What do I need to do to weld on a tank thats already had gas ?

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Aaugman

Well-Known Member
Messages
135
So on the way to Bike night last night we stopped to pick someone up and I noticed a spot on the floor under my bike...To make a ling story short I have a crack in my gas tank. The tank was sealed by a radiator shop and the guy said the stuff they use to seal it is very flammable so i cant weld after the sealing has been done..To get that stuff out would ruin the paint and the crack in on the bottom of the tank So I can fix it without having to repaint the whole tank, I could paint the bottom black and it wont matter.

Problem 1: Anyone know anything about the sealer radiator shops use
problem 2: How do I get all the gas out and make the tank able to weld on without it being a bomb???

I have made a gas cap with a compressor bung in it, So I currently have been pumping air through the tank to try get all the gas and vapors out.


I'm sure everyone who has added steel extensions or done tank work must have had this dilemma, Am I over thinking it ?


Mike
 

Aaugman

Well-Known Member
Messages
135
its got a crack on the underside right at the back of the tank where the rear mounts is. (right in front of the seat) I did some reading and it talks about soapy water then alcohol, then I could pump air through it again to get all the alcohol residue (if any) out. Why nitrogen ?
 

crutter

Site Supporter
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844
Location
Frederick, Md
Would not use alcohol. It is very flammable. Nitrogen is inert and will not burn but will displace the oxygen and other gasses in your tank
 

Opunui

Well-Known Member
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3,325
Location
Oahu/ East side
Critter is correct nitrogen is inert and displaces oxygen. I have heli- arc tanks that I have flushed out and filled with water. Or make a nitrogen dam by regulating the gas in and then welding.
 

TXSNIPER

Well-Known Member
Messages
343
Location
Northeast Texas
Use water, if you choose to use nitrogen, have plenty of ventilation. Nitrogen displaces oxygen and can asphyxiate you quickly without warning.


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kurtlange

New Member
Messages
2
"...air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases."

the way i've welded on gas tanks was to run a hose from a car exhaust into the tank to purge any flammable vapors.
 

crutter

Site Supporter
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844
Location
Frederick, Md
Re read your post. I am assuming that they are saying to use alcohol as a surface prep. Tig welding is very susceptible to surface contaminants and the rubbing alcohol helps eliminate them. But I would still purge your tank
 

Coach

Well-Known Member
Messages
202
Location
Dallas TX
Damn crutter! Nice comparison. Any time i have welded on a tank that had gas it. I purged it with nitrogen and filled it with water and a little detergent/dishsoap. Once the welding was done dumpt the water and used alcohol and compressed air to dry the inside of the tank. I always used a tank liner as well. Pressure testing it is a good idea too. Make sure all of this is done in a well ventilated area. Its a process but no that big o deal. Seen lots of guys do it the wrong way and never have a prob but who wants to end up on a 1000 ways to die!
 

yardsale

Up in da one fiddy...
Messages
1,272
Location
Colorado
"...air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases."

the way i've welded on gas tanks was to run a hose from a car exhaust into the tank to purge any flammable vapors.

Gynocologist here... I can confirm none of this.

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Marc

""The Chopped Baggers Guy""
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ChoppedBaggers.com WORLD HEADQUARTERS.
If you fill with water and seal you'll split the tank from the steam created from superheated water. I'm my experience with a 400amp tig and water directly touching the back side, it want get hot enough to weld.

Like a Dixie cup of water in a fire, the plastic want melt due to the water.

Just saying.
 
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