Mooney M20K - Corrosion Detection & Prevention

SERVICE
AND
MAINTENANCE
MANUAL
M20K
MOONC/
AIRCRAFT
CORPORATION
2040-02
~CORROSION
DETECTION
C.
Concentration
Cell
Corrosion
PREVENTION
Corrosion
forming
under
rivet
heads,
along
faying
Most
metallic
fabn’cation
materials
are
susceptible
to
surfaces,
at
skin
to
longeron
contad
surfaces
other
cormsion.
Corrosion
may
occur
on
aircraft in
any
similar
areas
is
called
concentration
cell
corrosion.
climate,
but it
will
be
a
problem
more
often in
climates
Detection
requires
close
inspection.
Rivets
must
be
where
the
aircraff
is
exposed
to
salt
air
or
high
removed
and
skin
laps
must
be
sepal-ated
to
remove
humidity
or
where
there
are
industnal
contaminants
in
concentration
cell
corrosion.
Use
aluminum
wool
soaked
the
atinbsphere.
The
aircraft
should
be
inspected
in
solvent
such
as
methyl-ethyl-ketone
to
scour
corosion
frequently
to
detect
and correct
corrosion
before
deposits
from
the
surface
before
painting
both
faying
senous
damage
occurs.
surfaces
with zinc
chromate
primer
and
reassembling.
Any
form
of
conosion
should
be
removed
at
once.
If
it
is
D´•
Galvanic
Corrosion
necessary
to
remove
paint,
only
an
approved
aircraft
Dissimilar
metals,
such
as
stainless
steel
and
paint
remover
such
as
Eldorado
PR-3400,
(EMoradc
aluminum,
in
contact
with
each
other
sometimes
Chemical
Co.,
Inc.,
6700
Lookout
Road,
P.O. Box
32101,
develop
galvanic
corrosions.
To
remedy
this
form
of
San
Antonio,
TX.
78216)
should
be
used.
Paint
removing
corosion,
separate
the
parts,
remove
the
corrosion,
and
substances~leff
in
m~tal crevices
will
cause
further
paint
both
surfaces
with
Zinc
Chromate
or
corrosion.
Turco
2662C or
3002
will
remove
corrosion
epoxy-polymide
pn’mer
before
reassembling.
from
aluminum
and
treat
the
metal
surface
in
one
2.
Corrosion
Prevention
application.
This
paragraph
discusses
corrosion
types
and
their
prevention
along
with
suggested procedures
for
A.
Thcroughly
examine
unpainted
metal
surfaces
at
zinc
chromating
intemal
airframe
surfaces.
inspections,
and
check
cormsbn
when
found.
Carefully
examine
seams,
lap
joints,
and
crevices
where
moisture
1.Types
of
Corrosion
Aluminum
or
dirt
can
celled.
Areas
e~cposed
to
e~haust
gases
Corrosion
normally
appears
in
one
or
more
of
four
require
frequent
inspection
and
cleaning.
forms.
Each
type
of
corrosion
can
be
precluded
or
B.
Corrosion
may
attack
metal
even
though
the
surface
controlled
by
a
preventative
maintenance
program,
is
painted.
Inspect
painted
areas
for
a
blistered
or
scaly
A.
Chemical
Corrosion.
appearance
that
warns
of
conosion
below
the
paint
layer.
Chemical
corrosion
normally
occurs
where
battery
acid
C.
Use
only
liquid
(non-alkaline)
soap
to
wash
the
or
exhaust
gases
come
in
contact
with
metal
surfaces.
e>den’or
airframe.
Cover
vent
scoops
when
the
aircraft
A
few
simple
precautions
will
prevent
chemical
is
being
washed.
Rinse
aircraft
e>derior
after
e~q>osure
corrosion,
to
salt
air
or
industrial
fallout.
(1)
Be
sure
battery
vent
is free
from
obstruction
at
D.
Since
moisture
promotes
con~osion,
thoroughly
alltimes.
and
frequently
inspect
areas
where
water is
apt
to
collect.
Use
an
air hose
to
drive
water
from
crevices
(2)
Repaint
all
scratches
and
wom
spots
found
in
before
wiping
the
e~derior
surface
dry
after
washdown.
areas
painted
with
acid-resistant
paint
E.
Hangarthe
aircraft
when
not
in
use.
(3)
If
acid
is
spilled
on
metal
surfaces,
flush
entire
area
with
sodium
bicarbonate
and water.
The
solution
F.
If
battery
acid is
spilled
on
any
part
of
the
should
be
rinsed
away
at
once
and
the
area
dried
by
aircraft,
immediately
wash the
area
with
a
solution
of
sodium
bicarbonate
in
water.
Rinse
with
water
and
dry
driving
all
water
from
crevices
with
an
air
hose
before
with
clean
towels.
wiping
surface
dry
with
a
clean
cloth.
(4)
Frequently
clean
exhaust
gas
deposits
from
NOTE
metal
surfaces.
FAA
Advisory
Circular
434 addresses
corrosion
problems.
B.
Local-Cell
Corrosion.
3.
Zinc
Chromating
(or
Equivalent).
On
bare
metal
surfaces,
in
an
early
stage
development,
airframe
local-cell
corrosion
appears
as a
light,
whitish
powder
Zinc
chromating
or
equivalent
of
intemal
deposit.
Surface
pits
wam
of
advanced
loca~cell
surfaces
will
not
eliminate
the
necessity
for
periodic
corrosion.
On
painted
surfaces,
the
first indication
of
inspections.
The
most
likely
areas
for
corrosion
to
corrosion
will
be
evidenced
by
paint
blisten’ng.
begin
are
in
hidden
crevices
such
as
skin
laps,
under
rivet
heads
or
any
opening
where
moisture can
collect.
(1)
Intergranular
Corrosion
Selective
attack
periodic
inspection
of
these
areas
is
most
important
so
along
grain
boundaries
of
metal
alloys
is
referred
to
as
that
any
corrosion
which
may
be
present
can
be
Intergranular
corrosion.
Aluminum
alloys
2024
and
detected
and
treated
in
its
very
earliest
stages.
7075
are
vulnerable
to
this
type
of
attack. Aluminum
Vli~en
corrosion
is
detected,
it
should
be
treated
as
foll~Ns:
extrusions
may
contain nonuniform
areas,
which
in
tum
may
result
in
galvanic
attack
along
grain
boundaries.
A. Remove
all
corrosion
product
(usually
white
or
7hls
type
of
corrosion
is
difficult
to
deted
in
its
original
grey-white
powder
on
aluminum)
from the
corroded
stages.
When
the
attack is
well
advanced,
the
metal
is
area
down
to
sound
metal.
usually
blistered
or
delaminated.
This
is referred
to
as
(1)
If
the
base
metal
is
aluminum,
clean
off the
"exfoliation".
It
is
very
difficult
to
completely
remove
conosion
produd
by
scrubbing
with
aluminum
wool
or
and
stop
this
type
of
corrosion,
and
replacement
of
the
nonmetallic
scouring
pad
such
as
the
nylon
pads
affected
part
is
recommended
wherever
possible,
made
by
the
Carborundum
Company,
P.O.
Box
277,
Niagara~Falls,
N.Y.
14302.
20-00-02
OLDWILLWAYNE