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diagnostics of technical condition of steels of a number of long-term operated critical
structures.
A negative role of several operational factors (cyclic compressive loading, marine
atmosphere, moisture condensation due to fluctuations in ambient temperature) in degra-
dation of carbon and low-alloyed structural steels has been established.
For ferrite-pearlite pipeline steels a known stage of their in-service degradation,
namely, development of dissipated damaging, is divided into two periods, basing on re-
search results: formation of chaotically oriented defects and formation of lamination
cracks oriented in rolling direction.
Mechanism of ferrite-pearlite pipeline steels embrittlement under operation
consisted in carbon compounds enrichment not only grain boundaries, but also
intragranular defects boundaries, has been revealed, as it is indicated by an electrochemi-
cally determined increase of carbon content on transgranular fracture surfaces.
The method of conservative estimation of degradation of structural steels ope-
rated in corrosion-hydrogenating environments has been developed. The method is
based on modification of regulated limit values of impact toughness for as-received and
operated metal conditions separately. The method considers sensitivity of operated
metal to stress corrosion cracking and indicates limitation of regulating the same limit
value of impact toughness for metal in different condition, namely, as-received metal
and operated one.
Mechanical approaches to diagnostics of in-service degradation of steels by
destructive methods have been developed. Criteria of consistency of estimation of brittle
fracture resistance and plasticity characteristics of operated metal with dissipated dama-
ging or susceptibility to delamination have been established. They consist in providing
specimens to fracture in the plane, parallel to potential lamination plane, and in deforma-
tion localization in one cross-section actually. For consistent evaluation of mechanical

properties of long-term operated steels methodical recommendations have been deve-
loped and specimens’ geometry has been proposed.
A new scientific and methodical approach to diagnostics of technical condition of
long-term operated structural steels by an electrochemical method has been developed. It
is based on determination of electrochemical properties of fracture surfaces, being
obtained under brittle fracture testing, as informative features of in-service metal condi-
tion. The correlation dependence between operational changes in brittle fracture
resistance of metal and in electrode potential of its fracture surface, being the basis of the
developed electrochemical method for diagnostics of in-service degradation of steels, has
been determined.
A complex of diagnostic features of hydrogen induced macrodelamination in pipe
wall of main pipelines is supplemented with a new diagnostic electrochemical feature,
namely, polarization resistance. It is proposed to predict increase of stress-strain state of
metal on external pipe surface and risk assessment of opening macrodefect at pipe out-
side by its decrease.
The non-destructive electrochemical method of diagnostics of brittle fracture
resistance characteristics of steels has been improved by elimination of screening effect
of passive films on electrochemical response of degraded metal. It increased sensitivity
of diagnostics and it enabled to extend the method to use for class of stainless