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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devices, etc.). Main gas pipelines are often located underground and, hence, are particularly prone to processes occurring in the surrounding soil massive. Therefore, for accurate analysis of the mechanical state of these objects, it is required to take into account the interaction between the gas flow (speed up to 25 m / s), the metal pipe walls and the soil in which the pipeline is immersed. Nowadays there is great interest in the creation of automated systems for monitoring the mechanical state of such objects. The stress-strain state of pipelines is assessed with strain-gauge systems, fiber-optic sensor systems and using magnetic and ultrasonic methods. Main causes of parametric vibrations of pipelines, in particular, the microseismic pipeline vibrations associated with compression station effects were considered by Ishemguzhin I.E. et al. (2011). Panfenov V.I. and Fevralev A.A. (2008), Panfenov V.I.and Panfenov S.V., (2007) evaluated analytically and numerically pressure pulsations as a result of opening the valves, Bochkarev N.N. and Kurochkin A.A. (2012) investigated vibrations caused by the movement of in-line objects, Sultanov R.G et al. (2012), Shen G. et al. (2012) studied the vibration response of the pipeline to gas leaks. For the experimental study of the mechanical state of gas pipelines, various methods were used: Bernasconi G. et al. (2008) used vibration sensors, Jia Z. et al (2015) reports on the use of strain gauges, Lim K. et. Al. (2015) and Bernini R et. Al. (2013) examined the capabilities of fiber-optic sensors; Nam J.Y. et al. (2006) used accelerometers. An analysis of wave and vibration processes that occur during the operation of a gas pipeline provides abundant information for assessing the mechanical state of a pipeline system. These data make it possible to judge about the deformation interaction of the gas pipeline elements, the frequency and energy parameters of disturbances propagating through the gas pipeline, and the reasons that provoke the vibration process. Within the framework of this work, a series of experimental studies of wave vibration processes that arise in a gas pipeline in response to various external factors has been performed. The influence of such factors as impacts on the pipeline and the ground surface in the vicinity of the pipeline, the operation of valves, gas leaks through the fistulas in the pipe was analyzed. The object of the study is a section of an operating main gas pipeline. The length of the observed section is 2800 m, the pipeline is submerged in the ground 2–3 m deep. The pipe is made of steel, its diameter is 1400 mm, and wall thickness is 18.7 mm. Effective gas pressure in the pipe is 60–75 kg/cm 2 . Figure 1 schematically shows an experimental section of the pipeline with two block valve stations. To register vibration processes in the pipeline, a measuring complex developed by the authors was used. It includes a system of one-component accelerometers based on fiber-optic sensors with Bragg gratings, supplemented by equipment for collecting, recording and primary processing of data. Figure 1 shows the locations of the sensors. Sensor characteristics are as follows: frequency range is 5–1500 Hz; acceleration range is up to 4.9 m/s 2 ; sensitivity threshold is 0.001 m/s 2 . The interrogator provides measurements of the optical wavelength in the range of 1528–1562 nm with a sampling frequency of 2500–5000 Hz. At all three points (S1, S2, S3), accelerometers are installed on the upper outer surface of the pipe; they measure the acceleration components along the pipeline axis and normal to the pipe surface. Accelerometers are combined with an optical fiber into a single sensor system. The results of measurements are transmitted via an optical fiber to the system of data collection and processing. Data transfer is carried out automatically in the on-line mode. To process the results of vibration measurements, the mathematical apparatus of Fourier and wavelet analysis is used.

Fig. 1. Diagram of a pipeline section with installed sensors