**4. Conclusions**

The effect the corrosive environment produces on the structure, elemental composition, mechanical properties and the impact toughness of the pipe steel have been studied. The XRD analysis, optical spectrometry and uniaxial tension tests revealed that the corrosion environment affects the parameters of the inner and outer surfaces of the steel specimens as well as the steel pipeline bulk.

In the initial state, on the inner surface of the specimens H content was 0.00062 wt.%, whereas after exposure to the corrosive heating environment it reached 0.00086 wt.%. That indicated hydrogen permeation in the steel during the experiment. Hydrogen accumulation resulted in steel embrittlement proven by the mechanical tests.

**Author Contributions:** A.I.T. conceived the paper; all the authors contributed to the data collection, analysis and comments; all authors wrote the paper.

**Funding:** This work was carried out within the framework of the Competitiveness Enhancement Program of National Research Tomsk Polytechnic University (VIU-OEF-66/2019).

**Conflicts of Interest:** The authors declare no conflict of interest.
