Worst of the Elements
Moisture (Corrosion)
Moisture

Corrosion is defined as the destruction of a metal through an electrochemical reaction. When exposed to the Earth’s atmosphere under typical conditions, most metals have a tendency to corrode – to return to their natural, oxidized state.

When you look at how rust develops all the ingredients for the reaction to occur already exist in the base metal (an anode, cathode, and e- pathway) except for the electrolyte (water). No reaction (corrosion) can take place if the electrolyte (water) is not present to complete the cycle. In most places around the world, the average relative humidity (RH) is over 75%.

Corrosion Diagram

Corrosion occurs dramatically greater in environments where relative humidity is above 55%. As relative humidity rises, more water molecules lack the energy to escape the surface such that layers of water molecules build up to form a liquid film on the metal surface – the electrolyte required to start the process of corrosion.

Atmospheric corrosion and its severity is essentially determined by four variables – air pollution (both man-made and natural, such as volcanic gases), airborne salt spray or droplets, temperature, and moisture. The presence of moisture is an absolute necessity for most corrosion processes and, when combined with elevated temperatures and salt or pollutants, further enhances the atmospheric corrosion process.

Dry air prevents the process of oxidation from occurring by controlling relative humidity (RH) to a level of ~45%. By removing water molecules (moisture) from the air, the electrolyte required to complete the process of oxidation is eliminated and corrosion cannot occur. This condition is typically applied to equipment in extended periods of non-operation.

In most places around the world, the average relative humidity (RH) is over 75%.