Electrochemical investigations of corrosion-cavitation damage on low-alloy steels: Fid-Bau Portal

Electrochemical investigations of corrosion-cavitation damage on low-alloy steels

Shtern, E. P. / Nechesa, I. F. / Trifel’, M. S. / Glikshtein, E. D.

Conclusions Damage to the metal members of turbines in a cavitation flow is of a mixed nature and develops under the simultaneous mechanical action of the flow and the electrochemical action of the medium. At the flow velocities in turbines working with heads up to 50 m the prime factor in corrosion damage on the metal is electrochemical action.In model tests on cavitation resistance, carried out on magnetostriction rigs, the parameters of the test process do not correspond to the actual operating conditions of turbines. In these tests, the corrosion characteristics of the metal are disregarded, resulting in a discrepancy between the results of the investigations and the behavior of the materials in actual operation.On the basis of concepts regarding the primarily electrochemical nature of cavitation erosion processes, considered up to the present as purely mechanical, it appears possible to use low-alloy steels as the materials for manufacturing hydraulic machinery, thus reducing the cost of hydraulic units. At the same time, fresh demands must be made on the design of hydraulic machinery, on account of the formation of macropairs being impermissible when manufactured from metals with different electrode potentials (for example, St. 3 and 1Kh18N9T).A simple and effective procedure for improving corrosion resistance of the metal members of hydraulic turbines is cathodic protection, both on machines already in service, including those constructed of different types of metals, and on new machines manufactured from low-alloy steels.Cathodic protection provides normal operation of machines under much more severely stressed working hydraulic conditions than assumed at present, thus lowering the cost of the machines, raising their engineering economic efficiency and lowering the cost of constructing hydroelectric stations.A check on the action of cathodic protection under laboratory conditions, and on machines under operating conditions, has demonstrated the high efficiency of this new method for protecting rotating-blade hydraulic units against wear under cavitation conditions.