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ions) and decreases with inhibition of hydrogen evolution in the reaction of cathodic

-
depolarization due to competitive adsorption (presence of О 2, NO 3 ) and increase of
3-
2
barrier properties of surface films of corrosion products (presence of О 2, РО 4 , СО 3 ).
Therefore, hydrogen embrittlement caused by evolution of hydrogen due to the

reduction reaction of bicarbonate ions is the main mechanism of both the nucleation

and development of corrosion-static fracture of the 17Г1С steel in bicarbonate

aqueous solutions.

Based on the analysis of the influence of anions (at a concentration of

0.005 N) added to 0.01 N NaHCO 3 solution on the characteristics of restoring the

equilibrium state of the metal of freshly deformed surface of the 17Г1С steel under

corrosion potential (maximum dissolution current І 0, current drop rate S and

quantity of electricity for metal oxidation of the deformed surface q) a correlation

between the resistance to initiation of corrosion fatigue crack in the 17Г1С steel

from the stress concentrator and the rate of electrochemical relaxation of freshly

deformed surface has been revealed. It indicates a determining effect of fracture of

surface protective films and dissolution rate of freshly deformed steel surface on its

corrosion fracture durability.

An electrochemical express method for predicting corrosion fracture durability

of ferritic-perlite pipeline steels in bicarbonate environments depending on their

composition has been developed. It is based on the established correlation between the

resistance to initiation of corrosion fatigue crack and of electricity for metal

oxidation of the deformed surface under corrosion potential.

It has been found that at low loading cycle asymmetry (R = 0.1) 0.01 N

NaHCO 3 solution has almost no effect on the rate of fatigue crack growth in the

17Г1С steel, and at high loading cycle asymmetry (R = 0.9) – increases the rate of

crack growth due to superposition of mechanisms of corrosion fatigue and corrosion-

static fracture.

It has been established that the common mechanism of crack propagation
under both cyclic and static loading of the 17Г1С steel in 0.01 N NaHCO 3 solution

-
-
2-
3-
with anion additions (at a concentration of 0.005 N) Cl , СО 3 , РО 4 , NO 3 is