Technical Realisation
The NDU measurement system was developed by Bank Elektronik - Intelligent
Controls GmbH in Co-operation with Hoechst AG and the Institute for Materials
Testing and Materials Engineering Dr. Dölling + Dr. Neubert GmbH.
The NDU bases on the combination of a low - noise potential meter,
a low - noise current sink and a control unit for polarisation of the
electrodes.
The analogue signals are filtered, amplified and, after A/D conversion,
processed by a personal computer.
Noise signals are small. Usually the potential noise spans some few
millivolts, and the current some nanoamps. Therefore, much effort was
done to
reduce undesired influences using e.g. battery powered analogue
circuitry and optical data transfer to the PC.
Left:
Extractable sensorhead of the NDU mounted on a 2" flange with ball
valve.
Advantages
The measured signals allow the interpretation of the state of corrosion
activities.
Qualitatively:
- common corrosion (active or passive metal dissolution)
- localised corrosion (pitting, crevice corrosion, stress corrosion
cracking)
Quantitatively:
So, it is possible to detect the development of damages very soon, and
to draw conclusions from the relation of actual process parameters
to corrosion activities.