There are a number of electrochemical techniques of corrosion rate measurement. These pages giva a brief introduction to some of them. There are many other web sites which go into more detail.

Introduction - gives a basic introduction to the electrochemistry of corrosion

Tafel - deals with corrosion current density estimation from full polarisation sweeps.

LPR - explains the basic idea behind the linear polarisation resistance measurement technique.

EIS - is to do with electrochemical impedance spectroscopy (what we used to call a.c. impedance measurement)

Harmonics - covers corrosion rate measurement using harmonic analysis.

ZRA - stands for zero resistance ammetry.

Noise - is electrochemical noise.