Corrosion Mapping – C Scan Testing

Corrosion mapping is an ultrasonic technique which maps and identifies variations in material thickness due to corrosion. Corrosion is the deterioration of a metallic material by chemical (or electrochemical) attack.T his is normally caused by the environment (most often water), and sometimes by another material. There are several types of corrosion:

Uniform corrosion that extends evenly across the surface

Pitting corrosion that is uneven and has smaller deep areas (pits)

Exfoliation corrosion that moves along layers of elongated grains

Inter-granular corrosion that grows along grain boundaries

To perform corrosion mapping an automatic or semi-automatic scanner is used to scan an inspection surface, using various ultrasonic techniques including pulse echo, eddy current and phased array. Corrosion mapping is widely used in the oil, gas and nuclear industries for the inspection of pipework, pressure vessels, storage tanks and reactors. In the Aerospace sector, corrosion mapping is often referred to as ‘C-Scan’ for the inspection of composite materials. Results for corrosion mapping provide a high degree of repeatability and the advantage of position and size data for every flaw which can be compared for repeat scans of the same area to track flaw growth or corrosion rates both generally and for individual pits.