FR2594854A1 - Process for cathodic protection against corrosion of steel diving bottles - Google Patents

Abstract

Process for cathodic protection against corrosion in an aqueous medium of the walls of a steel diving bottle intended to contain a gas for breathing. According to the invention a sacrificial electrode in the form of a bead 8 of a pure metal or in the form of alloy is placed inside the said bottle, so as to bring the steel constituting the casing of the bottle into the so-called "immunity" zone.

Description

DESCRIPTION
The present invention relates to a cathodic protection method against corrosion in an aqueous medium of the walls of a steel diving tank intended to contain a breathing gas.

 The problem of corrosion in an aqueous medium, in particular in sea water, of a metal surface, is a well known problem. There are three methods for treating metal surfaces against corrosion in an aqueous medium.

 The first method consists in depositing a protective coating on the surface to be protected, so as to physically isolate the metal from the ambient environment. Such a method is particularly difficult to apply in the case of protecting the internal surface of diving tanks, given the difficulty of ensuring the good qualities of the protective coating.

 A second method consists in the use of passivable metals and alloys: these are passive in aqueous media such as sea water. The metals and alloys generally used in these applications are aluminum and its alloys, inawdable steel, nickel-based alloys, titanium, etc ... All these materials are expensive and / or do not meet the conditions required to make diving tanks capable of containing compressed air at 200 bars .

 The third known method of protection against corrosion in an aqueous medium is electrochemical protection. A distinction is made between anodic protection, the implementation of which is particularly complex, and cathodic protection, a variant of which consists in using an anode of a less noble metal than the rital to be protected, said anode dissolving in contact with water and being of this fact called the sacrificial consumable anode. Consateable anodes of this type are generally made of magnesium, zinc, aluminum, tin, etc.

 If a cathodic protection with a consumable anode is known in particular for the protection of ship hulls against corrosion in seawater, no indication is given in the literature allowing this type of protection against corrosion to be simply achieved. a steel diving tank.

 The problem of using a consatssble electrode for cathodic protection against corrosion in an aqueous medium of the walls of a steel diving tank intended to contain a breathing gas is solved in a particularly simple manner by the method according to invention.

 This is characterized in that a consumable electrode is placed inside said bottle in the form of a ball of pure metal or in the form of an alloy so as to bring the steel constituting the envelope of the bottle in the so-called immunity zone.

 The use of a campable anode ball has many advantages in its application to the protection against corrosion of steel diving tanks. In fact, this process is particularly easy to carry out in the first place since it suffices to introduce into the bottle a ball of pure metal or under a cast of alloy of less noble metals than steel, in this bottle, the diameter of the ball being of course much less than the diameter of the neck of said bottle.

 Secondly, a ball has the advantage, whatever the position or the inclination of the bottle, of always being punched in contact, on the one hand with the steel wall of the bottle, and on the other hand aqueous medium present at the bottom of the bottle, taking into account the fact that the ball rolls on the bottom of said bottle as well as the water being inside of it. Thus, the water and the ball cannot move separately.

 Thirdly, the use of a ball also has the advantage of auditory control of the presence of the means of protection against corrosion inside said bottle. Indeed, the ball being a consumable electrode, it is enough to shake the bottle in order to check its presence inside it. The absence of its audible dizziness when the bottle is shaken indicates that it is necessary to introduce a new ball into it in order to correctly ensure its protection against corrosion in an aqueous medium.

 Of course, generally less noble metals or alloys of metals will be used than steel, preferably chosen from those having food qualities such as zinc and its alloys, aluminum and its alloys, etc. generally, with regard to the choice of metal or alloys constituting the consumable anode as a function of the aqueous medium, reference will be made to the literature well known to those skilled in the art in the dandin of cathodic protection, so as to bring 1 steel constituting the envelope of the bottle in the so-called immunity zone in which the metal is immune to corrosion.

 The invention also relates to a steel diving tank intended to contain a breathing gas, characterized in that it contains a ball of a metal or an alloy of metals less noble than steel, which can move freely in contact with the walls of the bottle under the effect of gravity.

 The invention is illustrated by the single figure which represents a diving bottle in which a ball according to the invention is arranged.

 This bottle 1 has a steel casing 3 surmounted by a tap 2, screwed by its lower part 5 onto the neck 4 of said bottle 3. The latter contains a breathing gas 6 while in the bottom of said bottle are arranged on the one hand traces of water 7 generally 1 seawater cccpte given the use of this bottle in the marine environment, and on the other hand the ball 8.The underside 9 of the bottle 1 is preferably of convex, flat or concave shape or of cast iron such that, whatever the position or the inclination of the bottle, the ball can freely follow the wall of the bottle without encountering obstacles, so as to always be in contact with traces seawater 7 possibly present in it. These traces of seawater exist on the one hand, because the bottle is used for diving and that a certain condensation inside the bottle does not is not to be excluded, but essentially on the other hand the fact that when e the bottle is empty divers generally remove the regulator attached to the valve 2 without taking any special precautions which leads to the introduction of seawater into the bottle when this operation is carried out in a marine environment.

 Of course, the "ball" tent designates within the framework of the present invention a sphere but also any volume of metallic material capable of fulfilling the Itfre function, that is to say moving by gravity along the internal walls of said bottle in sillultaneity with the displacement of the aqueous medium capable of denying the corrosion of the walls of the surface, so as to always maintain a physical contact between said volume, the aqueous medium and the steel wall, whatever the position and / or the orientation of the bottle.

Claims (4)

 1. Method for cathodic protection against corrosion in an aqueous medium of the walls of a steel diving bottle intended to contain a breathing gas, characterized in that a consumable electrode is placed inside said bottle a ball (8) of pure metal or in the form of an alloy so as to bring the steel constituting the envelope of the bottle into the so-called "imxnitE" zone.  2. Proodé according to claim 1, characterized in that the pure metal or in the form of alloys consists of less noble metals than steel.  3. Method according to claim 2, characterized in that the metals less noble than steel are chosen from those having food qualities.  4. Steel diving tank intended to contain a breathing gas (6), characterized in that it contains a ball (8) of a metal or of a metal alloy less noble than 1 steel, being able to move free in contact with the walls (3) of the bottle (1) under the effect of gravity.