Copper boiler plate flanging, or not?

[Roger BestParticipant @rogerbest89007]

Posted by Phil H1 on 18/08/2020 15:31:24:

Can I ask a question about Minnie please? It has a remarkably small boiler (page 3) – hence the name I guess but what can it realistically do? e.g., on a really nice flat surface, can it pull the driver or do you run it like the little Mamod traction engines using a long control rod?

Phil H

I am pretty sure they will pull a man of reasonable build. Any on YouTube?

[JasonBModerator @jasonb]

Posted by Bob Worsley on 18/08/2020 16:18:24:

FEA! Count me out. But why does the barrel show patches of blue and green? The whole shell is pressurised to the same pressure, so variations like that show something os wrong with the calculations?

As Dave has said the blue green patches are where the tube is being stressed less due to the flanged plate joined to it giving the barrel additional support

Zan, narrowing the firebox rather than the water spaces is obviously the way to go, get no water movement at all in 1.5mm. I don't dispute that many, tens of thousands, of boilers have been made, it was the question in the ME I was echoing, where are they? I rather suspect that more get scrapped than run an engine. Nothing to back it up, but the always repeated how to stop leaks with every design. One was to put some bran, or something, inside and pressurise it whilst shaking.

I tend to see 3 or 4 different Minnies at each show that I go to and I don't attend them all so there could be say 5 new ones being shown each year which is not a bad number. As they are not really upto running on a rally field I expect most may just get the odd run up and down the owners drive or round their patio and spend the rest of the time on a shelf or mantle piece. The trend is for bigger engines these days so you don't see much smaller than 3" on the rally field

I don't wish to take on the whole ME community about boilers, of which I have made none, but they are expensive in materials, solder, gas, time and everything else and didn't want a dud. I decided to make a couple of Minnie boilers, simply because they were small and would cost around £350 each, before trying the BB boiler, £1000+?

Before making either speak with your inspector as neither have drawings that will meet current requirements

[Roger BestParticipant @rogerbest89007]

Not much on YouTube.

The 2" version is pretty big, I would say it would easily pull a man. The 1" would need some advantageous conditions, good flat surface, good bearings on the cart etc.

I have seen some tiny engines move a big load, its all down to leverage at the end of the day, tinker with the gears and it comes good.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Bob Worsley on 18/08/2020 16:18:24:

…

FEA! Count me out. But why does the barrel show patches of blue and green? The whole shell is pressurised to the same pressure, so variations like that show something os wrong with the calculations?

…

SoD makes the statement that copper tears slowly. From where does he get that fact? Used to have lots of The Engineer, and read the explosion reports, and the size of the area that the bits were thrown. Iron is much stronger than copper yet it didn't seem to stop an explosive explosion. Go and read the srticle about the failing boilers made with Silfos, weeping joints, would have been interesting to have pressurised them until they failed.

If by variations in colour you mean the patches of blue, yellow, red and blue appearing apparently randomly in some places, then they do look a bit odd. However remember the colours indicate areas of concern rather than precise values. First cause of odd patches is only 4 colours are used to represent a wide range of safety values, so values near the edge can flip into the wrong band. Second problem is the way the calculations are done. The software doesn't apply standard engineering formula (like Barlow's Formula for bursting pipes) , rather it triangulates the model into a mesh and solves the forces in each triangle one at a time, gradually building a picture based on geometry and material. The granularity of the mesh determines the accuracy of the result, more accuracy reducing anomalies. Tight meshes mean lots more number crunching, which can take an age on a big model. My FEA example was done on about 11,000 triangles each of which depends on the others – millions of calculations, not needed for a forum demo. But don't doubt the calculations – the colour contours clearly show flanged discs are stronger than plain ones.

My point about Copper is to do with exploiting materials during design. Metals have properties making them more or less suitable for particular applications. Steel is attractive for full-size boilers because it's cheap and strong and is able to work at much higher pressures than Copper. Unfortunately it also goes rusty, causing – for example – weaknesses along the water line where the shell flexes in the corrosion zone between water and steam. Corrosion lines concentrate stress, and because boiler steel 'gives' suddenly, the boiler is liable to go bang. They need to be built and maintained carefully. As Copper is ductile – see telephone wires – Copper boilers give early warning in the form of slowly opening leaks that delay the process by helpfully relieving some of the pressure.

The speed at which energy is released governs how bad an explosion is and small plastic copper boilers are more likely to go whooosh than bang. They also give more warning. Copper's ability to stretch also makes it unsuitable for high-pressure boilers, as does it's tendency to dissolve in high-temperature steam. Copper fittings long banned in Nuclear Steam Plant because dissolved copper rapidly erodes turbine blades, eventually causing the turbine to disintegrate…

What happens to old boilers? Like everything else model boilers have a limited service life. Once beyond economic repair, they are either replaced or the loco becomes a static model. If not pretty enough for display, recycling beckons. None of my old cars is in a museum…

Dave

[duncan webster 1Participant @duncanwebster1]

SOD's latest attempt:

According to the Copper Development Association, the yield strength of annealed copper is 9370 psi, 64 MPa, twice what he's got.

50mm ID with 3mm wall at 0.7 MPa pressure gives a hoop stress of 5.8 MPa (846 psi), so safety factor is 11.1, not surprising on a small fairly thick tube (by model boiler standards)

The circumferential line of high stress is I would guess the stress concentration caused by the sudden change of section where the 3mm thick shell meets the 3mm thick flange, but as this isn't a fatigue issue and copper is very ductile we don't need to worry.

FEA on something like this might be an intellectual challenge, but is well over the top. If SOD models the stresses round a stay I'll bet it shows points of really high stress, but again as copper is ductile it just bends and shares the stress out. This is one reason for testing at twice operating pressure, to put it simplistically, having been up at twice, when operating at normal it will be well in.

And as regards stresses in a traction engine boiler caused by running over rough ground, your guess is as good as mine, but I've never heard of a model failing due to this.

[SillyOldDufferModerator @sillyoldduffer]

Posted by duncan webster on 18/08/2020 18:19:21:

SOD's latest attempt:

According to the Copper Development Association, the yield strength of annealed copper is 9370 psi, 64 MPa, twice what he's got.

…

Does yield strength make a difference to a Safety Analysis? Being ductile the yield strength of copper is low so a soft boiler would balloon before it failed. But for the purpose of an FEA, isn't the boiler's safety factor determined by Copper's tensile strength, about 220Mpa in whatever form, annealed, cast etc.

I don't remember this coming up at Bog Lane Primary School, where any cat with two ears was a tourist!

Dave

[duncan webster 1Participant @duncanwebster1]

I reckon it's failed if it has suffered significant permanent distortion, OK it hasn't necessarily killed anyone. I'm not talking about a bit of quilting between stays, and I'm not going to define 'significant' or 'a bit'. Suffice to say that relevant BS use proof stress as a basis, and that's a good enough precedent for me. The only big time fail I've ever seen on hydraulic test was where the firebox crown came down, still didn't leak, but the boiler inspector didn't pass it either. I'm not talking about pinhole leaks, get them now and again on new boilers

Edited By duncan webster on 18/08/2020 20:02:36

[Bob WorsleyParticipant @bobworsley31976]

It gets worse.

There have been some mentions, and many more elsewhere, that the boiler needs to be made to a published design otherwise you have to sort the safety factors out.

Just bought a Fowler BB boiler set from Reeves. It turned up as a short length or tube plus a firebox wrapper and a jointing ring. The plans say the tube is one solid piece from smokebox to backhead.

Contacted Reeves to ask for the amended drawing, not available, besides it is common now to supply the wrappers as a separate piece of copper.

This is not as the designer designed it.

Where does this leave me?

I was also somewhat surprised that the barrel, wrapper and all the firebox copper was 13swg, not 10swg. This is as the designer specified, but whilst not exhaustive the other plans I have seen in ME all call for 10swg, 3mm, on 2" scale engines. Any thoughts? Should I chuck these pieces and get some 3mm?

[JasonBModerator @jasonb]

A scraf joint or internal butt strip for extending the firebox sides down from the opened out barrel is no longer preferred so you would be unlikely to get the boiler approved if you went with a single tube. The photos that went with the original articles show it as short tube and separate wrapper

The original articles state 13swg and I think the drawings also showed this but it was soon changed to 10wg, if you have a set of drawings taken from the original tracing you can see the 10 is darker where it has been written over the scratched of 13. his Countryman's Steam book mentions the change in thickness and also different staying of the firebox crown

As I always say to people wanting to make a boiler before buying or cutting metal talk to whoever will be testing and certifying the boiler as at the end of the day what we say here will be overridden by their decision. Had you taken the drawings along to your inspector and talked things through I'm sure they would have said what they now want to see and you could have taken it from there.

There are a few otherconstruction changes for the BB1 copper boiler that will make it perform better and maybe even get some way to compounding by allowing the boiler to run at 120psi WP rather than Hainings lowly 75psi

 

Edited By JasonB on 21/08/2020 14:11:27

 

Edited By JasonB on 21/08/2020 19:48:50

[Roger BestParticipant @rogerbest89007]

Bob – send it straight back to Reeves as not fit for purpose and quote your rights for internet purchases. They should be responsible about this sort of thing, you are paying for a competent technical service.

Agreeing with Duncan – a design has failed if there is any distortion. There needs to be a margin between load and resistance to cater for wear and tear, in this case erosion and mechanical fatigue. That margin is established by a proof test at above working load.

Some design codes allow minimal "set", lifting beams for instance, where there is some stress re-distribution. This is OK in a simple structure that can easily be examined and shown to be undamaged, a locomotive boiler is a lot more complex than an I-beam with a few holes in it, how can you tell what is happening deep inside without an awful lot of work?

The other issue with distortion is buckling – the point at which the shape is so distorted that its strength is no longer adequate. Fortunately a very large amount of development has gone into the locomotive-type boiler and copper is wonderful stuff, so it tends not to be a problem, but in principal if its stretched it won't be as designed and will be weaker than intended.

[JasonBModerator @jasonb]

Posted by Roger Best on 21/08/2020 15:03:45:

Bob – send it straight back to Reeves as not fit for purpose and quote your rights for internet purchases. They should be responsible about this sort of thing, you are paying for a competent technical service.

Why?

As Bob states Reeves have supplied thicknesses "as the designer specified" and Bob was just comparing them to what is used on other engines mostly with a higher working pressure.

They have been responsible in supplying a short tube and wrapper, had they supplied just a long tube Bob would have difficulty finding an inspector who would approve a scarf or butt stripped joint.

[Dave HalfordParticipant @davehalford22513]

Posted by JasonB on 21/08/2020 13:32:26:

There are a few other construction changes for the BB1 copper boiler that will make it perform better and maybe even get some way to compounding by allowing the boiler to run at 120psi WP rather than Hainings lowly 75psi

Edited By JasonB on 21/08/2020 14:11:27

How does Bob comply with the 'new design' that seems to be undocumented. Does each boiler inspector keep up to date with the changes to each and every boiler? It seems like Bob has to find an inspector that knows the BB1 boiler and it's extra stays or what ever in a club world dominated by Rail.

 

Edited By JasonB on 21/08/2020 19:48:24

[JasonBModerator @jasonb]

He could do the same calculations that were done for the 120psi design and present those to an inspector, this is not a generally available published design and I'm not able to share it. It does have a number of enhancements which the involved parties felt desirable (some input from me) and incorporates current thinking on construction as well as meeting all the requirements of the current code (UK). There is no requirement for him to comply with this design if he wants to stick with the original 75psi ones but they will need some modification to meet code.

 

Bob has not said what drawings he is working from or whether he is going for Haining's "Sheathed" option which is under less external load than one where the drum etc are supported by brackets soldered directly to the boiler. if the Sheathed then there should be less need for Bob to want to use thicker materials

 

Edited By JasonB on 21/08/2020 19:53:27

[Paul KempParticipant @paulkemp46892]

Posted by Roger Best on 21/08/2020 15:03:45:

Bob – send it straight back to Reeves as not fit for purpose and quote your rights for internet purchases. They should be responsible about this sort of thing, you are paying for a competent technical service.

My thoughts are if anyone thinks a model engineering supplier is giving a competent technical service to a degree they are in la la land where they are selling "drawings" with no manufacturing tolerances and many littered with dimensional errors!

The other issue raised by Dave H is there is no UK constructional code to underpin the model test code to give the inspectors any definitive guidance so you are reliant on the experience and knowledge of the individual inspector and any reference they make to commercial standards.

That said, I do think the "system" as it stands is fit for purpose as if it wasn't there would be boilers exploding left right and centre, insurers would be going bust under the claims, premiums would be rocketing and officialdom would be clamping down hard on the hobby!

If we ignore the hysterics of model boilers are bombs, will distribute shrapnel over many metres if they fail and look at the facts, miniature copper boilers are pretty safe and even one constructed to mediocre standards is very unlikely to fail catastrophically. Probably the most likely failure on a boiler likely to cause injury is poor threads on fittings allowing the fitting to be blown out. I have witnessed the failure of a back head to wrapper joint on a commercially made boiler as it happens which was entirely unspectacular bar the cloud of steam in the cab and the loco coming to a halt. It certainly didn't explode violently and the copper tear itself the shreds!

We should not be cavalier about these things for sure and every effort should be made to ensure as far as possible they are safe but we also should not instill in ourselves and others an illogical fear and suspicion.

Paul.

[Phil H1Participant @philh196021]

Jason,

It is possible that I have misunderstood but I was under the impression that this kind of 'swaged' extension joint for the firebox sides is acceptable. Is this now frowned upon? Forgive the rough sketch – I hope it makes sense. I would agree that without lagging and cladding – it isn't pretty.

[JasonBModerator @jasonb]

It may well be, Haining shows a scarf or internal rivited butt strap as two methods that can be used both of which don't seem to be in favour particularly as his are Brazed not silver soldered.

The problem with a joint as you show it that it will cause issues with the fitting of the hornplates as the plate thickness will be about twice that of the stays projection so not suitable for the BB1 and a couple of other traction engines that I can think of such as MJ Engeneering's Fowler A7 wer there is no stay projection.

[Roger BestParticipant @rogerbest89007]

Posted by Paul Kemp on 21/08/2020 20:09:10:

Posted by Roger Best on 21/08/2020 15:03:45:

Bob – send it straight back to Reeves as not fit for purpose and quote your rights for internet purchases. They should be responsible about this sort of thing, you are paying for a competent technical service.

My thoughts are if anyone thinks a model engineering supplier is giving a competent technical service to a degree they are in la la land where they are selling "drawings" with no manufacturing tolerances and many littered with dimensional errors!

The other issue raised by Dave H is there is no UK constructional code to underpin the model test code to give the inspectors any definitive guidance so you are reliant on the experience and knowledge of the individual inspector and any reference they make to commercial standards.

That said, I do think the "system" as it stands is fit for purpose as if it wasn't there would be boilers exploding left right and centre, insurers would be going bust under the claims, premiums would be rocketing and officialdom would be clamping down hard on the hobby!

If we ignore the hysterics of model boilers are bombs, will distribute shrapnel over many metres if they fail and look at the facts, miniature copper boilers are pretty safe and even one constructed to mediocre standards is very unlikely to fail catastrophically. Probably the most likely failure on a boiler likely to cause injury is poor threads on fittings allowing the fitting to be blown out. I have witnessed the failure of a back head to wrapper joint on a commercially made boiler as it happens which was entirely unspectacular bar the cloud of steam in the cab and the loco coming to a halt. It certainly didn't explode violently and the copper tear itself the shreds!

We should not be cavalier about these things for sure and every effort should be made to ensure as far as possible they are safe but we also should not instill in ourselves and others an illogical fear and suspicion.

Paul.

Its nice in la-la land Paul!

If the design has been updated then they should sell material for the updated design. Its not difficult. Bob wants the safer design so he is allowed to return the goods.

Equally if they are selling certified material they should control the material certs properly; its why certified material is expensive. If you are saying they can't do either competently then shout louder as there will be a lot of boiler certificates that aren't worth wiping your butt with.

Selling a photocopy of someone else's copyright material is not relevant to this issue.

[Nick Clarke 3Participant @nickclarke3]

Posted by Roger Best on 21/08/2020 21:18:28:

If the design has been updated then they should sell material for the updated design. Its not difficult. Bob wants the safer design so he is allowed to return the goods.

In this particular issue (and probably ONLY in this particular issue), The boiler illustrated in the original ME article was constructed by Alec Farmer, the then proprietor of Reeves and it was accepted in the text of that article, subject to adequate workmanship – in fact barrel was also was rolled up from sheet with a coppersmith's joint along the whole length.

So if the original designer is happy, and the then supplier was happy – suggesting the successors to that supplier have got it wrong ……….

I can hear the sound of another lawyer ordering their next Jag!

Edited By Nick Clarke 3 on 21/08/2020 21:43:59

[duncan webster 1Participant @duncanwebster1]

Phil's joggled joint is not a good feature, it will try to straighten out under load. An external butt strap would be better. Internal strap could interfere with circulation in the fairly narrow gap twixt wrapper and firebox wall.

If butt straps are accepted on taper shells I can't see why they would not be accepted on firebox sides, which have  lower direct tensile stress if using firebox roof stays connected to the wrapper, the same stress if using girder stays, but you'd have to be a bit careful dodging the stays

Jason refers to the 'current code' (UK). Could he point us towards it, as I've never seen any reference? The SFED/NAME rules are about testing, not design

Edited By duncan webster on 21/08/2020 22:30:13

[Paul KempParticipant @paulkemp46892]

Posted by Roger Best on 21/08/2020 21:18:28:

Its nice in la-la land Paul!

If the design has been updated then they should sell material for the updated design. Its not difficult. Bob wants the safer design so he is allowed to return the goods.

Equally if they are selling certified material they should control the material certs properly; its why certified material is expensive. If you are saying they can't do either competently then shout louder as there will be a lot of boiler certificates that aren't worth wiping your butt with.

Selling a photocopy of someone else's copyright material is not relevant to this issue.

Roger, I think that is the problem? The design hasn't been updated, Bob was commenting the material supplied didn't match his drawing and asked for an updated drawing and was told there isn't one! Material supplied has been sent based on modern convention. The simple answer that will stop all the speculation and posturing that has been given several times is speak to whoever is going to certify the boiler! Job done.

No model drawings are properly controlled and subject to periodic revision, this has been done to death on here many times!

Let the lawyer claim his new Jag, end of the day it won't benefit any of us or Bob because all of a sudden prices for drawings will become unaffordable.

As to material certs, it's irrelevant as the test code does not require certs for silver soldered copper boilers, only TIG welded ("where required by the build procedure" is the relevant quote). It would only be relevant if Bob had requested certs and supplier failed to supply.

Paul.

[John OlsenParticipant @johnolsen79199]

There is or was another way of extending the firebox sides, I wonder if it is still acceptable. I refer to the idea of a castellated joint. The two pieces are both cut into castellations and then silver soldered together. For typical 3mm plate, I would think that about 10 to 12 mm pitch castellations might be about right. Obviously the work has to be quite accurate, you want to maintain that 2 to 5 thou gap for the silver solder to run into. Properly done, such a joint should be as strong as the parent metal, with the advantage of being no thicker. But since my own boiler is steel and much larger, I am not au fait with current regulation.

John

[Roger BestParticipant @rogerbest89007]

OK Paul – I do see your point – that it is too difficult for a vendor to keep track of a design if the originator can't be bothered to record the corrections.

Thanks for reminding me about silver-soldered boilers – that's another problem I have elsewhere.

[JasonBModerator @jasonb]

Duncan, As per at least the three published drawings the boiler will not have the preferred separate water gauge feed as it only has a single manifold hole, test code prefers separate if practcable to fit which it is.(test CODE 6.6)

Paul, there are at least two updated drawings from the original ME article ones but upto the builder which they use. As I have already mentioned there is the hand drawn "Haining" drawing set that has been altered to show 10swg and there is the one in his Countryman's Steam" book where he shows 10swg and there is also a paragraph about the changes. But who says which to use?

John, the scarf joint that I mention is basically a castellated joint except the shape is "dovetailed" rather than square cut and is one of the options Haining suggests. He shows these joints Brazed not silver soldered.

[Paul KempParticipant @paulkemp46892]

Jason,

But does either version show the short barrel, firebox wrapper and joining ring? Bob says supplier says not? That I think was Bob's fundamental point? In which case adopting your previous advice of talking to the certifying inspector the question can be resolved and there is no problem. Unless the inspector says no, which is another can of worms and then maybe Bob can try and send his bits back and set the inspector against the supplier!

As you know my version has a steel boiler – another can of worms altogether lol.

Paul.

[Bob WorsleyParticipant @bobworsley31976]

This is certainly getting some comments! Thanks to all.

My BB drawing is dated "JF/5July 64"and looks exactly the same as the one in the book Model Boilers for Road and Ploughing Engines by John Haining dated 1974.

Nothing in the drawing about extending the sides of the opened up full length barrel, perhaps assumed. I don't have the ME articles describing the construction of the BB, I do for the 16hp single cylinder.

It is ironic that it was the 16hp one I was going to build, but Graham Howard of Brunell Model Engineering decided he wasn't going to supply more than a few of the castings. Paid £2300 for nearly nothing, plus £2500 for a commercial boiler and now got a pile of scrap. At the time I was in serious arguments with a planning department and knew if I met Howard there would be a death, so time now expired to take him to court.

The Minnie boiler is done with a short barrel and separate wrapper with ring, perhaps copy that?

I don't want to give the impression that this particularly worries me. But, I don't belong to a local club, Stamford or Melton, due to virus, I have not made a copper boiler, I have bought two Minnie kits to practise on, hopefully one with unflanged plates, in the end it has to be acceptable to the inspectors.

I will go back to Reeves to put the points to them, including the change to 10swg/3mm for all the copper.

I have also made comments about using oxy-acetylene. Just come across an article to send shivers up your back from ME 2 May 1986 number 3776 about just that, a 3.1/2" Britannia with combustion chamber. A beginner, using O-A welding gear, leaks everywhere, cut boiler in half to repair, burnt copper, solder run everywhere, repaired and joined back together and passes all tests. I obviously can't copy and paste the article here, but the mods might find it a useful exercise. I have to say that it is this that frightens the daylights out of me.

After reading so much, and this forum, I think now that copper is a safe material to make a 100 psi boiler from. Why? It is malleable and ductile, the flanging give a huge safety margin on the joints, propane can't damage the copper, silver solder is a safe material because if the joints are too larhe then it simply won't join. If the boiler is going to fail then all these make it fail slowly, it will tear or pull apart. Actually rather impressive. Apparently LBSC tested a boiler to destruction but no issue number where the results are given, can it be found and added this thread please?

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