.

Paul.

[Paul KempParticipant @paulkemp46892]

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.

[Andrew TinsleyParticipant @andrewtinsley63637]

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 webster 1Participant @duncanwebster1]

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 KempParticipant @paulkemp46892]

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 webster 1Participant @duncanwebster1]

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 KempParticipant @paulkemp46892]

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 webster 1Participant @duncanwebster1]

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

[Nick Clarke 3Participant @nickclarke3]

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 ConnellyParticipant @martinconnelly55370]

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

[JasonBModerator @jasonb]

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 webster 1Participant @duncanwebster1]

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

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