基于磁场梯度感测的旧油管腐蚀缺陷脉冲涡流可视化检测

Pulsed eddy current screening of corrosions in the in-service tubing based on gradient magnetic field sensing

油管是油气井管柱中用于直接汲取石油、天然气的最内部管道。服役中的油管长期接触含硫物质,其内壁会出现腐蚀缺陷,影响管柱完整性。基于磁场梯度感测,提出一种结合双传感器差分机制的脉冲涡流检测探头,以实现旧油管内壁腐蚀缺陷的高灵敏度成像。在确定检测探头构型的基础上,通过系列试验,探究下降沿对数曲线斜率和归一化差分信号峰值两类信号特征与腐蚀缺陷尺寸间的关联规律;同时,基于两类信号特征探索腐蚀缺陷成像方法。提出了信号特征融合方法,形成基于融合信号特征的旧油管腐蚀缺陷可视化手段。试验结果表明,相比传统脉冲涡流检测,所提方法得到的基于融合特征的腐蚀缺陷成像结果具有更高的图像信噪比;采用所提检测探头及信号特征融合方法,可对旧油管内壁缺陷实现高灵敏度、高信噪比的可视化检测。

As the inner most pipe of the oil-and-gas well shaft,the tubing is used to directly extract either oil or gas.The in-service tubing is subject to the sulfurous substances which lead to the corrosion occurring on its internal surface.This undermines the integrity of the well shaft.In this paper a pulsed eddy current probe was proposed for high-sensitivity imaging of internal-surface corrosion of the in-service tubing,based on gradient magnetic field sensing alongside the differential mechanism of dual magnetic sensors.Following the determination of the probe structure,two signal features,i.e.,the gradient of the logarithm curve of the testing signal and peak value of normalized differential signal were intensively investigated through experiments.The correlation of each signal feature with the corrosion sizing parameters was established.And the corrosion imaging method was explored based on each signal feature.A signal-feature fusion approach was proposed.Based on the fusion of the two signal features,the visualization method for tubing corrosion was exploited in conjunction with the fused feature.The results revealed that compared with the traditional pulsed eddy current testing,the fused feature-based imaging method was advantageous in terms of higher signal-to-noise ratio(SNR)of produced corrosion images.This further indicated that the proposed probe together with the signal-feature fusion approach was beneficial to the visualization of internal-surface corrosion in the in-service tubing with high sensitivity and SNR.