Tack then braze?

[Screwdriver]

Plenty of info out there (and on here!) on purging, I should leave it to those here who know vastly more than I do. But you can mitigate the “losses” in having an open purge tube with a suitable valve or filter etc but for the size of job you’re doing, probably just best to flow gas in there and be a little wasteful.

 

[GraemeVW]

Plenty of info out there (and on here!) on purging, I should leave it to those here who know vastly more than I do. But you can mitigate the “losses” in having an open purge tube with a suitable valve or filter etc but for the size of job you’re doing, probably just best to flow gas in there and be a little wasteful.

Yes, I agree. It's not going to take long at all.

 

[Maker]

CO2, Argoshield etc. They’re all inert gasses.

I can't believe your inner pedant let you say that!

 

[Gareth J]

If you know that any remnants are minute, safer to purge with air than nothing. A constant high volume airflow will not allow sufficient fuel ratio to build as to create an explosive mix, (in a well cleaned tank). Clearly an inert gas is preferable to air but masses of air is better than a tank's worth of air letting potential combustible vapours build up.

 

[Screwdriver]

I can't believe your inner pedant let you say that!

lol. Well I suppose a trade name shouldn’t be referenced in the same way as a pure gas but ykwim.

 

[500e]

I'm not convinced about anything coming out of the seams when heated, and even if their is a chance it's not going to be enough to go bang. I would also take stories where someones cleaned a tank out properly and its still gone bang with a pinch of salt, i'd put money on the tank wasn't cleaned out properly and the idiot welding it prefaced his story with "I cleaned it out for days, honest" just to try and save some face.

Believe what you want, I looked at the tank after, Yes it may have not been soaked as he was told but he had done others and they went through the same process.

 

[outofthefire]

Believe what you want, I looked at the tank after, Yes it may have not been soaked as he was told but he had done others and they went through the same process.

People get over confident or blasé and cut corners when they do the same thing numerous times, thats why people have accidents doing what they do day in day out, and most people are too embarrassed to admit they cocked up so blame something else.

 

[northwest]

You are really over thinking this, you could have had it done by now. Four tacks on that bracket and it would be done, the purge is to stop the steel oxidising and flaking inside the tank, a good blast of Argoshield and off you go,

 

[GraemeVW]

You are really over thinking this, you could have had it done by now. Four tacks on that bracket and it would be done, the purge is to stop the steel oxidising and flaking inside the tank, a good blast of Argoshield and off you go,

Overthinking? Yeah, that sounds like me

I would have tacked it already, main reason i started this thread was to see if it will still braze ok if i tack it first. Wasnt sure if the flux would flow under the bracket.

 

[Justme]

Tack with mig braze, finish with mig braze?

Mig tack & mig weld to finish?

Mig tacj & mig braze to finish?

 

[GraemeVW]

Well, it's all done.

4 rosette mig welds to hold the bracket, then brazed all round.

Also brazed the hole.

Not my neatest work, a combination of nagging doubt and trying to braze with mapp gas saw to that.
Pics when it's cooled.

I have done a few bits of brazing with mapp. Helps to have some vermiculite board to surround it and keep the heat in. Takes AGES to get it hot enough, and hard to flow it really nice, but it does work.

 

[GraemeVW]

Ok, no laughing. I really have very little brazing experience, and as I say, doing it with plumbers mapp gas!

One of the rosette welds had a hole, so I braze that in too. I tried to just keep flooding the edges until I thought it had crept under all of it.

The brazing of the hole

I'd lost the will to live by this point, it was taking so long. But it's flowed in, and built up, and the hole is covered, so all good.

I'll put it in the citric next to get rid of the rust, then test it.

 

[Bsmith]

I have soldered a 2p coin on a Cortina petrol tank after tipping the petrol out in a container, no de gassing.

 

[GraemeVW]

I have soldered a 2p coin on a Cortina petrol tank after tipping the petrol out in a container, no de gassing.

Brave man! No flame, but still not something I'd be 100% comfortable with!

I didn't bother purging this in the end. I put the blowtorch flame inside and nothing happened. Welded it, then did the flame again to double check before brazing it.

I've seen a few vids of people just pouring the petrol out, then putting a flame inside to just burn off what's left. Risky, but the flame created really isn't that fierce and it doesn't go off with any energy.
I wonder if exploding tanks is limited to tanks with a bigger volume and a smaller opening.

 

[Bsmith]

No flame, just hot heavy copper soldering iron.
Iv'e never done it but I have heard of people welding petrol tanks with an extension from the exhaust of a running engine inside the tank.

 

[Seadog]

Explosions happen when the fuel/oxygen ratio is correct forvthe fuel ( stoichiometric ratio, look it up).

At school it was not uncommon, as a demonstration, to fill a conical flash with hydrogen then light the top. The hydrogen burnt away until the O/H ratio was achieved, wherein it went bang.