Papers by Keyword: Pulsed Eddy Current

Abstract: Finite element analysis software ANSYS is used to establish a three-dimensional finite element model of the pipeline corrosion defects by applying the boundary conditions of square wave excitation to simulate the distributions of current and induced magnetic field in the pipeline under various defect volumes. The results of the study show: When there is no corrosion defect in the pipeline, the electric current in the pipeline is basically even distribution. The magnetic field is distributed for the symmetrical vortex shape from head to foot, and it has not obviously gather phenomenon. When there are some corrosion defects in the pipeline, the electric current forms partial symmetrical vortex shape in both sides of the corrosion defect, and it is obviously assembled in the defect place. The simulation results of the different size defects show that the maximum magnetic field strength and the maximum current value increase with the defect depth increasing, while the output voltage decreases with the defect depth increasing. For the analysis of the stress distributions of the pipeline corrosion defect with certain size under different pressures, it was found that the maximum stress is 596 MPa when the bearing limit work pressure of the pipeline is 7 MPa, which is smaller than the yield strength with ensuring the safely running of the pipelines with defects.

Abstract: According to the principle and the type of the oil pipeline corrosion, we use the square wave of wide spectrum, strong signal transmission capability and a certain duty ratio as the excitation source of the pulsed eddy current. The finite element analysis software ANSYS is used to establish a three-dimensional finite element model of the pipeline corrosion defects by applying the boundary conditions of square wave excitation to simulate the distributions of current and induced magnetic field in the pipeline under various defect volumes. It can solve the induced voltage variation with time on detection coil, and can accomplish the finite element analysis and the nondestructive testing about the pipeline internal corrosion defects with the insulation layer and the protection layer. The results of the study show: When there is no corrosion defect in the pipeline, the electric current in the pipeline is basically even distribution. The magnetic field is distributed for the symmetrical vortex shape from head to foot, and it has not obviously gather phenomenon. When there are some corrosion defects in the pipeline, the electric current forms partial symmetrical vortex shape in both sides of the corrosion defect, and it is obviously assembled in the defect place. The simulation results of the different size defects show that the maximum magnetic field strength and the maximum current value increase with the defect depth increasing, while the output voltage decreases with the defect depth increasing. By extracting the induced voltage signals on the detection coil in a certain excitation condition, the quantitative detection of the pipeline corrosion defects can be achieved.

Abstract: Pulsed eddy current (PEC) technique has been successfully used for measuring wall thinning of carbon steel equipments without removal of the insulation. In field applications, the probe performance decreases in presence of ferromagnetic claddings. This paper presents a method based on saturation magnetization to solve this problem. The main principle of this method is to weaken the magnetic shielding effect of the cladding by magnetizing it to saturation. A U-shaped magnetizer is designed to realize this method. Contrast experiments are performed on a Q235 steel plate covered by a galvanized steel cladding. The experiment results show that the thickness measurement range and lift-off range are increased by applying this method to the common PEC probe.

Abstract: The conventional eddy current testing uses a sinusoidal signal with very narrow frequency bandwidth. Whereas, the pulsed eddy current method uses a pulse signal with a broad frequency bandwidth. This allows multi-frequency eddy current testing, and the penetration depth is greater than that of the conventional eddy current testing. In this work, the pulsed eddy current instrument was developed for evaluating the metal loss. The developed instrument was consist of the pulse generator generating the square pulse of maximum 40 V, the amplifier controlled to 52dB, the A/D converter of 16bit 20MHz, and the industrial personal computer for operating with Windows program. And, the probe for the pulsed eddy current was designed as the pancake type in which the sensing coil was located in the driving coil. The peak voltage did not linearly increase with the voltage of the step pulse. For the driving coil with inductance of 670µH, the peak voltage linearly increased with the step pulse voltage to 30V. But, for the other driving coils with the inductance of 1.7mH, 2.7mH, 3.6mH, 22mH, the peak voltage linearly increased with the step pulse voltage to 20V. The output signals of the sensing coil rapidly increased when the step pulse driving voltage was off, and the latter part of the sensing coil output voltage exponentially decreased with a time. The decrement value of the output signals of sensing coil increased with the thickness of the aluminum test piece.