管道周向超声导波EMAT内检测技术研究

IMR OpenIR

	管道周向超声导波EMAT内检测技术研究
	沙高峰
学位类型	硕士
导师	蔡桂喜
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	周向导波电磁超声探头管道内检测器信号处理 Circumferential Guided Wave Electromagnetic Acoustic Transducer Pipeline Inspection Gauge Signal Processing
其他摘要	" 管道无损检测并进而进行完整性评价对油气管线安全运营十分重要，周向导波管道内检测器具有低耗能、高效率、全面扫查等优点，是近年来国内外研究的热点。本文的主要内容是针对周向导波管道内检测器的关键技术进行研究。本文首先讨论了周向超声导波检测技术的基本理论问题，通过对管道中周向SH波的频散曲线、振动位移、模态转换和衰减特性的分析研究，为内检测器的设计和应用奠定了理论基础。电磁超声探头（EMAT）是周向导波管道内检测器的关键部件，本文基于磁路分析模型，提出了一种新型的EMAT结构设计，其主要特点是在周期性排列的永磁铁之间放置非磁性材料片以保持其间距，磁铁顶部放置铁磁性材料片以增强工件中磁感应强度。利用有限元分析软件模拟研究了磁铁间距、导磁片厚度等几何参数对探头性能的影响，最终提出了EMAT设计优化方案。实验结果表明，优化后的新型EMAT可以有效激励出周向SH波，而且优化后的EMAT激励性能明显提高。目前国外管道内检测是采用EMAT收发分离的工作方式，这种工作方式导致检测结果分析难度较大。本文为了便于表征缺陷，设计了发收一体式的EMAT来进行油气管道内检测，其主要特点是接收线圈和激励线圈叠放在一起，且激励线圈更靠近工件。这种EMAT在实际油气管道内检测中具有结构简单、重量轻的优点。由于EMAT的内禀特性是超声的激励和接收换能效率很低，导致检测信号微弱、信噪比低。本文在硬件上设计了带有传输线变压器的激励电路和具有程控放大功能的接收电路，在软件方面采用信号平均技术、带通滤波以及互相关和自相关等信号处理方法对原始信号进行处理。上述软硬件设计使得信噪比明显提高。在上述研究基础之上，本文研制了由管内扫查行走机构、激励电路和接收电路等组成的周向导波管道内检测实验系统，并在12英寸管道上进行实验。实验结果表明，此管道内检测系统可以识别出宽8mm深1mm的凹痕，显示出该内检测实验系统初步具有实用性的检测能力。"; Nondestructive testing and integrity evaluation of long distance oil and gas pipelines are important for their operation safety. A kind of inspection tool, which is well known as PIG, predominates in the field of pipelines NDT. The newly developed PIG based on EMAT which excites and receives ultrasonic circumferential guided wave has a series of advantages: lower energy consumption, high efficiency, ability of overall scanning, etc. Therefore it attracts more attentions. This study focuses on the key techniques of the new PIG. At first, fundamental theory of circumferential guided wave, especially the SH wave, which is tightly related with the technique of new PIG is introduced. It includes solution of wave equation, computation of velocity dispersion curves, and computation of displacement distribution in radial direction in pipe wall. Some important characteristics of the guided wave such as mode conversions and attenuation are also described. A novel EMAT for circumferential SH guided waves is designed based on magnetic circuit analysis in the article. Plastic sheets of proper thickness are located between neighboring magnets to keep the distance between them. A steel plate is put on the tops of all magnets and consequently the magnetic impedance is decreased. Then the dependences of performance of the new EMAT on its geometry parameter, such as plastic sheet thickness, steel plate thickness and so on, are studied by finite element simulation, and finally an optimized design of the EMAT is presented. The experiments show that the excitation performance of the novel EMAT is improved dramatically. The other feature of the novel EMAT is that receiving coil and exciting coil of the same shape are put together, the former contacts the poles of the magnets and overlaps the later. The widely used EMATs must be applied in a set of two independent ones; one is applied for receiving and the other for exciting. The new EMAT has the advantages of simple structure and light weight, so it is fit for pipeline internal inspection. Because of the poor efficiency of EMAT as transducer, its signals are weak and have very strong noise. Therefore high power driving circuit, high sensitivity receiving circuit and digital signal processing are absolutely necessary in order to recognize the echoes from defects. The transmission line transformer is utilized in the driving circuit and gain-programmed amplifier is in the receiving circuit. Signal processing software developed and used in this study includes moving average preprocessing method, bandpass filtering and cross-and-self-correlation detection technique. Experimental NDT on steel pipes of 308mm diameter and 9mm wall thickness is conducted with the system composed of the EMAT, the scanning equipment, the driving circuit, and the receiving circuit. The echo from an artificial defect which is a dent of 8mm width and 1mm depth is clearly recognized. That means the sensitivity of the system approaches the level of PIGs used practically in early years."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64525
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	沙高峰. 管道周向超声导波EMAT内检测技术研究[D]. 北京. 中国科学院金属研究所,2012.