Answer to Question #88999 in Physical Chemistry for Sasha

Question

Analyse how conditions which are likely to be present in a given industrial situation (e.g. oil-platform, industrial boilers) differ from ideal conditions and are likely to affect predictions of corrosion tendency based on standard reduction potentials.

Answer 1

Corrosion on the oil canopy is an electrochemical process. Sea water acts as an electrolyte, and

various potentials between different parts of the steel structure make the ions of the metal move

from the surface of the structure and diffuse into a solution of the electrolyte. Here they react

with oxide and hydroxide ions to form corrosion products (see Figure below). The presence of

dissolved oxygen is also an important problem. Since dissolved oxygen is more in the surface of

the water, it causes a large corrosion strain near this area in comparison with the metal under the

surface.

As a result of this process, pits can be formed on the metal surface of the platform. Corrosion

inside these pits, as well as inside cracks, such as joints or defects during welding, occurs in the

form of an irregular corrosion front on the steel surface of the platform. Subsequently, elevated

stresses caused by pits, cracks and other structural anomalies arising as a result of electrochemical

reactions, lead to cracks and breaks within the structure. The rate of corrosion depends on the

microstructure of the metal itself, which is steel for oil tiles.