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steel with higher strength and more dispersed microstructure is less susceptible to it

under pre-electrolytic hydrogenation than the 50Г steel with lower strength and

coarse-grained microstructure (coarse-grained pearlite edged by ferrite).

For the first time, the degradation degree of the ferritic-pearlitic 20H2M and

35ХМ steels of sucker rods after their long-term (5.5 years) operation has been

assessed by reducing their corrosion resistance, resistance to stress corrosion

cracking, fatigue and corrosion-fatigue failure at the stages of crack initiation and

crack propagation in model solution of formation water with pH = 3.1.

For the first time, the effectiveness of protection of the operated low-alloyed

20H2M steel in model solution of formation water with pH = 3.1 against corrosion

and corrosion-fatigue failure at the stages of crack initiation and propagation with

environmentally friendly tannin (protection degree of 80-85%) has been revealed. The

correlation between amount of electricity spent for metal oxidation of freshly formed

surface of the 20H2M steel and corrosion-fatigue crack initiation period in this

solution at different tannin concentration has been established. On this basis, the

method for predicting corrosion-fatigue durability of ferritic-pearlite steels in

formation water with addition of inhibitor has been developed.

Intensification of anisotropy of characteristics of resistance to brittle fracture

of rolled pipeline steels by hydrogenation has been revealed using specimens enabled

orientation of the plane of fracture propagation in axial, tangential and radial

directions. It has been established that the tensile deformation energy of the

hydrogenated specimen with a crack before its start in the direction between the

fibres is 60 times less than across the fibres.

Practical significance of the obtained results.

The research results of macrodelamination of pipes of gas transit pipelines

due to operational degradation of pipeline steels were used in Affiliate

“Prykarpattransgaz” for substantiation of the conditions of their possible further

operation. The established regularities of the influence of the conditions of
preliminary electrolytic hydrogenation and loading of specimens on the mechanical

and corrosion-mechanical characteristics of pipeline steels were used for