## 3 Discussion of Results
### Experimental Observations and Analysis
Corrosion rate further increases and reaches a value of 0.1727 mm/yr is at 3.5% NaCl concentration. The effect of flow velocities on the corrosion rates of API-5L-X65 QT is shown at different temperatures in Figure 9. When the feed solution is maintained at 1% NaCl concentration shown with black color lines (see Figure 9), the corrosion rate reaches 0.0782 mm/yr at 30 \({}^{\circ}\)C, 0.1028 mm/yr at 35 \({}^{\circ}\)C, and 0.1424 mm/yr at 40 \({}^{\circ}\)C. An increase in NaCl concentration to 2%, shown with blue color lines, causes an increase in the corrosion rates in the range of 0.1143 mm/yr to 0.2032 mm/yr when flow velocity and the temperature is varied. The red line shows corrosion rats at 3.5% NaCl concentration, and the corrosion rates are increased up to 15-28% than the 2% NaCl concentration conditions. At 40 \({}^{\circ}\)C, the corrosion rate reaches a maximum value of about 0.254 mm/yr (10 mpy)  
Figure 8: Corrosion rates of API-5L-X65 QT are shown at different flow velocities for feed solution maintained at pH-7, varying NaCl concentrations and temperatures (25 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, 35 \({}^{\circ}\)C, and 40 \({}^{\circ}\)C). at a flow velocity of 0.4 m/s, and a further increase in flow velocity is not affecting the corrosion rates. The increase in temperature shows a 5% to 10% increase in corrosion rates in all concentrations except for some data points. In Figure 10, a study is conducted to determine the influence of pH on the corrosion rate. The results are shown at a temperature of 25 \({}^{\circ}\)C at different flow rates and NaCl concentration. In the literature, significant studies have been done that analyze the relation between pH and the corrosion rates, but very limited studies to model the effects in a flow loop, as discussed earlier. The physical and chemical properties of the corrosion products and the corrosion layer formed on the surface lead to variation in corrosion rates in different pH and flow velocities [28]. The studies show conflicting results at different pH as the high testing period leads to different corrosion mechanisms depending upon the material property [28]. As the LPR technique is short term method, observed trends eliminate the possibilities of different corrosion mechanisms at different pH and show a consistent trend in corrosion rates. At zero velocity for pH 7, the corrosion rate observed is about 0.04321 mm/yr for 2% concentrated solution and 0.05419 mm/yr for 3.5% NaCl solution. When the pH is maintained at 5, at zero velocity, the corrosion rate observed is 0.0732 mm/yr for 2% NaCl solution, and at 3.5% NaCl concentration, the corrosion rate shows an increase of 75% than pH 7 and records a value of 0.0956 mm/yr. As shown in the previous results (Figures 8 and 9) at different pH and temperatures, the majority of the data suggests that the corrosion rate is insensitive to flow at high velocities and maintains a steady rate. The results of Figures 8 and 9 show the corrosion rate tends to increase when the hydrogen ion concentration in the feed solution increases. Figure 9: Corrosion rates of API-5L-X65 QT are shown at different flow velocities for feed solution maintained at pH-5 varying NaCl concentrations and temperatures (25 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, 35 \({}^{\circ}\)C, and 40 \({}^{\circ}\)C).