## 3 Results and Discussion
The fifth notch had a change of tangential MMM signal of 68.75 uT \(\pm\) 1.10 uT, which is higher than that registered by the other defects. In addition, Table 3 contains the normal MMM signal variations around the two edges of the five V-shaped notches, considering the maximum and minimum peak values. In the first notch, a shift (27.95 uT \(\pm\) 1.14 uT) in the normal MMM signal is registered between the two edges of the defect. The second notch has a normal MMM signal shift of 26.4 uT\(\pm\) 0.54 uT. For the third and fourth notches, the normal MMM signal variations were 62.63 uT \(\pm\) 0.50 uT and 51.98 uT \(\pm\) 0.64 uT, respectively. On the other hand, the fifth notch achieves a maximum normal MMM signal shift of 71.37 uT \(\pm\) 0.72 uT. For these normal MMM signals, the first and second notches have the lowest tangential MMM signal variation. The first defect (500 uDepth) generates an alteration of tangential and normal MMM signals around the pipe, which could be used for monitoring its position and size. Figure 13 depicts la maximum variation of tangential MMM signal with respect to the depth of the V-shaped notch. For the first three defects, the maximum variation of this MMM signal increases when the depth increases. For the fourth and fifth defects, the variation of the tangential MMM signal is lower. For instance, the fourth defect has a lower variation with respect to third defect. This could be due to the saturation of the variation of this MMM signal. The fifth defect has a slight increase with respect to the third and fourth defect. Thus, this variation of tangential MMM signal has a nonlinear behavior. Figure 14 depicts the maximum variation of normal MMM signals with respect to the width of the V-shaped notches. In addition, this signal has a nonlinear behavior. The third and fifth width have highest variations of tangential MMM signals. The fourth width has  
Figure 3:2 Variation of normal MMM signals measured around the fifth V-shaped notch (3500 uDepth and 2500 uDepth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. a variation slightly lower than the third width. For both tangential and normal MMM signals, the third and fifth notches had highest variations. On the other hand, the fourth notch had a small reduction of the variations of the tangential and normal MMM signals in comparison with those of third notch. The five notches had the highest alteration for both MMM signals in comparison with those of the first four notches. Moreover, the maximum variations of tangential MMM signals increased for the first three defects. However, this signal registers a magnetic saturation for the fourth and fifth defect, achieving a small difference in comparison with those of the third defect. Based on the results measured in this work, this MMM method could be used to detect V-shaped notches with depth and width higher that 500 \(\upmu\)m. The study about the variations of tangential and normal MMM signals around small V-shaped notches of an ASTM-A36 steel pipe could be used for monitoring the location and size of these defects. The MMM method could be employed for real-time inspection of small V-shaped notches (at scale of a few hundred micrometers) of steel pipes using low-cost equipment and without high-skilled operators. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**V-Notch Defect**} & **Minimum Tangential (Bz) MMM** & **Maximum Normal (By) MMM** & **Minimum Normal (By) MMM** \\  & **Signal around Notch Center** & **Signal around Notch Edge** & **Signal around Notch Edge** \\  & **(\(\upmu\)T)** & **(\(\upmu\)T)** & **(\(\upmu\)T)** \\ \hline S1 & \(-252.8\pm 1.39\) & 71.2 \(\pm\) 0.66 & 43.3 \(\pm\) 0.52 \\ S2 & \(-224.4\pm 1.31\) & 113.8 \(\pm\) 0.28 & 87.4 \(\pm\) 0.40 \\ S3 & \(-202.9\pm 0.90\) & 159.3 \(\pm\) 0.48 & 96.7 \(\pm\) 0.26 \\ S4 & \(-162.4\pm 1.33\) & 87.1 \(\pm\) 0.86 & 35.1 \(\pm\) 0.30 \\ S5 & \(-157.3\pm 0.94\) & 155.2 \(\pm\) 0.43 & 83.8 \(\pm\) 0.41 \\ \hline \hline \end{tabular}
\end{table}