Testing of mechanical properties of products is one of the most important production stages because they, most objectively, allow determining whether products manufactured by a certain technological process meet the necessary requirements. Impact strength is the most important parameter in assessing the mechanical characteristics of tubular steel products, impact values at low temperatures are especially important. Brittle fracture is very dangerous, since it proceeds at a high speed and with a load much less than with viscous fracture. This characteristic depends on many factors, including: the number, size and nature of the distribution of non-metallic inclusions, grain size, the presence of reinforcing particles, the uniformity of their distribution, and much more. Impact strength is strictly controlled during testing of pipeline components operating at elevated pressures and freezing temperatures; transition to brittle fracture can provoke disruption of the entire pipeline. The task of determining the causes of a local decrease in impact strength remains relevant due to the many individual factors acting on it, or even a complex of factors. Due to the fact that the probability of a defect contributing to brittle fracture, because of the relatively small crosssectional area of impact samples, is not high, it is necessary to test several samples from the same area of the product to average the results. The aim of this work was to determine the causes of reduced viscosity when testing pipeline components made of 10G2FBY steel by comparing fractures and sample structures with reduced and required impact strengths.