ATMOSPHERIC CORROSION

ATMOSPHERIC CORROSION

The atmospheric environment varies drastically with regards to corrosivity depending on the geographical location.

Electrolyte.

In atmospheric corrosion, the electrolyte is moisture from precipitation, fog or dew, sea spray, or other sources.

The three factors that have the most influence on the corrosivity of the atmosphere at a given site are:

(1) the amount of time that exposed surfaces remain wet at the site,

(2) the amount of chloride from the sea that reaches the surfaces

(3) the amount of industrial pollutants (mainly acids) that reach the surfaces.

In all atmospheric environments there is an excess of oxygen, thus the corrosion of most metals in atmospheric environments is not limited by the amount of oxygen present and can proceed rapidly when the electrolyte is present.

The corrosivity of the atmosphere varies drastically.

The corrosion rate of steel, for example, can vary by a factor of 100.

In general, the least corrosive atmospheres are found in dry inland (desert) sites and the most corrosive sites are industrial or industrialmarine sites.

Moist tropical locations are very corrosive due both to the time of wetness and the high temperatures experienced.

However, local conditions and features of design have an influence on corrosive attack that often exceeds the differences experienced due to geographical conditions.

Thus, generalizations regarding specific site corrosivity based on the corrosion of a single metal at a single location at a given site can be misleading.

It is not prudent to ignore the possibility of corrosion at a dry inland site nor to consider corrosion inevitable at a marine industrial site.

The rates of attack can vary at different sites, but the mechanisms of attack, features that cause accelerated attack and corrective measures for corrosion prevention and corrosion protection that can reduce the attack are similar.

Galvanic Corrosion Prevention