## 3 Results and Discussions
### Effect of Velocity and Sand Loading  
Figures 9 and 10 show the velocity and sand loading effect on the \(TWL\), \(E_{0}\) and \(I_{EC}\) after 4 h of exposure. Tables 2 and 3, and the figures show how the weight loss increases linearly with both the velocity and sand loading at an increased rate of the velocity than for sand loading alone. In both cases pure erosion is dominant. The \(I_{EC}\) was calculated by subtracting the \(E_{0}\) and \(C_{0}\) from \(TWL\). Figure 8: Tafel curve obtained for mild steel sample after 4 h immersion. Figure 9: Effect of velocity on weight loss at 600 mg/L. Figure 11 shows SEM images of the specimen after erosion-corrosion impingement tests under two different conditions with a 1500x magnification. Figure 11a shows the formation of metal shards along with discrete isolated pits and cracks after the impingement test at the minimum velocity of 10 m/s and maximum sand loading of 600 mg/L. Figure 11b shows the SEM image at the minimum sand loading of 300 mg/L and maximum velocity of 20 m/s. The SEM (in Figure 11b) shows discrete pits and ploughing tracks larger in size than those seen in Figure 11a. These larger pits and ploughing tracks are a result of the large impact energy of the higher velocity sand having the potential to cause more damage. The image also shows areas on the surface which are free from the impact of sand particles. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{_TWL(mg)_} & \multicolumn{2}{c}{_Pure Erosion_} & \multicolumn{2}{c}{_E-C Interaction_} \\ \cline{2-7}
**Velocity (m/s)** & \multicolumn{2}{c}{_TWL_} & \multicolumn{2}{c}{_Error_} & \multicolumn{2}{c}{_Weight Loss_} & \multicolumn{2}{c}{_Error_} & \multicolumn{2}{c}{_Weight Loss_} & \multicolumn{2}{c}{_Error_} \\  & **(mg)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** \\ \hline
10 & 35.13 & \(\pm\)0.66 & 22.20 & \(\pm\)0.54 & 12.52 & \(\pm\)0.12 \\
13 & 45.07 & \(\pm\)0.81 & 29.23 & \(\pm\)0.70 & 15.42 & \(\pm\)1.45 \\
16 & 55.83 & \(\pm\)0.80 & 34.87 & \(\pm\)0.61 & 20.55 & \(\pm\)0.95 \\
20 & 71 & \(\pm\)1.17 & 42.67 & \(\pm\)1.02 & 28.12 & \(\pm\)1.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Weight loss due to velocity effect at 600 mg/L. Figure 10: Effect of sand loading on weight loss at 20 m/s. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{_TWL(mg)_} & \multicolumn{2}{c}{_Pure Erosion_} & \multicolumn{2}{c}{_E-C Interaction_} \\ \cline{2-7}
**Sand Loading** & \multicolumn{2}{c}{_TWL_} & \multicolumn{2}{c}{_Error_} & \multicolumn{2}{c}{_Weight Loss_} & \multicolumn{2}{c}{_Error_} & \multicolumn{2}{c}{_Weight Loss_} & \multicolumn{2}{c}{_Error_} \\ \cline{2-7}
**(mg/L)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** & **(mg)** \\ \hline
300 & 52.33 & \(\pm\)0.61 & 28.23 & \(\pm\)0.32 & 23.68 & \(\pm\)0.85 \\
400 & 58.23 & \(\pm\)0.65 & 32.47 & \(\pm\)0.80 & 25.35 & \(\pm\)0.98 \\
500 & 64.33 & \(\pm\)0.70 & 36.57 & \(\pm\)0.70 & 27.35 & \(\pm\)0.98 \\
600 & 71 & \(\pm\)1.17 & 42.67 & \(\pm\)1.02 & 28.12 & \(\pm\)1.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Weight loss due to sand loading effect at 20 m/s. Figure 12 shows the SEM image of the surface 2 mm away from the center after the pure erosion test under the same conditions, as in Figure 6 which is the SEM image after the erosion-corrosion test. At this region (2 mm away from the center) the impact angle is expected to be at an angle of less than 90\({}^{\circ}\). In erosive wear, the angular impingement of particles experiences deformation based on its orientation when it contacts the surface whether it is rolling forward or backward while in contact. The image shows that metal flakes are formed on the surface due to the multiple impacts of particles. According to [PERSON]'s platelet mechanism [43] these flakes are the signs of plastic deformation of the surface. This deformation in the direction of flow indicates the removal mechanism [44; 45; 46; 47].