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operation is the change of intergranular fracture facets from single and separate to

their conglomerates which surrounded from 2 to 7 grains against the background of

intergranular fatigue relief of the specimens after fatigue crack growth testing.

8. A new methodology of the estimation of the structural-mechanical state of

structural steels after their long-term operation in various structural elements under

ambient and high temperature has been elaborated and approved. It is based on the

obtained relationships between mechanical and metallographic (or fractographic

S / S) parameters sensitive to steel operational degradation. The loss in brittle
crit
fracture resistance (KCV expl / KCV , the critical value is 0.23) was used as the
in
mechanical indicator of steel degradation under ambient conditions, and, in the case

of high-temperature conditions, hardness and the relative change in the effective

threshold of fatigue crack growth resistance (ΔK expl th eff / ΔK in th eff , the critical value is

0.58 for blades of steam turbines and 0.3 for steam pipelines) were used.

Practical significance of the obtained results. Recommendations have been

developed for the administration of «Ukrzakhidnaftohazservis» regarding the

replacement of oil pipeline sections where welded joints are situated in the zone of a

contact with residual water and bottom precipitations, which facilitated stress

corrosion cracking of pipes on the internal surface and damage occurrence in the pipe

cross-section.
Basing on the fractographic research of operational fracture surfaces of steam

turbine rotor blades, the reasons of their premature fatigue fracture has been
established and the regularities of changes in the threshold values of fatigue crack

growth resistance for operated steels with high chromium content depending on the
changes of their structural-mechanical state during operation, which was used by a

number of TPPs for the substantiation of a periodicity of the rotor control and

ensuring of their safe service.

The built relationships between mechanical properties and structural and

fractographic indicators, sensitive to the changes of the technical state heat-resistant

steels of steam pipelines were used on TPPs for the assessment of their degradation

degree caused by creep and shut-downs of the technological process, and for the