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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Fig. 4. Distribution of magnetic anomalies of the gas pipeline: A and B – increased stress concentration zones in the gas pipeline; intensity of the total magnetic field of the earth and the gas pipeline, measured by the upper Hy1 and lower Hy2 sensors of scanning device

In accordance with the set of rules SP36.13330.2012 “Main gas pipelines”, a stability test under these conditions showed: The maximum total stresses from standard loads and the effects of the temperature difference of open areas and elastic bending are 305 MPa. Allowable effective values of mechanical stresses should be 75% less than the yield strength of the pipe material, i.e. when using steel grade 13G1SU, the permissible stresses are 300 MPa. Consequently, the current values of mechanical stress are higher than permissible, which can lead to the destruction of the gas pipeline. Additionally, the method of calculating the minimum allowable bending radius of the position of the pipelines according to the Ainbinder method by Ainbinder and Kamershtejn (1982) was applied, while the calculated minimum bending radius (r min . denied ) for this section, with a difference in installation and operating temperatures Δ t = 50 ℃ is 891 m (1), with the actual 888 m (Fig. 3). � ���������� � � ∙ � ������� � ∙ �� � ∙ � ���� � � � ������ ∙ � � � ����� ∙ � ∙ � �������� � ������� �� ∙ �� ∙ ��� (1) From the calculation of the minimum bending radius, it can be seen that the bending radius exceeds the minimum allowable. It should be noted here that the temperature difference t, provided that the gas transportation stops for a long time and the outside temperature drops significantly (in some regions, the air temperature can drop to subzero – 65 ° C), increases significantly, respectively, the minimum allowable bend radius of the gas pipeline also increases as described above formula. It is known that regulatory documents binding on the territory of the Russian Federation do not take into account the effects of combined pipe stresses, pipe stresses arising from the natural deformation of permafrost soils and residual stresses from welded pipe joints during installation. Accordingly, it is not rare that the total stress of residual stresses and acting stresses from natural deformations of permafrost soils exceeds the yield strength of the gas pipeline material, which affects the emergence of favorable conditions for the development of corrosion processes. Thus, the stresses in this section of the gas pipeline arising under the presented conditions exceed the standard strength conditions, therefore, dangerous and plastic deformations in the gas pipeline metal can occur. Considering