Mooney M20R - Epoxy-Polymide Painting; Types of Corrosion

SERVICE
AND
MAINTENANCE
MANUAL
M20R
MOONEY
AIRCRAFT
CORPORATION
1.
Types
of
Corrosion Aluminum
2.
Corrosion
Prevention
Corrosion
normally
appears
in
one
or
more
of
four
A.
Thoroughly
examine
unpainted
metal
surfaces
forms. Each
type
of corrosion
can
be
precluded
or
at
inspections
and
check
corrosion
when
found.
Care-
controlled
by
a
preventative
maintenance
progran.
fully
examine
seams,
lap
joints,
and
crevices
where
A.
Chemical Corrosion.
moisture
or
dirt
can
collect.
Areas
exposed
to exhaust
Chemical
corrosion
normally
occurs
where
battery
acid
gases
require frequent
inspection
and
cleaning.
or
exhaust
gases
come
in
contact
with
metal
surfaces.
B.
Corrosion
may
attack
metal
even
though
the
a
few
simple
precautions
will
prevent
chemical
cor-
surface is
painted.
inspect
painted
areas
for
a
blistered
rosion.
or
scaly
appearance
that
warns
of
corrosion
below
the
(1)
Be
sure
battery
vents
are
free from
obstruc-
paint
layer.
tions
at
all
times.
C.
Use
only liquid
(nota-aska9ine)
soap
to wash
the
(2)
Repaint
all
scratches and
worn
spo~si
found
exterior
airframe.
Cover
vent
scoops
when
aircraft
is
in
areas
painted
with
acid-resistant
paint, being
washed.
Rinse
aircraft
exterior
after
exposure
to
(3)
If
acid is
spilled
on
metal
surfaces,
flush
en-
salt air
or
industrial
fallout.
tire
area
with
sodium bicarbonate
and
water.
Th$
solu-
D.
Since
moisture
promotes
corrosion,
thoroughly
tion should
be
rinsed
away
at
once
and
the
area
dried
and
frequently
inspect
areas
where
water
is
likely
to
by
driving
all
water
from crevices
with
an
air hose
collect.
Use
an
air hose
to drive
water
from
crevices
before
wiping
surface
dry
with
a
clean
cloth.
before
wiping
exterior
surface
dry
after
washdown.
(4)
Frequently
clean
exhaust
gas
deposits
from
E.
Hangar
aircraft
when
not
in
use.
metal
surfaces.
F. if
battery
acid
is
spilled
on
any
part
of the
B.
B_ocaO-Cell
Corrosion.
aircraft,
immediately
wash
the
area
with
a
solution
of
Qn
bare metal
surfaces,
in
an
early
stage osevelopment,
sodium
bicarbonate
In
water.
Rinse
with
clear
water
local-eels
corrosion
appears
as a
light,
whitish
powder
and
dry
with
clean
towels.
deposit.
Surface
pits
warn
of advanced
local-call
cor-
rosion. On
painted
surfaces,
the
first
indication
Qf
6;or-
NOTE
rosiola
will
be evidenced
by paint
blistering.
ACF-50
or
equivalent
can
be
fogged
into
fuselage,
(1)
Intergranular
Corrosion
Selective
iattack
empennage
or
wing
skin
areas.
It
is
recommeded
along grain
boundaries
of metal
alloys
is
referred
to
as
that
electrical
connections
and
electrical
intergranulaa
corrosion.
Aluminum
alloys
2024
and
components
be
protected
(sealed
off)
during
7875
are
vulnerable
to
this
type
of
attack.
Aluhlinum
fogging
procedures.
extrusions
may
contain
non-uniform
areas,
which
in
turn
may
result
in
galvanic
attack
along
grain;boun-
NOTE
daries. This
type
of corrosion is
difficult
to
detect
in
its
FAA
Advisory
Circular
454
addresses
corrosion
original
stages.
When the
attack is well
advanced,
the
problems.
metal
is
usually
blistered
or
delaminatecs.
This
is
referred
to
as
"exfoliation".
It
is
very
difficult
to´•
eom-
3.
Epoxy-polymide
Painting.
pletely
remove
and
stop
this
type
of
corrosion,
and
re-
Epoxy-polymide
coating
of
internal
airframe
surfaces
placement
of the
affected
part
is
recommended
will
not eliminate
the
necessity
for
periodic
inspections.
wherever
possible.
The
most
likely
areas
for
corrosion
to
begin
are
in
hid-
C.
Concentration
Cell Corrosion
den
crevices
such
as
skin
laps,
under
rivet
heads
or
Corrosion
forming
under
rivet
heads,
along
faying
sur-
any
opening
where
moisture
can
collect.
Periodic
in-
faces,
at
skin
to
longeron
contact
surfaces
andi
other
spedion
of these
areas
is
most
important
so
that
any
similar
areas
is called
concentration
cell
coriosion,
corrosion
which
may
be
present
can
be
detected
and
DePectiola
requires
close
inspection.
Rivets
m4sP
be
treated in
Its
very
earliest
stages.
removed and skin
laps
must
be
separated
to
r~move
When
corrosion
is
detected,
it
should
be
treated
as
fos-
concentration
cell corrosion.
Use
aluminum-woo9
lows:
soaked
in
solvent
such
as
methyl-ethyl-ketone
to;scour
A.
Remove
all
corrosion
product
gusually
white
or
corrosion
deposits
from
the
surface
before
ps~inting
grey-white
powder
on
aluminum)
from
the
corroded
both
~aying
surfaces
with
epoxy-polymide
primdr
and
area
down
to
sound
metal.
re-assembling.
(1)
If
the
base
metal is
aluminum,
clean
off
the
D.
Galvanic Corrosion
corrosion
product
by
scrubbing
with
aluminum
wool
or
Blssinsilar
metals,
such
as
stainless
steel!
and
a
non-metallic
scouring
pad
such
as
the
nylon
Bads
aluminum,
in
contact
with
each
other
som$times
made
by
the
Carborundum
Company,
P.O.
Box
277,
develop galvanic
corrosions.
To
remedy
this
form of
D\liaElara
Falls,
N.Y.
14302.
corssion,
separate
the
parts,
remove
corrosion,
and
%21
If
the base
metal is
steel,
remove
the
cor-
paint
both
surfaces
with
epoxy-po9ymide
primer
before
rosion
product
with
emery
cloth
(320
grit
or
finer)
or
reassembling.
steel
wool.
28-00-02
Island Enterprises