JPS6345471B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sacrificial corrosion protection electrode structure suitable for use in cathodic protection of marine structures such as oil drilling platforms. The anode used for sacrificial corrosion protection of steel materials is mainly composed of metals such as aluminum, magnesium, and zinc, which are electrochemically less noble than the steel material to be protected. It is manufactured by casting an alloy consisting of the ingredients plus some additives. The shape of this anode varies depending on the location and purpose, such as a block or a bracelet. A rod-shaped piece with a core metal cast into it is used. In recent years, as oil drilling sites have become more remote offshore, the water depth, or the size of the above-mentioned offshore structures, has also increased.
As the size of the anodes gradually increases from 100 to 200 m, it is extremely difficult to install and replace the anodes once the offshore structures have been installed. The method is to attach an anode with a long lifespan of 20 to 30 years to an offshore structure. FIG. 1 is a plan view showing a conventional sacrificial corrosion protection electrode structure, and FIG. 2 is a side view of FIG. It is attached to the main body of a marine structure as an object to be protected from corrosion, that is, a cathode 4, by means of attachment legs 3 connected to the core metal 2. The minimum dimension between the anode 1 and the cathode 4 (hereinafter referred to as installation distance L) is usually about 300 to 330 mm. If the above installation distance is smaller than the above value, a large current will concentrate in the close part for both poles and sufficient protective current will not flow in the far part.
If the above-mentioned installation distance is larger than the above-mentioned value, although the current density balance is improved to some extent, it is not appropriate because problems such as a decrease in the generated current due to an increase in circuit resistance occur. However, when the mounting distance is set within the appropriate range, the current density distribution on the surfaces of both electrodes becomes considerably non-uniform, resulting in a phenomenon in which the side of the anode 1 facing the cathode 4 melts faster. That is, FIGS. 3A and 3B are dissolution state diagrams of the anode showing the aging changes of the cross sections of the anodes having two different cross-sectional shapes by superimposing the progress lines investigated every five years. Furthermore, Tables 1 (A) and (B) show the results of a study showing the melting depth relative to the initial shape of the anode cross section. In Figure 3 and Table 1, A shows the case where the anode has a trapezoidal cross section with bases of 265 mm and 230 mm and height 245 mm, and B shows the case where the anode has a circular cross section with a diameter of 280 mm and the same capacity as in A above.

【table】

[Table] Yes. In addition, in these A and B, a core metal 2 having an outer diameter of 114.3 mm is arranged at the center inside the anode, and the mounting distance between the anode 1 and the cathode 4 is 320 mm.
According to the research results of the present inventors in Fig. 3A and B and Tables 1 (A) and (B), the melting depth on the cathode side, where the amount of melting of the anode 1 is the largest, and the melting depth on the opposite side. It is recognized that there is a difference of 1.6 to 2.0 times in depth. That is, in the conventional sacrificial corrosion protection electrode structure, the core metal 2 is cast so as to be located approximately at the center of the cross section of the anode 1, as described above. That is, for example, Publication of Utility Model Publication No. 35-2246, Publication of Publication of Utility Model Publication No. 41-14683, Publication of Publication of Publication of Utility Model No. 48-41300, Publication of Publication of Utility Model Publication No. 48-41300, Publication of Publication of Utility Model Publication No. 48-41300, Publication of Publication of Utility Model Publication No. 50-37368.
No. 1, Publication No. 18373 of 1987, etc., describe ideas regarding the means for attaching the electrode and the shape of the electrode, but in those specifications and drawings, the core metal is placed approximately at the center of the cross section of the anode. has been done. When using the above electrode, the 20
As the aging line shows, although there is still a considerable amount of anode material remaining that meets the design life, the core near the cathode is exposed earlier than the design life, and from then on, the gap between this exposed part and the surrounding anode material is The battery action progresses rapidly, and not only does sufficient current no longer flow to the original cathode side, but the anode material also falls off, causing the anode to stop functioning several years earlier than its designed life, resulting in damage caused by underwater welding in the deep sea. This will result in difficult work such as reinstallation of the anode. On the other hand, as shown in Japanese Utility Model Publication No. 38-20442 or Japanese Unexamined Patent Publication No. 51-54042, an overhanging part called an auxiliary core metal is provided on the core metal in order to prevent the anode from falling off at the end of its use. A method has also been proposed, but although it is effective in preventing the anode from falling off, it has the disadvantage of complicating the shape of the core metal and prematurely exposing the core metal. An object of the present invention is to provide a sacrificial corrosion protection electrode structure that can ensure a long-term stable corrosion protection function. In order to achieve the above object, the present invention provides a sacrificial corrosion protection electrode structure in which an anode having a metal core in its cross section is attached to a cathode as an object to be protected from corrosion.
When the installation distance between the anode and cathode is 300 to 330 mm, the wall thickness from the cathode side surface of the anode material to the core metal is set to 1.6 to 2.0 times the wall thickness from the anti-cathode side surface of the anode to the core metal. The core metal is eccentrically arranged closer to the cathode than the center of the cross section of the anode. Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a plan view showing a sacrificial corrosion protection electrode structure according to an embodiment of the present invention, and FIG. 5 is a side view of FIG. 4. That is, the anode 11 is cast from an alloy whose main component is a metal such as aluminum, magnesium, or zinc, which is electrochemically less base than the steel material constituting the object to be protected, and has the core metal 12 in its cross section. It is attached to the main body of the marine structure, ie, the cathode 14, as an object to be protected from corrosion, by means of attachment legs 13 connected to the core metal 12. Therefore, when casting the anode 11, the center 12C of the core metal 12 is eccentrically arranged by a distance E closer to the anti-cathode than the center 11C of the anode 11 (that is, approximately at the center position of the final shape of the anode 11). . According to the research results of the inventor mentioned above, the above eccentricity E is determined by setting the installation distance between the anode and the cathode to 300 to 330 mm.
In this case, the depth from the surface of the anode 11 to the core metal 12, that is, the thickness of the anode material may be 1:1.6 to 2.0 on the anti-cathode side and on the cathode side. As is clear from Table 1, a value of about 1.6 is effective for a circular cross section where the current density distribution is relatively uniform, and a value of about 1.8 is effective for a rectangular cross section where the current density distribution is more non-uniform. These values E are
Although it naturally varies depending on the mounting distance L of the anode 11 to the cathode 14, as mentioned above, the mounting distance is generally in the range of 300 to 330 mm, so as long as this is the case, the above eccentricity E may be sufficient. The anode 11 may be cast by either a method in which hot water is poured into a horizontal mold while the core metal is held at a predetermined height in the mold, or a so-called continuous casting method in which the anode is vertically cast. However, in either case, it is easy to decenter the core metal by a predetermined amount. Figure 6 shows the outer diameter of the anode 11 is 277.9 mm, and the core metal 12.
FIG. 3 is a state diagram showing the aging of the cross section of the anode 11 when the diameter of the anode 11 is 114.3 mm, and the eccentricity E of the center 12C of the core metal 12 with respect to the center 11C of the anode 11 is 9.5 mm. In this case, the thickness of the anode material in the initial dimensions is 62.8 mm on the anti-cathode side and 100.8 mm on the cathode side, and the ratio is 1:1.6. That is, as shown in FIG. 6, even after nearly 20 years, the anode 11 has a uniform remaining thickness, and the core metal 1
It is recognized that it is possible to prevent the exposure of No. 2 and the falling off of the anode material, and to ensure a stable anti-corrosion function over a long period of time. As described above, the present invention provides a sacrificial corrosion protection electrode structure in which an anode having a metal core in its cross section is attached to a cathode as an object to be protected, in which the attachment distance between the anode and the cathode is 300 to 330 mm. At the time, the core metal is placed from the center of the cross section of the anode so that the wall thickness from the cathode side surface of the anode material to the core metal is set to 1.6 to 2.0 times the wall thickness from the anti-cathode side surface of the anode to the core metal. It is also arranged eccentrically toward the anti-cathode. Therefore, it is possible to ensure a long-term stable anti-corrosion function.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a sacrificial corrosion protection electrode structure according to a conventional example, FIG. 2 is a side view of FIG. , FIG. 4 is a plan view showing a sacrificial corrosion protection electrode structure according to an embodiment of the present invention, FIG. 5 is a side view of FIG. 4, and FIG. 6 is a cross-sectional view of an anode according to an embodiment of the present invention over time. It is a state diagram showing a change. 11... Anode, 12... Core metal, 14... Cathode.

Claims (1)

[Claims] 1. In a sacrificial corrosion protection electrode structure in which an anode with a metal core in its cross section is attached to a cathode as an object to be protected, when the installation distance between the anode and cathode is 300 to 330 mm, the cathode side surface of the anode material The wall thickness from the anode to the core metal is equal to
An electrode structure for sacrificial corrosion protection, characterized in that the core metal is eccentrically arranged closer to the cathode than the center of the cross section of the anode so that the corrosion resistance is set to 1.6 to 2.0 times.