*2.2. Experimental Set-Up*

In Figure 1 a typical vessel for test exposure is shown. Each vessel contains two identical steel samples (duplicates, as working electrodes (WEs)) and a platinum counter electrode (CE). A reference electrode (KCl saturated Ag/AgCl) was inserted just before electrochemical measurements and taken out after the measurements. The reference electrode was always cleaned in alcohol before it was inserted in a glass bottle through the hole in the rubber cover to prevent the interference of microorganisms from outside of the vessels. The vessels were closed during the tests. In Table 2 an overview of the test methods, including samples, electrolytes (artificial seawater (SW) and artificial seawater with addition of bacteria (SW + bacteria (MIC))), and test period is given. The steel samples P1 and P2 were for PDP measurements, samples B1–B4 for combined LPR and EIS measurements, and samples with initial code S for only LPR measurements.


**Table 2.** Experimental methods and conditions.

**Figure 1.** A typical sample exposure vessel for linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements.

Samples were exposed to stagnant electrolytes (600 mL) at room temperature. The pH of the solutions at the start was 8.0. The electrolytes were described in Section 2.3. Using stagnant electrolytes aimed to decrease disturbance to the growth of biofilms.

Different test durations were designed to study how biofilm and corrosion develop in different time durations, e.g., tests for samples S8, S9, S14 and S15 were stopped after exposure for 7 days and they were taken out for surface analysis. This information may help us to understand how biofilms build up and about the initiation and progress of localized corrosion is in different media.
