【作者】 郝芸；

【导师】 金宁德；

【作者基本信息】 天津大学 ， 控制理论与控制工程， 2004， 硕士

【摘要】 本文针对油井套管最常见的井径异常和裂缝缺陷,利用涡流无损检测技术,将一个载有交变电流的检测线圈探入套管,套管的井径异常和裂缝直接表现为与检测线圈距离的变化。在测量系统参数固定的条件下,线圈阻抗与这个距离呈单值对应关系,在满足场论向路论转换的条件下,推导出了引起线圈交流阻抗变化的理论公式。通过理论计算曲线可以得出:井径的变化与线圈输出阻抗在一定范围内呈线性关系,并且对裂缝的检测有较高的灵敏度;测量时应注意选取发射线圈尺寸,发射线圈尺寸大,线性范围增加,但灵敏度降低,灵敏度与线性范围相互矛盾;发射线圈尺寸相同时,井径越小,测量裂缝越灵敏。利用发射线圈与电容并联的谐振调幅电路,将线圈阻抗变化转换成电压的输出。文中对井径、裂缝长度与厚度、发射探头激励频率、套管磁导率、探头偏心等因素对测量结果的影响作了理论分析,为套管缺陷检测提供了定量解释理论依据。更多还原

【Abstract】 This paper gives an eddy current inspection method for the most common defects occurring in oil pipe casing ,which are known as diameter abnormity and crack. The detection coil carrying alternating current were lowered into pipe and the diameter abnormity and crack were directly represented by the changes in distance between the defect and the detection coil. Under condition that the measurement system parameters were fixed, the alternating current coil impedance is corresponding to such distance in monotropy. Based on the assumption that the field theory can be converted to circuit theory, a theoretic formula representing the change in alternating current impedance of the coil was derived. It is shown that there is a linear relationship between the change in pipe diameter and coil impedance within a certain range by the theoretic calculation, in addition, the coil impedance is sensitive to the crack of casing. When measuring, the size of emitting coil shall be carefully selected in order to match the pipe diameter. The linear range is increased with the increase of emitting coil size, but the sensitivity will be decreased, exhibiting a contradiction between the sensitivity and the linear range; If the size of emitting coil keeps unchanged, the sensitivity of casing crack measurement is increased with the decrease in pipe diameter. The emitting coil and capacitance are connected in parallel and form a resonant amplitude-modulation circuit,which converts the impedance into output voltage. The influence factors are analyzed on the measurement such as pipe diameter, length of casing crack and thickness, excitation frequency of emitting coil, casing magnetic conductivity and emitting coil eccentricity , etc. it provids a theoretic foundation for the quantitative interpretation of casing inspection.更多还原