| Corrosion Potentials: It
is relatively easy to measure the corrosion potential of a corrosion sensor or of an
actual structure/component against a stable reference electrode. As such, the corrosion
potential is a basic indicator of the thermodynamic corrosion status. It can be used in
conjunction with Pourbaix diagrams. Unfortunately, on its own, the potential value does
not provide information on the rate of corrosion (kinetics). Corrosion potentials can
provide a useful indication of active or passive behavior in certain systems.
| When measuring the potential of a polarized structure,
such as a buried pipeline subject to cathodic protection, the potential measured against a
reference electrode will contain an "IR" drop error. This error arises from the
resistance of the electrolyte between the structure and the reference electrode and the
flow of (ionic) current through this electrolyte. The current can be interrupted
instantaneously during a potential measurement to correct for this "IR" effect.
By definition, corrosion potentials usually refer to open circuit (no current flow)
measurements. |
The monitoring of potentials has found widespread application in cathodic protection
systems, anodic protection systems, steel reinforcement in concrete and stray current
corrosion problems.
References/Literature:
V. Ashworth: "The Theory of Cathodic Protection and Its Relation to
the Electrochemical Theory of Corrosion", in Cathodic Protection, Ellis Horwood,
Chichester (U.K.), 1986.
ASTM C876 Standard: "Standard Test Method for Half Cell Potentials of
Reinforcing Steel in Concrete", American Society for Testing and Materials,
Philadelphia, PA.
Links:
Information on Pourbaix diagrams and reference electrodes can be found at
the Corrosion Doctors site
www.corrosion-doctors.org
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