Laboratory scale experiments to evaluate the role of environmental parameters on the corrosion rate
At the SMS research group (UGent), the aim is to perform experiments at the laboratory scale by investigating how different environmental parameters affect the corrosion rate in a number of specific conditions in artificial seawater, prepared based on ASTM Standard D1141. Therefore, in contrast to field demonstrations, where the environment is not controllable, in laboratory experiments only the effect of one variable parameter can be measured. In the SOCORRO project, these experiments have generated valuable data for developing and training the SOCORRO Artificial Intelligence models. The effect of different temperatures, salinity, and pH on corrosion rate is studied at the beginning of this fundamental project.
Initially, we used a linear polarization resistance (LPR) probe provided by the Cosasco company (USA), and an Aquaread AP700 probe by Eijkelkamp (The Netherlands) was used to monitor the corrosion rate and the mentioned environmental parameters. The outputs of the Cosasco probe were loop current (IL) at the completion of each measurement cycle in the range of 4 – 20 mA, which was converted to corrosion rate by utilizing a specific equation (Eq.1).
The selected electrodes were stainless steel S316L and construction steel grade A. The acceptable results were generated for grade A carbon steel electrodes. Investigating S316 L stainless steel electrodes was impossible since the low corrosion rate for this kind of steel was outside of the detection range of the probe. Afterwards, the main parameters influencing the corrosion rate of grade A were investigated by principal component analysis. Generally, PCA is defined as a dimensional reduction method to simplify the exploration and visualization of data. Therefore, for our large dataset, PCA helps to reduce the relevant number of variables and still include as much information as possible.
In later experiments, Aquaread AP700 probe was replaced by Manta 20 probe, provided by the Eijkelkamp company. Moreover, the corrosion rate measurement was performed by a potentiostat (Gamry). For this purpose, the defined area of abraded grade A steel, platinum mesh, and Ag-AgCl electrode were used as working electrode, counter electrode, and reference electrodes, respectively, as it is shown in Fig.1.
The corrosion resistance results were converted to corrosion rate by equation (2), where Icorr, EW, ρ, A and K represent the corrosion current, equivalent weight, density, surface area, and constant, respectively.
Therefore, by running cycles of linear polarization resistance every hour for 90 hours, the corrosion rate was measured more precisely in different conditions. Tests at 10, 15, 21, and 26°C were performed to investigate the temperature effect. In such an under-control environment, the increase of corrosion rate with increasing temperature was confirmed.
Furthermore, the corrosion rate measurements at different pH (different OH- concentrations) are currently being worked on. So far, interesting results have been generated, which need to be further addressed about their reproducibility. After producing the essential data, we will perform a principal component analysis to examine how the variables affect each other and the corrosion rate.