154
Fundamentals of Corrosion
stimulants. They originate from adhesives, tobacco smoke, combustion of
biomass, and plastics.
Another factor contributing to a decreased indoor corrosion rate is the
decreased levels of indoor atmospheric oxidants, many of which are photochemically produced.
As discussed previously, not only the concentration of pollutants but also
the air velocity determines the dry deposition velocity of corrosion stimulants. Because the air velocity is decreased indoors, significantly lower dry
deposition velocities will take place.
Based on the differences between the indoor and outdoor factors affecting
atmospheric corrosion rates, it follows that the corrosion rate of many metals
is lower indoors than outdoors. This has been verified by examining the corrosion rates of copper, nickel, cobalt, and iron in eight indoor locations. In all
cases, they exhibited a lower corrosion rate indoors than outdoors.
These factors do not eliminate the possibility of indoor atmospheric corrosion of materials. Designs must take into account the possibility of indoor
atmospheric corrosion.
In an uncontaminated atmosphere at constant temperature, and with the
relative humidity below 100%, corrosion of metals would not be expected.
However, this is never the case because there are always normal temperature
fluctuations: as the temperature decreases, the relative humidity increases;
and because of hygroscopic impurities in the atmosphere or in the metal
itself, the relative humidity must be reduced to a much lower value than
100% in order to ensure that no water condenses on the surface. For all metals there is a critical relative humidity below which corrosion is negligible.
These critical relative humidities fall between 50 and 70% for steel, copper,
nickel, and zinc.
In design, areas where dust particles can accumulate should be eliminated,
as well as any crevices or pockets. Even in indoor atmospheres, carbon steel
should be protected from corrosion by means of rust preventatives, painting,
galvanizing, or other protective coatings, depending on the conditions of
exposure. The use of low-alloy steel also helps to reduce or eliminate corrosion. Atmospheric corrosion is reduced when steel is alloyed in small concentrations with copper, potassium, nickel, and chromium.
References
1. Schweitzer, P.A., 1999, Atmospheric Degradation and Corrosion Control, New York:
Marcel Dekker, p. 20.
2. Schweitzer, P.A., 1999, Atmospheric Degradation and Corrosion Control, New York:
Marcel Dekker, p. 17.
Fundamentals of Corrosion
stimulants. They originate from adhesives, tobacco smoke, combustion of
biomass, and plastics.
Another factor contributing to a decreased indoor corrosion rate is the
decreased levels of indoor atmospheric oxidants, many of which are photochemically produced.
As discussed previously, not only the concentration of pollutants but also
the air velocity determines the dry deposition velocity of corrosion stimulants. Because the air velocity is decreased indoors, significantly lower dry
deposition velocities will take place.
Based on the differences between the indoor and outdoor factors affecting
atmospheric corrosion rates, it follows that the corrosion rate of many metals
is lower indoors than outdoors. This has been verified by examining the corrosion rates of copper, nickel, cobalt, and iron in eight indoor locations. In all
cases, they exhibited a lower corrosion rate indoors than outdoors.
These factors do not eliminate the possibility of indoor atmospheric corrosion of materials. Designs must take into account the possibility of indoor
atmospheric corrosion.
In an uncontaminated atmosphere at constant temperature, and with the
relative humidity below 100%, corrosion of metals would not be expected.
However, this is never the case because there are always normal temperature
fluctuations: as the temperature decreases, the relative humidity increases;
and because of hygroscopic impurities in the atmosphere or in the metal
itself, the relative humidity must be reduced to a much lower value than
100% in order to ensure that no water condenses on the surface. For all metals there is a critical relative humidity below which corrosion is negligible.
These critical relative humidities fall between 50 and 70% for steel, copper,
nickel, and zinc.
In design, areas where dust particles can accumulate should be eliminated,
as well as any crevices or pockets. Even in indoor atmospheres, carbon steel
should be protected from corrosion by means of rust preventatives, painting,
galvanizing, or other protective coatings, depending on the conditions of
exposure. The use of low-alloy steel also helps to reduce or eliminate corrosion. Atmospheric corrosion is reduced when steel is alloyed in small concentrations with copper, potassium, nickel, and chromium.
References
1. Schweitzer, P.A., 1999, Atmospheric Degradation and Corrosion Control, New York:
Marcel Dekker, p. 20.
2. Schweitzer, P.A., 1999, Atmospheric Degradation and Corrosion Control, New York:
Marcel Dekker, p. 17.