Welded copper boiler joint design

[fang]

Hi

I am shortly going to be starting on building my first copper boiler, but i see now that some copper boilers are being TIG welded rather than silver soldered.

Just to keep this discussion on track I work as a welder (not coded as not necessary at work) and I use all processes on all materials, anything from 0.5mm stainless steel to 1" thick steel plates, all prototype and research work, so I am not an amateur welder who has just bought a nice cheap chinese set off ebay!!!

I have spoken to my club and they are happy for my boiler to be welded

The drawing I have is for a copper silver soldered boiler, what I would like to know is, is there any guidelines or recommendations for joint design when welding copper boilers, so I can see what changes I need to make for the boiler design I have.

Many thanks

[ejparrott]

No problems with doing your own welding, its all allowed for in the new code.

Its a while since I've read it but there are right and wrong grades of copper and filler rod as I'm sure you're aware, just make sure you get material certs for them so that you've got a paper trail. There's no guidlines in the UK boiler code for welding joints, but there may be in the Australian code - unfortunately I've only got the book for steel boilers. I would imagine you're going to want a V prep butt weld, fully welded from the outside, and I would want to inspect it before you carried on if you were a member of Rugby club.

Good luck!

[Deleted]

My Brit boiler was professionally TIG welded by Steam Technology Ltd. Here is the thread showing the production sequence and the comments that went with it.......
Best wishes
JB

modeleng.proboards.com/thread/4623

[bhk]

Hi,

I recently welded up a rather lot of copper nickel ballast pipes for a ship.

If you have not worked with copper before it is a bit different to weld, sort of a mix between Ali and 316 but overall is an absolute pleasure to weld.

I'd be warry of too much edge prep, on the ballast pipes which were 4mm wall I just wizzed round with a soft disc on the grinder on the front and the back left square. with a 1.5mm root gap 130ish amps, back purged I was able to gain a very good weld with a good back bead.

[jma1009]

hi fang,
you need de-oxidised copper sheet (C106) for tig welding to avoid porous and brittle joints.
cheers,
julian

[Shawki Shlemon]

In our code ( OZ code ) , there is no details , basically it says what one can or can't use and that only qualified ( licensed ) person can do the welding . The rest of the requirement are the same as silver soldered .

[jackrae]

On the basis that you are building the boiler for use in the UK at a club track operating under the NAME "green book", section 6.3 states the following :

""If welding is undertaken by a person who is not a coded welder the inspector shall require that weld samples be made available for inspection and testing prior to the commencement of the welding of the boiler, or that the welder shall have proof of test pieces being satisfactorily tested within the 12 months prior to the jointing being undertaken. Weld samples shall be tested by appropriate testing laboratories.""

You have stated you are not a coded welder (even if skilled) so to comply with the code of practice you will be required to provide test samples for testing (generally both non-destructive and destructive). Nothing problematic in that , we all voluntarily produce test pieces for ourselves when trying new techniques. However, the last sentence of the paragraph is somewhat onerous.

[ejparrott]

Might be worth a copy of your certificate as well if you are lucky enough to be coded. Just something that cropped up a little while ago when I was talking to RSA about design approval for a steel boiler for my Manning Wardle. I was going to source and machine all platework myself, and I know a coded welded who might be prepared to glue it together.

[jackrae]

If it's steel then you generally also need material certs for welded pressure vessels, to prove the steel used is fit for purpose.

Considering the need for deoxidised copper (C106) for a welded copper boiler, I'd expect materials certs for all copper used to also be supplied.

Fang, it might be a lot less painful, and probably a lot simpler (from the certification point of view) if you deferred to using silver solder.

[ejparrott]

I don't know, I'd be wanting material certs for all platework these days anyway, and my bronze for the bushes, so from that point of view it doesn't really make it any harder. To be honest, you only have to ask when you order it.

I imagine, if a coded welder, Fang would be able to find his certs

[fang]

At the moment I'm not a coded welder, but considering the cost of bottles of propane and the astronomical price of silver solder, becoming certified for copper welding might be the way to go, especially if I was to build several boilers at the same time. I do find it a bit strange how silver soldering requires no certification but welding does, you can still have a total lack of penetration in a soldered joint, which can be very difficult to see, but it is fairly obvious if a weld has penetrated or not. How is it that the relevant regulations do not require samples of silver soldered joints to be submitted for testing, but they do for welding???

[bhk]

I agree completely, but also feel its a can of worms that should be left closed, As if it was ever to come up they (the safety deamons) would rule in favour of testing silver solder joints and the already high cost would escalate further!

[jackrae]

Probably something to do with the fact that welding requires the parent metal to actual be molten whereas silver soldering does not. Strange things can happen to metal alloy properties once they have been melted and reformed.

[pault]

I would suggest that the reason maybe because with silver solder you can see penetration through a joint which makes inspection easy. With welding you can’t see penetration

[fang]

If you can't see penetration with a welded joint, it's because the weld has not been done correctly, and there is no penetration!!! Penetration on the reverse of a weld I would say is far easier to see than that of a soldered joint.

I agree that welding does need the parent metal to be molten, but what about the risks of overheated, or remelted, silver solder??

My personal opinion is that if the person carrying out the work is competent, and I believe it was in the old boiler code book, that it used to be that welding could be carried out by a competent person, not needing to be coded and the boiler is pressure tested and passed, then I don't really see the problem with whatever joining method is used. But if a coding is required then I think I will look into becoming a coded copper welder!!

I think with a lot of these things, and hence my original question, is more the design of the item. I haven't seen anywhere any published guidelines on construction of welded copper boilers. Maybe if more people were to use welded copper boilers the cost of boilermaking could actually be reduced, especially for commercially made boilers. Less preparation of plates as no flanging required, huge reduction in cost of consumables (silver solder, gas,etc) and a reduction in the time taken to prepare the plate and join it together.

[nonort]

Can we stick to the point here. I would suggest that open corner designs. A look at a drawing for one of the John Haining ploughing engines Superba or Z7 allthough meant to be steel boilered, but many of the same preps would be acceptable. It may require a 'J' prep on the foundation ring but I am sure this could be worked around. Flanging is counter productive as you cant possibly penetrate the depth of the flange were as the open corner joint you can actually see the pentration. Many of the steel boiler makers use TIG to seal the joint then fill using stick weld. Hope this helps with the original question.