CORROSION PREVENTION CONTROL MANUAL

CORROSION PREVENTION AFTER CHEMICAL EXPOSURE — CORROSION PREVENTION

1. Procedure After Mercury Spillage
A. General
The corrosive action of mercury is very rapid. Therefore, immediate remedial action must be taken
when mercury spillage has been discovered.
Mercury combines readily with aluminum alloys to form an amalgam at room temperature if the oxide
film on the aluminum has been scratched or damaged. Once a small area of aluminum has been
affected, corrosion occurs. This process (amalgamation) is accelerated by moisture and particularly
by salt water.
The amalgamation of stressed aluminum structure may also result in rapid cracking similar to stress
corrosion cracking.
Unfortunately, mercury is not consumed in the amalgamation process. As the aluminum oxidizes, it
separates from the amalgam and the mercury continues to attack fresh aluminum.
The presence of organic finishes, grease or an anodized coating retards the amalgamation process.
B. Detection
(1) The presence of corrosion caused by spilled mercury is indicated by a grayish white powder or
fuzzy coating on aluminum surfaces.
(2) The presence of even small amounts of mercury can be detected by an electronic device that is
sensitive to mercury vapor.
(3) Mercury can best be detected using X-ray and will show up on the film as small, white spots.
Corrosion may show up as tree like forms penetrating the structural component.
C. Personnel Precautions
WARNING: ALWAYS PROVIDE AMPLE VENTILATION WHILE CLEANING AREAS
CONTAMINATED BY MERCURY.
(1) Appreciable amounts of mercury will vaporize into the air at normal temperatures to the extent
that a stagnant air mass can become dangerous to personal health.
(2) Free mercury or an amalgam must not be picked up by hand.
WARNING: DO NOT EAT, SMOKE OR BLOW NOSE AFTER CONTACTING MERCURY
WITHOUT FIRST THOROUGHLY WASHING HANDS.
(3) Clean tools with soap and hot water or steam bath. Discard drill bits after use on a structure
contaminated with mercury.
D. Isolation of Contaminated Areas
On discovery of spilled mercury, steps should be taken to avoid enlargement of the contaminated
area. The following precautions are advised:
(1) Do not remove access / inspection plates or even fasteners which could result in the spread of
the mercury, until such times as the area has been thoroughly cleaned up.
(2) If hands become contaminated, do not touch any exposed metal in the surrounding area.
(3) Mercury spreads easily from one surface to another by adhering to hands, shoes, clothes, tools,
etc. Keep traffic to a minimum in the contaminated area.
(4) Wear foot covers (wing socks) to prevent damage to finish thus exposing bare metal to attack.

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(5) Consider protection of uncontaminated areas by taping down protective material such as plastic
sheets or toweling. Plastic sheets or toweling can also be taped over a contaminated area to
isolate it while equipment is being collected for the removal of mercury.
E. Mercury Removal
(1) The first action to be taken is to remove all visible mercury without delay. The following methods
of removal are suggested: The more primitive methods are less effective than those requiring
special equipment, but any possible method should be quickly attempted, as speed is essential.
(a) Use paper or cardboard troughs to scoop up the mercury.
(b) Use adhesive tape to pick up small droplets.
(c) Use a medicine dropper for globules.
(d) Use a high powered vacuum cleaner with a trap. See Figure 101 for a suggested method
of making a trap.
(e) Use one of the special mercury pickup brushes that attract mercury. Foam pads and
mercury sponges are also commercially available that will pick up mercury. See Step 1.F
for details of a suitable brush.
(f) Use the special Hg Vac vacuum cleaner, if available.
(2) After removal of any visible mercury, more sophisticated means must be employed to ensure
that hidden mercury is located and removed. A sensing device known as a mercury sniffer can
be used, or even more effectively, X-ray pictures can be taken.
WARNING: ALL DETECTABLE MERCURY MUST BE REMOVED FROM THE AIRCRAFT.
(3) Where there is evidence of the presence of mercury in joints between faying surfaces or
mercury is trapped in any way between structural members, disassemble as necessary to
permit its complete removal.
F. Removal of Mercury Using Brushes
(1) A special brush is available, made from nickel plated carbon fibers, that will pick up mercury.
See Step 1.G for a source of supply.
(2) A brush made from fine copper wire can also be used to pick up mercury. It is suggested that a
suitable brush could be manufactured locally by using the fine wires used in domestic flexible
electrical cable. the procedure for using the copper brush is as follows:
(3) Immerse the brush in nitric acid (HNO3) to chemically clean the wires.
(4) Rinse the brush in clean water to remove the acid.
(5) Immerse the brush in alcohol to remove the water.
(6) Pick up the mercury with the brush. Mercury adheres to the copper wires by forming an
amalgam. After a quantity of mercury has been collected by the brush, it can be shaken off into
a suitable container and the picking up process continued.
G. Special Equipment
Because of the urgency involved in removing mercury from the aircraft most of these procedures
utilize materials which are readily available locally. However the use of some special equipment is
beneficial in ensuring that all traces of mercury are removed and the sources of supply for these
items are as follows:
(1) Mercury vacuum cleaner: Nilfisk of America Inc., 1-800-NIL-FISK, Pennsylvania.

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(2) Nickel plated carbon fiber brushes: N.E.I. International Research and Development Co. Ltd.,
011-44-91-265-0451, Newcastle Upon Tyne, NE6 2Yd, UK.
(3) Mercury sponge: J.T. Baker Chemical Co., 908-859-2151, New Jersey.

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Vacuum Cleaner Mercury Trap

Figure 101

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2. Procedure After Alkaline Spills

A. General
Alkaline spills are caustic and can cause corrosive damage to aircraft structures unless neutralized.
Alkali based, corrosion removal compounds and aircraft cleaners are used quite extensively during
routine maintenance operations. Without neutralizing and / or thoroughly rinsing, a spilled alkaline
compound can produce corrosion damage.
Containers of alkaline compounds may be part of a cargo and can be broken during loading or
unloading. Spillage from such sources are usually large in scale. It is therefore recommended that
neutralization of spilled alkaline compounds be accomplished as soon as possible.
B. Detection
(1) Alkalines are clear and are not detectable by color. However, spillage is usually readily noticed
by personnel working in the immediate spillage area. Such spills should be neutralized as soon
as possible.
(2) In cases where spillage has gone undetected and has penetrated the protective finishes, a
white powdery deposit (aluminum oxide) indicates corrosion of the aluminum structure.
(3) In other instances, particularly around the top of nickel cadmium battery cells, alkaline
electrolyte which has spewed or overflowed the vent caps will react with carbon dioxide in the
air and produce a white powdery deposit. This white deposit is not corrosive and is harmless.
However, it is an indication that the electrolyte has spilled or has otherwise escaped.
C. Personnel Protection
WARNING: ALKALINES ACCIDENTALLY SPILLED ON SKIN, CLOTHING OR OTHER
MATERIAL SHOULD BE FLOODED IMMEDIATELY WITH CLEAN WATER. IF EYES
ARE INVOLVED, FLOOD WITH CLEAN WATER OR BORIC ACID SOLUTION AND
IMMEDIATELY CONSULT A PHYSICIAN.
(1) Adequate protective clothing (rubber or plastic gloves, goggles, face shields, aprons, boots,
head gear, etc.), should be worn when handling or working in alkaline contaminated areas.
(2) Wash hands after using alkaline neutralizing solutions / materials and before eating or smoking.
(3) Waste materials, solvents, chemical solutions, wiping rags, masking materials, etc., shall be
collected and disposed of safely.
D. Isolation of Contaminated Area
On discovery of alkaline spills, steps should be taken to contain the contaminated area. The following
precautions are advised:
(1) Do not allow alkaline spills to spread to adjacent areas which cannot be readily cleaned.
(2) In battery areas, placing plastic sheets beneath equipment will provide added protection. If
equipment is operating, venting requirements should be maintained.
(3) Consider protecting uncontaminated areas by taping down protective material such as plastic
sheets.
E. Alkaline Spillage Cleanup
(1) If equipment is adjacent to the treatment area, use plastic sheets to cover the equipment to
prevent inadvertent splashing of alkalines or treatment fluids.
(2) Wipe up excess fluids with rags and discard into a plastic container for disposal.

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(3) Neutralize the treatment area with a 5% acetic acid solution or full strength household vinegar
applied with a brush or cloth swab. Check for neutrality with litmus paper.
(4) Thoroughly dry all areas and restore any deteriorated finishes (if possible) as described in
Standard Surface Treatment Methods, 20-50-05, Corrosion Prevention.
(5) Apply Type II corrosion inhibiting compound (LPS-3 preferred) over the affected areas as
described in Standard Preventive Maintenance Methods, 20-53-00, Corrosion Prevention.
3. Procedure After Acid Spills
A. General
Acid spills, unless neutralized, can rapidly corrode metallic structure.
Acid based corrosion removal compounds and aircraft cleaners are used quite extensively during
routine maintenance and repair. Spills do occur at times and thorough neutralizing and / or rinsing is
necessary to prevent corrosion damage.
Containers of acid concentrates or acid based chemicals may be part of baggage or cargo and can
be broken during loading or unloading. Spillage from such sources are usually larger in scale than
maintenance / servicing chemical spills mentioned in the paragraph above. It is therefore advisable
that any acid spillage be neutralized as soon as possible.
Acid spills may come from lead-acid batteries.
Operators should also be aware that acids will deteriorate nonmetallic materials such as fabrics,
wood, leather, etc.
B. Detection
(1) Suspect and investigate any discoloration on the aircraft surface. Black, white, yellow and
brown are the predominant colors of chemical corrosion residues. The color of the residue
depends on the acid spilled and the material on which it was spilled.
C. Personnel Protection
WARNING: ACIDS ACCIDENTALLY SPILLED ON SKIN, CLOTHING OR OTHER MATERIAL
SHOULD BE FLOODED IMMEDIATELY WITH CLEAN WATER. IF EYES ARE
INVOLVED, FLOOD WITH A LARGE QUANTITY OF CLEAN WATER AND
IMMEDIATELY CONSULT A PHYSICIAN.
(1) Adequate protective clothing (rubber or plastic gloves, goggles, face shields, aprons, boots,
head gear, etc.), should be worn when handling or working in acid contaminated areas.
(2) Wash hands after using acid neutralizing solutions and / or materials before eating or smoking.
(3) Waste materials, solvents, chemical solutions, wiping rags, masking materials, etc., shall be
collected and disposed of safely.
D. Isolation of Contaminated Area
On discovery of acid spills, take steps to contain the contaminated area. The following precautions
are advised:
(1) Do not allow acid spills to spread to adjacent areas which cannot be readily cleaned.
(2) Consider protecting uncontaminated areas by taping down protective material such as plastic
sheets.
E. Cleanup of Acid Spills
(1) If equipment is adjacent to the treatment area, use plastic sheets to cover the equipment to

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prevent inadvertent splashing of acids or treatment fluids.

(2) Wipe up excess fluids with rags and discard into a plastic container for disposal.
(3) Neutralize the treatment area with a 20% sodium bicarbonate solution (baking soda) applied
with a brush or cloth swab. Pay particular attention to faying surface joints. Pressure application
may be required to thoroughly flush the joints.
NOTE: One pound of bicarbonate of soda mixed into 1 gallon of water provides the proper
mixture.
(4) Continue to apply the solution until all bubbling ceases. Then allow the solution to remain on the
surface for an additional 5 minutes.
(5) Remove the neutralized solution with a mop or sponge.
(6) Rinse the affected area with generous quantities of clean water. Occasionally stir the surface
with a soft brush.
(7) Check for neutrality of the fluid with litmus paper.
(8) Dry all areas using clean rags.
(9) After thoroughly drying all areas, restore any deteriorated finishes (if possible) as described in
Standard Surface Treatment Methods, 20-50-05, Corrosion Prevention.
(10) Apply Type II or Type III corrosion inhibiting compound (LPS-3 preferred) over the affected
areas as described in Standard Preventive Maintenance Methods, 20-53-00, Corrosion
Prevention. Apply an overcoat of Type VII or Type VIII to the affected area(s).
4. Procedure After Salt Water Exposure
A. General
Salt water is corrosive to all metallic parts in the aircraft structure. Exposure of unprotected steel will
cause immediate rusting, will start pitting attack and can result in hydrogen damage in high strength
steel. Cadmium plated steel is protected from salt water corrosion provided the salt residues are
removed before the cadmium plating can be corroded away.
Salt water causes pitting in unprotected aluminum alloys, accelerates galvanic and crevice corrosion
and is a known contributor to stress corrosion cracking in high strength aluminum.
Fluid containers of food, fish or chemicals may spill during flight and can cause significant damage if
the spill is not detected and treated.
External exposure of the aircraft to salt water will occur in tropical areas and if untreated can result in
serious corrosion on bare metal surfaces and in crevices where moisture accumulates.
B. Equipment
(1) Additional care must be exercised when loading and stacking containers to minimize possible
spillage. Reports have been received of boxes tipping on their sides during flight with eventual
leakage of fluids, including fish slime, salt water, etc.
C. Shipping Standards
(1) Operators frequently carrying liquid products should establish packaging standards so that the
containers are appropriate for the product to be shipped and the location of the packaged
product in the aircraft. In addition, the standards will provide some guidance to the shipper as to
packaging requirements and to operating personnel regarding refusal of improperly packaged
shipments.

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D. Shipping Containers
In order to minimize problems associated with spillage of liquids, consider using water tight shipping
containers that are used by air carriers and shippers.
(1) Wax Impregnated Cardboard Boxes
(a) A two piece, fully telescoping, wax impregnated cardboard box is currently used with some
degree of success. It has reinforced gussets at the bottom and top. An example of such a
box is that made by the Menasha Corporation (V1L860), Menasha, Wisconsin, and is
sometimes referred to as a wet lok carton.
(b) The size of the box should be limited to a maximum net weight of 100 pounds.
(c) If frozen food is being shipped, dry ice may be used to ensure that the liquids remain
frozen during flight.
CAUTION: IF DRY ICE IS ADDED TO THE SHIPMENT, THE OPERATOR MUST BE
NOTIFIED AS TO THE QUANTITY USED TO ASSURE THAT ADEQUATE
OXYGEN CONCENTRATION IS MAINTAINED IN THE PASSENGER
COMPARTMENT.
(d) Nylon or plastic tape should be used to wrap the width and the length of the box.
(e) On large shipments some operators place the boxes in large open topped fiberglass
containers.
(2) Specialized containers are available for containing material with liquids to prevent spillage. See
Transportation of Fish, 20-53-05, Corrosion Prevention.
E. Shipment of Salt Solutions
(1) Some requirements exist for the shipment of salt solutions or chemicals. Aggressive preventive
action to contain any possible spillage is the best approach to control potential corrosion. To
guard against salt solution spillage into the aircraft structures, the floor and walls can be lined
with a one piece plastic or vinyl mat. The mat should curve up the wall about 6 inches where it
is taped.
F. Preventive Maintenance (Interior)
(1) The carriage of liquid products may require removal of the cabin lining and insulation blankets
for periodic cleaning, drying and deodorizing. This provides an excellent opportunity to perform
corrosion preventive maintenance.
(2) At each available opportunity, inspect the inner skin surface and fuselage structure for signs of
corrosion. Ensure that all drains are unobstructed and that there are no trapped liquids.
(3) When known spills have occurred, local clean up procedures include wiping up spills with
swabs. The affected area should be scrubbed with soap and water and wiped dry with swabs.
Use scrub water sparingly to avoid spreading the spilled fluids or soaking through the floors.
(4) Carpets soaked with spills should be removed for cleaning.
(5) Clean spills on seat tracks as described in Step 4.F.(3).
(6) Dry all insulation blankets before installation.
(7) After the aircraft has been cleaned and before installation of the insulation blankets and cabin
lining, treat the inner skin surface and structure with Type II water displacing corrosion inhibiting
compound (LPS-3 preferred) as described in Standard Preventive Maintenance Methods,
20-53-00, Corrosion Prevention.

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G. Preventive Maintenance (Exterior)

(1) In the instance of salt spray exposure to the outside of the aircraft, the occurrence shall be
treated immediately with a thorough cleaning of the exterior and application of lubricants (see
Chapter 12 of the Aircraft Maintenance Manual) and corrosion preventives for the applicable
exterior areas using procedures for application of corrosion preventives as described in
Standard Preventive Maintenance Methods, 20-53-00, Corrosion Prevention.

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