JPH0222782B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a corrosion-preventing sealing material used for sealing parts of seawater, desalination plants, pumps, refrigeration heat, heat exchangers, and their piping. [Background of the Invention] Conventionally, in piping for transporting fluids such as seawater and industrial water, the connecting portions thereof are sealed with a sheet-like or ring-like rubber material, asbestos, or the like to form minute gaps. Furthermore, the bolt tightening portions and the joint surfaces between two planes in general machines and devices also form fine gaps in the same way as described above. Since it is difficult for substances to move in the above-mentioned minute gaps, it is difficult to replenish dissolved oxygen, which is contained in a certain amount in the liquid in the gaps, although it is consumed in the formation of a passive film on the metal. There are drawbacks. For this reason, there is a risk that the metal surface within the gap (hereinafter referred to as the surface within the gap) that is not covered with the film may be exposed due to the incomplete passive film. On the other hand, since the outer surface adjacent to the inner surface of the gap is sufficiently supplied with dissolved oxygen, the passive film on the metal surface is stable. In such a state, electrochemically, the inner surface of the gap exhibits a base potential with respect to the liquid, and the outer surface adjacent to the inner surface exhibits a noble potential, so there is a gap between the inner surface of the gap and the adjacent outer surface. Since a potential difference is generated and the inner surface of the gap is actively dissolved, the adjoining outer surface undergoes a reduction reaction (cathode reaction) of dissolved oxygen equivalent to the charge released from the inner surface of the gap. In addition, since the hydrogen ion concentration increases within the gap due to dissolution of the inner surface, the liquid quality within the gap becomes acidic. In such a state, the passive film on the inner surface of the gap becomes unstable and dissolves, so that crevice corrosion progresses. As mentioned above, the occurrence of crevice corrosion is due to the fact that the inner surface of the crevice is polarized as an anode and the adjacent outer surface is polarized as a cathode, and as the inner surface of the crevice dissolves, the liquid quality within the crevice becomes acidic. . Conventionally, there is rubber containing magnesium oxide and graphite powder (July 30, 1960, "Rubber Technology Guidebook" published by Nikkan Kogyo Shimbun, No. 191)
Page), even if these rubbers are used as sealing materials, they do not contain zinc powder or other metal powders that serve as sacrificial anodes, so they cannot be expected to prevent corrosion, and various sealing materials have been developed for the purpose of preventing corrosion. (For example, JP-A-52-35230, JP-A-58-5351)
In both cases, no metal powder is added to serve as a sacrificial anode, and galvanic corrosion protection cannot be expected. [Object of the Invention] In view of the above, the present invention aims to provide a corrosion-preventing sealing material that can prevent the occurrence of crevice corrosion in seawater, which is a highly corrosive natural environment, for a long period of time. purpose. [Summary of the Invention] The corrosion-preventing sealing material of the present invention has a rubber (rubber-like elastic material) base material added with metal powder to serve as a sacrificial anode, and electrostatically charged graphite powder is used to remove the metal. The powder is electrically bonded to give the sealing material a sacrificial anode effect. The metal powder used as the sacrificial anode may be any metal that has an electrode potential more base than that of the member to be protected; for example, the electrode potential of zinc powder or an aluminum-magnesium alloy containing 30 to 60% magnesium (by weight) is There is a wide range of materials that have a very low potential and can therefore be subject to galvanic protection. The corrosion-preventing sealing material of the present invention dissolves liquid in the gap in a process in which the substance contained therein dissolves preferentially on the sealed gap inner surface (metal surface in the gap) and the outer surface adjacent to this inner surface. This prevents the quality from becoming acidic and maintains it at a slightly alkaline state, thereby stabilizing the passive film on the inner surface of the gap. When, for example, zinc powder is added to the rubber base material as described above, the sealed gap inner surface,
This is to prevent a potential difference from occurring between the inner surface of the gap and the adjacent outer surface. Zinc added and dispersed in the rubber base material is exposed near the surface, so when this exposed zinc comes into contact with the inner surface of the gap, it polarizes the outer surface adjacent to the inner surface of the gap into a cathode, and is polarized and dissolved at the anode. Since the inner surface of the gap and the adjacent outer surface are cathodically polarized in this way, there is no potential difference. Therefore, since the inner surface of the gap does not corrode, it can be protected from corrosion along with the adjacent outer surface. Furthermore, zinc preferentially dissolves on the metal surface, becomes amorphous zinc hydroxide, and diffuses into the gap. At the same time, the liquid quality within the gap also changes to slightly alkaline, which stabilizes the passive film on the surface inside the gap. When adding zinc powder for the above reasons, if the amount added is less than 5% by weight based on the rubber base material, the effect of inhibiting crevice corrosion of the rubber material will be small;
In addition, at 350% or more, the crosslinking reaction of the rubber becomes faster.
Since it inhibits the elasticity of the rubber base material, it is preferably 5 to 350%. In the rubber base material, magnesium oxide dissolves zinc as amorphous zinc hydroxide, so it has the effect of imparting hygroscopicity to the rubber base material in order to effectively consume the zinc powder. If the amount of magnesium oxide added is less than 20%, the effect will be small;
If it exceeds 100%, it will inhibit the elasticity of the rubber base material.
It is preferable to set it to 20-100%. In the case of an aluminum-magnesium alloy containing 30 to 60% magnesium, the content is preferably 5 to 200% for the same reason as above. Due to its polarity, the electrostatically charged graphite powder is chained in the rubber base material, which electrically interconnects the metal powders that serve as sacrificial anodes dispersed in the rubber base material. It works to effectively consume metal powder. If the amount added is less than 20%, it will have little effect, and if it is more than 200%, it will be uneconomical.
It is preferable to set it to 20-200%. When the zinc powder, aluminum-magnesium alloy powder, and graphite powder are added to a rubber base material, it is preferable to form them into a spherical or polygonal shape in order not to impede sealing performance, and from the viewpoint of uniform dispersion, it is preferable to form them into a spherical or polygonal shape. It is preferable to form the
Moreover, if the diameter of the powder is less than 0.1 μm, it is uneconomical, and if it is more than 100 μm, the sealing performance will be impaired.
The thickness is preferably 0.1 to 100 μm. Furthermore, the rubber base material has good seawater resistance and does not easily cause crevice corrosion in seawater, so the crosslinking reaction of the rubber material is performed using organic peroxides such as ethylene propylene, chloroprene rubber, and metal oxides. is suitable. [Embodiments of the Invention] Next, embodiments will be described. Chemical composition: C: 0.07%, Si: 0.56%, Mn: 1.31
%, Cr: 18.30%, Ni: 8.14% commercially available stainless steel (SUS304) was processed to make a circular test piece 1, and this test piece 1 was used as a product of the present invention as shown in Figs. 1 and 2. Test sealing material 2 (Table 1 A, B
Assemble the crevice corrosion test specimens by bonding them together via the
After soaking for a day, the potential within the gap was measured using a potentiometer, and changes in the liquid quality within the gap were investigated.

【table】

[Table] In the figure, 3 is a Teflon tube, 4,
5 is an electrode connected to a potentiometer (not shown), and 6 is a sealing material (Araldite). As a result of the above experiment, the crevice corrosion state is shown in Table 2 A and B.
As shown below. Corrosion area rate A in this table
is the ratio of the corroded surface to the internal gap surface area of 2512 mm ² . In addition, the incubation period (days) is the period until crevice corrosion occurs, and since crevice corrosion tends to occur from the edge of the gap, and reddish-brown rust is observed on the edge, the evaluation is based on the date the rust was discovered. Therefore, an incubation period of 30 days indicates no corrosion. [Effects of the Invention] As explained above, according to the present invention, the occurrence of crevice corrosion in stainless steel, aluminum alloy, etc. in highly corrosive seawater can be prevented for a long period of time, and machinery and equipment can be It is possible to obtain a corrosion-preventing sealing material that can improve the reliability of.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the assembled state of a crevice corrosion test piece for testing the sealing material of the present invention. 1... Test piece, 2... Test sealing material, 4, 5...
…electrode.

Claims (1)

[Scope of Claims] 1. A corrosion-preventing sealing material formed by adding magnesium oxide and graphite powder to a rubber base material and molding the material, in which a metal powder serving as a sacrificial anode is added to the base material,
A corrosion-preventing sealing material characterized in that graphite powder is electrostatically charged and the metal powder is electrically bonded to the graphite powder. 2. The corrosion-preventing sealing material according to claim 1, wherein the metal powder serving as the sacrificial anode is zinc powder. 3. The corrosion-preventing sealing material according to claim 2, wherein 5 to 350% (weight ratio) of zinc powder is added. 4. The corrosion-preventing sealing material according to claim 1, wherein the material serving as the sacrificial anode is an aluminum-magnesium alloy. 5 Aluminum-magnesium alloy from 5 to 200
% (weight ratio) of the corrosion-preventing sealing material according to claim 4.