## 3 Results
### Surface Roughness and Profile Roughness  
Table 4 illustrates the surface topography of the API 5L X65 samples obtained from the Alicona InfiniteFocus 3D measurement tool. These images were then analyzed with the help of the IF Measure suite provided by Alicona in order to obtain the surface roughness parameters, such as \(\mathrm{S_{a}}\) (average aerial roughness), \(\mathrm{V_{mp}}\) (peak material volume), \(\mathrm{V_{mc}}\) (core material volume), \(\mathrm{V_{vv}}\) (core valley volume), and profile roughness parameters, such as \(\mathrm{R_{a}}\) (average profile roughness). All the parameters were obtained by following ASME standard B 46.1. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample Number** & **3D View** & **3D View with** **Distribution** & **Top View with Selection** **(500 μm)** & **Top View Filtered Area** **3 mm \(\times\) 3 mm (200 μm)** \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Surface roughness at 5\(\times\) magnification using Alicona InfiniteFocus. The surface roughness parameters and profile roughness parameters are given in Table 5. For the samples before corrosion, the S\({}_{\text{a}}\) is found to be 3.4 \(\upmu\)m, which then increases as the corrosion rate increases. For the zero flow condition, when there is no magnetic field, the S\({}_{\text{a}}\) value increases to 7.4 \(\upmu\)m. However, when an N-S magnetic field is applied, at A2, the S\({}_{\text{a}}\) value obtained is 8.4 \(\upmu\)m, and, at A3 when a N-N magnetic field is applied, the S\({}_{\text{a}}\) value obtained is 8.4 \(\upmu\)m. Only a very small increase of 0.06 \(\upmu\)m is observed when the polarity is changed. Similar results are observed for samples B1 to B3. For 1 m/s velocity in the no magnetic field condition, an S\({}_{\text{a}}\) value of 6.5 \(\upmu\)m is observed, which then increases to 8.2 \(\upmu\)m at B2 and 9.23 at B3. When a flow velocity of 2 m/s is applied, the material loss \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample Number** & **3D View** & **3D View with** & **Top View with Selection** & **Top View Filtered Area** \\  & & **Distribution** & **(500 \(\upmu\)m)** & 3 mm \(\times\) 3 mm (200 \(\upmu\)m)** \\ \hline B2 & & & & \\ B3 & & & & \\ C1 & & & & \\ C2 & & & & \\ C3 & & & & \\ C3 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: \(Cont.\)from the surface is very uniform as the S\({}_{\text{a}}\) value obtained is 3.5 \(\upmu\)m, which is relatively small compared to other cases. However, it again increases to 7 \(\upmu\)m at C2 and 7.7 \(\upmu\)m at C3. As the corrosion rate increases from A1 to C3; the S\({}_{\text{a}}\) values also increase for the same flow velocity alone, but their increase is not relative to nature when a magnetic field is applied. For sample B1, the S\({}_{\text{a}}\) value is observed as 6.5 \(\upmu\)m, but it then reduces to 3.5 \(\upmu\)m for C1. This shows that the there is no direct relation between the corrosion and the surface topography in different cases. As for the profile roughness, the R\({}_{\text{a}}\) value does not show any relation with the corrosion because the profile roughness measurement is done on a very small region, in our case, at 50X magnification, which is given in Table 6. This could be observed from Table 5, where, for the samples before corrosion, the R\({}_{\text{a}}\) is 132 nm, which then increases to 234 nm for A1 at zero flow and no magnetic field but then decreases to 117 nm for A2 at zero flow and the N-S magnetic field condition, and then again reduces to 109 nm for A3 at zero flow and the N-N magnetic condition. Similar results are observed for the cases when the velocities are 1 m/s and 2 m/s. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample Number** & **3D View 50\(\times\)** & **3D View Distributed 50\(\times\)** & **Location 1 (100 \(\upmu\)m)** \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Profile roughness images at 50\(\times\) magnification using Alicona InfiniteFocus.