Galvanic corrosion measured currents

Galvanic corrosion measurement with the three different eounter electrode materials was accomplished here. The resulting current curves for 200 points measured over 200 s are illustrated in Fig. 7.3. 

In this paper, an inverse problem for galvanic corrosion in two-dimensional Laplace s equation was studied. The considered problem deals with experimental measurements on electric potential, where due to lack of data, numerical integration is impossible. The problem is reduced to the determination of unknown complex coefficients of approximating functions, which are related to the known potential and unknown current density. By employing continuity of those functions along subdomain interfaces and using condition equations for known data leads to over-determined system of linear algebraic equations which are subjected to experimental errors. Reconstruction of current density is unique. The reconstruction contains one free additive parameter which does not affect current density. The method is useful in situations where limited data on electric potential are provided. 

The evaluation of field of current density is essential in problems of galvanic corrosion. In many cases the direct measurement of current density is not feasible, while the electric potential can be obtained from experimental measurements. This is particularly true in case of cathodic protection systems in general, where many surveying techniques (for example DCVG and CIS for underground structures) rely in potential measurements at different points at the electrolyte in order to identify the current distribution along the metallic structures. 

Galvanic corrosion test (DIN 50 919) and galvanic current measurement... 

The passage of current through an ionic electrolyte of finite resistivity results in an ohmic potential drop along the current path according to Ohm s law. There are two aspects of corrosion that are influenced by ohmic potential drops measured polarization curves and any form of corrosion in which the anodic and cathodic reactions are separated spatially, such as in galvanic corrosion. 

Corrosion testing for galvanic corrosion may be predicted by ASTM standards in the form of potential measurements. The driving force for galvanic corrosion is the potential difference between the anode and cathode. The galvanic currents between two dissimilar metals are measured using a zero resistance ammeter (ZRA) for a chosen length of time. The ratio of anode to cathode areas is 1 1. 

The anode and cathode corrosion currents, fcorr.A and fcorr,B. respectively, are estimated at the intersection of the cathode and anode polarization of uncoupled metals A and B. Conventional electrochemical cells as well as the polarization systems described in Chapter 5 are used to measure electrochemical kinetic parameters in galvanic couples. Galvanic corrosion rates are determined from galvanic currents at the anode. The rates are controlled by electrochemical kinetic parameters like hydrogen evolution exchange current density on the noble and active metal, exchange current density of the corroding metal, Tafel slopes, relative electroactive area, electrolyte composition, and temperature. 

Fig. 6.18 Modified electrochemical polishing cell for measuring galvanic corrosion potential and current density abrasion [22]. Reproduced by permission of The Eiectrochemical Society.

Kasper, R. G. and Crowe, C. R Comparison of Localized Ionic Currents as Measured from 1-D and 3-D Vibrating Probes, Galvanic Corrosion ASTM STP 978, H. P. Htick, Ed., ASTM International, West Conshohocken, PA, 1988, p.ll8. 

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