Corrosion mapping is an ultrasonic technique that maps and identifies changes in material thickness due to corrosion. Corrosion is the breakdown of a metallic material by chemical (or electrochemical) attack. This is normally caused by the environment (mostly water) and sometimes another material. There are several types of corrosion:

• Uniform corrosion evenly spread across the surface
• Dimpled corrosion (pits) with unevenness and smaller deep areas
• Exfoliation that moves along the layers of elongated grains
• Intragranular corrosion growing along grain boundaries

An automatic or semi-automatic scanner for making corrosion mapping is used to scan an inspection surface using various ultrasonic techniques such as pulse echo, eddy current, and phased array. Corrosion mapping is widely used in oil, gas and nuclear industries for the inspection of pipes, pressure vessels, storage tanks and reactors. In the aviation industry, corrosion mapping is often referred to as "C-Scan" for the examination of composite materials. Corrosion mapping results provide a high degree of repeatability and the advantage of location and size data for each defect that can be compared for repeat scans in the same area, both in general and for individual pits, to track defect increase or corrosion rates.