electrochemical corrosion monitoring

Electrochemical Techniques:

Electrochemical techniques rely on electrochemical corrosion theory and the measurement of electrochemical potentials and/or currents to monitor corrosion damage. The electrochemical potential is fundamentally related to thermodynamics of corrosion reactions, while currents are related to reaction kinetics (rate of corrosion). The relationship between electrochemical potential and current is important in several electrochemical corrosion monitoring techniques.

Electrochemical monitoring techniques range from simple to highly complex techniques and include the following:

Corrosion potential
Zero resistance ammetry (ZRA)
Linear Polarization Resistance (LPR)
Polarization Diagrams
Electrochemical Impedance Spectroscopy (EIS)
Harmonic Analysis
Electrochemical Noise

In general, electrochemical corrosion measurements at best provide semi-quantitative corrosion data. Although commercial corrosion monitoring instrumentation may provide a numerical value for corrosion rates, these values are typically based on fundamental simplifying assumptions and on uniform thickness loss. Generally, confidence in electrochemical corrosion data has to be acquired over time, due to the qualitative or semi-quantitative nature of this data.

References/Literature:

N.G. Thompson and J.H. Payer: "Corrosion Testing Made Easy: DC Electrochemical Test Methods", NACE International, 1998, Houston, TX.

J.R. Scully, D.C. Silverman and M.W. Kendig (Eds.): "Electrochemical Impedance: Analysis and Interpretation", ASTM STP 1188, American Society for Testing and Materials, West Conshohocken, PA., 1993.

ASTM G102-89 Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements, American Society for Testing and Materials, West Conshohocken, PA.

Links:
Overview by KH Design and Development:
http://www.khdesign.co.uk/Techniques.htm

Basic theory