## 2 Materials and Methods  
### Experimental Test Set-Up  
The test solutions are prepared from deionized water (1 \(\times\) 104 Ohm-cm\({}^{-1}\)) produced from a Metrohm Ion exchange still, with pH 5.8 supplied from a 20L reservoir. Solutions are then made according to the required parameters. The concentration of NaCl in the test solution is varied from 1% to 3.5%. The pH of the test solution is maintained to the desired values using acetic acid sodium acetate buffer solutions. The pH of the test solution is measured using an Orion pH meter and monitored at infrequent intervals. The Orion pH meter is manually calibrated before each use. The dissolved oxygen content in the solution, which is a vital factor in the corrosion rate, is maintained by bubbling air into the reservoir at 6 mg/L (6 ppm) and measured using a Milwaulkie D.O meter every hour. The corrosion electrode sensor is a 3-electrode sensor where the material sample is the working electrode, a graphite electrode is the counter electrode, and Ag/AgCl is the standard reference electrode. The three-electrode sensor is designed to fit into the flow and arranged such that the working electrode faces the oncoming flow. Microbial corrosion is prevented by the periodic addition (each day) of disinfectant (Dettol) to the solution.  
A circulating loop system, as shown in Figure 2, was used for measuring the corrosion rate. The schematic diagram of the flow loop and the actual flow loop are shown in Figures 3 and 4. The flow loop consists of a plastic reservoir, a 0.50 horsepower/0.37 kW submersible pump (made of plastic) with a float switch, a pipe (made of PVC plastic) of internal diameter 28.9 mm and an outer diameter of 33.55 mm, PVC pipe fittings, PVC valves, a plastic calibrated flow meter, and the electrode test section. A 20 L test solution is supplied from the reservoir using the submersible pump, and the flow velocity is changed and continuously monitored using the flow meter. The entire flow loop is purposely made from plastic to make sure the only corroding component in the flow loop is the test specimen. The operating conditions are maintained in desired values, and the temperature of the test solution is varied from 25 \({}^{\circ}\)C to 40 \({}^{\circ}\)C (\(\pm\)0.5 \({}^{\circ}\)C) in the study and the operating conditions are maintained at desired values. The temperature is maintained using a heating and cooling system and continuously measured using a thermocouple and a mercury thermometer at infrequent intervals. The corrosion electrode system is connected to Gamry 600 potentiostat and a computer with Gamry instruments software. After mounting the electrode system in the flow loop, the required flow rate is obtained by adjusting the manifold valves in the loop and varying the amount of bypass, and monitoring the LPM values in the digital gauge. Once the flow is stable, the potentiostat is turned on, the readings can be recorded, and further analysis can be performed using the respective Gamry software. After recording one reading, the sample is removed and cleaned before continuing the experiments. There is a 2.02 m run of straight unaffected pipe, equivalent to 69 diameters, to allow for a fully developed flow to occur and for pump noise to dissipate. The test specimen is at the bottom of a vertical flow loop, as shown in Figure 4. This is to ensure that only single-phase flow impinges on the test specimen. On the top (return) side of the loop, there is an additional deaerator that catches bubbles