Ultrasonic corrosion monitoring is a non-intrusive (non-invasive) technique for mapping material thickness. The technique can be used to identify variations in material thickness due to corrosion or other degradation phenomena, graphically portraying problems such as stress corrosion cracking (SCC) or hydrogen-induced cracking (HIC). Data can be stored as a digital image for subsequent analysis, and it can also be used as a reference for future inspections, using colour coding to show differences in thickness readings.
 
The technique is used in a wide range of industries. In the oil and gas industry, for example, it is used for the in-service inspection and characterisation of corrosion in pipes, storage tanks and vessels.
 
Corrosion may be mapped using zero-degree ultrasonic probes or phased-array probes. Most commonly, the technique makes use of a single zero-degree compression-wave probe scanned in a raster pattern over the area of interest. A combination of different probes can be mounted into a scanner to expand the probability of detection (POD) by scanning the entire area of interest.