Abstract
This paper proposes a testing methodology for barrier properties of large non-conductive anti-corrosion coatings on steel structures. Electrochemical impedance spectroscopy (EIS) was adapted to in situ testing of steel structures by using a prototypical flexible measuring probe and a gel electrolyte that filled the probe, to take measurements on any surface regardless of its position. The first stage of the testing methodology was to perform time-consuming impedance measurements and quick electromagnetic measurements of coating thickness at selected test points. The results were used to determine correlation relationships between the logarithm of the impedance modulus for the coating at a measuring frequency of 0.1 Hz measured with the EIS method and the average thickness of the coating measured with an electromagnetic thickness gauge. Quick electromagnetic measurements were performed in the second stage to specify thickness of the other surface of the steel structure coating. The barrier properties of this coating were identified on the basis of the determined correlation.
Highlights
Steel structures are exposed to gradual corrosive degradation due to the impact of aggressive environments [1]
In case of the sheet with a thinner red layer, the logarithm of impedance modulus was within the range of 5–6 Ωcm2, whereas for the sheet with a thicker grey layer, the modulus was within a higher range of 6.7–8.1 Ωcm2
Adaptation of the Electrochemical impedance spectroscopy (EIS) to the in situ tests was mainly based on using the flexible housing of the measuring probe with the integrated flexible auxiliary electrode, the shape of which adjusted to the test surface, and using electrolyte gel instead of the traditional aqueous electrolyte
Summary
Steel structures are exposed to gradual corrosive degradation due to the impact of aggressive environments [1]. The most common anti-corrosive method for steel structures is to apply a (non-conductive) paint coating on its surface [2,3,4] Thickness of this coating, which is an element used to verify the correctness of its application, can be measured during its application—WFT (wet film thickness), using combs or discs. DFT (dry film thickness) gauges are used These gauges usually measure thickness using the principle of magnetic induction or the eddy-current method [5]. Durability of this coating is time-restrained, and its regular renewing is necessary [6,7]. Identifying the moment at which the paint coating lacks its proper barrier properties and its protective properties against corrosion are reduced is crucial for economic and durability reasons [8,9]
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