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Abstract：
Bimetallic lined pipe (BLP) has been increasingly used in offshore and subsea oil and gas structures, but how to identify the invisible inner defects such as liner wall thinning and interface debonding is a challenge for future development. A nondestructive testing (NDT) method based on pulsed eddy current testing (PECT) has been proposed to face these difficulties. The inspection of the BLP specimen (AISI1020 base tube and SS304 liner) is implemented from outside of the pipe by using a transmitter-receiver-type PECT probe consisting of two induction coils. By simplifying the BLP specimen to stratified conductive plates, the electromagnetic field interaction between the PECT probe and specimen is analytically modeled, and the probe inspection signals due to liner wall thinning and interface debonding are calculated. In order to highlight the weak response (in microvolts) from the liner, the inspection signals are subtracted by the signal, which is calculated in the case of only having a base tube, yielding differential PECT signals. The peak voltage of the differential signal is selected to characterize the liner wall thinning and interface debonding due to its distinguishable and linear variation. Experiment verification is also carried out on a double-walled specimen simulated by a combination of a Q235 casing pipe and SS304 tubes of different sizes. The experimental results basically agree with the analytical predictions. The peak value of the PECT signal has an ascending and descending variation with the increase in the remaining liner wall thickness and debonding gap, respectively, while the negative peak value shows opposite changes. The peak value exhibits a larger sensitivity than the negative peak value. The proposed method shows potential promise in practical applications for the evaluation of the inner defects in BLP lines.
摘要：
双金属衬管（BLP）已越来越多地用于海上和海底油气结构，但是如何识别内衬壁变薄和界面脱粘等不可见的内部缺陷是未来发展的挑战。针对这些困难，提出了一种基于脉冲涡流检测（PECT）的无损检测（NDT）方法。通过使用由两个感应线圈组成的发射器-接收器型PECT探头，从管道外部对BLP样品（AISI1020基管和SS304衬里）进行检查。通过将BLP试样简化为分层导电板，对PECT探头和试样之间的电磁场相互作用进行了分析建模，并计算了由于衬里壁变薄和界面脱粘引起的探头检查信号。为了突出衬垫的弱响应(微伏)，检查信号减去信号，这是在只有基管的情况下计算的，产生差分PECT信号。选择差分信号的峰值电压以表征内衬壁变薄和界面脱粘,这是由于其可区分的和线性的变化。还对由Q235套管和不同尺寸的SS304管组合模拟的双壁试样进行了实验验证。实验结果与分析预测基本吻合。PECT信号的峰值随着剩余衬里壁厚和脱粘间隙的增加而有上升和下降的变化。分别,而负峰值显示相反的变化。峰值表现出比负峰值更大的灵敏度。所提出的方法在评估BLP线路内部缺陷的实际应用中显示出潜在的希望。
