Enclosed Differential Driver-Pickup Eddy Current Sensor for Internal and External Defect Detection in Reformer Tubes
Journal
IEEE Transactions on Magnetics
ISSN
00189464
Date Issued
2026
Author(s)
Abstract
This paper presents an enclosed differential driver‐pickup eddy current (EC) sensor for detecting internal and external defects in HP‐40 Mod Nb reformer tubes. These tubes are widely used for hot‐gas transport in petrochemical plants and are susceptible to thermal cracking during long‐term operation. Inspection of this alloy is challenging because of its low electrical conductivity and low magnetic permeability. By employing a differential coil configuration, the sensor effectively suppresses environmental noise while significantly enhancing crack detection sensitivity. Finite‐element analysis (FEA) simulations are performed to design sensor geometry and evaluate its performance for external‐defect inspection, while the optimal excitation frequency for internal‐defect detection is also investigated. For experimental validation, a prototype sensor and an automated constant‐velocity rotational scanning platform are developed. High-pass filtering and empirical curve fitting are further employed for defect‐feature extraction and external-defect depth estimation. Experimental results show that the proposed system accurately characterizes external defects deeper than 0.5 mm, with a mean absolute percentage error of 3.03%, while also detecting relatively shallow internal defects under nonideal specimen conditions.
Subjects
defect detection
Eddy current sensor
non-destructive testing
reformer tubes
Publisher
Institute of Electrical and Electronics Engineers Inc.
Type
journal article