The stresses occurring during transport, handling and storage are much greater than those occurring at the place of use. Such stresses may be manifested, for example, as extreme variations in temperature, which result in a risk of condensation. Especially in maritime transport, the elevated salt content of the water and air in so-called seasalt aerosols may cause damage, as salts have a strongly corrosion-promoting action. The following are the main temporary corrosion protection methods:

1. Protective coating method
2. Desiccant method
3. VCI (Volatile Corrosion Inhibitor) method

• Protective coating method

  The protective coating method is a passive corrosion protection method. The protective coating isolates the metallic surfaces from the aggressive media, such as moisture, salts, acids etc.
  The following corrosion protection agents are used:

  • Solvent-based anticorrosion agents
  • Water-based anticorrosion agents
  • Corrosion-protective oils without solvent
  • Dipping waxes

Very high quality protective films are obtained.

Once the anticorrosion agent has been applied, the solvent must vaporize so that the necessary protective film is formed.

Depending upon the nature of the solvent and film thickness, this drying process may take as long as several hours. The thicker the film, the longer the drying time. If the drying process is artificially accelerated, there may be problems with adhesion between the protective film and the metal surface.

Since protective films are very thin and soft, attention must always be paid to the dropping point as there is a risk at elevated temperatures that the protective film will run off, especially from vertical surfaces.

Since solvent-based corrosion protection agents are often highly flammable, they may only be used in closed systems for reasons of occupational safety.

Water-based anticorrosion agents
Water-based anticorrosion agents contain no solvents and thus do not require closed systems.

Drying times are shorter than for solvent-based anticorrosion agents.

Due to their elevated water content, water-based anticorrosion agents are highly temperature-dependent (risk of freezing or increased viscosity).

The advantage of this method is that the protective film is readily removed, but the elevated water content, which may increase relative humidity in packaging areas, is disadvantageous.

Corrosion-protective oils without solvent
Corrosion-protective oils without solvent produce only poor quality protective films. Good quality protection is achieved by adding inhibitors. Since these corrosion-protective oils are frequently high quality lubricating oils, they are primarily used for providing corrosion protection in closed systems (engines etc.).

Dipping waxes
The protective layer is applied by dipping the item to be packaged into hot wax. Depending upon the type of wax, the temperature may have to be in excess of 100°C. Removal of the protective film is relatively simple as no solid bond is formed between the wax and metal surface. Since application of dipping waxes is relatively complex, its use is limited to a few isolated applications.

• Desiccant method

  According to DIN 55 473, the purpose of using desiccants is as follows: "desiccant bags are intended to protect the package contents from humidity during transport and storage in order to prevent corrosion, mold growth and the like."
  The desiccant bags contain desiccants which absorb water vapor, are insoluble in water and are chemically inert, such as silica gel, aluminum silicate, alumina, blue gel, bentonite, molecular sieves etc.. Due to the absorbency of the desiccants, humidity in the atmosphere of the package may be reduced, so eliminating the risk of corrosion. Since absorbency is finite, this method is only possible if the package contents are enclosed in a heat sealed barrier layer which is impermeable to water vapor. This is known as a climate-controlled or sealed package. If the barrier layer is not impermeable to water vapor, further water vapor may enter from outside such that the desiccant bags are relatively quickly saturated, without the relative humidity in the package being reduced.
  Desiccants are commercially available in desiccant units. According to DIN 55 473:
  "A desiccant unit is the quantity of desiccant which, at equilibrium with air at 23 ± 2°C, adsorbs the following quantities of water vapor:
  
  • min. 3.0 g at 20% relative humidity
  • min. 6.0 g at 40% relative humidity
  The number of desiccant units is a measure of the adsorption capacity of the desiccant bag."
  Desiccants are supplied in bags of 1/6, 1/3, 1/2, 1, 2, 4, 8, 16, 32 or 80 units. They are available in low-dusting and dust-tight forms. The latter are used if the package contents have particular requirements in this respect.

• VCI (Volatile Corrosion Inhibitor) method

  Inhibitors are substances capable of inhibiting or suppressing chemical reactions. They may be considered the opposite to catalysts, which enable or accelerate certain reactions.
  Unlike the protective coating method, the VCI method is an active corrosion protection method, as chemical corrosion processes are actively influenced by inhibitors.
  The mode of action dictates how VCI materials are used. At item to be protected is, for example, wrapped in VCI paper. The metallic surfaces of the item should be as clean as possible to ensure the effectiveness of the method. The VCI material should be no further than 30 cm away from the item to be protected. Approximately 40 g of active substances should be allowed per 1 m³ of air volume. It is advisable to secure this volume in such a manner that the gas is not continuously removed from the package due to air movement. This can be achieved by ensuring that the container is as well sealed as possible, but airtight heat sealing, as in the desiccant method, is not required.
  The VCI method is primarily used for articles made from carbon steel, stainless steel, cast iron, galvanized steel, nickel, chromium, aluminium and copper. The protective action provided and compatibility issues must be checked with the manufacturer.