ME4651 – Flangeless Boilers

[Nick Clarke 3Participant @nickclarke3]

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

[Nick Clarke 3Participant @nickclarke3]

[Martin KyteParticipant @martinkyte99762]

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 3Participant @nickclarke3]

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,

Nick

[Martin KyteParticipant @martinkyte99762]

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 RutzenParticipant @johnrutzen76569]

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 HaleParticipant @keithhale68713]

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.

Keith

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

[duncan webster 1Participant @duncanwebster1]

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

DIN

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

[BazParticipant @baz89810]

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.😃

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