PSI - Issue 28

I. Shardakov et al. / Procedia Structural Integrity 28 (2020) 1795–1801 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3. Vibration response of the pipeline to impact on the ground: the scheme of the experiment (a); vibrogram (b) and wavelet (c) spectrum of the radial component of acceleration at point 2; attenuation coefficient depending on the distance from the impact point to the sensor (d)

2.3. Vibration response of the pipeline caused by shutoff valves When the shut-off valves operate on the block valve station, a complex mechanical effect on the pipeline occurs, and this leads to equipment vibration and change in gas pressure. The registered pressure jumps reach 3 atm. The response to these influences was recorded by all three accelerometers. Vibrograms of pipeline vibrations and the corresponding wavelet spectra are shown in Figure 4. The dominant vibration frequencies (f * ) decrease with distance from the source of disturbance. So, the S3 sensor closest to the valve station (at a distance of 140 m) registered oscillations with a dominant frequency of 300 Hz, S2 sensor (at a distance of 1510 m) showed a dominant frequency of 200 Hz, and the most distant sensor S1 (at a distance of 2110 m), – dominant frequency of 120 Hz. The above data indicate that vibrations with higher frequencies are attenuated more intensively. This fact is consistent with the results of numerical simulations Tsvetkov R. et al. (2013). The propagation speed of the wave propagating through the gas was ~ 350 m/s. 2.4. Vibration response of the pipe caused by a hole in the pipe The ability to react to gas leaks is an important function of the monitoring system. Gas leaks can occur when a pipe is mechanically damaged, as a result of the formation of holes due to corrosion, as a result of a breach of the tightness of welded seams, etc. In this work, the reaction of a gas pipeline to a sharp opening of a hole in the wall was simulated. During the experiment, a special plate with sequentially opening holes of various diameters was installed in the valve unit P2 (Figure 1). The holes were 2, 4, 6, 8, 10, 20 and 50 mm in diameter. The vibration response of the pipeline was recorded using vibration sensors of the monitoring system. At the same time, sound vibrations of air were recorded near the pipeline. Sound vibrations were registered with the aid of a microphone fitted with an active amplification and sound card, which converts the electrical signal into digital format with a sampling frequency of 44100 Hz. The nearest vibration sensor S3 was located 110m from the gas leak. Sound vibrations were recorded in the immediate vicinity of the hole.