Application Cases

Experiment Name: Research on Ultrasonic Guided Wave Detection Method for Scaling of Equalizing Electrodes in Converter Valve Cooling Systems

Research Direction: Nondestructive Testing

Experimental Objective:
To investigate the sensitivity of ultrasonic guided wave detection, this study established a detection model for scaling on equalizing electrodes in converter valve cooling systems. The interaction process between acoustic wave signals and scaling of different thicknesses was analyzed in detail. Addressing the complex operational conditions during in-service liquid-filled pipeline detection, guided wave mode identification and signal denoising techniques were studied, establishing a functional relationship between changes in echo signal attenuation, mode conversion, and scaling thickness. Finally, an experimental system for ultrasonic guided wave detection of scaling on equalizing electrodes in converter valves was constructed. Experimental results demonstrated that the online scaling detection accuracy based on L(0,2) ultrasonic guided wave echo characteristics reached 0.1 mm, providing an efficient method for scaling detection on equalizing electrodes in converter valves.

Test Equipment:
Power amplifier ATA-4011, transceiver integrated ultrasonic transducer, excitation probe, preamplifier, arbitrary waveform generator, oscilloscope, etc.

Experimental Procedure:

Figure: Schematic Diagram of Experimental Design

The experimental system was set up, and the arrangement for detecting scaling on equalizing electrodes in converter valve cooling systems is illustrated in the figure above. The dimensions of the bus pipe and equalizing electrodes were consistent with actual data from the Liaoyang converter station cooling system. The inner diameter of the pipe was 54 mm, and the outer diameter was 60 mm, filled with static water. A five-cycle excitation signal modulated by a Hanning window with a center frequency of 150 kHz was imported into an arbitrary waveform signal generator. After amplification by the power amplifier, the signal was applied to an excitation probe positioned at the end of the pipe, exciting the L(0,2) longitudinal ultrasonic guided wave and interacting with the platinum electrode. The received guided wave signal was amplified by the preamplifier and displayed on an oscilloscope. The signal was then extracted to a PC for denoising and mode identification processing.

Figure: Experimental System

To further investigate the effectiveness of the scaling detection method based on longitudinal guided wave echo characteristics, experiments were conducted on actual water pipes. The experimental pipe had an inner diameter of 54 mm, an outer diameter of 60 mm, and was filled with static water. The geometric dimensions and material properties of the experimental pipe were identical to those used in the numerical simulations. A wedge and ultrasonic probe were positioned at the end of the pipe, while the equalizing electrode was placed at the center of the pipe, approximately 300 mm from the probe. The experiment mainly considered nine scaling states of equalizing electrodes with the same dimensions: scaling thicknesses ranging from 0.1 mm to 0.8 mm in 0.1 mm increments, with an unscaled state as the control group.

Experimental Results:

Figure: Echo Signals in the Experiment

The figure above shows the echo signals received for the nine scaling states. The first red circle indicates the main mode L(0,2), and the second red circle indicates the converted mode, consistent with the mode timing and amplitude variation patterns observed in the simulation analysis.

Modal analysis of the echo signals revealed the acoustic wave propagation characteristics during the interaction between longitudinal guided waves and equalizing electrodes with different scaling states. From the echo signals of equalizing electrodes with scaling of different thicknesses, it was observed that the L(0,2) mode and mode conversion signals were sensitive to the thickness of the equalizing electrode, exhibiting specific trends as the thickness varied. Based on the experimental results of the relationship between the amplitudes of the L(0,2) mode and mode conversion signals and scaling thickness, a relationship curve was plotted to further determine the sensitivity and accuracy of ultrasonic guided wave detection for equalizing electrode thickness.

Figure: Analysis Results of Experimental Data

The analysis of experimental results is shown in the figure above. It can be observed that, consistent with the numerical simulation results, the amplitudes of the L(0,2) reflection signal and mode conversion signal decreased as the thickness of scaling on the equalizing electrode increased, with the attenuation magnitude proportional to the thickness. The energy difference between the main mode and converted mode also decreased.

The curve shows a clear distinction between scaled and unscaled conditions. For scaling thicknesses above 0.4 mm, the differences were smaller, indicating that the ultrasonic guided wave detection method performs well for thinner scaling and is suitable for scaling detection on equalizing electrodes in converter station valve cooling systems. The converted mode provides characteristic information about the defect, while the main mode L(0,2) reflection signal and the converted mode component exhibit similar trends. The change in the main mode reflection signal becomes more sensitive as the thickness increases, suggesting that in practical applications, the main mode reflection signal can be directly used for inspection and analysis.

Aigtek ATA-4011C High-Voltage Power Amplifier:

Figure: Specifications of the ATA-4011C High-Voltage Power Amplifier