General information about corrosion and corrosion protection

[German version]

	The phenomenon of corrosion
	Causation of corrosion
	Pretreatment and cleaning of items for packing

The phenomenon of corrosion


Corrosion is the term used to describe the degradation in quality of a usually metallic material due to chemical or electrochemical attack. Corrosion is now also used to describe similar effects on other materials such as glass, plastics, construction materials. The aggressive medium is known as the corrosive agent. The following types of corrosion are among those distinguished by DIN 50900:

	Uniform surface corrosion, in which the surface suffers uniform damage.
	Wide pitting, in which the surface suffers damage of varying severity.
	Pitting, in which only small areas of the surface are destroyed.
	Galvanic corrosion, in which small areas of the surface are attacked forming crevices.

Figure 1

Figure 2

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Causation of corrosion

	Formation of condensation as a result of temperature changes combined with elevated levels of relative humidity.
	Condensation may start from relative humidities of > 40% and rapidly increase at relative humidities of > 60%.
	Seawater
	Dirt and gases in the air, such as SO2, salts, hygroscopic dust, all of which promote corrosion.
	Hygroscopic packaging materials with an elevated water content
	Finger marks on metal surfaces also promote corrosion.
	Residues of processing agents used for metal cleaning (soldering agents, pickles etc.).
	Residues of chlorides, sulfides, sulfates and acids

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Pretreatment and cleaning of items for packing


There is little awareness of just how carefully metal components must be cleaned before application of the corrosion protection methods. Careful pretreatment and cleaning 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 and the item completely dried, in the protective coating method, for example, corrosion may occur under the protective coating.

Cleaning is performed either with water, which, depending upon the item being cleaned, may contain certain additives, or with solvents, which, being multipurpose cleaners, may be used in a greater number of applications. After cleaning, whether with water or with solvents, the cleaned items are then dried before further processing continues. Care must be taken to ensure at this point that no further contamination, e.g. finger marks, occurs.


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