PSI - Issue 28

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

1800

6

Figure 5c shows the wavelet spectra of accelerations recorded by the S3 accelerometer closest to the hole. On the wavelet diagram, one can see the moments of opening and closing the hole – 8 sec and 53 sec, which corresponds to the excitation of short-term oscillations of the pipe with frequencies of 800 Hz and 1100 Hz, respectively. At the same time, the diagram contains a long-lived signal with a frequency of 270-280 Hz, which is excited during the entire interval of the gas outflow. These oscillations decay quickly, and the more distant sensors S1 and S2 did not register them. When gas was discharged through holes of a smaller diameter, similar vibration processes were observed, but their intensity was less. Table 1 shows the parameters of vibration signals recorded by the S3 accelerometer during the gas outflow through the holes of various diameters. At the initial moment of gas outflow, pipe vibrations can be detected if the hole diameter is at least 10 mm. In the steady state of gas outflow, vibrations are recorded if the hole diameter is at least 50 mm. Remote sensors S1 and S2 did not detect gas leakage through holes of any diameter.

Table 1. Parameters of the vibration response to a gas outflow through holes of various diameters Hole diameter, mm Max. acceleration amplitude when opening the hole, mm/s 2 Max. amplitude in the frequency range260-300 Hz, mm/s 2

Max. amplitude in the frequency range 700-1200 Hz, mm/s 2 4,6 (4 times the noise level) 1,9 (2 times the noise level)

50 20 10

5,5 3,6

1,9 (5.5 times the noise level) 1,9 (5.5 times the noise level) 0,7 (2 times the noise level)

noise noise

noise noise

< 8

noise

3. Conclusion On the basis of the experimental results, we came to following conclusions regarding the nature of vibration processes that occur in the pipeline under external shock effects and the appearance of leaks.  • External impact loads applied to the pipe walls or ground surface generate vibrations in the local region near the impact site. The frequencies of vibrations reach 1000 Hz and decay quickly due to dissipation of energy into the ground. At the impact on the ground with a striking energy of 320 J, the size of the sensitivity zone of the accelerometer is about 60 m.  The low-frequency (frequency range 1000 Hz) oscillations from shut-off valves propagate over a distance of up to 2 km and can be detected by the accelerometers located on the pipe surface. The occurrence of such oscillations is due to the acoustic conductivity of gas.  The gas leaking through the holes of 2 mm to 50 mm in diameter causes the pipe walls to vibrate in the frequency range from 800 Hz to 8000 Hz. The strength of vibrations depends on the hole size and can be recorded at a maximum distance of 100 m from the hole. Gathering information and its assessment carried out in our research may help to develop new automated monitoring systems for gas pipelines. In addition, our results can be used to evaluate primary sensor parameters, to determine an optimal distance between these sensors, and to identify external load parameters. The data obtained can be used to verify the available mathematical models describing vibration processes in gas pipelines. References Ishemguzhin I.E. et al., 2011. Damping parametric vibrations of the pipeline. Oil and Gas Business 3, 84-95. Panfenov V.I., Fevralev A.A., 2008. Numerical simulation of the transitional processes in the gas pipelines. Vestnik Yuzhno-Ural'skogo Gosudarstvennogo Universiteta. Seriya Stroitel’stvo i arkhitektura 25, 40-44. Panfenov V.I., Panfenov S.V., 2007. Modeling of unsteady processes in gas pipelines // Vestnik Yuzhno-Ural'skogo Gosudarstvennogo Universiteta 14, 44-47. Bochkarev N.N., Kurochkin A.A., 2012. Vibrodiagnostic motion control of intratubal objects in gas pipeline. Oil and Gas Business 5, 86-98. Sultanov R.G., Urazov R.R., Mugafarov M.F., 2012. About the rise of accuracy of the pipeline damage location. Oil and Gas Business 3, 128-135. Shen G, Qin X, He R., Xiu C., 2012. Theoretical analysis and experimental study of gas pipeline leak acoustic emission signal transmit speed. International Conference on Acoustic Emission University of Granada, 12-15 Sept. 2012. Bernasconi G., Giunta G., Chiappa F., 2015. Gas filled pipelines monitoring using multipoint vibroacoustic sensingProceedings of the ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. St. John's, Newfoundland, Canada, OMAE2015-41265.