Almost all airline companies’ maintain / store engines in standby for quick replacement. The engines are very expensive and are usually needed in emergencies, in case of engine failures.
Jet Engines are generally stored in a room in / near the hangars at Airports. While in storage, they are prone to damage due to corrosion. Ferrous material like iron and steel corrode in presence of moisture. Electronic equipment and components also suffer from micro-corrosion.
Corrosion never occurs in dry air and is a result of moisture/humidity presence in the ambient conditions.
Water vapour condenses, on any surface, colder than the dew point temperature of the surrounding air mass. Also, sudden changes in temperature, within the room, affect the internal humidity environment and lead to condensation, hence, leading to corrosion.
Corrosion rate is dependent on Relative Humidity of the ambient air and is prevalent above 45% RH. Presence of pollutants in the air also drastically increases corrosion rate.
To prevent corrosion, the relative humidity of the air needs to be controlled at a level where it not only prevents condensation but is reduced to a critical level below which corrosion does not occur. As a general rule, rust and other oxidizing type corrosion reactions will not occur if the relative humidity in the area is maintained at or below 40% RH. Materials or product residing in this atmosphere need not be coated with oil or other surface protecting materials, and can thus be kept in ready-to-use condition
This significantly reduces the cost of painting and other maintenance normally required to control corrosion.
Most metal parts do not need to be stored in areas which need temperature control. Thus humidity control through desiccant dehumidification is a much more economical method than air conditioning.
Corrosion can be eliminated by controlling the moisture levels to less than 45% RH at ambient condition in the storage area. Humidity control by dehumidifying such storage areas ensures that the engines in storage do not get corroded.