Kavitha Arunachalam

Steam generators (SGs) used in power plants have several hundreds of ferromagnetic SG tubes which are periodically inspected using non-destructive testing (NDT) methods. Pre-service and in-service inspections of these magnetic tubes are carried out using RFEC technique for plant safety and structural integrity. In this paper, a 3D numerical model was developed for SG tube inspection using remote field eddy current (RFEC) technique. The numerical model was used to estimate the electrical properties of the SG tube using RFEC signals gathered from a SG tube with machined defects. The influence of magnetic coupling between the surrounding SG tubes on defect detection was investigated for the estimated SG tube electrical properties. Simulations in the presence of six neighbouring SG tubes were carried out for centre to centre tube spacing of 32.2 mm with respect to the centre tube. Numerical simulations for the SG tube with machined defects indicated very good agreement with measurements for tube electrical conductivity σ of 2 MS/m and relative magnetic permeability μr of 30. Numerical simulations carried out to study the influence of magnetic coupling with the surrounding SG tubes indicated negligibly small perturbation in the simulated RFEC signal for a 2D groove defect in the centre tube and no false call in the centre tube for a 2D grove defect in the neighbouring tube.

Eddy current (EC) methods of nondestructive evaluation are used extensively in steam generator tube inspection in nuclear power plants. With advances in technology, new sensor designs are being proposed for improving data acquisition and defect detection. Limitations associated with manual analysis of the large volume of EC data have led to the development of automated data analysis. In this paper, we present statistical models for automated analysis of the complex array probe data. The EC data is modeled as independent random ariables with identical distribution and the statistical parameters of the two class problem are estimated using Maximum Likelihood (ML) method. Defect identification in the noisy EC data is assessed using minimum error rate (MER) detection rule. Receiver operating characteristics (ROC) generated for in-service steam generator tubes are used to assess the model performance. © 2012 The authors and IOS Press. All rights reserved.

The focal plane characterization of spot focusing horn antennas used for microwave NDE is presented using three experimental methods. Reflections from a metal sphere were analyzed in time domain to quantify the focal spot and spot size in the first method. In the second method, a rectangular waveguide padded with absorber was used as the sensor. Finally, graphene based miniaturized electric (E)-field sensor printed on photo paper using inkjet printing was used to measure antenna focal plane characteristics. The focal plane measured using the metal ball and waveguide techniques was within 5% of the simulated value. Higher error was recorded in focal spot measurement (≥25%) for the first two methods. The focal plane and spot size measured by the miniaturized E-field sensor was within 10% of the simulated antenna characteristics. The results indicate that the flexible printed sensor has better measurement accuracy and simple setup for field measurement.

Real-time monitoring and detection of partial discharges (PDs) inside gas insulation transmission lines (GITLs) are necessary to avoid complete breakdown of insulation. Understanding PD signal propagation through GITLs provides insight on the PD signals. GITLs are of length several kilometres, and so, studying PD characteristics on real GITL is expensive and time consuming. A simulation environment is a better alternative in which the entire GITL can be modelled for design and analysis. But high computational resources are required for simulation. So, a hybrid modelling technique is proposed to simulate PD propagation in GITL with reduced computational burden. Numerical modelling is studied for Corona PD signal propagation through straight and L sections of a GITL. The time and frequency domain characteristics of the PD signal after propagation through straight and L sections of GITL were used to compare model results with measurements. The pulse width of Corona PD signal through a 1 m long straight GITL was estimated to be 3.4 ns as compared with measured pulse width 4.4 ns with spectrum content of 0.5 to 4 GHz. The pulse width of measured and modelled Corona PD signal after propagation through a 3 m long L-GITL was 2.7 and 2.8 ns, respectively, and bandwidth spanned over 0.5 to 3 GHz.

In this work, a linear eight element array of electric field sensors is realized for non-destructive testing of dielectric composite widely used in aerospace, medical, and automotive fields. An electrically short dipole antenna array was printed on photo paper using silver conductive ink, and the antenna transmission line was printed using polymer-based resistive ink. A zero bias Schottky diode was employed as the RF detector, and the output voltage was fed to a micro-volt meter. Planar dielectric composite sample of 3 mm thickness was illuminated by an X band (8–12 GHz) spot focusing horn antenna. An FR-4 sample of size 300 mm × 300 mm with a defect diameter of 20 mm was tested with this setup. First, the response from a defect free calibration sample is taken. Then, the measurement is carried out on the defective sample. The sensor array was used to map the electric field strength in defect free and defective regions of the sample.

The feasibility of non-contact and non-destructive evaluation (NDE) of planar aerospace dielectric composites using microwave is examined in this paper. Free space microwave measurement set up includes spot focusing horns to gather the scattering parameters of the composites with the help of (Gated-thru reflect line) G-TRL calibration. The dielectric properties are studied from the measured scattering parameters to characterize the material's defective and non-defective region. Particulate reinforced composite with an air gap of 0.1 mm thickness and 10 mm width is used for validation of the technique.