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ME4651 - Flangeless Boilers

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Nick Clarke 308/11/2020 12:35:25
1156 forum posts
48 photos

I was surprised by some of the suggestions in this article, and do not know answers, but am interested in others' ideas.

The Janes boiler failures (OK they may not be considered dangerous) appear to have happened at about twice normal working pressure (particularly 5, but also probably 3) far less than the factor of safety usually employed yet (lead free) softsolder is still suggested as a suitable boiler sealant.

If 2mm screws are inserted into the edge of 3.2mm flangeless plates to secure them the plate itself could be securely soldered on both sides and the heads of the bolts secured but unless silver solder penetrated the full depth of the tapped hole the plate is 2 thicknesses of 0.6mm separated by a hole with a bolt in it. Would this be a safety issue?

Apologies for the sketch, but this is what I wonder might happen:-


(error in sketch corrected)

Edited By Nick Clarke 3 on 08/11/2020 13:05:40

Martin Kyte08/11/2020 13:37:42
2313 forum posts
38 photos

My reading of the article was that the failure was down to the soft soder caulking which stopped the test before structural failure rather than the structural failure of the silver soldered shell which is what the article is trying to demonstrate. The second set of tests show quite conclusively that in a silver soldered flangeless boiler the eveltual structural failure s were in the boiler material rather than any of the silver soldered joints.

I am in no way a boiler expert, this is just what I read from the article. I have no comment on the second question, sorry.

regards Martin

Nick Clarke 308/11/2020 14:26:33
1156 forum posts
48 photos
Posted by Martin Kyte on 08/11/2020 13:37:42:

My reading of the article was that the failure was down to the soft soder caulking which stopped the test before structural failure rather than the structural failure of the silver soldered shell which is what the article is trying to demonstrate. The second set of tests show quite conclusively that in a silver soldered flangeless boiler the eveltual structural failure s were in the boiler material rather than any of the silver soldered joints.

Hi Martin -

I read the second set of tests as you did - hence my surprise at the start of the third page of the article when he is suggesting using soft solder, not even high melting point, to repair leaks rather than re-silver-soldering.

Take care,


Martin Kyte08/11/2020 16:17:37
2313 forum posts
38 photos

Surely that is the whole point. That structural integrety is not compromised by soft solder caulking.

Maybe some boiler inspectors would care to comment. As I say I'm no boiler expert.

regards Martin

John Rutzen08/11/2020 18:02:32
317 forum posts
16 photos

I can't comment on the flangeless boilers but Alec Farmer in his well respected book on boiler making says you should never re silver solder a finished boiler with a small leak. Aways caulk with soft solder. Attempts to silver solder a small leak usually result in more leaks.

Keith Hale09/11/2020 09:39:35
293 forum posts

The answer, as always, to preventing and/or overcoming leaking joints lies behind the torch.

The basic principle of soldering and brazing has been ignored. If you achieve capillary flow of the solder, it will penetrate the joint. If you don't, then you will reach the situation as per the sketch where a superficial joint is made on the surface but a crack is built into the back of the joint. The joint fails as a result of a poor heating technique. Where a silver solder has been used, you can be sure that the joints have been made using a welding technique with an oxy-acetylene torch.

If in attempting to repair a leak you find another, is more evidence of a poor heating technique. The second, third, fourth......leak is developed in other weak joints created at the same time as the first.

It is virtually impossible to repair a leak in isolation. Leaks can be repaired. You just have to adopt a better heating technique. It can be done, it just requires a better heating technique and a little patience.

As in all cases, prevention is better than a cure.

For more information consult BS EN 14324 available for £220+ or get a specialist book from your supplier of brazing materials.

But bear in mind that if you decide to repair a silver solder joint with a soft solder that you are entering the"Last Chance Saloon" . If you don't succeed, some consolation will be obtained from the scrap price of copper.


PS. It's an excellent book - I wrote it!

duncan webster09/11/2020 12:53:27
3141 forum posts
52 photos

In the unlikely event of anyone wanting to buy the BS then get the DIN version

DIN EN 14324 Brazing - Guidance on the application of brazed joints


it's a lot cheaper. Cheaper still if you can read German

Ian B.09/11/2020 16:22:45
163 forum posts
5 photos

I am glad to see that this is being aired again. In Australian Model Engineer a recent edition, there was an excellent treatise on this subject. It advocated flangeless tube plates of thicker section etc. Over the years ME has for example demonstrated via ME societies controlled testing to destruction just how safe we are generally. Further there has also been much dire doom and alarm spread about the regulations. Firstly Aussie boiler codes are among the toughest globally yet smaller flangeless boilers pass without question. Much of the doom could be dispelled if those spreading it realised that whatever colour the cover is that is merely a testing regime only. That was fully explored a few years ago by a highly qualified Doctor at Law and barrister in ME itself. The regulations are contained in the PSSA not the Blue/Red/Green/White book. He explained very thoroughly. I have yet to meet a boiler inspector in amateur circles who actually understands the difference between working pressure and operating pressure. Scantlings apparently come from another planet.

Baz09/11/2020 17:05:53
524 forum posts
2 photos

Ian B perhaps you would like to enlighten us all. I am not a boiler tester, too thick for that, just a general run of the mill idiot.😃

Ian B.09/11/2020 19:43:36
163 forum posts
5 photos

Well Baz. I am not an educator and have no intention of becoming one. However I would encourage those who have any real interest to do their own research. Hence I will not provide chapter and verse or even in the ME world sacred parlance the words and music. I will give just a few pointers as to where I go and learn the hard way. You with respect should consider doing similar.

As regards operating pressure and working pressure. One is a calculated figure based on the scantlings (the materials and structure) the other is the pressure at which you intend to operate the boiler. I will leave you to work out which is which. A certain Mr Simpson of model marine steam fame wrote at length on the subject. But for a definitive analysis and the calculations you will require K.N.Harris wrote an excellent book on the subject. That details what you will require if you design from scratch. He was imperial but the regulations are now metric. The base principles are the same. A boiler structure problem about which very little is known is the behaviour of tubes under external pressure. They convolute with an odd number of convolutions. Jack Buckler wrote about it in some depth to what was known at the time when the Sweet Pea was being designed. And then we come to a back issue of ME which contains the article I mentioned by a certain Doctor at Law. He explains it in simple terms and cross references the proper regulations with the Southern Fed documentation on the subject. Remember the EU along with HSE in their wisdom actually moved all our boilers UP a category in the regs.A back issue search of Australian Model Engineer will take you to a treatise on flangeless plates for boiler structures. Google won't do it for you. There is leg work to be done unfortunately.

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