A Study of the Automated Eddy Current Detection of Cracks in Steel Plates

Abstract

Applying life estimation approaches to determine in-service life of structures and plan the inspection schedules accordingly are becoming acceptable safety design procedures in aerospace. However, these design systems shall be fed with reliable parameters related to material properties, loading conditions and defect characteristics. In this context, the role of nondestructive (NDT) testing reliability is of high importance in detecting and sizing defects. Eddy current test (ECT) is an electromagnetic NDT method frequently used to inspect tiny surface fatigue cracks in sensitive industries. Owing to the new advances in robotic technologies, there is a trend to integrate the ECT into automated systems to perform NDT inspections more efficiently. In fact, ECT can be effectively automated as to increase the coverage, repeatability and scanning speed. The reliability of ECT scanning, however, should be thoroughly investigated and compared to conventional modes of applications to obtain a better understanding of the advantages and shortcomings related to this technique. In this contribution, a series of manual and automated ECT tests are carried out on a set of samples using a split-D reflection differential surface probe. The study investigates the level of noise recorded in each technique and discuss its dependency on different parameters, such as surface roughness and frequency. Afterwards, a description of the effect of crack orientation on ECT signal amplitude is provided through experimental tests and finite element simulations. Finally, the reliability of each ECT technique is investigated by means of probability of detection (POD) curves. POD parameters are then extracted and compared to examine the effect of scanning index, frequency and automation on detection reliability.

Mechanism study for directivity of TR probe when applying Eddy current testing to ferro-magnetic structural materials

“…Nishimizu [11,12] detected cracks in a non-ferromagnetic material using an arrayed multi-coil probe with two scanning angles and demonstrated that the sensitivity was affected by the two angles. Mohseni [13] investigated the scanning angle for a ferromagnetic material with a split D-probe and found that the signal amplitude varied with the scanning angle. The changing trend for ferromagnetic material is opposite that for non-ferromagnetic material.…”

A probabilistic method for structural integrity assurance based on damage detection structural health monitoring data

“…An eddy current sensor is considered for manual inspection in this study. The POD curve of the eddy current sensor for a crack-like defect is obtained from existing literature for an eddy current sensor by Mohseni et al 36 where its detection capabilities are evaluated experimentally with qualified inspectors and fitted to a logistic function. Though this POD study was done on steel plate structures instead of pipes, it provides a reasonable estimate on the typical detection capabilities of an eddy current sensor.…”

Computation of Eigenvalues and Eigenfunctions in the Solution of Eddy Current Problems

“…What poses a real challenge is the determination of complex eigenvalues when the region under consideration consists of several sub-regions (containing conductive material or air). Such a situation occurs when modeling disks [ 8 , 9 , 10 , 11 ], tubes [ 12 , 13 , 14 , 15 , 16 ], rods [ 17 , 18 ], materials with a defect [ 19 , 20 , 21 , 22 , 23 , 24 ], and wherever there are edges [ 25 , 26 , 27 , 28 , 29 ] or discontinuities [ 30 , 31 , 32 ] ( Figure 1 ). Determination of the eigenvalues then boils down to finding complex roots of the appropriate complex function.…”