Electrochemical LPR (Linear Polarization Resistance) measurements are done on a large scale. A disadvantage of LPR is that localised corrosion cannot be measured. Besides the given (calculated) corrosion rate often is not callibrated to the real corrosion rate leading to a uncertainty factor. New probes have been developed in order to get more realistic corrosion rates for example the Corrtran of Pepperl and Fuchs measures HDA (Harmonic Distortion Analysis) a floating B-constant and electrochemical noise. Electrochemical noise measurements give information about the tendency for localised corrosion (pitting crevice corrosion and environmental cracking). With such modern and sophisticated electrochemical technology much more information is given compared to LPR only. However the uncertainty with regard to the real corrosion rate still remains.
This paper will describe the combination of sophisticated electrochemical technology with ER measurements (Electrical Resistance). The ER signal will allow callibration of the electrochemical data with regard to uniform corrosion rates. To achieve this in one 2" probe 3 LPR elements and 1 ER element are integrated. The instrument gives 4x 4-20 mA HART online signals to the DCS computer:
1. Uniform corrosion (ER)2: Uniform corrosion (LPR floating B-constant and HDA)
3: Localised corrosion (EN)
The probes are standard 2" probes which fit in the hollow plugs as currently used in oil and gas and industry. Instrumentation is ATEX certified and probes are PED certified.