have welding question on gas tank

[airsmith282]

i have gas tank on an old snow blower i have to reattach the pecock tube and i have a crack in the sournding area , can i use flux welder or is it best to braze it together its pretty thin stuff but i want this tank functional again ,

[EddyCurr]

Do you have some thoughts about purging the tank before applying flame
for a repair?

.

[airsmith282]

already been done

[danlb]

Unless you are a crackerjack welder, I'd go with brazing. It's more forgiving and not as likely to burn through.

Dan

[davidh]

i've had good luck using a old soldering iron (copper head monster) and and solder. then to insure it would be good i used por-15 tank coating. this was on a farmall c

[airsmith282]

I already tried to solder it and that didnt work out at all and yes i know how to solder got 30 + years in at soldering and it does not want to hold i get to the last 3/8 of an inch and it wont seal up

can brazing be done with just the use a map fule tourch only and the brazing rod,as i ran out of O2 for my tiny little kit

[Duffy]

I think that you will have real trouble brazing an area where you have previously tried soft solder. Apparently the intermetallic compound of tin and iron, (from the tin/lead solder,) screws up the brazing process. At least it does for silver brazing. ALL the "steam boys" say that it is hopeless to try and braze over a former solder joint.
Since this is not a pressure joint, how about using some 30/70 body solder and "wipe" the joint. there will then be enough metal for strength.

[arcs_n_sparks]

Tank is open as you try to solder/braze it?

[Willy]

I too would try again with solder rather than attempt to brazing it after the first failed attempt at soldering as I too find it very difficult to braze after soldering. Unless one has the luxury of getting in there with an angle grinder and getting back to white virgin metal it won't work. I don't think you have that option.

I'm sure you are aware of this as you've done lots of soldering before but I just want to reemphasize the fact that in soldering cleanliness of the metals to be joined is paramount. It almost sounds like there might be a trace of contamination left on the metal.
And as as arcs_n_sparks suggested, make sure you don't have any air pressure build up in the tank as that too would cause the last bit of the joint to not seal.

Also as a last resort I have had good luck with repairs of this nature while in the field without tools by using JB Weld. I know some will avoid this type of repair but done properly it can sometimes save the day.

Good luck and let us know how you make out.

[ironmonger]

If you were to weld this I think that you would be better off using tig or gas welding. If you are out of O2, you might try silfos brazing alloy with a silver solder brazing flux.
You might be able to clean up most of the soft solder, but without the gas torch it is going to be very difficult to control the warpage while trying to heat the tank hot enough to even silfos the joint using a mapp gas torch... it's only a few hundred degrees lower melting point than BAg alloy silver solder.

Regardless of the alloy you use, the crack should have a patch to increase the surface area of the joint and reinforce the crack. none of the brazing alloys are very flexible, and flexing might cause even a perfect joint to fail if you are successful in butt brazing it.

I know that the conventional wisdom is that you can't braze over soft solder joints, but some years ago we did silfos some 3/4" copper tube joints in that manner, while they were not pretty they did hold a pressure test.
paul