Effect of Operating Degradation in Arctic Conditions on Physical and Mechanical Properties of 09Mn2Si Pipeline Steel

The structure and mechanical properties of 09Mn2Si steel of the main pipeline “Kysyl-Syr-Mustakh-Yakutsk” cut out from a linear part fragment of the pipe with the outer diameter of 530 mm and a wall thickness of 7 mm at the region “Berge-Yakutsk” after 37 years of operation were investigated. It was revealed that values of the basic mechanical properties of the steel have not changed as compared with the emergency reserve one. In doing so the impact toughness was shown to be the most sensitive parameter indicating the degradation processes development. At testing temperature of 20 °C it has decreased by 1.48 times whereas at T = -70 °C by 2.42 times. One of the main reasons of the steel degradation is the strain aging which gives rise to the dislocation structure and microstructure modification that substantially impairs its resistance to brittle fracture. A scheme to characterize mechanical properties degradation of the 09Mn2Si steel in the structural state under investigation is suggested.