Application Cases

Experiment Name: Damage Detection in Viscous Fluid-Filled Pipelines

Experimental Principle:
An ultrasonic energy pulse is excited by a sensor attached to the pipeline. This pulse propagates along the length of the pipeline and spreads throughout the circumferential direction. When the guided wave encounters a defect during propagation, the incident wave reflects and transmits at the defect location. The same sensor receives both the incident signal and the defect echo signal, allowing the time difference Δt between the received incident wave and the defect echo to be determined. If the propagation velocity C of the guided wave (using Young's modulus velocity) is known, the location of the defect can be estimated.

The position of the defect is determined by the time at which the defect echo signal is received, while the size of the defect is determined by the intensity of the defect echo signal. Larger cracks result in stronger guided wave echoes, enabling quantitative analysis of defect size using the reflection coefficient.

Figure a: Schematic Diagram of the Experimental Setup

First, signal data is generated through computer programming and transmitted to a signal generator via a USB interface to produce the original excitation signal required for the experiment. The signal generator inputs the original excitation signal into a digital oscilloscope through channel 1 (ch1). Simultaneously, the excitation signal is amplified by a power amplifier through channel 2 (ch2) to drive the connected piezoelectric ceramic ring, generating vibrations at the corresponding frequency. This excites ultrasonic guided waves in the pipeline, which propagate along it. Finally, the waves are received by a piezoelectric ceramic strain gauge and input into the digital oscilloscope to form the end-face echo waveform.

The experimental setup for ultrasonic guided wave pipeline detection mainly consists of a signal generator, power amplifier, sensors, digital oscilloscope, and a computer. The test object is a 4-meter-long steel pipe with an outer diameter of 88 mm and a wall thickness of 4 mm. The schematic diagram of the experimental setup is shown in Figure a.

Testing Equipment:
Signal generator, ATA-M4 power amplifier, piezoelectric ceramics, oscilloscope, steel pipe

Figure b: Experimental Test Specimen

Experimental Procedure:
The main research objectives of this experiment are:

1. To study the propagation characteristics of ultrasonic guided waves in viscous fluid-filled pipelines and compare them with those in water-filled and empty pipelines.

2. To investigate ultrasonic guided wave damage detection in viscous fluid-filled pipelines.

Experiments were conducted on the same 4-meter-long steel pipe (outer diameter: 88 mm, wall thickness: 4 mm) under three conditions: filled with engine oil, filled with water, and empty. The experimental steps are as follows:

1. Attach piezoelectric sensors to the pipeline. A piezoelectric ceramic ring with the same cross-section as the pipeline is tightly affixed to the pipe end to excite guided waves. Sixteen piezoelectric ceramic chips of the same specifications are evenly distributed along the outer circumference of the pipeline, 10 mm away from the piezoelectric ring, to receive the guided waves. Additionally, six piezoelectric ceramic chips are evenly distributed along the outer circumference at 25 cm intervals along the length of the pipeline to track and record the guided wave propagation signals.

2. After connecting all experimental instruments, perform tests on the intact empty pipeline. The excitation signal frequency is measured at intervals of 10 kHz, ranging from 100 kHz to 40 kHz, with cycle numbers of 10 and 20.

3. Stand the pipeline upright, fill it with water, and then lay it horizontally to conduct experiments on the intact water-filled pipeline. After the measurements, drain the water from the steel pipe, as shown in Figure 3-2-8.

4. Stand the pipeline upright again, fill it with engine oil, and then lay it horizontally to conduct experiments on the intact oil-filled pipeline.

5. Perform experiments on the oil-filled pipeline with defects. Use a hacksaw to create three types of defects at a distance of 2 meters from the pipe end: a circumferential 1/8 arc, a circumferential 3/16 arc, and a circumferential 1/4 arc. Conduct ultrasonic guided wave detection for each of these defects. Then, drain the engine oil from the pipeline.

6. Perform experiments on the empty pipeline with defects.

7. Perform experiments on the water-filled pipeline with defects.

Experimental Results:
Through ultrasonic guided wave detection on a 4-meter-long oil-filled pipeline without defects, the study analyzed the effects of center frequency and cycle number on guided wave attenuation, signal peak values, and single-mode excitation to determine the optimal center frequency for detecting defects in viscous fluid-filled pipelines using ultrasonic guided waves.

With a fixed cycle number of 10, guided wave signals were excited at frequencies of 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, and 100 kHz, as shown in Figures c to i.

Figure c: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 40 kHz

Figure d: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 50 kHz

Figure e: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 60 kHz

Figure f: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 70 kHz

Figure g: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 80 kHz

Figure h: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 90 kHz

Figure i: Time-Domain Curve of Oil-Filled Pipeline at 10 Cycles and 100 kHz

From the time-domain curves of the guided waves shown in Figures c to i, it can be observed that the guided wave at 10 cycles and 70 kHz exhibits the highest number of end-face echoes (six times), propagates the farthest distance, and excites the fewest modes, making it suitable for ultrasonic guided wave detection in viscous fluid-filled pipelines. As shown in Figure d, the guided wave at 10 cycles and 50 kHz also produces six end-face echoes and propagates a relatively far distance. However, it excites more modes and is therefore unsuitable for ultrasonic guided wave detection in viscous fluid-filled pipelines. When the cycle number is 20, the time-domain signal duration is longer, and waveforms are prone to overlap. After weighing the trade-offs, signals with 10 cycles were selected for the experiments.

The ATA-M4 power amplifier is an ideal single-channel amplifier. It delivers a maximum output of 345 Vrms voltage and 400 VA power, capable of driving 0–100% resistive or non-resistive loads. The output impedance matching offers multiple selectable levels, allowing users to adjust according to testing requirements.

The experimental materials in this article were compiled and released by Xi’an Aigtek Electronics. For more experimental solutions, please continue to follow the Aigtek official website.