Fuel tank welding repair query ?

[berger]

borax works well for soldering as well

[BSA_54A10]

In reply to joolstacho, we use spirits of salts also called hydrochloric acid or muratic acid which is highly corrosive and needing thorough cleaning after soldering. Or, you could use a non corrosive resin flux if the item is easily tin able.

Spirits of salt is Zinc Chloride not hydrochloric acid
Dad used to make his own by dropping old galvanised clouts that had been pulled out of timber into hydrochloric acid till it no longer bubbled
BAck then we knew how to be frugal
Bakers is basically ZnCl
To solder onto steel you need to use a nitrate flux
Usually a stuff called "Tinning Butter" "Panel Paste " or "Panel Butter "
This is because neither tin nor lead will take to raw steel
Then you need to use tinmans solder which is 40:60 or plumber solder which is 50:50.
Good tinmans solder will have around 0,5% Cu & 0.1% Fe
Soldering things like petrol tanks needs a slow solidifing solder which is very similar to lead wiping
Totally different to electrical soldering where you want the stuff to solidify the instant you take the iron off it

[Swarfcut]

 The more I see of mig weld body repairs on old metal on TV, the more anguish I feel for the folks that buy the restored vehicle for several thousand ££££'s. In my experience MIG will only work well on new clean metal. Plug welding a new panel onto a joggled edge still carries the risk of distortion on unsupported original panels....a rear wheel arch for instance. Try and run even a short bead and the buckles still appear. So all these restorers use a join the dots method, hardly a recipe for a good strong cohesive fusion joint.

  Brazing is better for a tank repair. Like soldering, the parent metal is not melted, but the filler material added at a lower temperature so less chance of distortion. A brazed joint is much stronger and durable than a soldered one, but as always distortion is your enemy, and success depends to a degree on the rigidity of the metal surrounding the repair. Soldering or brazing needs the parent metal to be clean, Bakers Fluid was the acid dip in a can, back in the day. You bought a can, did the job, and of course the next time it was needed the contents had turned brown or the stuff had eaten thro' the can. Nice to see it's still available, now packed in a modern single use plastic bottle.......Progress indeed.

 Swarfy

[Bsareg]

BSA54A10, of course you're right, I forgot the zinc part. We used to call it "killed spirits".

[Stephen Foster]

The more I see of mig weld body repairs on old metal on TV, the more anguish I feel for the folks that buy the restored vehicle for several thousand ££££. In my experience MIG will only work well on new clean metal. Plug welding a new panel onto a joggled edge still carries the risk of distortion on unsupported original panels....a rear wheel arch for instance. Try and run even a short bead and the buckles still appear. So all these restorers use a join the dots method, hardly a recipe for a good strong cohesive joint.

As usual from Yourself..excellent points ..
I am experiences in using MIG , TIG , Oxy acetylene & MMA having worked in the Nuclear industry ..its the distortion aspect Im concerned about .
Im inclined to butt weld the sides with TIG ,stitching in small runs whilst gently dollying the distortion as I work My way along the seam ..Ive even considered temporarily tacking a strong back to the existing tank sides whilst I complete the weld bead..removing this upon completion ..although Im worried this may introduce additional stresses into the tank material ?

Will prepare test plates later to set parameters ,technique , etc .

Thank You "Swarfcut" and all contributors for your collective insights .

  Brazing is better for a tank repair. Like soldering, the parent metal is not melted, but the filler material added at a lower temperature. and  so less chance of distortion. A brazed joint is much stronger and durable than a soldered one, but as always, distortion is your enemy, and success depends to a degree on the rigidity of the metal surrounding the repair. Soldering or brazing needs the parent metal to be clean, Bakers Fluid was the acid dip in a can, back in the day. You bought a can, did the job, and of course the next time it was needed the contents had turned brown or the stuff had eaten thro' the can. Nice to see it's still available, now packed in a modern single use plastic bottle.......Progress indeed.

 Swarfy

[BSA_54A10]

The more I see of mig weld body repairs on old metal on TV, the more anguish I feel for the folks that buy the restored vehicle for several thousand ££££'s. In my experience MIG will only work well on new clean metal. Plug welding a new panel onto a joggled edge still carries the risk of distortion on unsupported original panels....a rear wheel arch for instance. Try and run even a short bead and the buckles still appear. So all these restorers use a join the dots method, hardly a recipe for a good strong cohesive fusion joint.

  Brazing is better for a tank repair. Like soldering, the parent metal is not melted, but the filler material added at a lower temperature so less chance of distortion. A brazed joint is much stronger and durable than a soldered one, but as always distortion is your enemy, and success depends to a degree on the rigidity of the metal surrounding the repair. Soldering or brazing needs the parent metal to be clean, Bakers Fluid was the acid dip in a can, back in the day. You bought a can, did the job, and of course the next time it was needed the contents had turned brown or the stuff had eaten thro' the can. Nice to see it's still available, now packed in a modern single use plastic bottle.......Progress indeed.

 Brazing is better for a tank repair. Like soldering, the parent metal is not melted, but the filler material added at a lower temperature so less chance of distortion. A brazed joint is much stronger and durable than a soldered one, but as always distortion is your enemy, and success depends to a degree on the rigidity of the metal surrounding the repair. Soldering or brazing needs the parent metal to be clean, Bakers Fluid was the acid dip in a can, back in the day. You bought a can, did the job, and of course the next time it was needed the contents had turned brown or the stuff had eaten thro' the can. Nice to see it's still available, now packed in a modern single use plastic bottle.......Progress indeed.

Braizing ( as in with brass or bronze filler rods ) is not good for fuel tanks as it has a very low fatigue linlit so is not suitable for for joints subjected to flexing.
Silver soldering (  using a nickle silver rod ) is substantially better for tanks.
This is why vintage & veteran bikes had braised frames with tubes held rigidly by the forged / cast lugs & soldered the tanks
Lead is very flexiable which is why quality cars were lead wiped rather than filled with epoxy to cover seams & joints .
It is also why plumbers used it on hot water tanks and external water tanks subject to expansion & contraction and guttering plus down here for joining bull node sheets of corri iron together ,
Do not mix this up with modern no lead silver solder which is a Sn-Ag alloy and not particularly good for anything other than circits

[RDfella]

Good information from Trevor. I always braze such joints but did ponder the alternative silver solder. Requires slightly lower temperature too, which is helpful. Also has a greater capillary action (in my experience).

Having thought about the job a little more, I'm convinced joining with a rebate (joggler created) and brazing / silver soldering through the drilled (or punched) holes is the way to go. There should be minimal distortion - if any.
Remember, braze / SS ONLY the holes - not the whole join. And do not go 'down the line' - do one hole then leave out several to do the next one (you don't want to build up heat in one location). To keep the join tight, use self-tapping screws through some of the holes into the metal behind. When all the other holes are done, remove screws and braze / SS those holes. Finally, seal join with solder to ensure join is leakproof.

[Greybeard]

I have in my possession a bar of genuine ex telephone jointers soft solder. If it's realistic to send it we can talk about it.