Page 365 - Corrosion Engineering Principles and Practice

334 C h a p t e r 9 A t m o s p h e r i c C o r r o s i o n 335

FIGURE 9.5 Electric junction box badly corroded only four years after a new
residence was completed. (Courtesy of Kingston Technical Software)

to constant immersion for which a component may not have been chosen
or prepared for. Such systems are commonly encountered in confined
areas close to ground level or, worse, below ground where high humidity
may prevail. Figure 9.5 shows the advanced corrosion of the frame and
contacts in an electric junction box only four years after a building was
completed. While the junction box in this example was only at the ground
level, the wires coming to the box were buried without additional
insulation and in constant contact with much cooler ground than ambient
air in the room. The repeated condensation of ambient humidity on the
electrical box support and on many of its connections caused enough
corrosion in such a short period of time to require the complete replacement
of the system to avoid unscheduled power interruptions.

9.3 Factors Affecting Atmospheric Corrosion
The most important factor in atmospheric corrosion, overriding the
presence of any other surface contamination, is moisture, either in the
form of rain, dew, condensation, or high relative humidity (RH).