Corrosive Environments

TM 38-260

c. Heated storage. Area in which the temperature can be controlled within specified limits by the application of

heat.

d. Interim preservation procedures. Procedures identified as interim preservation of IPE are those set forth in

chapter 3 of this manual. They have been established for use in maintaining IPE for a period not to exceed 1 year with

reprocessing required if the period must be extended. These procedures are an absolute minimum.

e. Long-term (maximum) preservation. This type of preservation is used when IPE is to be stored for indefinite

periods without the benefit of controlled humidity storage. Procedures are contained in chapter 4 of this manual.

f. Noncontrolled humidity storage. All storage buildings/facilities that are not equipped with proper equipment to

maintain controlled relative humidity level.

g. Open storage. Improved or unimproved outside (outdoor) storage areas.

h. Preservation. Application of protective measures including cleaning, drying, preservation materials, barrier

materials, cushioning, and containers when necessary.

5-3. Corrosive Environments

a. General. The condition of IPE in storage depends on the prevailing physical and chemical forces of

deterioration. These forces are influenced by heat, moisture, dusts, gases and fungi. The dust particles, oxygen, and

moisture are natural products of the atmosphere, however, sulphur, chlorine, and other chemicals are by-products of

industrial facilities located in the vicinity of the storage site. Moisture is probably the most critical agent since it affects

the corrosiveness of all the others, but, like the others, it is not destructive by itself. Corrosion can occur at extremely low

levels of relative humidity. Therefore, the construction of humidity controlled hutments along with temperature regulation

are recommended wherever possible.

b. Dew point and relative humidity. The amount of moisture the air can hold depends upon temperature. Warm

air is capable of holding more moisture than cold air. When the temperature of a given volume of air which contains a

given amount of moisture drops to a certain point (the dew point), the moisture will condense and appear in liquid form.

This liquid water on metallic surfaces of IPE may cause corrosion to occur. Relative humidity is the ratio between the

actual amount of moisture in the air and the amount that the air can hold at that temperature. Relative humidity of 50

percent means that the air contains one-half the moisture it could hold at the existing temperature.

c. Corrosion in the presence of moisture. Corrosion can occur in the presence of extremely small amounts of

moisture on a metallic surface. The temperature of the atmosphere does not have to be falling through the dew point for

exposed metal surfaces to become moist and begin to corrode. Most types of dust and dirt are hygroscopic, that is, they

are able to absorb or attract moisture from the air at relative humidities less than 100 percent. Moisture may be picked

up while the particles are still in the air or after they are deposited on exposed surfaces. Dirt and

5-2