I have recently been Tig brazing some motorcycle frames, during my research for the best rods for this, I came across several posts on motorcycle forums about repairing petrol tanks using Tig with silver soldering, this got me wondering if anyone had tried this for copper boiler making, for the frames I'm using Sifbronze No 32 which is aluminium bronze, I use this with AC Tig, with AC balance of 15% its flows very well and creates a lovely bright bronze fillet, I have not personally tried Tig with Silver solder but suspect it would produce a nice neat and strong joint with the added bonus of less clean up after welding.

just a thought, I will be interested to see what others think and its implications for boiler testing.

Shaun

Edited By Involute Curve on 24/02/2018 16:23:33

I think your plans probably date from when Sifbronze was considered OK to use on boilers. As it has since been found that the sulphur from burning coal attacks the phosphorus it so no longer allowed for anywhere that will come into contact with combustion gasses.

I think the Aussies still allow it for places like the throat plate to barrel joint where the fillet that can be produced adds strength and it will only come into contact with water.

Over the past 40 odd years I've brazed welded soldered hundreds of petrol tanks with both oxy acetylene and tig, never ever had a problem and never heard of anyone getting killed doing this, I personally have several friends who have done this on lots of occasions over the years, race bikes get cracks in tanks due to stress vibration etc its common practice to weld these up..

I have welded hundreds of fuel tanks. There is no danger what so ever if you follow the correct procedures. You need to use a good degreaser to clean the inside and then flush with water.

Edited By vintagengineer on 24/02/2018 17:32:11

That was back in 2012, I dont think I hijacked anything, I thought my post was relevant to brazing copper.

or am I wrong? JasonB

Shaun

Hallo Shaun,

I think that you and Fizzy raise an interesting point – in terms of new(er) brazing/welding technologies and boiler brazing/soldering methods.

The current boiler codes really assume that a boiler is constructed either of copper (and is therefore silver soldered e.g. silver brazed) or of steel (and is therefore "welded" ). Your question seems to fall in-between these two assumptions, in that you are suggesting a silver soldering/brazing operation using a welding method. I think this is somewhat different to the recent EIM article where Jan-Eric Nystrom did actually TIG-weld his (copper-nickel) boiler.

However, to my mind, you are still "silver-soldering" – the difference simply being the heat source used. So I would not have a problem with this approach, as I would inspect the joints as I would any other silver soldered joint. I don't think I would care too much (and might not know) whether the soldering/brazing has been done by propane torch, Oxy-A, Carbon Arc or TIG – as long as the joints had visible penetration and had the other characteristics of a good silver soldered joint. The boiler would also need to be of acceptable design/materials and of course be capable of passing a Shell test (at 2 x Wp).

In terms of Jan-Eric's TIG-welding approach, he states that any amateur should seek instruction from "a professional welder" – however, even if this was an acceptable 'qualification' – I think there is another important factor, which would be the Inspectors ability to undertake such an inspection. Personally, I would not feel qualified to inspect a fully TIG-welded boiler, as I have no TIG-welding experience (apart from a short evening course) and therefore would not describe myself as "competent" to undertake such an inspection. Others may feel differently of course.

These may seem fine distinctions but they are the ones that I would make.

Regards,

IanT

Edited By IanT on 24/02/2018 22:23:37

Yeah, it's a one in a thousand chance any residual flammable petrol will explode while welding a tank. Keep going…

Edited By Hopper on 25/02/2018 05:13:28

Sorry, that should be 1980, not '84 !

My no.1 tip for silver soldering/brazing using a TIG torch as the heat source is DON'T

The heat source is too localized. The whole joint does not get to temperature to facilitate capillary flow. You will not achieve full penetration of the alloy into the joint. You will create a weak joint with an in-built crack.

The shield gas will not remove oxides from the component surfaces which is essential to get the filler metal flowing. You still need a separate flux.

Betcha end up melting the copper and overheating the alloy. You don't melt parent materials when brazing and you don't heat the rod. It is very easy to overheat the alloy and boil off the zinc. (In this instance thank god you're not using a cadmium bearing alloy.)

If you want to weld – then weld. Use a copper welding rod.

If you want to braze – then braze.

But no matter which option you choose – do it properly

Finally

ON NO ACCOUNT USE ANY PHOSPHORUS BEARING BRAZING ALLOY ON A COAL FIRED BOILER. THE SULPHUR IN THE FUMES WILL GO THROUGH THE JOINT LIKE A HOT KNIFE THROUGH BUTTER.

Keith