Affiliation:
1. PipeChina Institute of Science and Technology, LangFang, HeBei, P.R. China
2. School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu, P.R. China
Abstract
Local corrosion flaws (LCFs) widely exist in large diameter pipelines (LDPs) (e.g. steam, oil/gas pipeline) due to flow-accelerated corrosion, environmental corrosion, and material aging. Frequency-band-selecting eddy current testing (FBS-ECT), as an improved eddy current technique (ECT), has rich harmonic components in exciting signals as a pulsed eddy current technique (PECT), as well as more effective utilization of electromagnetic energy by selecting a frequency band. It is expected that FBS-ECT has promising applications in detecting and evaluating the LCFs in LDP. Therefore, a solution to the magnetic field of FBS-ECT for LCF detection in LDP is of great concern to reveal the features of the FBS-ECT signal and the parameters of the LCF. Extending our previous work, the semi-analytic expression of the magnetic flux density for FBS-ECT in regions 1 and 2 (where the magnetic sensor is located) is deduced according to the superposition principle and TREE, the computation accuracy is validated by numerical simulation; next, a semi-analytic solution to the magnetic field of FBS-ECT for LCF in LDP is proposed; then, the sampling distance in FBS-ECT is optimized by considering the magnitude of △ Bz and the sensitivity of △ Bz with the LCF depth; finally, a case study is carried out to verify the optimal strategy and find the mapping relationship between the radius/depth and the FBS-ECT signal. The proposed semi-analytic solution for the magnetic field of FBS-ECT is not only helpful to understand the theoretical relationship of the magnetic field and LCFs with higher computation efficiency but also lays a theoretical foundation to promote FBS-ECT to apply in the characterization of other flaws in metal components.
Funder
National Natural Science Foundation of China
Sichuan Science and Technology Program
Science and Technology Research Project of Pipechina
National Key R&D Program of China