uniform corrosion

Uniform (or general) corrosion refers to the relatively uniform reduction of thickness over the surface of a corroding material. It is relatively easy to measure, predict and design against this type of corrosion damage. While uniform corrosion may represent only a small fraction of industrial corrosion failures, the total tonnage wasted is generally regarded as the highest of all forms. Uniform corrosion is usually controlled by selecting suitable materials, protective coatings, cathodic protection and corrosion inhibitors.

It is relatively easy to monitor uniform corrosion; generally the simplest methods suffice (coupons, ER, NDT techniques for thickness measurements). Much data on uniform corrosion has been published that can be used for design purposes and estimating a "corrosion allowance".

In most practical cases, corrosive environments tend to differ from "textbook" cases (even small differences can be very significant). Furthermore, actual uniform corrosion rates tend to vary with time; this variability is not accounted for by single "textbook values". Corrosion monitoring is therefore advisable.

Caution: Unexpected rapid uniform corrosion failures can occur if the material's surface changes from the passive (low corrosion rate) to the active (high corrosion rate) state. The resultant increase in uniform corrosion rate is typically several orders of magnitude. This undesirable transition can occur if the passive surface film is disrupted by mechanical effects, flow rate changes, a chemical change in the environment etc. Real-time corrosion monitoring systems can detect such transitions.

References/Literature:

D.L. Graver (Ed.): Corrosion Data Survey-Metals Section, Sixth Edition, NACE International, Houston, 1985.

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