Careful cleaning of the packaged goods is essential if the corrosion protection methods are in any way to be successful. If all particles of dirt and dust and any acid and salt residues are not completely removed from the surfaces and the packaged item completely dried, in the protective coating method, for example, corrosion may occur under the protective coating.

Solvents or special cleaners which have frequently been developed for specific types of contamination are generally used for cleaning. A large number of industrial cleaning products are available for this purpose, and care must be taken to ensure that the cleaning product selected has no corrosive effect. After cleaning has been completed, the item must be completely dried and steps must be taken to ensure that no further contamination, such as fingermarks can arise.

4.4  Corrosion protection methods during shipping

There are three main methods used for corrosion protection during shipment of packaged goods:

• the protective coating method
• the VCI method
• the desiccant method

A further method is also used in the case of closed interior spaces:

• the inert gas method

When selecting the method to be used, the characteristics of the packaged item and any existing protective measures along with the properties as specified by the manufacturer of the protective agent must be taken into account.

It must be remembered that the desiccant method loses its efficacy if the inner packaging is opened and then not re-closed properly by inspectors (customs, etc.) - an unfortunate, but necessary aspect of shipping goods to some countries before they reach their destination. A modern alternative in this context is the active VCI protection method. This method also provides temporary, active corrosion protection in the event that the internal packaging is opened deliberately (goods inspection) or accidentally (damage to the protective cover).

4.4.1  The inert gas method

The inert gas method is used to protect closed spaces (containers/pipes) and works by replacing oxygen by nitrogen in the atmosphere. If the inert gas method is used, steps must be taken to ensure that the protective atmosphere cannot escape. This is done by filling the open spaces at a slightly increased pressure and checking this using a manometer.

4.4.2  The protective coating method

The protective coating method is a corrosion protection method in which coatings are applied to bare metal surfaces to protect them. For this protection method to be effective, the surface itself must be carefully cleaned and dried.

Figure 12: Bare shaft protected by an anti-corrosion coating

The protective coating method is a passive corrosion protection method. It can be employed for packaged goods with simple surfaces, which do not present any problems to removal of the protective coating – in general, this is done by washing off the anti-corrosion coating and dissolving it with a solvent.

• Solvent-based anticorrosion agents:
  
  The quality of these protective films is very high. 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, especially on vertical surfaces, that the protective film will run off or be washed off by condensation. In addition, it is vital that the products are thoroughly stirred before or during application in order to ensure that the components are properly mixed.
  
  Since solvent-based corrosion protection agents are flammable, they may only be used in closed systems for reasons of occupational safety. Figure 13 shows how they work.

Figure 13: The way in which solvent-based anticorrosion agents work

The coating reduces access for corrosive substances for the planned transport and storage period.

• Water-based anticorrosion agents:
  
  Water-based anticorrosion agents contain no chemical solvents and thus do not require closed systems when they are used. 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, gearboxes, etc.).