Pipe strings are critical facilities for well drilling, production, and transportation in oil and gas industry. Due to the stress corrosion cracking, longitudinal cracks are the most common defects on pipe strings. This paper presents a simple two-step interpolation algorithm based on a circumferential current field testing method for the measurement of longitudinal cracks on pipe strings. The theory and finite element method model of the circumferential current field testing method are analyzed. The two-step interpolation algorithm fitted by characteristic signals obtained from simulations is proposed to size longitudinal cracks. The first-step is to measure and calibrate the crack length by a quadratic polynomial interpolation formula and the second-step is to measure the crack depth by a cubic polynomial interpolation formula. Experiments are conducted to verify the efficacy of the proposed two-step interpolation algorithm based on the circumferential current field testing system. The results suggest that the two-step interpolation algorithm can obtain the length and depth information of longitudinal cracks effectively on pipe strings using the circumferential current field testing system.

中文翻译：

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周向电流场测试系统测量管柱纵向裂纹的两步插值算法


管柱是石油天然气工业钻井、生产、运输的关键设施。由于应力腐蚀开裂，纵向裂纹是管柱上最常见的缺陷。本文提出了一种基于周向电流场测试方法的简单两步插值算法，用于管柱纵向裂纹的测量。分析了环向电流场测试方法的理论和有限元方法模型。提出了根据模拟获得的特征信号拟合的两步插值算法来确定纵向裂纹的尺寸。第一步是通过二次多项式插值公式测量和校准裂纹长度，第二步是通过三次多项式插值公式测量裂纹深度。基于周向电流场测试系统进行实验验证所提出的两步插值算法的有效性。研究结果表明，利用环向电流现场测试系统，两步插值算法能够有效地获取管柱纵向裂纹的长度和深度信息。