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A finite element simulation analysis of micromagnetic signals of surface crack defects on a titanium (Ti) alloy plate was performed, and a verification experiment was designed. Simulation results s...

This study focused on the inter-granular crack defects of tubing coupling wherein a non-destructive magnetic testing technique was proposed to determine the magnetic flux leakage features on coupling surface in the geomagnetic field using a high-precision magnetic sensor. The abnormal magnetic signatures of defects were analysed, and the principle of the magnetic test was explained based on the differences in the relative permeability of defects and coupling materials. Abnormal fluctuations of the magnetic signal were observed at the locations of the inter-granular crack defects. Imaging showed the approximate position of defects. The test results were proven by metallographic phase.

Purpose This paper aims to clarify the transient electromagnetic method used for the nondestructive testing of the corrosion of an in-service buried metal pipeline in trenchless state. Design/methodology/approach The paper designed corrosion models indoor and infield for testing. A method for calculating the residual wall thickness of metal pipelines was also proposed. The calculation method was verified by the test results. In the test, the receiving probe was improved by the addition of a Mn-Zn ferrite core. The amplitudes of the test results obviously increased, and the calculation accuracy was improved. Findings The paper states that the transient electromagnetic method can detect the uniform corrosion distribution of a certain section of a pipeline. A multi-channel profile of the induced electromotive force and the calculated values of the residual wall thickness can be used to confirm the position and degree of corrosion defects, respectively. Research limitations/implications The transient electromagnetic method is more effective for large-area corrosion than for localized corrosion (pitting). Practical implications The paper includes implications for the development of nondestructive testing method of the corrosion of an in-service buried metal pipeline. Originality/value This paper proved the feasibility and reliability of using transient electromagnetic method to test the corrosion of a buried metal pipeline based on experimental study.

This study proposed micromagnetic nondestructive detection technology to detect the surface residual compressive stress of 304 stainless steel specimens after annealing treatment and loading. X-ray diffraction was used to determine the changes in residual compressive stress, microstrain, and grain size to aid in verification. Variations in surface residual compressive stress and magnetic induction intensity were analyzed. When residual compressive stress changed markedly, the change in magnetic induction intensity reflected the change in residual compressive stress. With the increase in residual compressive stress, the surface magnetic induction intensity and residual compressive stress of the specimen exhibited an approximate linear relationship, manifesting an increasing trend. Therefore, residual compressive stress was analyzed by detecting the changes in the surface magnetic induction intensity of specimens. Micromagnetic nondestructive detection allows the effective detection of the surface residual compressive stress of 304 stainless steel.

This paper proposes a method of lossless micromagnetic detection in the geomagnetic field for detecting traces of carbon impurity defects in crystalline silicon. The magnetization tests show that crystalline silicon is a diamagnetic substance with a stronger relative permeability than carbon. Micromagnetic decay theory is gained according to the energy decay. When the geomagnetic field penetrates through the materials, the apparent magnetic susceptibility can be calculated and subsequently used to project the images. The resulting image clearly showed the location of the defects. Test results are proved by the metallographic phase and spectral analysis. New method and ideas are provided for effective detection of trace carbon impurity defects in the crystalline silicon.

The present paper put forward a magnetic non-destructive testing method for the complex tiny flaws existing in the friction stir welding (FSW) of aluminium alloy. Through magnetisation testing, it is confirmed that the relative magnetic permeability of aluminium alloy material is larger than the relative magnetic permeability of aluminium. Aluminium alloy is a paramagnetic material. The anomalous characteristics of the magnetic field in the flaw were analysed according to the differences of the relative magnetic permeability of the flaws. Magnetic detection technology detects flaws in FSW based on theoretical analysis. High precision measuring magnetic sensors were used to detect the magnetic field. Test results show that the magnetic field signal in flaw have obvious anomalous fluctuations. The reliability of the magnetic method is confirmed through comparison with the micrograph specimens. A new detection method for the tiny flaws in FSW specimens was provided.

The current study proposes a non-destructive testing method for thin-plate aluminum alloys based on the geomagnetic field. A high-precision magnetic sensor was used to measure slight changes in the magnetic field strength. The relative permeability of aluminum alloys was proven to be greater than that of aluminum through the magnetization of aluminum alloy materials. Therefore, aluminum and its alloys are paramagnetic materials. The aims of the current study are to analyze the effect of magnetic field on defects and to determine the test mechanism based on the differences in relative permeability. A thin-plate aluminum alloy 2024, with a thickness of less than 2 mm, was used as a specimen. An artificial groove defect was set in the specimen. The result shows that the signal from the magnetic field was obvious and unusual at the location of the artificial defect. A metallographic test verified that the other abnormities observed from the signal were consistent with the natural defects of the specimen. The magnetic method was found to be accurate, and a clear test mechanism was observed. The magnetic method provides the foundation for non-destructive testing of thin-plate aluminum alloys.

Corrosion and cracks of casing string in oil wells is a serious problem on which little research has been done when inspecting casing through tubing. In this study, inspecting casing through tubing with pulsed eddy current is investigated. Longitudinal and transverse probes are centred inside the tubing to detect wall thinnings and cracks in casing. A time slice of induced voltage in the receiving coil of the probe is used as the feature to recognise defects. The experimental results show that large area wall thinnings and long cracks in casing are detected successfully through the tubing with appropriate inspection parameters. The probe's orientation to the crack is important and a particular discovery is that the transverse probe should be parallel to the transverse crack and not be perpendicular to it when inspecting. A method based on linear regression is proposed to estimate flaws in casing while wall thinning in the tubing occurs at the same location. The method is effective for large area thinning ...