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SAE AIR 4069B Document Information:
Title
(R) Sealing of Integral Fuel Tanks
SAE International
Publication Date:
Jan 1, 2010
Scope:
This SAE Aerospace Information Report (AIR) presents preferred
practices for sealing of aircraft integral fuel tanks, including
rework of applied fuel tank seals. It addresses engineering designs
for integral fuel tanks as they are currently found in practice;
and discusses the most practical and conservative methods for
producing a reliable, sealed system.
Although this AIR presents practices for sealing of integral
fuel tanks, the practices presented within this report are
practices that are carried throughout sealing that include both
pressure and environmental aircraft sealing.
Design preferences for optimum sealing are not within the scope
of this document. Such discussions can be found in the Air Force
sponsored report, entitled Aircraft Integral Fuel Tank Design
Handbook, AFWAL-TR-87-3078.
Key objectives of the fuel tank sealing process are to produce a
sealing plane that is leak-free and corrosion resistant, especially
at fastener locations, at environmental and operational conditions
expected for the life of each air aircraft. Factors that can
influence the outcome of this process are:
a. How well the basic design lends itself to good sealing (key
design factors to consider include accessibility and minimal
movement, among others).
b. The choice of sealant; where it is applied; how it is
applied.
c. How well the substrate surface is prepared.
d. Whether sealant fillet dimensions are optimum for aircraft
configuration and flight dynamics.
e. The degree of resistance of the sealant to the fluid and
thermal environment.
f. The degree of engineering insurance — i.e., application of
adhesion promoters to sealant bond surfaces, application of organic
topcoats over sealants, proper drainage of the fuel tank, etc. —
employed for technical risk reduction.
Effective and efficient sealing of aircraft fuel tanks are prime
considerations in both commercial and military aircraft designs.
Sealant fillets inside the tanks are considered to be primary
seals.
Of nearly equal importance is corrosion control. Sealants are
used for fuel containment and corrosion protection, but the purpose
of use should never be confused. It is generally accepted, for
example, that a major objective of faying-surface sealing is
corrosion control. The faying-surface seal is not considered to be
a primary seal, except in adhesive-bonded systems; the faying
surface seal, however, plays an extremely important role as a
secondary seal. It limits the length of a leak path and is a
permanent, stable, protected, and essentially non-dislodgeable seal
that is sandwiched between two mating surfaces. Extensive use of
faying-surface sealing is highly recommended.
Sealing philosophies differ within industry and government.
However, as stated in 3.1, there is much greater agreement than
dispute. If a particular fuel tank sealing approach appears to be
clearly more reliable, keeping production cycle time and costs in
mind, it will be identified as a preferred method.
This report is based on technical opinions from a broad
cross-section of engineering experts who specialize in aircraft
sealing.
The user should consider the engineering requirements and
options provided by this report; then develop an individual course
(or plan) of action from a somewhat more informed position.
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