We study the conditions of surface cracking of steels for pipelines of power-generating equipment subjected to cyclic deformation in aqueous media. A new parameter is proposed for the evaluation of the corrosion fatigue of materials, namely, a certain characteristic level of stresses within the limits of the loading cycle (sigma = sigma_s) above which the deformed surface undergoes noticeable electrochemical activation. A model scheme of the surface corrosion-fatigue cracking regarded as a result of the synergetic action of cyclic stresses and electrochemical processes is proposed. A criterion of initiation of a surface crack of length a relating the characteristic stress sigma_s to the maximum stress in a cycle sigma_(max) the strength of corrosion current I_(cor) and the constants of electrochemical dissolution of the metal on the deformed surface is established. On this basis, we propose an engineering estimate for the period of initiation of surface corrosion-fatigue cracks.
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