Cent. Eur. J. Eng. • 4(4) • 2014 • 408-415 DOI: 10.2478/s13531-013-0178-6 Central European Journal of Engineering Low temperature impact toughness of the main gas pipeline steel after long-term degradation Research Article Pavlo O. Maruschak 1 ∗ , Iryna M. Danyliuk 1 , Roman T. Bishchak 2 , Tomaž Vuherer 3 1 Ternopil Ivan Pul’uj National Technical University, 46001, Ruska 56, Ukraine 2 Ivano-Frankivsk National Technical University of Oil and Gas, 76019, Karpatska 15, Ukraine 3 University of Maribor, Smetanova 17, SI-2000, Slovenia Received 26 March 2014; accepted 28 July 2014 Abstract: The correlation of microstructure, temperature and Charpy V-notch impact properties of a steel 17G1S pipeline steel was investigated in this study. Within the concept of physical mesomechanics, the dynamic failure of specimens is represented as a successive process of the loss of shear stability, which takes place at different structural/scale levels of the material. Characteristic stages are analyzed for various modes of failure, moreover, typical levels of loading and oscillation periods, etc. are determined. Relations between low temperature derived through this test, microstructures and Charpy (V-notch) toughness test results are also discussed in this paper. Keywords: impact toughness • fracture • damage • gas pipeline • steel • degradation © Versita sp. z o.o. 1. Introduction A significant part of the main gas pipelines of Ukraine have been in operation for a long time, therefore, a comprehensive study of the structural and mechanical degradation and the factors leading to it is very topical now [1, 2]. The operating conditions of such structures are characterized by the effect of the external force factors (loading, temperature, medium, etc.), which periodically vary with time, degradation of the physical and mechanical properties of metal with time, nucleation and propagation of defects in them [3, 4]. These factors are crucial to the assessment of the ultimate state and predicting ∗ E-mail: Maruschak.tu.edu@gmail.com the residual life of the structural elements with defects (cracks). In previous works, the form and nature of the occurrence of pitting and other concentrators were investigated, which were caused by the imperfect electrochemical protection, negligence in the process of construction or repair. Another type of damage is the corrosive cracking under loading, which is caused by simultaneous effect of the corrosive medium and tensile stresses [5, 6]. As a rule, this type of damage occurs on the external surface of the gas pipeline and has a form of multiple cracks oriented along the pipe. It is these defects that can be stress concentrators causing unpredictable failure of the film-insulated gas pipeline with diameter of 1020-1420 m [7]. The most objective investigation of the properties of pipes of the main pipelines is their full-scale pneumatic field testing. However, due to its high cost and laboriousness 408