Corrosion mapping is an ultrasonic technique (UT) which maps and identifies variations in material thickness due to corrosion. Corrosion is the deterioration of a metallic material by chemical (or electrochemical) attack. This 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 critical components or infrastructure, using various ultrasonic techniques including pulse echo, eddy current and phased array (PAUT). Corrosion mapping is widely used in the oil, gas and nuclear industries for the inspection of pipework, pressure vessels, storage tanks and reactors.
Corrosion mapping with conventional UT probes offers a simple solution, however, can be a time-consuming method as the probe must be scanned in both directions across the inspection surface. Using a coarser resolution can improve scanning speeds but produces a loss in resolution, which can result in missing small indications such as pitting. Alternatively, PAUT probes can cover a larger surface at higher speeds, significantly reducing scanning times. Collecting high-resolution data at increased scanning speeds improves the probability of detection (POD), enhances imaging, and improves defect characterisation.
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.
Corrosion Mapping / C-Scan Inspection Solutions:
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