PSI - Issue 20

Yakov Mikhailovich Andreev et al. / Procedia Structural Integrity 20 (2019) 167–173 Yakov Mikhailovich Andreev et al. / Structural Integrity Procedia 00 (2019) 000–000

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the increase in brittleness of metal with lowering temperatures, which is a frequent and long-lasting phenomenon in the Arctic regions, as well as a long duration of operation, catastrophic destruction of gas pipelines can occur. Observations of failures and accidents of gas pipelines and metal structures operating in the northern regions over a long period of time testify to the facts of their rapid catastrophic destruction. In this case, the main mechanism of destruction is separation - a particularly dangerous indicator of accidents and destruction that occurred Bolshakov and Andreev (2014), Bolshakov and Prokopyev (2016), Bol’shakov and Andreev (2016). Also, in cold climates, the crack formed in new gas pipelines usually stops, and branches out for a long time in operation and leads to a catastrophic, i.e. fragmentation, nature of destruction. 4. Conclusion From an analysis of the works aimed at studying the cold resistance of metal structures operating in low temperature conditions, it follows that the main factors affecting the reliability of main gas pipelines operating at low climatic temperatures in the Subarctic zone of Yakutia are a change in mechanical properties in the direction of decreasing strength and embrittlement of pipe metal when low temperatures together with current and residual stresses. On the example of the considered incident that occurred in the linear part of the main gas pipeline, it is shown that due to the peculiarities of the soils of the regions in the permafrost zone, the probability of loss of operability of gas pipelines sharply increases Bolshakov and Prokopyev (2016), Bolshakov and Andreev (2015). The cold resistance of gas pipeline materials during long-term operation is not sufficiently taken into account in the current regulatory requirements for the construction of gas pipelines in permafrost soils. Basically, the stresses arising in a gas pipeline under non-design conditions are calculated according to the generally accepted laws of building mechanics and do not take into account actual methods of solving problems by Bolshakov and Andreev (2015, 2016) and Oswell J.M. (2011), where the outside temperature is often released to subzero –65 ° С . Based on the analysis of the above problems, for already operating gas pipelines, new solutions are needed to ensure the reliability of gas pipelines in the permafrost zone with a wide temperature difference. In connection with the unprofitability of replacing or repairing gas pipelines based on the results of traditional diagnostics, it is proposed to use new methods and technologies for ensuring the safety of gas pipelines. One of the promising methods for diagnosing «defect-free» gas pipelines is the operational determination of one of the indicators of cold resistance of the material, the determination of changes in the actual yield strength from the duration and operating conditions. In the case of diagnosing gas pipelines with various defects, it is necessary to use new methods of operational non-destructive testing and new ways of calculating the propagation of probable cracks. Based on the tasks, it is proposed to use a new method of non-destructive testing based on acoustic emission control. The proposed method is illustrated in the creation of elastic deformation of the controlled area of the gas pipeline by local cooling of its surface in order to obtain tensile stresses and acoustic impulses from the movement of dislocations at the tops of defects. For example, low-temperature energy is supplied to the middle part of the monitored section as a result of exposure to the surface of the local section of the Dry Ice «CO 2 » dry carbon dioxide pipeline. The occurrence of a temperature gradient in the local zone of the oil and gas pipeline will cause the formation of tensile stresses in the controlled area, which leads to the movement of dislocations at the tops of defects in the welded joint or base metal, while the movements of the dislocations are accompanied by acoustic pulses. By measuring the energy, duration of acoustic pulses and measuring the difference in the time of arrival of acoustic signals to two piezoacoustic transducers, the coordinates of the cross section of the pipeline with defects are determined and their degree of danger is estimated. Moreover, the advantage of using a refrigerant in the form of solid carbon dioxide over other types of refrigerants: safe for human health, fire safety, low evaporation rate, sublimation temperature subzero 72 ℃ . The low-temperature effect will cause an increase in the stress-strain state in it, as a result, elastic deformation of the material will occur, in which dislocations of the boundary zones of defects at the crystalline level begin in the material, which will be accompanied by acoustic impulses. Acknowledgements The reported study was funded by Ministry of Science and Education of Russian Federation, Project III.28.1.1 in the frames of Program for Basic Research of the Siberian Branch of Russian Academy of sciences.