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22.04 – 4139181_04
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8 BASIC PRINCIPLES ON MICROCHANNEL COIL CORROSION
The main material in Aermec heat exchangers is aluminium.
Aluminum is a very reactive metal, which is easily oxidized on its surface. As long
as this hard layer of aluminum oxide remains intact, the aluminum at the base will
remain resistant to corrosion (unlike other materials, such as steel, where the oxide
layer peels off the surface and flakes off, allowing the constant attack of the under-
lying metal).
However, aggressive environments can damage the oxide layer, which may not re-
generate as quickly as necessary to provide the product with sufficient protection.
These harsh environments are typified by very high or very low pH levels.
Normally, aluminum’s protective oxide layer is generally stable in the pH range of
4.5 to 8.5; the lack of exposure to excessively acidic or basic pH conditions is not in
itself sufficient to exclude the need for appropriate protective treatments on the
batteries.
The presence of salt (associated with marine environments) as well as the presence
of other aggressive substances can in fact induce widespread or localized galvanic
corrosion (pitting or anthill corrosion).
OTHER RISK FACTORS FOR CORROSION
The principal cause of corrosion is elevated humidity and/or temperatures in the
presence of contaminant gases. These conditions alone, or in combination, acceler-
ate the natural corrosion process in metals.
Humidity
Moisture in air can be considered the lifeblood of galvanic corrosion. A galvanic
corrosion cell requires an electrolyte or current carrying media, to reach a dynamic
state. The electrolyte can be water or any water-soluble substance with good con-
ducting properties. Moisture in the air is one such electrolyte. Humid air contami-
nated with corrosive gasses further accelerates the corrosion rate as the air’s current
carrying otential increases.
Temperature
Chemical reactions generally depend on the temperature, for reactions that involve
corrosion of aluminum by an increase in temperature, faster reaction frequencies
usually arise.
Corrosive gases
Not all gases cause corrosion. Specifically, we are concerned with three types of
gases:
— Acidic gases, such as hydrogen sulfide, sulfur oxides, chlorides, hydrogen fluo-
ride (HF) and nitrogen oxides;
— Caustic gases, such as ammonia;
— Oxidizing gases, such as ozone
Of the gases that can cause corrosion, the acidic gases are typically the most harm-
ful.
FLOW OF ELECTRONS
FLOW OF IONS (+)
FLOW OF IONS (-)
ELECTROLYTE
ANODE
AND-
CATHODE
9
CLEANING MICRO-CHANNEL COIL
Keeping the surfaces of the microchannel coils clean is essential to en-
sure the correct operation of the unit and to avoid punctures on the coil
with the consequent loss of refrigerant gas which would lead to the re-
placement of the coil itself.
WARNING Damage to the coil due to neglect or lack of or poor clean-
ing is not covered by the warranty.
Dirt, grease, oil, and other foreign material must be removed periodically from the
surface of the battery according to the following recommendations.
Required elements:
— Personal protective equipment
— Hot water
— High-pressure washing
Procedure:
Use a high-pressure washer with a large cast and enough force to remove all foreign
material, proceed with care to avoid damage and possible wear of the louvers.
Lastly, also rinse the carpentry and the fans thoroughly to be sure that all impurities
have been removed.
Aermecwe assume no liability for the completeness of the information contained
in this document.
