The detection and characterization of cracks is one of the key issues in oil and gas transmission pipeline inspection. The weak degree of spatial magnetic field distortion caused by the small size of the crack creates great difficulties for signal extraction. In this paper, we propose an ACM crack detection probe with poly-magnetic structure, and investigate the influence of the core, shield on the detection signal through numerical simulations. The results show that the crack detection probe with the core and shield can effectively improve the distorted magnetic field component in space acquired by the magnetic element, increasing the distorted magnetic field signals in the vertical and horizontal directions by a factor of 2.10 and 1.76 respectively. Verification that ACM probe with poly-magnetic structure can effectively increases the crack-induced magnetic field distortion signal and reduce the probability of misses.
The stress concentration of oil and gas pipelines will produce corrosion cracks and axial fatigue cracks under the action of long-term and repeated internal pressure, and will rapidly expand under fluctuating internal pressure, resulting in serious pipeline accidents. In order to effectively detect the stress concentration of oil and gas pipelines, a stress concentration detection technology of unsaturated local magnetization pipeline is proposed. This paper introduces the theoretical basis of local pipeline stress concentration detection, establishes a two-dimensional finite element model of pipeline stress concentration transient force-magnetic coupling, and analyzes the influence of excitation source position, sensor lift-off value, and stress concentration value on the response signal. The simulation results show that the corresponding signal
B
x
of the stress concentration changes more obviously than
B
y
and the signal is regular, Bx
has a good two-stage linear positive correlation with the stress concentration value. The above research provides technical support for the development of pipeline on-line stress concentration detection probe.
Deformation is one of the leading causes of oil and gas pipeline accidents, affecting pipeline transportation efficiency and operational safety. This paper proposes a pipeline deformation detection method and prediction models based on alternating current magnetisation (ACM) technology.
Firstly, the mechanism of pipeline deformation detection based on ACM technology is introduced and mathematical models are proposed to evaluate the deformation length and height using magnetic detection signals. Next, finite element models of detection signals for deformations with various
lengths and heights are analysed and original signal waveforms are obtained. Furthermore, linear and polynomial fitting mathematical models are developed to invert the deformation length and height using the measured peak signal and L' (distorted signal length) value. Finally, experiments
are conducted to demonstrate that the length and depth of a deformation can be estimated by linear and polynomial models with tolerable errors. The proposed approach combining ACM and a prediction model is verified to size deformation in pipeline inspection quantitatively.
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