RU2204625C2 - Method of destruction-protection of metallic surface - Google Patents

Abstract

FIELD: corrosion protection. SUBSTANCE: invention relates to protection against destruction of anode-grounding metal in constant-current power lines. Method consists in that titanium surface optionally coated by oxide film is immersed in chlorine ion- containing milieu, e.g. in sea water or in wet soil, under anode potential, after which that milieu is subjected to forced regulated continuous or periodical circulation caused by controlled gas feeding. Forced circulation is commenced when predetermined value of metal surface potential is attained. Surface to be protected is washed by circulating liquid milieu for a period of time constituting no less than 10% time during which surface is exposed to anode potential. EFFECT: enhanced protection of metal surfaces in chlorine- containing media and prevented emission of chlorine in sea water. 5 cl, 1 tbl

Description

 The invention relates to the protection against metal destruction of the anode ground electrode on direct current power transmission lines. One of the metals used to make grounding conductors may be titanium.

 A known method of protecting titanium products from destruction in seawater by oxidizing the surface (G. G. Ulig, R.U. Revi. Corrosion and control, Leningrad, Chemistry, Leningrad branch, 1987, pp. 372-378) . This method is adopted as a prototype.

 The disadvantage of this method is that during prolonged anodic polarization of the titanium surface, chlorine ions accumulate at the surface and destroy the oxide film. In addition, chlorine effluent has a harmful effect on the environment.

 Practical proposals are known for preliminary coating the surface of anode grounding conductors with platinum group metals in order to significantly reduce the polarizability of the electrodes, which should avoid the onset of discharge of chlorine anions. However, due to a number of features of the occurrence of electrode processes in seawater on platinum and its analogues, chlorine evolution was not avoided in that case either.

 An object of the invention is to prevent the release of chlorine on the anode ground and increase the stability of the anode film.

 The solution to this problem lies in the fact that the protected metal surface or titanium surface coated with an oxide film, immersed in a medium containing chlorine ions, for example in sea water, and located under the anode potential, is continuously or periodically washed by the flows of a liquid medium due to its forced circulation created by controlled gas flow.

The destruction of the oxide film occurs when a critical potential is reached that can create an electrostatic field that allows the penetration of chlorine ions to the metal surface. The critical potential of titanium at a temperature of 25 ^o C exceeds 1 V. After reaching the critical potential, chlorine ions can replace the oxygen of the oxide film, destroying it and the metal.

 Grounding is washed continuously or periodically when the surface anode potential reaches 0.9 V.

 In a batch process, the washing time of the surface to be protected should be at least 10% of the time the surface was under the anode potential.

 An example of the method.

Two titanium electrodes, the surface of which is coated with an oxide film, were immersed in sea water at a temperature of sea water of 4 ^o C.

 One electrode was washed with jets of electrolyte. The control electrode was not washed.

At the electrodes, the current density was gradually increased to 3.5 mA / cm ² .

 The results are shown in the table.

The table shows that on the control electrode, when the anodic current density reaches 1 mA / cm ^2, the surface potential reaches 3.3 V, and with a further increase in current density, a decrease in potential is observed due to depolarization caused by the destruction of the oxide film and titanium itself.

On the electrode, washed by jets of electrolyte, at an anode current density of 0.6 mA / cm ² , the surface potential has a value of 0.925 V and with a further increase in current density to 3.5 mA / cm ² varies in the range of 0.925-0.940 V, t .e. practically remains constant and the destruction of the oxide film and titanium does not occur.

 The use of the invention will protect titanium products from destruction in environments containing chlorine ions, for example in seawater, and prevent the release of chlorine into the marine environment.

Claims (5)

 1. A method of protecting an anodically polarized metal surface from destruction in a medium containing chlorine ions, for example in seawater, comprising oxidizing it, characterized in that a forced controlled circulation of the liquid medium is created along the metal surface, which is created by a controlled gas supply.  2. The method according to p. 1, characterized in that the forced controlled circulation of the liquid medium, created by a controlled flow of gas along a metal surface, is carried out continuously.  3. The method according to p. 1, characterized in that the forced controlled circulation of the liquid medium created by a controlled gas supply along the metal surface is carried out periodically.  4. The method according to one of paragraphs. 1 and 3, characterized in that the forced circulation of the liquid medium created by the controlled gas supply along the metal surface is started when a certain value of the potential of the metal surface is reached.  5. The method according to one of paragraphs. 1, 3 and 4, characterized in that the time of forced circulation of the liquid medium created by a controlled gas supply along the metal surface is at least 10% of the time the protected surface is under the anode potential.

Images