336
Fundamentals of Corrosion
but he/she should be aware of the factors that aggravate atmospheric corrosion so as to be in a position to guard against them.
The potential for the degradation of materials resulting from atmospheric
corrosion is always present. General factors that are responsible for atmospheric corrosion are relative humidity, average temperature and temperature range, pollutant concentration, suspended dust particles, and total time
of wetness. These factors are always present and should be guarded against
as much as possible during the design stage because these factors themselves
cannot be controlled.
Because of increased concern about the environment, the atmosphere is
generally less polluted today than it was several years ago. However, industrial pollution still exists in sufficient concentrations to cause degradation
of materials. Industrial pollution exists in rural atmospheres that may also
have routinely high humidities. In other areas, mixtures of marine and
industrial pollutants are common, with each type of contaminant aggravating the other. Prevailing winds will determine the distance from the shore
that marine atmospheres will be found. All these factors must be considered
during the early design stages.
The time of wetness must also be taken into account. Geographic location
plays a part in the total time of wetness because the total time of wetness is
affected by rain, fog, dew, snow, and dust as well as temperature.
Location is the first factor that must be considered before the design
is started. This determines the type of area, whether it be rural, urban,
industrial, marine, or a combination thereof. Theoretically, each of these
atmospheric types is indicative of specific degrees and types of atmospheric contaminants. However, for all practical purposes, this does not
hold true because there is no sharp distinction between the atmospheric
types. In many cases, there is no “pure” urban or rural area. Depending
on prevailing winds, contamination from industrial or marine areas might
find its way into urban or rural areas. Because of this, it is a good policy
to analyze samples from the area where the facility will be located. The
atmospheric conditions of the area should be defined in terms of temperature, humidity, and acid contaminants. Thought should also be given to
special conditions that may exist in the area, such as location of stacks,
cooling tower drift or spray, spills, release of water or chemicals, or other
abnormal conditions.
Proper maintenance programs, frequency of inspections, and economics
of upkeep should also be considered. These items will assist in selecting the
proper material of construction and/or protective measures.
11.3.1.1 General Design Considerations
The mechanisms of atmospheric corrosion were discussed in previous chapters for various materials of construction. This chapter deals with other
aspects of the prevention and control of atmospheric corrosion.
Fundamentals of Corrosion
but he/she should be aware of the factors that aggravate atmospheric corrosion so as to be in a position to guard against them.
The potential for the degradation of materials resulting from atmospheric
corrosion is always present. General factors that are responsible for atmospheric corrosion are relative humidity, average temperature and temperature range, pollutant concentration, suspended dust particles, and total time
of wetness. These factors are always present and should be guarded against
as much as possible during the design stage because these factors themselves
cannot be controlled.
Because of increased concern about the environment, the atmosphere is
generally less polluted today than it was several years ago. However, industrial pollution still exists in sufficient concentrations to cause degradation
of materials. Industrial pollution exists in rural atmospheres that may also
have routinely high humidities. In other areas, mixtures of marine and
industrial pollutants are common, with each type of contaminant aggravating the other. Prevailing winds will determine the distance from the shore
that marine atmospheres will be found. All these factors must be considered
during the early design stages.
The time of wetness must also be taken into account. Geographic location
plays a part in the total time of wetness because the total time of wetness is
affected by rain, fog, dew, snow, and dust as well as temperature.
Location is the first factor that must be considered before the design
is started. This determines the type of area, whether it be rural, urban,
industrial, marine, or a combination thereof. Theoretically, each of these
atmospheric types is indicative of specific degrees and types of atmospheric contaminants. However, for all practical purposes, this does not
hold true because there is no sharp distinction between the atmospheric
types. In many cases, there is no “pure” urban or rural area. Depending
on prevailing winds, contamination from industrial or marine areas might
find its way into urban or rural areas. Because of this, it is a good policy
to analyze samples from the area where the facility will be located. The
atmospheric conditions of the area should be defined in terms of temperature, humidity, and acid contaminants. Thought should also be given to
special conditions that may exist in the area, such as location of stacks,
cooling tower drift or spray, spills, release of water or chemicals, or other
abnormal conditions.
Proper maintenance programs, frequency of inspections, and economics
of upkeep should also be considered. These items will assist in selecting the
proper material of construction and/or protective measures.
11.3.1.1 General Design Considerations
The mechanisms of atmospheric corrosion were discussed in previous chapters for various materials of construction. This chapter deals with other
aspects of the prevention and control of atmospheric corrosion.