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Angst U.,Swiss Society for Corrosion Protection | Angst U.,ETH Zurich | Buchler M.,Swiss Society for Corrosion Protection
Materials and Corrosion | Year: 2015

The well-known Stern-Geary equation was derived on the basis of the theory by Wagner and Traud and relies on the so-called mixed potential of an electrode subject to uniform corrosion. Nevertheless, it is common practice to apply the linear polarization method to determine instantaneous corrosion rates in situations of galvanic corrosion. In the present work, the applicability of the Stern-Geary equation to galvanic corrosion was in detail discussed both with help of theoretical considerations and experimental measurements. The primary reason why the application of the Stern-Geary equation to galvanic corrosion is fundamentally incorrect is the fact that a well-defined mixed potential does for galvanic elements not exist. In this work, equations were derived that allow a correct calculation of the corrosion rate for galvanic cells. However, the required variables can, in usual practical situations, not be measured. Application of the Stern-Geary equation to galvanic cells is in the literature claimed (or assumed) to yield adequate results. An explanation for this apparent applicability was identified in the fact that two major errors have a compensating effect so that they tend to cancel each other out. The extent to which this is possible depends strongly on the actual conditions such as the geometry of the galvanic cell as well as on the position of the counter and the reference electrode (RE). Nevertheless, since this apparent applicability is owing to specific conditions rather than a fundamental applicability of the method, further research is clearly needed to characterize these conditions and their limits in detail. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Angst U.M.,ETH Zurich | Angst U.M.,Swiss Society for Corrosion Protection | Polder R.,TNO | Polder R.,Technical University of Delft
Cement and Concrete Research | Year: 2014

The concept of variability is increasingly considered in service life predictions. This paper reports experimental data on the spatial distribution of chloride in uncracked concrete subjected to homogeneous exposure. Chloride concentrations were measured with potentiometric sensors embedded in concrete exposed to chloride ingress by cyclic wetting and drying. The sensors allow highly localised, non-destructive measurements. Six different concrete mixes were tested, each with more than 20 sensors embedded within a plane at constant depth. The resulting dataset is discussed with respect to causes for the observed spatial variability of chloride as well as implications for service life predictions and experimental methods. It is concluded that the observed spatial chloride variability is a true property of chloride penetration into concrete and not an uncertainty arising from limited measurement precision. The primary cause was identified to be the presence of coarse aggregates rather than w/c ratio, cement type or exposure conditions. © 2013 Elsevier Ltd. All rights reserved. Source

Buchler M.,Swiss Society for Corrosion Protection
Materials Performance | Year: 2015

According to ISO 15589-1, the effectiveness of cathodic protection (CP) for a buried steel structure is demonstrated by measuring the IR-free potential of the steel-to-soil interface. The physical-chemical significance of this criterion is discussed by means of theoretical considerations, numerical simulation, and comparisons with field data. The importance of mass transport at the steel surface is also considered. It is hoped this perspective will stimulate further discussion on the true nature of CP. Source

Angst U.M.,ETH Zurich | Angst U.M.,Swiss Society for Corrosion Protection | Elsener B.,ETH Zurich | Elsener B.,University of Cagliari
Corrosion Science | Year: 2014

In this work, a novel method for the determination of instantaneous corrosion rates icorr is proposed. It relies on recording the current response in the time domain upon imposing an AC voltage signal, and a computational procedure to remove non-faradaic currents and to analyse the data. The method was applied to steel in stirred, unstirred, and sand-filled 1M KCl; the resulting icorr compared well with different conventional techniques. The proposed method is robust, non-destructive and fast. In addition to icorr, it provides also an estimate of the capacitance and Tafel slopes (thus, no assumption on constant B is required). © 2014 Elsevier Ltd. Source

Buchler M.,Swiss Society for Corrosion Protection
Australasian Corrosion Association Annual Conference: Corrosion and Prevention 2015, ACA 2015 | Year: 2015

Cathodic protection has proved to be an efficient way to control corrosion and increase the service life of pipelines. While there is general agreement on the effectiveness of cathodic protection, there is a widespread discussion with respect to the mechanism of protection, the significance of the protection criteria, the methodology of their assessment and their interpretation. Moreover, there are significant differences in the application of these criteria, despite AS2832.1 and ISO 15589-1 that describe clear and strict requirements. The physical-chemical meaning of the protection criteria is discussed and a model for the mechanisms involved in cathodic protection is proposed. The fundamental applicability of the model concept is validated based on the comparison with extensive field data. The extension of the concept allows explaining the mechanisms involved in a.c. and d.c. interference. The consequences on protection criteria under these conditions are elaborated and compared to experimental data. Based on this analysis a possible explanation for the failure of cathodically protected structures is presented and a new methodology for assessing protection is proposed. Source

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