Aircraft Fuel Tanks and Cells

Fuel tank repair
Welded or riveted fuel tanks that are
made of commercially pure aluminum,
3003, 5052, or similar alloys, may be
repaired by welding. Aircraft fuel
tanks made from heat-treatable
aluminum alloys are generally assembled by riveting. In case it is necessary to rivet a new
piece in a tank, use the same material
as used in the tank undergoing repair,
and seal the seams with a compound
that is insoluble in gasoline. Special
fuel tank sealing compounds are available and should be used in the
repair of aircraft fuel tanks. Inspect
fuel tanks and cells for general
condition, security of attachment, and
evidence of leakage. Examine fuel
tanks or cell vent line, fuel lines, and sump drain attachment fittings closely.
CAUTION: Purge de-fueled tanks of explosive fuel/air mixtures in
accordance with the manufacturer's
service instructions. In the absence of
such instructions, utilize an inert gas
such as CO2 as a purgative to assure
the total deletion of fuel/air mixtures. a. Integral fuel Tanks. Examine the
interior surfaces and seams for sealant
deterioration and corrosion (especially
in the sump area). Follow the
manufacturer's instructions for repair
and cleaning procedures. b. Internal Metal Tanks. Check the
exterior for corrosion and chafing.
Dents or other distortion, such as a
partially-collapsed tank caused by an
obstructed fuel tank vent, can
adversely affect fuel quantity gauge accuracy and tank capacity.

Check the
interior surfaces for corrosion. Pay
particular attention to the sump area,
especially for those where sumps are
made of cast material. c. Removal of Flux After fuel tank
welding. It is especially important,
after repair by welding. to completely
remove all flux in order to avoid
possible corrosion. Promptly upon
completion of welding, wash the inside and outside of the tank with
liberal quantities of hot water and then
drain. Next, immerse the tank in either
a 5 percent nitric or 5 percent sulfuric
acid solution. If the tank cannot be
immersed, fill the tank with either solution, and wash the outside with
the same solution. Permit the acid to
remain in contact with the weld about
one hour and then rinse thoroughly
with clean water. Test the efficiency of
the cleaning operation by applying some acidified 5 percent silver nitrate
solution to the small quantity of the
rinse water used last to wash the tank.
If a heavy white precipitate is formed,
the cleaning is insufficient and the
washing should be repeated. Flexible Fuel Cells. Inspect the interior for checking,
cracking, porosity, or other signs of
deterioration. Make sure the cell retaining fasteners
are properly positioned. If repair or
further inspection is required, follow
the manufacturer's instructions for cell
removal, repair, and installation. Do
not allow flexible fuel cells to dry out. Preserve them in accordance with the
manufacturer's instructions.