Page 208 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

186 CORROSION CAUSES

exposed. The potential differences between the noble (positive) carbon
and the metal substrate, a galvanic couple may develop, leading to rapid
galvanic-induced dissolution of the magnetic material (43).
Magneto-optic devices utilize extremely reactive alloys for the recording media
(because of a high terbium content). Exposure of magneto-optic films to aqueous
solutions or high-humidity conditions results in a localized pitting attack even during
storage in ambient office conditions (43).
While attempts have been made to mitigate corrosion of electronics by encapsu-
lating the components in plastics, it is useful to note that polymers are permeable
to moisture. Hermetically sealed ceramic packaging is more successful. However,
care must be taken to prevent moisture and other contaminants from being sealed
in. A useful common approach for mitigating corrosion of circuits housed inside a
relatively large-size chassis includes the use of volatile corrosion inhibitors.

3.30 CORROSION PROBLEMS IN HOME APPLIANCES

There are some common areas of significant corrosion impact for major home appli-
ances and comfort conditioning appliances. The corrosion types are internal corrosion
from process water and external corrosion from wet conditions.
The most important reason for corrosion in appliances is the water that is being
handled by the equipment. This type of corrosion affects the internal components
of appliances and limits life expectancy. In the case of home appliances, the appli-
ances most susceptible to internal corrosion are refrigerators, water heaters, washers,
dishwashers, and water softeners. The air conditioners, humidifiers, high-efficiency
furnaces, dehumidifiers, and boilers are susceptible to internal corrosion.
Internal corrosion in appliances is a problem because it limits useful life. This is a
direct cost of corrosion. A unitary air conditioner has an average life of 13 years. One
of the reasons for this limited life expectancy is that condensate in the air conditioner
corrodes the internal metal components.
External corrosion of appliances results in deterioration in the appearance of the
surface of the appliance without affecting its capability in performance. However, the
value of the corroded appliance will decrease because of the corroded appearance. In
addition to corrosion of noncoated surfaces, corrosion can occur when painted or
coated surfaces become chipped or nicked. Some of the wet environments around
appliances are a furnace or a boiler in the humidity of a wet basement, an air con-
ditioner in the yard or window being exposed to rain and moisture, and kitchen
equipment and whose exteriors are often cleaned with water or wet towels.
External corrosion of appliances results in the deterioration of their appearance
and therefore affects their resale value. External corrosion of appliances generally
does not limit the capability of an appliance to function properly. The reduction in
the resale cost of a corroded appliance is the direct cost of corrosion.
Corrosion problems vary with the type of appliance. Corrosion can build up and
destroy parts of the entire appliance. The appliances that are subject to corrosion are:
(i) water heaters, (ii) boilers, (iii) high-efficiency furnaces, and air conditioners.