Conformable Eddy-Current Sensors and Arrays for Fleetwide Gas Turbine Component Quality Assessment

Abstract

The conformable Meandering Winding Magnetometer (MWM®) eddy current sensors and MWM-arrays provide new inspection capabilities for gas turbine components. The sensors provide measurements of coating thickness and absolute electrical conductivity, which can capture features of interest for a population of components, e.g., for tracking fleetwide trends in quality and aging, failure evaluations, and correlating failure origins to features of specific fleet population segments. Inspection applications include metallic and nonmetallic coating thickness and porosity measurement, detection of cracks on complex surfaces, imaging and detection of small flaws, thermal degradation monitoring, and cold work quality assessment. For example, the U.S. Air Force uses the MWM for cold work quality control on all of the C-130 propeller blades that go through the Warner Robins ALC. For P-3 and C-130 propeller blades, trend analysis is being performed fleetwide. This paper describes MWM technology advances for absolute property measurements and specific capability demonstrations. Multifrequency quantitative inversion methods used for coating characterization are also used for characterization of process-affected zones, such as shot peen quality or titanium alpha case characterization.

Multi-channel transimpedance measurement of a planar electromagnetic sensor array

“…It can be seen from table 2 that the amplitude and phase of transimpedance will decrease when the sensor array is placed on an aluminum specimen; this is because the conductivity is increased and the lift-off is shortened, which is explained in reference [8]. However, the change in channel 1 is smaller than that in other channels, which can be seen more obviously from two characteristic parameters listed in table 3, in which the amplitude ratio is the amplitude in table 1 divided by the amplitude of the corresponding channel in table 2, and the phase difference is the phase in table 1 minus the phase of the corresponding channel in table 2.…”

“…The arrayed eddy current technique is a new electromagnetic non-destructive testing (NDT) method developed in recent years, which has wide foreground applications in damage detection and the evaluation of metal structures [1][2][3][4][5]. Compared with traditional eddy current arrays, such as pulsed eddy current arrays and eddy current pulsed thermography, planar electromagnetic sensor arrays have advantages such as nice coherence, fast response speed and high sensitivity, which can be used for micro damage inspection of crucial parts in equipment, such as aircraft and rotorcraft structural components and high-temperature components in power plants [6][7][8].…”

Flexible eddy current sensor array for proximity sensing

“…At present, the eddy current sensor array has found a lot of applications in industry [5][6][7][8], such as the crack detection of welds in offshore industry [9], monitoring of the corrosion and fatigue in aging aircraft and pipelines [10][11][12][13], the nondestructive testing of tubes in steam generator or gas turbine [14][15][16][17]. And as the geometries of the measured objects become more and more complex, flexible eddy current arrays with the coils fabricated on thin flexible substrate are also introduced for its excellent conformability to curved surfaces [1,13,14,16]. Most of the eddy current arrays referred above are used for nondestructive testing, but nearly for proximity sensing.…”

<title>Shaped-field eddy-current sensors and arrays</title>

“…When scanned across a component such as an aircraft skin, an image of either the absolute electrical conductivity or thickness of a skin is obtained using pre-computed databases of sensor responses for the range of anticipated electrical conductivity or skin thickness. These scanning arrays have also been used to map crack locations, hidden corrosion, and residual stresses in steels [6][7][8]. In a third application, the use of shaped-field drive windings with giant magnetoresistive (GMR) sensing elements are described for the detection of deeply hidden flaws.…”