Corrosion of Steel Part A.PDF

Part A

Corrosion of metals

This section on the corrosion of metals is

greatly simplified for purposes of clarity. It

is not meant to train the student with the

intention of making him/her an expert in this

area but rather to give a sense of the depth

and scope of the problem.

Why theory?

If we are to be effective in controlling corrosion,

and in making an intelligent selection and

recommendation of protective coating systems, we

need to understand clearly the actual processes by

which a clean, useful iron or steel structure can

eventually be reduced to a collection of rusty

scrap.

What is Corrosion?

NACE definition:

The deterioration of a substance, usually a

metal, or its properties, because of a

reaction with its environment.

Corrosion of Iron

• Electrochemical process, involving:

• a chemical change of iron to iron oxide,

and

• an electrical process involving current

flow.

Five things must be present for

normal atmospheric corrosion

to occur:

Oxygen

Electrolyte (moisture and ions)

Anode

Cathode

Metallic pathway