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Posted by Leo Lichtman on July 3, 2008, 9:55 pm
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"Maxwell" wrote: (clip) after just a few seconds of welding, I got an
extremely hard
> POP from the combustion gasses on the inside. It bloated the metal pan,
> and could have been very dangerous. (clip)
^^^^^^^^^^^^^^^^^^^
I know of a welding shop that welds gas tanks after running the exhaust from
a small engine into the tank for an hour or so. Another idea might be to
shove in several handfulls of dry ice. The CO2 will force virtually all the
air out. CO2 is heavier than air, so if any air remains, it would not be at
the bottom.
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Posted by Maxwell on July 3, 2008, 11:21 pm
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>
> "Maxwell" wrote: (clip) after just a few seconds of welding, I got an
> extremely hard
>> POP from the combustion gasses on the inside. It bloated the metal pan,
>> and could have been very dangerous. (clip)
> ^^^^^^^^^^^^^^^^^^^
> I know of a welding shop that welds gas tanks after running the exhaust
> from a small engine into the tank for an hour or so. Another idea might
> be to shove in several handfulls of dry ice. The CO2 will force virtually
> all the air out. CO2 is heavier than air, so if any air remains, it would
> not be at the bottom.
>
I have heard that, but never had any first had experience with anyone that
actually did. I would be afraid of it. I would hate to find out the hard
way, that it was just a legend. I have welded gas and diesel tanks, but only
after flushing them with water, then filling them completely with water,
leaving a bubble only where I wanted to weld. Even at that, I have had them
huff a bit.
Have you had the opportunity to witness the exhaust purge technique first
hand Leo?
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Posted by Leo Lichtman on July 4, 2008, 1:05 am
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"Maxwell" wrote: (clip) then filling them completely with water,
> leaving a bubble only where I wanted to weld. Even at that, I have had
> them huff a bit.
^^^^^^^^^^^^^^^^^^^^^^
I once tried gas welding some cracks around the petcock on the bottom of a
Harley tank. I filled it with water, and propped it up on my bench, bottom
side up. It blew. The gas cap came off, and water shot out the neck,
drenching me and everything around. I figured out afterwards what had
happened: water dripped put the vent hole in the gas cap, so the water
level dropped slowly. Some gasoline floated on top of the water, and then
ignited.
^^^^^^^^^^^^^^^^^^^^^
> Have you had the opportunity to witness the exhaust purge technique first
> hand Leo?
^^^^^^^^^^^^^^^^^^^^^
No. I was told by someone who seemed to know what he was talking about.
Still, only hearsay.
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Posted by Don Young on July 4, 2008, 10:14 pm
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>
> "Maxwell" wrote: (clip) then filling them completely with water,
>> leaving a bubble only where I wanted to weld. Even at that, I have had
>> them huff a bit.
> ^^^^^^^^^^^^^^^^^^^^^^
> I once tried gas welding some cracks around the petcock on the bottom of a
> Harley tank. I filled it with water, and propped it up on my bench,
> bottom side up. It blew. The gas cap came off, and water shot out the
> neck, drenching me and everything around. I figured out afterwards what
> had happened: water dripped put the vent hole in the gas cap, so the
> water level dropped slowly. Some gasoline floated on top of the water,
> and then ignited.
> ^^^^^^^^^^^^^^^^^^^^^
>> Have you had the opportunity to witness the exhaust purge technique first
>> hand Leo?
> ^^^^^^^^^^^^^^^^^^^^^
> No. I was told by someone who seemed to know what he was talking about.
> Still, only hearsay.
>
>
I am not recommending the procedure but we used to torch braze Harley and
Indian (pre 1958) tanks by draining, blowing out with the air blow gun,
clamping a mounting ear in the vice, and sticking the lit torch into the cap
opening. You would get a small explosion but the small tank was plenty
strong enough to withstand it. I have successfully soldered an empty auto
gas tank with a 300W American Beauty iron but have never gotten near one
with a torch. The accepted method of purging them used to be with a steam
cleaner.
Don Young
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Posted by Ivan Vegvary on July 4, 2008, 1:56 am
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>
>>
>> "Maxwell" wrote: (clip) after just a few seconds of welding, I got an
>> extremely hard
>>> POP from the combustion gasses on the inside. It bloated the metal pan,
>>> and could have been very dangerous. (clip)
>> ^^^^^^^^^^^^^^^^^^^
>> I know of a welding shop that welds gas tanks after running the exhaust
>> from a small engine into the tank for an hour or so. Another idea might
>> be to shove in several handfulls of dry ice. The CO2 will force
>> virtually all the air out. CO2 is heavier than air, so if any air
>> remains, it would not be at the bottom.
>>
>
> I have heard that, but never had any first had experience with anyone that
> actually did. I would be afraid of it. I would hate to find out the hard
> way, that it was just a legend. I have welded gas and diesel tanks, but
> only after flushing them with water, then filling them completely with
> water, leaving a bubble only where I wanted to weld. Even at that, I have
> had them huff a bit.
>
> Have you had the opportunity to witness the exhaust purge technique first
> hand Leo?
>
While not pertinent to what I am doing, standard procedure for pulling
service stations out of the ground is to place enough dry ice on the bottom
to displace all the combustibles. Takes several hours for the ice to
release the gasses. Proof is by testing for hydrocarbons at the top
opening. Until tested clear, you are not allowed to put a chain around the
tank or make contact with anything made of steel (spark avoidance). After
tank is cleared you can start dismantling the attached piping and pull the
tank. Have done many, many of these in the past.
Ivan Vegvary
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> and could have been very dangerous. (clip)