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The use of the polarization resistance for monitoring small corrosion rates
Author(s) -
Rocchini G.
Publication year - 1999
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/(sici)1521-4176(199908)50:8<463::aid-maco463>3.0.co;2-p
Subject(s) - corrosion , corrosion monitoring , polarization (electrochemistry) , alloy , materials science , copper , analytical chemistry (journal) , metallurgy , chemistry , chromatography
Some basic considerations concerning the use of the polarization resistance for corrosion rate monitoring over potential intervals as wide as [E c − 20, E c + 20] mV are developed and a useful hint for determining the correct magnitude‐order of i′(0) through the best‐fitting of experimental data with a polynomial of the third degree is given. Some general concepts relating to the corrosion behaviour of copper alloy in sea‐water are also recalled. The experimental application concerns the behaviour of the copper alloys 687, 706 and 715 exposed to artificial sea‐water at pH 8.2 and 40 °C, and having flow rates of 1.0, 1.5 and 2.0 ms −1 . Polarization measurements of the dynamic type were performed under current control, the starting point being always E c , and usually refer to the ΔE interval [− 30, 0] mV. The values of the current sweep‐rate were 5.7, 17.5 and 28.9 μA/min. Experimental results showed that polarization measurements of the galvanodynamic type and the scheme based of the first derivative of i(ΔE) are effective to monitor corrosion rates of copper alloys and permit to determine values of R p as high as 2.8 × 10 5 Ωcm 2 with good accuracy and reproducibility. At last, for the alloy 715 this procedure is suitable to detect without uncertainty the random occurrence of localised corrosion attacks.