GB1146501A - Method and apparatus for automatic electric corrosion proofing - Google Patents

Abstract

1,146,501. Automatic control of corrosion prevention. MITSUBISHI JUKOGYO K. K. March 29, 1966 [March 30, 1965; May 31, 1965], No.13931/66. Heading G3R. [Also in Division C7] A cathodic corrosion prevention system comprises (1) a regulatable D. C. voltage source, e.g. supplied through Si-controlled rectifiers 12 and a slide rheostat-type transformer 11 from an A.C. source, for connecting to a metallic structure 13 (e. g. of mild steel) to be corrosion proofed as the cathode and a non-consumable anode 14 (e. g. of Pt, Pt alloy, Fe 3 O 4 , Pb-Ag alloy or Pt-plated Ti plate), both being immersed in an electrolyte e. g. NaCl solution, (2) means for measuring the difference between the P. D. and the (solution) resistance voltage drop between the electrodes 13, 14, such as voltmeters V 1 and V 2 respectively, the latter (V 2 ) indicating the voltage generated by a proofing current circuit (comprising a potential circuit 17 supplied through a Si-controlled rectifier 16 from a transformer 15 operatively connected to the main voltage source) to compensate for the voltage drop, and (3) means operable responsive to the measured difference e.g. voltage setting means 18 to regulate the current flow from the anode to the structure so as to maintain the difference constant. In a modification Fig. 7 (not shown) the difference is maintained within a predetermined range corresponding to the proofing potential of the structure. A current flow at a first constant value is supplied in response to any drop of the P. D. below a first predetermined value, to be interrupted when the P.D. attains this value; and, in response to the P.D. increasing above the first and above a second higher predetermined value, a current flow at a reduced second constant value is supplied. The silicon controlled rectifiers may be replaced by saturable reactors, transistors or relays. The latter are also used in the abovementioned modification for switching the current between its two values, but may be replaced Fig.8 (not shown) by a photo-transistor controlled by a moving pointer and having an output which is amplified to control silicon controlled rectifiers in the main current circuit.