Page 13 - Дисертація ГРЕДІЛЬ_ФМІ

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4. A methodology for investigating the influence of gaseous hydrogen on

the pipe steel interaction with corrosive-hydrogenating environments, which

simulates conditions of hydrogen transportation through pipelines, has been

proposed and scientifically substantiated. The reduction in corrosion resistance

and enhanced susceptibility to hydrogen-assisted cracking of steel under

conditions of hydrogen bubbling have been detected, which is associated with its

intensified absorption into the metal.
5. The anisotropy of corrosion resistance has been revealed for the first time

for reinforcing cold-drawn pearlite wires: polarisation resistance of their side

surface in 3% NaCl is 1.7 times higher compared to the cross-section.
6. The fracture mechanism for the reinforcing wires at the intermediate

stages of the 7-stage cold drawing process under the influence of corrosion-

hydrogen environment has been established for the first time. At the first three

stages of cold drawing, the crack is initiated from the side surface and gradually

propagates through the wire cross-section, and at the later stages, another crack

origin appears in the centre of the wire due to residual tensile stresses, with further

coalescence of two crack paths.
7. A mechanism of crack closure formation under the action of tannin,

which consists in its interaction with the freshly formed crack edge surfaces due
to fretting, and accumulation of solid interaction products in the crack cavity. This

causes crack arrest in a wide range of stress intensity factor values.

Practical significance of the obtained results

1. A method of accelerated degradation of steels is modified taking into

account the damage development, which has been used by SD “Galremenergo”

PJSC “DTEC Zahidenergo” for predicting the actual technical state of steels of

various long-term operated objects in the energy sector and substantiating the

conclusions on the prospects of prolongation of their further operation.

2. Testing conditions for low-strength rolled steels have been systematised,

which, in conjunction, enhance the sensitivity in assessing their resistance to

hydrogen embrittlement: preliminary hydrogen charging under a substantiated