Magnetic sensors used in NDT or NDE

 

2023-Jan-21:

Ramos, Science Direct (2014): Ramos, Helena G., and A. Lopes Ribeiro. "Present and future impact of magnetic sensors in NDE." Procedia Engineering 86 (2014): 406-419.

https://www.sciencedirect.com/science/article/pii/S187770581402013X/pdf?md5=fcd2f5583c592beb867b38163a3c157b&pid=1-s2.0-S187770581402013X-main.pdf

Sensitivities Comparison among Different types 

of commonly-used Magnetic Sensors in NDT Research 

GMR sensors

 

Methods:

1) Eddy Current Testing (ECT) and

2) Magnetic Flux Leakage (MFL).

In both of them a magnetic field is applied to the object under test and any resulting changes in the magnetic flux density in the region of interest are observed.

ECT or ECTP (Eddy Current Testing Probes)

 

MFL (Magnetic Flux Leakage) method - see figure 4 above.

 

With MFL methods a magnetic field is induced inside the part test and the distribution of the resulting lines of magnetic flux is determined by the magnetic permeability changes in the region under test. Fig 4 a) shows how a defect region disturbs the magnetic flux lines between two permanent magnets (not only at the surface). To obtain the maximum sensitivity of detection, the applied magnetic flux component should cut the defect at right angles [26 – 28].

[26]. G. S. Park and E. S. Park, “Improvement of the sensor system in magnetic flux leakage-type nondestructive testing (NDT)”, IEEE Transactions on Magnetics 38, Iss. 2 (2002), p 1277 – 1280.

[27]. G.A. Katragadda, W. Lord, Y.S. Sun, S. Udpa, L. Udpa, “Alternative magnetic flux leakage modalities for pipeline inspection”, IEEE Transactions on Magnetics 32-3 (1996) p 1581 – 1584.

[28]. W.S. Singh, B.P.C. Rao, S. Thirunavukkarasu, and T. Jayakumar, “Flexible GMR Sensor Array for Magnetic Flux Leakage Testing of Steel Track Ropes”, Journal of Sensors 2012 (2012), Article ID 129074, 6 pages.

 

 

Differential coils above

 

 

Eddy Current Probes:

 

 

 

 

Handheld EC probe with PC mouse as position system:

 

 

 

Fig. 13 (a) shows the experimental setup and (b) the results obtained for four similar cracks:  about 100 mm long, 0.5 mm wide and different depths: 0.5 mm / 1 mm / 1.5 mm / 2 mm respectively

 

To inspect tubes, the REFCT (Remote Field Eddy Current Test) probe (RFECTP) is modified from ECT probe techniques.