【作者】 张国光；

【导师】 杨理践；

【作者基本信息】 沈阳工业大学 ， 电工理论与新技术， 2010， 博士

【摘要】 管道运输是油气资源运输的主要方式,油气管道安全已经成为关系国计民生的重大问题。定期进行管道检测是防止管道事故、保证管道安全的主要方法。在多种油气输送管道内检测技术中,漏磁内检测技术应用最为广泛。论文针对管道漏磁内检测技术的有关难题,紧密结合检测实际需要,通过理论分析和实验系统分析,总结了管道漏磁内检测技术,对轴向励磁和周向励磁漏磁检测技术进行了深入研究。分析了缺陷漏磁场的形成机理,引出磁偶极子模型近似分析常见缺陷漏磁场,针对磁偶极子模型的不足,将有限元方法应用到缺陷漏磁场分析,实现了典型管道缺陷漏磁场的仿真。分析了管道轴向励磁漏磁检测原理,对漏磁检测信号的特性进行了分析,研究了缺陷的外形尺寸(长度、宽度和深度)和延伸方向等主要缺陷特征对漏磁信号的影响规律;设计了管道轴向励磁漏磁检测实验平台,进行管道牵拉实验,采集并分析了缺陷信号样本,实验结果验证了管道轴向励磁漏磁检测方法可以检测周向分布缺陷,对管道螺旋焊缝、圆孔、周向凹槽等缺陷反应明显,各路信号具有很好的一致性、稳定性和比较高的检测精度,可识别缺陷的最小深度为10%壁厚,最小面积为直径2mm的圆孔。但管道轴向励磁漏磁检测方法不能检测轴向分布缺陷(例如狭窄裂纹)。研究了管道周向励磁漏磁检测原理,通过有限元仿真分析对比,提出了符合工程设计要求的四磁极分离环型磁化器结构,应用磁路理论,建立了磁化器磁路数学建模,开发了磁路计算程序,并研究了磁化器永磁体参数对漏磁信号的影响规律,为磁化器参数设计提供依据;对漏磁检测信号的特性进行了分析,提出了缺陷漏磁信号及缺陷外形尺寸的特征量;环形磁路结构使得管壁在周向难以达到磁饱和,磁极附近区域的磁场最强,磁极中心区域的磁场最弱,非均匀磁场造成缺陷测量与评价困难,为此提出了缺陷漏磁信号补偿方法,以消除非均匀磁场的影响;研究了缺陷距磁极的距离、外形尺寸(长、宽、深)等因素对漏磁信号的影响规律,为缺陷评价和相关补偿提供了理论指导;采用多元线性回归原理,确定了缺陷参数与漏磁信号特征量的回归拟合方程,实现了缺陷参数的定量识别。周向励磁检测利用平行安装在磁极之间的传感器测量缺陷漏磁信号,采用霍尔元件作为缺陷漏磁检测传感器,设计了小间距传感器阵列结构,制作了高密度测量探头,实现了对窄小裂纹的全覆盖,提高了检测精度;开发了模块化结构的数据采集系统软件,实现了对信号的实时采集与处理;提出了管道周向励磁漏磁检测信号后处理和补偿方法,包括检测信号插值平滑方法、测量奇异点的修正方法、无缺陷漏磁信号的补偿方法以及漏磁信号微分处理方法,解决了由于传感器数量不足带来的缺陷漏磁信号空间采样点过少的缺点,克服了由于周向励磁管壁磁化不均匀,磁极附近的背底磁场过强等对检测造成的不良影响。设计了管道周向励磁漏磁检测实验样机和实验平台,进行管道牵拉实验,分析了牵拉实验采集的缺陷信号样本。实验结果验证了缺陷特征与信号特征的关系。实验结果表明管道周向励磁漏磁检测方法可以检测轴向分布缺陷(例如轴向矩形槽),可识别缺陷的最小深度为10%壁厚,最小周向宽度为3mm。管道周向励磁漏磁检测实验样机和实验平台的成功研制,解决了国内管道漏磁检测无法检测轴向分布缺陷的难题,为管道周向励磁漏磁检测设备的研制确定了技术基础。更多还原

【Abstract】 Pipeline transportation is the primary way of transporting oil-gas resource, and the safety of oil-gas pipeline has become a very important problem related to the national economy and the people’s life. Regular pipeline inspection is the main method to avoid the pipeline accident and ensure the pipeline safety. Magnetic flux leakage (MFL) internal inspection technology is most widely used in many on-line oil-gas pipeline inspections. Concerning the difficult problems of MFL internal inspection combining with the practical inspection demand, after theoretical analysis and analysis on the experiment systems, this dissertation has summarizes the MFL internal inspection technology of pipeline, and has done thorough research into axial MFL and circumferential MFL.After the detailed analysis on the formation mechanism of defect MFL, the theory models of defect MFL field are established. In accordance with the drawbacks in the magnetic dipole model, the finite element model is applied to the analysis on defect MFL.The dissertation analyzes principle of axial MFL inspection in pipelinend MFL signal features. It studies the law for the effect of such affecting factors of MFL signal features as defect geometry parameters (length, width and depth) and the extension direction of the main characteristics of defects. The experimental platform of axial MFL inspection in pipeline is designed, pipeline traction test is implemented, and MFL signal samples are collected and analyzed. The experimental results verify that the axial MFL inspection method can detect the circumferentially orientated defects with good confidence. The circumferentially orientated defects, such as spiral weld, hole, circumferential groove, produce clear MFL signal. Each channel signal measured from different sensors has a very good consistency, stability and relatively high detection accuracy. The axial MFL inspection can identify a minimum depth of defects in 10% of wall thickness, and minimum size of defects in the hole of 2mm diameter. However, the axial MFL inspection method is not ideal for detecting axially aligned defects(such as narrow crack).The dissertation studies principle of circumferential MFL inspection in pipeline, and comparison of the finite element simulation, the magnetizer structure that has the circular geometry of quadrupole separation is proposed which meets engineering design requirements. After the application of magnetic circuit theory, a mathematical modeling of magnetic circuit of magnetizer is established, a magnetic circuit calculation program is developed, the influence of the geometric size of permanent magnets on MFL signal is determined, these provide a method for the magnetizer design. MFL signal features are analyzed, the features of signals are extracted from the recorded flux leakage response and characterizing definition is introduced as well; It is much more difficult to saturate the pipe material in the circumferential direction, which is caused by the circular geometry providing alternative flux paths. The strength of the magnetic field is greatest near the magnetizer poles and smallest at the center, and this non-uniform field makes defect sizing more difficult, for these problems, compensation methods of MFL signal are proposed to eliminate the non-uniform magnetic field. The affecting factors of MFL signal features, such as the distance between the defect and magnetic pole, and defect geometry parameters(length, width and depth), are researched, then get some important law and offer theoretical direction for defect evaluation and defect signal compenstation. By adopting the multiple linear regression theory, the regression equation is established between the defect geometry parameters and the features of MFL signals to implement the quantitative identification of the defect parameters.The circumferential tool measures the MFL signal by using the sensors which are installed between the magnets in parallel, by selected Hall element as the sensor to measure the MFL signal, sensor arrays made up of multiple sensors with samller spacing intervals are constructed, and high-density measurement probe is produced which completely covers the narrow crack thus improves the inspection precision need to ensure axially oriented anomalies were detected efficiently. The data acquisition system software with modular structure is developed so that real-time signal acquisition and processing are achieved. MFL signal processing and compensation methods are implemented, such as detection signal interpolation smoothing method, measuring method of singular points of the amendment, defect-free magnetic flux leakage signal compensation method, as well as differential magnetic flux leakage signal processing method, the disadvantage of too few spatial sampling points caused by insufficient number of sensors is eliminated, the adverse effects on the detection caused by the non-uniform magnetic field in wall and the background magnetic field near the magnetic poles too strong are overcome. It has design the experimental platform of circumferential MFL inspection in pipeline, and has conductsed pipeline traction test, MFL signal samples collected by pipeline traction test are analyzed. The experimental results verify the relationship between the defect geometry parameters and the signal characteristics. The experimental results show that the circumferential MFL inspection method can detect axially aligned defects (such as axially oriented groove). The circumferential MFL inspection can identify a minimum depth of defects in 10% of wall thickness and a minimum width of defects in 3mm. These results and conclusions solve some difficult problems of not detecting axially aligned defects in the field of pipeline MFL inspection, and determine the technical foundation for the development of circumferential MFL inspecting equipment in pipeline.更多还原