PSI - Issue 5

S.V. Panin et al. / Procedia Structural Integrity 5 (2017) 401–408 S.V. Panin/ Structural Integrity Procedia 00 (2017) 000 – 000

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It is shown that the long-term operation does not result in a noticeable redistribution of cementite since during the exploitation the pipes operate at low pressure and low temperatures. However, its hydrogenation can occur which can give rise to decarburization. Deformation aging is poorly expressed and is manifested through the precipitation of finely dispersed carbides in the grain bodies which is responsible for the embrittlement under the impact bending test. The revealed structure degradation exerts little effect on the mechanical properties measured under static tension tests and hardness measurement. The reason is related to the development of two competing processes: i) softening as a result of the decarburization and ii) hardening as a result of pitting dislocations onto carbide precipitates. The fatigue durability of the steel after the long-term operation has decreased by ~ 16 %. It is shown that in the degraded steel the main fatigue crack originates earlier that is associated with the accumulation of structural and mechanical defects in the material and lower ductile. The reason for the latter is governed by the sensitivity to the accumulation of fatigue damages, especially at the stage of fatigue crack initiation. On the other hand, the impact toughness of 09Mn2Si steel after the operation has decreased by the factor of ~ 1.5 at ambient temperature testing. The maximum lost in the impact toughness takes place at T = -70  C which made ~ 2.2 times. Reduction in the crack development resistance under the impact bending is primarily related to the energy consumption decrease governed by the dispersion embrittlement. The latter is accompanied by decreasing the maximum load at which the main crack originates. Thus, it was the impact strength that becomes the most sensitive parameter to the microstructure changes occurred over 37 years of the pipeline operation in the Far North climate conditions. 1. Nykyforchyn, H., Lunarska, E., Tsyrulnyk, O.T., et. al., 2010. Environmentally assisted "in-bulk" steel degradation of long term service gas trunkline. Engineering Failure Analysis 17(3), 624-632. 2. Mil’man , Yu.V., Nykyforchyn, H.M., Hrinkevych, K.E., et. al., 2012. Assessment of the in-service degradation of pipeline steel by destructive and nondestructive methods. Materials Science 47(5), 583-589. 3. Meshkov, Yu.Ya., Shyyan, А .V., Zvirko, О . І ., 2015. Evaluation of the In-service degradation of steels of gas pipelines according to the criterion of mechanical stability. Materials Science 50(6), 830 – 835. 4. Panin, V.E., Derevyagina, L.S., Lebedev, M.P., Syromyatnikova, A.S., et. al. 2016. Scientific foundations of cold embrittlement of structural steels with BCC lattice and their structure degradation under negative temperatures. Phys. Mesomech 19(2), 5-14. 5. Bolshakov, A.M., Zakharova, M.I., 2014. Scientific and Technical bases of risk analysis for petrochemistry objects in the Arctic Zone. Chemical and Petroleum Engineering 50(5), 396 – 401. 6. Bolshakov, A.M., 2012. Methods for analysis of the remaining service life of pipelines and pressure vessels operating at low climatic temperatures. Chemical and Petroleum Engineering 47(11), 766-769. 7. Syromyatnikova, A.S. 2014. Degradation of physical and mechanical condition of the main gas pipeline metal at long operation in the conditions of the cryolitozone. Phys. Mesomech 17, 85-91 (in Russian). 8. Zav'yalov, V.V., Moiseeva, L.S., 2004. Chemical, Hydrodynamic, and metallurgical factors in West Siberian oil pipeline corrosion failure. Chemical and Petroleum Engineering 40(1), 45 – 50. 9. Gabetta, G., Nykyforchyn, H. M., Lunarska, E., et. al., 2008. In-service degradation of gas trunk pipeline X52 steel. Mater. Sci. 44(1), 104 – 119. 10. Nastich, S.Yu., Soya, S.V., Molostov, M.A., Vasiliev, I.S., Dyakonova, N.B., 2012. Effect of temperature for the start of finish rolling on coiled steel X70 microstructure and cold resistance. Metallurgist 56(7), 519 – 525. 11. Nykyforchyn, H., Lunarska, E., Tsyrulnyk, O., Nikiforov, K. and Gabetta, G. (2009), Effect of the long-term service of the gas pipeline on the properties of the ferrite – pearlite steel, Materials and Corrosion, 60: 716 – 725. 12 . Tsyrul’nyk, O. T., Nykyforchyn, H.M., Petryna, D.Yu., Hredil, M.I., Dz’oba , I.M. 2007. Hydrogen degradation of steels in gas mains after long periods of operation. Materials Science 43(5), 708 – 717. 13. Maruschak, P., Bishchak, R., Prentkovskis, O., Poberezhnyi, L., Danyliuk, I., Garbinčius , G., 2016. Peculiarities of the static and dynamic failure mechanism of long-term exploited gas pipeline steel. Advances in Mechanical Engineering 8(4), 1-8. Acknowledgements The study was conducted under support from Fundamental Research Program of Russian State Academies of Sciences for 2013 – 2020, RFBR projects No 15-08-05818 as well as grants of the Headquarter of the Russian Academy of Sciences on Arctic research. References