## 3 Results and Discussion
The maximum variation of the tangential MMM signal around defect center was 66.73 \(\upmu\)T \(\pm\) 1.13 \(\upmu\)T. Figure 8 depicts six measurements of normal MMM signals of this third notch, in which these signals have a shift in their variation direction close to the defect center. Near the first edge of this notch, the normal MMM responses achieved a maximum peak of 159.32 \(\upmu\)T \(\pm\) 0.48 \(\upmu\)T. On the other hand, around the second edge, the normal MMM signals had a minimum value of -96.68 \(\upmu\)T \(\pm\) 0.26 \(\upmu\)T. The difference between these two values occurs along an approximate distance of 2 mm, which is related to the width (2000 \(\upmu\)m) of the third notch (S3). Figure 6: Variation of normal MMM signals measured around the second V-shaped notch (1500 \(\upmu\)m width and 1000 \(\upmu\)m depth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. Figure 7: Variation of tangential MMM signals measured around the third V-shaped notch (2000 \(\upmu\)m width and 1500 \(\upmu\)m depth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. Figures 9 and 10 illustrate six measurements of tangential and normal MMM signals of the fourth V-shaped notch (S4). The tangential MMM signals registered a minimum peak value of \(-162.40\) uT \(\pm\) 1.33 uT close to the notch center (z = 0 mm). Thus, the maximum shift of the tangential MMM signal is 55.13 uT \(\pm\) 1.33 uT around defect center. This variation is due to the notch depth (2000 um) of the pipe surface. Furthermore, the normal MMM response has a change in its variation direction near to defect center, which is related with the two edges of the fourth defect (3000 um width). In addition, Figures 11 and 12 show six measurements of tangential and normal MMM signals about fifth V-shaped notch (S5). A minimum peak value (\(-157.27\) uT \(\pm\) 0.94 uT) of the tangential MMM response is measured along the notch center (z = 0 mm) and is related with to notch depth (2500 um depth). The maximum change of the tangential MMM signal around the defect center is 68.75 uT \(\pm\) 1.10 uT. On the other hand, the normal MMM signals has maximum and minimum values of 155.17 uT \(\pm\) 0.43 and 83.80 uT \(\pm\) 0.41 uT, respectively. These normal MMM signals registered a change in their variation direction close to the notch center. Thus, the measurement of the tangential and normal MMM signals can be used to quantify the size (depth and width) of the V-shaped notch. Figure 8: Variation of normal MMM signals measured around the third V-shaped notch (2000 μm width and 1500 μm depth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. Figure 9: Variation of tangential MMM signals measured around the fourth V-shaped notch (3000 μm width and 2000 μm depth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. Figure 11: Variation of tangential MMM signals measured around the fifth V-shaped notch (3500 μm width and 2500 μm depth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. Figure 3:0 Variation of normal MMM signals measured around the fourth V-shaped notch (3000 μm width and 2000 μm depth) of the ASTM-A36 steel pipe, which were measured using six experimental tests. Table 2 indicates the values of minimum tangential MMM signals at the center of the V-shaped notches, as well as the maximum and minimum normal MMM signals at the edges of each notch. Furthermore, the maximum variations of tangential MMM signals around five notches are indicated in Figure 3:1 Tangential MMM signals had variations of 14.32 uT \(\pm\) 1.62 uT and 16.08 uT \(\pm\) 1.86 uT close to center of the first and second notches, respectively. Moreover, the third notch shows a higher tangential MMM signal shift (66.73 uT \(\pm\) 1.13 uT) in comparison with those of the first two defects. In the fourth notch, we observed a tangential MMM signal variation of 55.13 uT \(\pm\) 1.33 uT, which is higher than those of the first and second notch.