Page 41 - Автореферат Греділь М.І.

39

ABSTRACT

Hredil М. І. Scientific and methodological approaches to assessing the
impact of corrosion and hydrogen factors on operational damage of carbon and
low-alloy steels. – Manuscript.
Thesis for the Doctor’s degree in Engineering Sciences by speciality 05.17.14 –
Chemical resistance of materials and corrosion protection. – Karpenko Physico-
Mechanical Institute of the National Academy of Sciences of Ukraine, Lviv, 2025.

The dissertation addresses a significant scientific and technical problem: evaluat-
ing the mechanisms and regularities of corrosion-hydrogen fracture of carbon and low-
alloy steels caused by operational damage, and developing methods for its assessment,
prediction, and enhancement of fracture resistance.
A methodology for investigating the influence of gaseous hydrogen on the pipe
steel interaction with corrosive-hydrogenating environments, which simulates the action
of corrosion and hydrogen factors under hydrogen transportation through pipelines, has
been proposed and scientifically substantiated. It implies determining the corrosion
resistance of steel in the model gas condensate under conditions of its bubbling by
hydrogen generated in the electrochemical cell by water electrolysis. The revealed

intensification of corrosion and hydrogenation of steel under the above conditions
indicates a need for strict control of the transported gas humidity.
The mechanism of damage development in low-strength pipe steels during their
operation under the combined action of hydrogen and working stresses has been
disclosed, which consists in weakening adhesion between nonmetallic inclusions and
the matrix by hydrogen, with their further delamination and deformation-driven growth
and coalescence of pores due to rising hydrogen pressure inside them. The damage
development is considered the crucial factor in reducing the resistance of the operated

pipe steels to stress corrosion cracking.
A semi-field method has been developed for assessing hydrogen embrittlement of
carbon steels of thin-walled gas distribution pipelines. The method implies prolonged
exposure of specimens to hydrogen gas under pressure in a pipe at a test stand,
subjected to climatic temperature variations close to operational ones. Its
implementation results in a significant increase in hydrogen concentration in steel
specimens and a decrease in fracture toughness of the operated metal, especially the
welded joint. The conditions for enhancing the sensitivity in assessing hydrogen
embrittlement of low-strength pipe steels have been systematised: (i) preliminary
hydrogen charging, (ii) specimen cutting transversally to the pipe axis, (iii) using thin

plane tensile specimens. The methodological approach to the transversal specimen
preparation from thin-walled pipes has been introduced.
A corrosion-mechanical technique has been developed for fatigue crack arrest in
structural steels in a wide range of stress intensity factor values. It is based on the
interaction of the active component of the technological environment (tannin) with
crack edges under fretting conditions, which leads to filling the crack cavity with the
solid interaction products and thus producing artificial crack closure.