JP4424059B2 - Method for forming anticorrosion film - Google Patents

Description

  The present invention relates to an anticorrosion film forming method, and more particularly to an anticorrosion film forming method in which a good anticorrosion film is formed on a marine steel structure in a short period of time.

  Conventionally, a marine steel structure is used as a cathode, an anode is placed in the seawater facing the marine steel structure, a direct current is passed between the electrodes, and the marine steel structure is coated with an electrolytic reaction of seawater (anticorrosion film). Methods have been proposed for corrosion protection of marine steel structures by forming

For example, in Patent Document 1, a steel member constituting the surface of a steel structure provided in the ocean is used as a cathode, an anode is disposed in seawater so as to face the steel member, and a direct current is passed between these electrodes. Then, the scale such as rust present on the surface of the steel structure is removed, and then a direct current is passed between the electrodes, and the surface of the steel structure and the pitting corrosion location are mainly composed of electrolysis products of seawater. It is described that a corrosion prevention film is formed by depositing a kimono.
JP-A-10-313728

As described above, the coating film formed on the marine steel structure by the electrolysis reaction of seawater is mainly composed of calcium carbonate CaCO ₃ and magnesium hydroxide Mg (OH) _2. It is known to be calcium carbonate formed with hardness. Therefore, in order to prevent corrosion of marine steel structures, it is necessary to form an anticorrosion film mainly composed of calcium carbonate.

  As shown in Patent Document 1, the relationship between the current density of the marine steel structure due to the current applied between the electrodes and the composition of the coating is as shown in FIG. That is, under the condition where the current density is low, the composition ratio of calcium carbonate in the coating is high and the composition ratio of magnesium hydroxide is low. As the current density is increased, the composition ratio of calcium carbonate decreases, while the composition ratio of magnesium hydroxide increases. And the composition ratio of the film excellent in anticorrosion property is said that calcium carbonate is 1 or more with respect to magnesium hydroxide.

Therefore, Patent Document 1 describes that the current density during electrodeposition is selected to be 0.2 A / m ^{2 to 2} A / m ² (1 A on average) in order to form a corrosion prevention film mainly composed of calcium carbonate. Yes. It describes that a hard anticorrosion film having a thickness of about 5 mm or more is formed on the surface of the marine steel structure.

However, as described in Patent Document 1, in order to form a calcium carbonate-based anticorrosion film having a film thickness of, for example, 5 mm or more at a current density as low as 1 A / m ² , for example, approximately 10 months or more. It is known that it takes a long time.

  Therefore, the method of forming the anticorrosion film by the conventional method such as Patent Document 1 requires a long construction period and requires management over a long period of time, and also increases power consumption and costs. It is currently not applied except in special cases such as where the water depth is deep, or where the tide is intense, such as a pier provided in

  The present invention has been made in view of the above circumstances, and can form an anticorrosion film in a short period of time and at a low cost, thereby forming an anticorrosion film that can be easily applied to a general-purpose marine steel structure. It was made for the purpose of providing a method.

  The invention according to claim 1 is characterized in that a marine steel structure is used as a cathode, an anode is disposed in seawater so as to face the marine steel structure, a direct current is passed between these electrodes, and marine steel is produced by an electrolysis reaction of seawater. An anti-corrosion film forming method in which an anti-corrosion film is formed on a structure to prevent corrosion of the marine steel structure, and the current density is such that a magnesium hydroxide-based film is formed on the marine steel structure. After a current is passed between the electrodes, a film with a predetermined thickness is formed, and then the supply of current is stopped, and an anticorrosive film is formed by a composition replacement action that replaces calcium carbonate with magnesium hydroxide generated in the presence of seawater. The present invention relates to a method for forming an anticorrosion film.

Invention of Claim 2 flows an electric current between electrodes so that the current density of the said marine steel structure may be 3-10 A / m < ² >, The anticorrosion film | membrane formation method of Claim 1 characterized by the above-mentioned. It is related to.

  According to the anticorrosion film forming method of the present invention, a film mainly composed of magnesium hydroxide is formed in a marine steel structure in a short period of time by passing a current between the electrodes so as to keep the current density of the marine steel structure high. After that, by stopping the supply of current, the anticorrosion film is formed by utilizing the composition substitution action in which calcium carbonate is replaced with magnesium hydroxide generated in the presence of seawater, so that the period of time is extremely short compared to the conventional case. Thus, there is an effect that a good anticorrosion film mainly composed of calcium carbonate can be formed.

  Because the anticorrosion film can be formed in a short period of time, the construction period is short, management is easy, power consumption can be reduced, and the cost can be reduced. It has the effect that it can be easily applied to all kinds of marine steel structures.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a side view showing an example of an apparatus configuration when the method for forming a corrosion protection film of the present invention is applied to a steel caisson of a breakwater, which is an example of a marine steel structure, and FIG. 2 is a view of FIG. It is a front view. In the figure, 1 is a steel caisson that forms a breakwater, 2 is a DC power supply installed on the upper part of the steel caisson 1, etc., and 3 is opposed to the surface of the steel caisson 1 in seawater with a required interval. It is a subsea member that is suspended and held in sea water and that is arranged in plural in a direction parallel to the surface of the steel caisson 1 at a required interval. The undersea member 3 can be made of a soluble material such as magnesium or aluminum, or an insoluble material such as titanium.

  Connecting the negative power source (−) side of the DC power supply device 2 to the steel caisson 1 makes the steel caisson 1 the cathode, while connecting the positive power source (+) side of the DC power supply device 2 to the underwater member 3. Thus, the subsea member 3 is used as an anode. The above configuration is provided for each of the plurality of steel caissons 1.

  Then, by passing a required constant current between the electrodes, that is, between the steel caisson 1 and the undersea member 3 by the DC power supply device 2, a coating film is formed on the steel caisson 1 by the electrolytic reaction of seawater. Yes.

  In addition, monitor electrodes 4 are installed at a plurality of locations on the underwater surface of each steel caisson 1 as shown in FIG. 2, and a monitor device 5 that obtains and displays the potential of the steel caisson 1 based on the detected value of each monitor electrode 4. Is installed in the upper part of the steel caisson 1. The monitor device 5 is for confirming that a current having a predetermined current density flows through the steel caisson 1 by applying a constant current to the steel caisson 1 by the DC power supply device 2. On the other hand, in a place where the tidal zone is large, the area of the steel caisson 1 in the sea greatly fluctuates, so the current density flowing through the steel caisson 1 changes greatly. Therefore, a constant potential method that keeps the potential (voltage) of the steel caisson 1 constant can be adopted in such a place. The monitor device 5 in this case may have a controller function that automatically adjusts the voltage of the DC power supply device 2 so that the detected potential becomes a predetermined constant potential.

  Next, the operation of the present invention will be described with reference to test examples.

First, in the apparatus of FIGS. 1 and 2, the present inventors sequentially set the current density flowing in the steel caisson 1 in a state where the total energization amount by the DC power supply apparatus 2 is maintained at a constant value of 60 A · h / m ^2. The amount of calcium carbonate and magnesium hydroxide produced during the change was investigated. FIG. 3 shows the results of investigation on the amount of calcium carbonate produced, and FIG. 4 shows the results of investigation on the amount of magnesium hydroxide produced.

In FIG. 3, when the current density is increased, the amount of calcium carbonate generated increases rapidly and shows a peak when the current density is around 0.5 A / m ² , and when the current density is further increased, the amount of calcium carbonate generated increases rapidly. Showed a tendency to decrease.

In FIG. 4, as the current density is increased, the amount of magnesium hydroxide produced increases until the current density reaches about 7 A / m ^2, and a peak is exhibited. When the current density is further increased, the amount of magnesium hydroxide produced decreases. Showed a trend.

  It has been found that the above-described trends in FIGS. 3 and 4 agree with the relationship between the current density shown in FIG.

Therefore, the present inventors pay attention to FIG. 4, and when the current density is set to a high value such as 3 A / m ^{2 to} 7 A / m ² , the film formation rate can be greatly increased. It was found that a thick film can be formed in a short period of time. On the other hand, FIG. 4 shows data in an indoor test (Shimizu environment), and in the actual sea area, the electrodeposition efficiency decreases due to the influence of the tidal current (for example, this technical report Vol. 24 No. 95 (200.12)). For this reason, when the production amount of the coating in the actual sea area was investigated, it was found that the optimum range of the current density in the actual sea area was 3 A / m ^{2 to} 10 A / m ² .

However, when the current density is set to a high value such as 3 A / m ^{2 to} 10 A / m ² as described above, the coating formed on the steel caisson 1 is composed mainly of magnesium hydroxide (eg, magnesium hydroxide 95%). Therefore, it cannot be used as an anticorrosion film.

  For this reason, it is considered that the magnesium hydroxide-based coating 7 formed in a short period of time as described above can be used as an anticorrosion film made of calcium carbonate. As a result, calcium carbonate is replaced with magnesium hydroxide in seawater. It was found that a composition substitution action occurs, and an anticorrosion film was formed by utilizing this action.

  In order to confirm the above-described composition substitution action, the present inventors first performed a film formation test using the same test apparatus as in FIGS.

In the above test apparatus, SS400 is used for the cathode base material facing the steel caisson 1, Mg is used for the anode material corresponding to the undersea member 3, natural seawater at a water temperature of 25 ° C., and the current density is 3 A / m ^2. Under the conditions described above, a film formation test for 30 hours was performed.

  As shown in FIG. 5, when the film thickness L was detected for the film 7 formed on the cathode substrate 6 in the above test, the film thickness was 105 μm, and the composition of the film 7 was determined by chemical analysis. As shown, magnesium hydroxide was about 95% with respect to calcium carbonate about 5%, most of which was magnesium hydroxide.

  Next, as described above, a test for confirming the composition replacement action of the magnesium hydroxide-based coating 7 was performed.

That is, after forming the magnesium hydroxide-based coating 7 on the cathode base 6 as described above, the supply of current by the DC power supply device is stopped, and then the soaked state is maintained in seawater, soaking starts (power supply The coating composition ratio of magnesium hydroxide and calcium carbonate, the coating amount (g / cm ² ), and the coating amount (mmol) were detected on the 7th, 14th, and 21st days from the stop).

  According to FIG. 7, when the immersion is started, the main magnesium hydroxide is decreased and the calcium carbonate is increased, and the composition ratio of magnesium hydroxide and calcium carbonate is reversed around the 17th day after the substantial immersion. There was found.

  In the morbase shown in FIG. 8, no change in the coating amount was observed even when the immersion time elapsed compared to the initial stage. On the other hand, the weight base shown in FIG. 9 shows a slight increasing tendency. As shown in FIG. 7, this tendency is that the magnesium hydroxide decreases with the immersion time, and the coating composition ratio changes due to the increase of calcium carbonate. That is, as shown in FIG. 8, the coating composition ratio changes without changing the coating amount in the total amount based on the molar amount. This means that the dissolution reaction of magnesium hydroxide in the coating and the precipitation reaction of calcium carbonate are almost 1. It is thought that it occurred at the same chemical equivalent of 1: As a result, the high molecular weight calcium carbonate (Mw = 100) was replaced with the low molecular weight magnesium hydroxide (Mw = 58), and as a result, the coating amount increased on a weight basis as shown in FIG. .

That is, it is considered that the following reaction formula (1) occurs, the reaction formula (2) occurs, and as a result, the reaction formula (3) holds.
Mg (OH) ₂ → Mg ²⁺ + 2OH ⁻ (1)
Ca ²⁺ + H ₂ CO ₃ + 2OH ⁻ → CaCO ₃ + 2H ₂ O (2)
^{_{Mg (OH) 2 + Ca 2+}} + H 2 CO 3 → Mg 2+ + CaCO 3 + 2H 2 O ... (3)

  Therefore, when the magnesium hydroxide-based coating 7 shown in FIG. 5 is replaced by calcium carbonate by the composition replacement action, as shown in FIG. 6, a hard anticorrosion film 8 mainly composed of calcium carbonate is formed while the film thickness L hardly changes. Will come to be.

  From FIG. 7, it can be seen that when the immersion is performed for 17 days or more, an excellent anticorrosion film 8 having a coating composition of 1 or more calcium carbonate with respect to magnesium hydroxide can be formed.

In the above test example, the case where the current density was set to 3 A / m ² was shown as the energization condition, but this was carried out at a low current density because the coating was easy to peel off in a test apparatus without seawater flow. In actual natural sea water, there is a flow, and as described above, the film does not peel off even when implemented at a high current density of 3 A / m ^{2 to} 10 A / m ^2. It was found that it can be formed.

  Therefore, while the formation of the anticorrosion film has conventionally taken 10 months or more, according to the present invention, the anticorrosion film can be formed in a very short period of about one month or one and a half months. This makes it easier to manage and further reduces power consumption and costs, so it can be easily applied to all kinds of marine steel structures, not limited to special places as before. be able to.

  In addition, when applying the anticorrosion film forming method of the present invention to the existing marine steel structure, it is necessary to remove in advance the deposits such as rust adhering to the surface of the marine steel structure. Various methods such as a method of removing rust by passing a direct current between the electrodes, a method of removing by rusting high-pressure water, or a method of removing manually can be employed.

  In the above embodiment, the steel caisson has been described as an example, but it can be applied to various marine steel structures such as steel sheet piles and bridge piers, and various other modifications can be made without departing from the scope of the present invention. Of course.

It is a side view which shows an example of an apparatus structure at the time of applying the anti-corrosion film formation method of this invention to the steel caisson of the breakwater which is an example of a marine steel structure. It is the front view which looked at FIG. 1 from the II-II direction. It is a diagram which shows the result of having investigated the production amount of calcium carbonate. It is a diagram which shows the result of having investigated the production amount of magnesium hydroxide. It is explanatory drawing of the film produced | generated on the cathode base material with the test apparatus. It is explanatory drawing which shows the state by which the film of FIG. 5 became the anti-corrosion film | membrane by the composition substitution effect | action. It is a diagram which shows the state from which the composition ratio of magnesium hydroxide and a calcium carbonate changes by stopping supply of an electric current, after forming the film | membrane mainly composed of magnesium hydroxide. It is the diagram which showed the change of the amount of coatings in the morbase. It is the diagram which showed the change of the coating amount on a weight basis. It is a diagram which shows the relationship between the current density of the marine steel structure by the electric current applied between electrodes, and the composition of a film.

Explanation of symbols

1 Steel caisson (marine steel structure) (cathode)
2 DC power supply 3 Subsea member (anode)
7 Coating 8 Anticorrosion film

Claims (2)

  A marine steel structure is used as a cathode, an anode is placed in the seawater facing the marine steel structure, a direct current is passed between the electrodes, and an anticorrosion film is formed on the marine steel structure by an electrolysis reaction of seawater. An anti-corrosion film forming method for anti-corrosion of marine steel structures, wherein an electric current is passed between electrodes so as to obtain a current density at which a film mainly composed of magnesium hydroxide is formed on the marine steel structure. A method for forming an anticorrosion film, comprising forming a film having a predetermined film thickness and then stopping the supply of electric current to form an anticorrosion film by a composition substitution action in which calcium carbonate is replaced with magnesium hydroxide generated in the presence of seawater. . Anticorrosive film forming method according to claim 1, the current density of the marine steel structure, characterized in that the current flow between the electrodes so as to 3~10A / m ^2.

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