Put some dry ice in the tank after purging it with air, let the CO2 evaporate and fill the tank?

-----Original Message----- From: Ernest Christley
Sent: Thursday, August 15, 2013 9:29 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Fuel tank repair

The Delta has one ~50gal tank that sits behind the back seat.  Not
wishing to fight the compatibility issues between epoxies and whatever
the government may mandate be put into our fuel supply next year, I went
with an welded up aluminum tank which I epoxied into the turtleback.

For fittings, I welded in two NPT adapter bungs to the bottom of the
tank.  One for fuel supply, and one for return.   I had a small, seeping
leak at the supply fitting. I needed to turn the NPT-to-AN6 90 degree
adapter one more turn to make it seal.  I got it most of the way around
before I heard a sharp ping.  The bung that I welded in is now split.
And that split is guaranteed to expand with vibration.

The only solution I can think if is to cut a round hole to remove the
bung, and then construct two plates (one for the inside of the tank and
one for the outside), with a hole in the center for the 90 degree
adapter.  The problem is, the tank can now be viewed as a bomb.  How can
I cut a hole in the bottom of the tank, which will require that I work
in an enclose space, without the possibility of a spark making short
work of everything?

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