GB854909A - A device for the protection of submerged or buried metallic surfaces from corrosion - Google Patents

Abstract

854,909. Preventing corrosion. COMPAGNIE DE CONSTRUCTION DE GROS MATERIAL ELECTRO-MECANIQUE. Jan 31, 1957 [Feb. 28, 1956], No. 3409/57. Class 123(1) [Also in Group XXXV] Electrolytic corrosion of submerged or buried dissimilar metals forming part of an electrically continuous metallic system, for example, a ship's hull 23 and propeller 20, by corrosion currents set up by the electro chemical potential differences existing therebetween is prevented by connecting a low resistance shunt 26 in parallel with the normal external flow path of the current between a brush 24 bearing on the propeller shaft 21 and the hull, measuring the current flow in the shunt and/or the voltage drop thereacross and applying a counter-voltage to the shunt which prevents current flow therethrough and is also effective to prevent flow in the normal path. The opposing voltage may be regulated manually or automatically by the arrangement shown in Fig. 5, wherein the shunt 26 is shown connected across a resistor 16 representing the normal external current flow path. One end of the shunt 26 is also connected to a point between two batteries 28, 281 serially connected to a potentiometer 29, the slider 30 of which is connected through a regulator 37 to the other end of the shunt. The regulator serves automatically to adjust the slider 30 according to signals received from a voltmeter 36 to maintain zero potential across the shunt and resistor 16 so that no corrosion producing current flows. A switch 33 enables a second shunt 39 and potentiometer 41 having a slider 42 automatically set by a regulator 44 according to signals received from a voltmeter 43 to be placed in circuit to give a fine adjustment of the applied opposing voltage.