Abstract
Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper.
Highlights
Non-destructive testing (NDT) is a quality control tool that is extremely important in heavy engineering sectors such as the petroleum and gas industry
This paper will describe the implementation of giant magnetoresistance (GMR) sensorw in non-destructive eddy current testing techniques, a previous study of the applications of GMR sensor in non-destructive eddy current testing and the issues that need to be addressed by future researchers
If a magnetic field is applied to the GMR structure in opposite directions, the electron spin in the FM layer starts rotating while the electron spin in the AFM layer remained unchanged (Figure 3(iii))
Summary
Non-destructive testing (NDT) is a quality control tool that is extremely important in heavy engineering sectors such as the petroleum and gas industry. Sensors 2016, 16, 298 thickness and coating measurements, electrical conductivity measurements for material classification and conductive monitoring during material heat treatment [1] Compared with another nondestructive testing methods, this technique offers many advantages such as high sensitivity to small defects for tests that require fast scanning inspection. To monitor the growth of cracks in large system structures, the test probe is placed on the detected cracks and the data continuously collected for defect profile analysis [1] In this application, ECT techniques are more suitable than another non-destructive testing methods. The magnetic field changes may provide information related to any defects inherent in the material, electrical conductivity and permeability of the material after a heat treatment process, surface and subsurface defects This discovery is the starting point for research on non-destructive testing using the eddy current principle. This paper will describe the implementation of GMR sensorw in non-destructive eddy current testing techniques, a previous study of the applications of GMR sensor in non-destructive eddy current testing and the issues that need to be addressed by future researchers
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