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This work is a continuation of our former investigations in the field of corrosion of steel by alternating currents. In‐vestigations of corrosion of construction ship steels by alternating currents in seawater have been made. Investigations were performed within the range of alternating current densities from 20 up to 1500 mA/dm2 at frequencies from 18 up to 20000 Hz. Investigations have shown that the corrosion rate increases with the increase of current density at constant frequency. Besides, it has been established that at constant current density the corrosion rate decreases with the frequency increase up to 2000 Hz, and with the further increase of frequency up to 20000 Hz the rate of corrosion is increased. The material effect of corrosion by alternating currents in our investigations amount to 4.35–17.57% of the corrosion by equivalent densities of direct current.

With the transition from supplying ships with direct current to alternating current, plus the increase in the number of electricity consumers within the coastline region, as well as with the construction of steel quays and docks and reinforced steel quays, the conditions have been created for the occurrence of wandering exchange currents in the sea. Corrosion due to these currents considerably exceeds all expectations. In this work, the rate of steel corrosion in synthetic sea‐water has been investigated in an alternating electric field. Electro‐chemical parameter measurements determining corrosion rate were performed on samples in sea‐water in an alternating current field and compared with the sample — applying a “blind test” — without an electric field. All measurements were performed at an electrolyte temperature of 20°C. Corrosion rate was investigated in dependence on the current density. The following factors were applied as measures of corrosion rate: specific concentration of Fe ions in the electrolyte and the change of potential of the steel electrode polarized within alternating electric field. Measurement results shown that in the sea‐water with an alternating electric field an increase in the corrosion of steel takes place, exceeding expected amounts. The change of steel potential in alternating current field is proportional to the corrosion rate and can be very simply applied for estimation of corrosion rate due to alternating currents.