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evolution of hydrogen due to the reduction reaction of bicarbonate ions, and not the

local anodic dissolution of the metal.

For the first time, the effect of addition of various anions to deaerated 0.01 N

aqueous NaHCO 3 solution on characteristics of electrochemical relaxation of

freshly deformed surface of the 17Г1С steel was quantified and the correlation

between resistance to initiation of corrosion fatigue crack in the steel and quantity

of electricity on oxidation of freshly deformed steel surface under corrosion potential

was determined. On this basis, an electrochemical rapid method of predicting

corrosion-fatigue durability of ferritic-pearlite pipeline steels in bicarbonate

environments depending on their composition was developed.

For the first time, it was revealed that the threshold stress intensity factor for

corrosion fatigue crack growth in the 17Г1С steel in NS4 solution, which simulates

the soil environment, is most intensively reduced by a combination of a number of

factors: long-term operation, high loading-cycle asymmetry R = 0.9 and, especially,

cathodic protection potential. Under such conditions, the growth rate of the

corrosion-fatigue crack in the area of the plateau for the operated base metal and

weld metal is 1.5 and 2.6 times higher, respectively, compared to the unused

condition. Under such conditions, values of corrosion fatigue crack growth rate in

the plateau area for the operated base metal and weld metal are 1.5 and 2.6 times

higher, respectively, compared to the as-received condition.

Practical significance of the obtained results.

The reduction of corrosion fatigue durability of steels under the combined

action of cavitation and cyclic loading was established, and the method of their

protection against corrosion cavitation using inhibitor was also proposed.

The electrochemical express method for estimation of corrosion

aggressiveness of components of water environments at fatigue failure of pipeline

steels based on quantity of electricity spent on electrochemical relaxation of a

freshly deformed surface was proposed.
The developed method for assessing the condition of operated pipe steels by

their resistance to corrosion-mechanical fracture was used in Affiliate