The method of calibration charts for Monitoring corrosion rates

✍ Scribed by G. Rocchini

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: German
• Weight: 781 KB
• Volume: 48
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19970481003

✦ Synopsis

Abstract

The definition and meaning of the polarization resistance, after Bonhöffer and Jena, are discussed, and its relationship with the corrosion rate is given. The basic mathematical ideas suitable to introduce the method of calibration charts, first proposed by Skold and Larson, are expounded by considering the current‐voltage characteristic i(Δ__E__) = I~c~(e^β__E__^ – e‐^β__E__^) and the correctness of their practical application based on a suitable relationship between I~d~ and R~P~ is proved. Some numerical methods which are useful to compute R~P~ by processing experimental data in the vicinity of β__E__ = 0 or inside intervals as wide as β−50, 50 mV are concisely given. Experimental applications refer to laboratory tests and show that usually I~d~ as a function of R~P~ must be best‐fitted with the function I~d~(R~p~) = NR~P~^−M^, M being different from 1. In the case of iron in 0.5 m H~2~SO~4~ solutions, containing some primary aliphatic amines, the corrosion rate takes the form I~d~ = NR~P~^−1^ and confirms the goodness of the polarization resistance method, even if the value of the proportionality constant N differs from that one predicted by the theory of Stern and Geary. The results were very satisfactory and proved that the calibration chart method is a valid tool to monitor the reaction kinetics when corrosion is of the uniform type.