Pulse-modulation eddy current probes for imaging of external corrosion in nonmagnetic pipes

• Published in: NDT & E international : independent nondestructive testing and evaluation Vol. 88; pp. 51 - 58
• Main Authors: Li, Yong, Yan, Bei, Li, Wenjia, Jing, Haoqing, Chen, Zhenmao, Li, Da
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2017
• Subjects: Corrosion imaging; Electromagnetic non-destructive evaluation; Pulse-modulation eddy current technique; Sensitivity analysis; Tubular conductor; Pulse-modulation eddy current technique; Tubular conductor; Corrosion imaging; Sensitivity analysis; Electromagnetic non-destructive evaluation
• ISSN: 0963-8695; 1879-1174
• DOI: 10.1016/j.ndteint.2017.02.009

Since the nonmagnetic pipe is normally utilized in corrosive and hostile environment, it is prone to the external corrosion which occurs on the outer surface of the pipe and severely undermines the structural integrity and safety. Although Pulsed Eddy Current technique (PEC) is currently preferred for detection and evaluation of subsurface defects in tubular conductors, it is subject to technical drawbacks. In light of this, Pulse-modulation Eddy Current technique (PMEC) is intensively investigated in the paper for enhancement of the evaluation sensitivity to external corrosion and accuracy of corrosion imaging. Closed-form expressions of the PMEC response and its sensitivity to external corrosion in tubular conductors are formulated via the Extended Truncated Region Eigenfunction Expansion (ETREE) modeling. Following simulations for analysis and comparison of field signals and evaluation sensitivities of PMEC and PEC, experiments of PMEC for evaluation and imaging of external corrosion are carried out. Through theoretical and experimental investigation, it has been found that regarding the evaluation and imaging of external corrosion in nonmagnetic pipes, the PMEC-based probe have higher sensitivity and imaging accuracy than that based on PEC. The superiority of PMEC to PEC in inspection of tubular conductors is further identified. •Pulse-modulation eddy current probes for inspection of tubular conductors are investigated.•Analytical model of the pulse-modulation eddy current probe is established.•Signal characteristics and sensitivity to external corrosion of the probe are analyzed.•The proposed probe has higher sensitivity and accuracy in external-corrosion imaging.