SYMPOSIA PAPER Published: 01 January 1993

Interpreting Electrochemical Impedance Spectra from Segmented Electrode Arrangements


Differential corrosion of carbon steels and in particular welded joints has long been recognized as a problem in aqueous environments. Minor differences in composition and microstructure can cause severe differential galvanic corrosion effects that lead to rapid rates of corrosion on particular types of steel or weld consumables.

To study this mode of corrosion a monitoring technique was developed that allows corrosion rates and galvanic currents to be assessed. The design of this instrumentation facilitates the use of impedance measurements on single electrodes while they are effectively coupled as part of a mixed metal system. The individual impedance responses may be analyzed to give information on the rates of corrosion for each element together with information on the separate anodic and cathodic reaction mechanisms.

The effects of differential galvanic corrosion have been studied in a range of environments both in the laboratory and in the field. Data are presented for aerated and deaerated seawater and also CO2 brine system with inhibitor additions.

Author Information

Rothwell, AN
CAPCIS MARCH Limited, Manchester, England
Dawson, JL
CAPCIS MARCH Limited, Manchester, England
Eden, DA
CAPCIS MARCH Limited, Manchester, England
Palmer, JW
CAPCIS Limited, Manchester, England
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Developed by Committee: G01
Pages: 237–251
DOI: 10.1520/STP18073S
ISBN-EB: 978-0-8031-5240-3
ISBN-13: 978-0-8031-1861-4