JPH01263285A - Method and device for electrolytically protecting all-titanium heat exchanger - Google Patents

Abstract

PURPOSE:To prevent the corrosion of a steel surface due to the electrolytic corrosion even at the carbon steel part jointly used with a titanium material by controlling the voltage and current value so that an electric potential capable of controlling the hydrogen embrittlement of a titanium material in the vicinity of the lower part of a tube plate in each water chamber. CONSTITUTION:A reference electrode 39a is set at the lower part of an outlet water chamber 9 lined an inside of the chamber 9 with an electrical insulating coating material 42, the potential is set at a value nobler than -600mVSCE, and a detection potential is returned to an electrolytic protection device 38 to prevent the hydrogen embrittlement of the titanium material. The region L2 of the outlet circulating water passage 10 communicating with the outlet water chamber 9 is also lined with the similar rubber 42. The region of the outlet circulating water pipe other than the region L2 is lined with a tar epoxy resin 43 as the anticorrosion coating material, a reference electrode 39b is set at the boundary with the rubber tube 42, and the detection potential is returned to the electrolytic protection device 38. Meanwhile, an external power source electrode 36 to be controlled by the electrolytic protection device 38 is set at a distance of L3 from the outlet water chamber 9. Accordingly, the hydrogen embrittlement of the titanium material is obviated, and further the electrolytic corrosion of the part of a carbon steel can be prevented.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention is aimed at preventing galvanic corrosion of piping equipment connected to an all-titanium heat exchanger that uses seawater as a refrigerant. This invention relates to a method and device for cathodic protection of all-titanium heat exchangers used in

(Prior Art) In general, a shell-and-tube type heat exchanger 9, for example, a condenser in a power generation plant, which uses seawater as cooling water is widely used. Since the cooling pipes of this condenser come into direct contact with seawater, the cooling pipes are made of noble metals that are difficult to corrode.For example, copper alloys, mainly aluminum brass, are used for the condenser tube sheets, and naval brass plates are used for the condenser tube sheets. is used. on the other hand,
Steel is used for the condenser water chamber, equipment and piping connected to the condenser. Monel and stainless steel are also used for instrumentation such as thermometer wells.

An example of a condenser that returns steam to water in a power generation plant, as well as equipment, piping, and instrumentation in the vicinity of the condenser will be described below with reference to FIG. 11.

Steam 1 discharged from the steam turbine is guided to a condenser 2, is cooled by contacting the outer surface of a plurality of cooling pipes 3 through which cooling seawater flows inside the condenser 2, and is condensed into condensed water. becomes.

This condensate is recovered from the condenser 2 by the condensate pump 4 for reuse in the power generation plant, and is sent to a feedwater heater (not shown).

Generally, aluminum brass pipes are used for the cooling pipes 3 of the condenser 2. On the other hand, the cooling seawater 6 is generally supplied through an inlet circulating water pipe 7 made of a carbon steel sheet coated with anti-corrosive coating or coating such as tar epoxy resin, and then passed through an inlet water chamber 8 made of the above-mentioned aluminum brass pipe. It passes through the inside of the cooling pipe 3 made of pipe, absorbs the heat of the steam 1 through the cooling pipe 3, and is discharged to the outlet (sea) through the outlet water chamber 9 and the outlet circulating water pipe 1O while increasing the temperature. . The inlet circulating water pipe 7 and outlet circulating water pipe 10 are generally equipped with a butterfly valve 1 for stopping and switching the cooling seawater 6, and a thermometer 12 for detecting and monitoring temperature, pressure, etc. ) and a pressure gauge 13 (pressure detection seat) are attached. Additionally, a ball cleaning device is installed to maintain the cleanliness of the inner surface of the cooling pipe 3. That is, the cleaning balls collected by the ball collector 14 from the cooling seawater are guided to the ball recirculation pipe 15, passed through the ball circulation pump 16, and transported to the ball collector 17, and from there, the balls are returned to the ball injection pipe 18. This is injected into the cooling seawater flowing through the inlet circulating water pipe 7, and by repeating this process, foreign matter adhering to the inner surface of the cooling pipe 3 is removed.

In addition, an inlet circulation water pipe 7 and an inlet water chamber 8. A rubber expansion joint 19 is attached to the connection between the outlet water chamber 9 and the outlet circulation water pipe 10 to absorb installation errors and minute displacements during operation.

Furthermore, an air vent pipe 20 and an air vent valve 21 are attached to the inlet water chamber 8 and the outlet water chamber 9 in order to vent air. Note that the reference numeral 22 in the figure indicates a tube plate.

By the way, in order to prevent seawater from corroding the parts of condensers and circulating wood pipes that come into contact with seawater, sufficient care is taken in the design, including selection of materials and protection with coatings on metal surfaces or anti-corrosion coatings. That is, in general, corrosion phenomena include natural corrosion in which a single metal is corroded in an acidic environment, and galvanic corrosion (hereinafter abbreviated as electrolytic corrosion) that occurs when dissimilar metals are in contact. Particular attention must be paid to this electrolytic corrosion, as the rate of corrosion is very fast. Electrolytic corrosion usually occurs when electrically connected dissimilar metals are placed in an electrolyte solution, and a natural potential difference is formed with the noble metal at the cathode and the base metal at the anode, and the anode metal interacts with metal ions. This is a phenomenon in which base metals are corroded by being eluted into the electrolyte solution. Figure 12 shows the natural potential of metals in seawater. The natural potentials of seven types of metals are shown here, with titanium being the scrap metal that is most often eaten away, and zinc being the metal that is most commonly used by cars.

For example, when the brass and iron on the car side are in contact with water in seawater, and the brass and iron are electrically connected, the natural potential difference V between these two metals causes the iron on the car side to This will result in electrolytic corrosion. In addition, when the stainless steel (passive state) and the iron on the car side come into contact in seawater, and the stainless steel (passive state) and iron are electrically connected, the natural potential difference between these two metals is The steel on the car side is subject to electrolytic corrosion due to the V. The same thing can be said for other metal combinations, and the greater the natural potential difference between these two metals, the more the electrolytic corrosion phenomenon progresses. Note that the unit of potential on the horizontal axis, VSCE, indicates the saturation potential.

These phenomena can also occur in the seawater systems of power plants.

For example, electrolytic corrosion can occur between exposed metal on instrumentation such as cooling pipes, strainers, valves, thermometer wells, etc. used in heat exchangers. Additionally, in addition to the above-mentioned materials, the following materials can be considered. That is, in order to prevent corrosion of the steel surface, the inner surface of the piping equipment is coated with an anticorrosive coating or coating material so that the steel surface does not come into direct contact with seawater.

However, if the painted or coated surface is damaged for some reason, the steel surface will be exposed in seawater, and when the aforementioned noble metal material and base metal steel surface are electrically connected, the two metals will If the steel surface on the vehicle side is subjected to electrolytic corrosion due to natural potential difference, for example, the cooling pipe 3 of the condenser 2 mentioned above is made of aluminum brass, and the condenser tube plate 22 is made of naval brass. are used, the inlet and outlet water chambers 8, 9 and the inlet and outlet circulation water pipes 7, 10 are usually made of steel plates, so the steel plates become the metal on the vehicle side.

As mentioned above, these inlet and outlet water chambers 8 and 9 and the inlet and outlet circulating water pipes 7 and 10 are coated with anticorrosive coatings or coatings, but these coatings or coatings may be damaged due to poor construction or Damaged by seawater flow, etc.
When the underlying steel surface is exposed, the base metal steel surface is subject to electrolytic corrosion due to the natural potential difference between brass and iron, as described above.

This phenomenon will be explained in detail below with reference to the drawings.

In FIG. 13, there is a damaged coating 23a in the outlet water chamber 9 of the condenser 2, and a damaged coating 23a is also found in the outlet circulating water pipe 1o.
Assume that 3b exists. Therefore, the damaged coating part 2
3a and 23b have exposed steel surfaces. Here, the condenser 2 is grounded 25 by the foundation etc., and
It is assumed that the outlet circulating water pipe 10 is also grounded 25 by a support of a piping device or underground piping. From the above, the cooling seawater 6 passes through the damaged coating part 23a of the outlet water chamber 9 and the damaged coating part 23b of the outlet circulating water pipe 10,
An electrical circuit is formed that passes through the body of the condenser 2 via the tube plate 22 and the cooling pipe 3, thereby removing the damaged coating 23a,
23b to condenser tube plate 22. A corrosive current 24 flows into the cooling pipe 3, causing electrolytic corrosion to the damaged coating parts 23a and 23b. It should be noted that this phenomenon is of course not limited to the outlet water chamber 9 and the outlet circulating water pipe 10, and the situation is the same for the inlet water chamber 8 and the inlet circulating water pipe 7.

On the other hand, although the above phenomenon has been described for the case where the cooling tube 3 and the tube plate 22 are made of noble metal, the ball collector 14 shown in FIG. Ball injection tube 18. Butterfly valve 11. If the take-out parts of the thermometer 12 and pressure gauge 13 are made of stainless steel, etc., which is nobler than iron,
These stainless steel etc. and coating damaged parts 23a, 23b
A natural potential difference occurs between the two irons, and the base metal iron undergoes electrolytic corrosion in the same way as described above.

This phenomenon will also be explained in detail with reference to FIG. 14. In FIG. 14, a ball collector 14 made of a material such as stainless steel is installed in the outlet circulating water pipe 10.
A ball recirculation pipe 15 is connected to this. Therefore,
As explained in FIG. 13, the tube sheet 22. Corrosion current 2 flowing through cooling pipe 3
In addition to 4, an electric circuit is formed which runs from the coating damaged portion 23b of the outlet circulating water pipe 10, through the cooling seawater 6, through the ball collector 14, and through the outlet circulating water pipe 10. As a result, a corrosion current of 2
4 will flow, and in this case too, the damaged coating portion 23b will be electrolytically corroded. This phenomenon is affected by the condenser tube plate 22 and the cooling pipe 3 when the damaged coating part 23b is close to the condenser 2, and when the damaged coating part 23b is close to the ball collector 14, it is affected by the influence of the condenser tube plate 22 and the cooling pipe 3. It is affected by the collector 14. The stainless steel mentioned here is a stainless steel with a stable passive film, and as shown in Figure 12, the potential of stainless steel (passive) is usually O ~ = 100 mV.
Although it is about SCE, if the thickness of the above-mentioned passive film is sufficient, brass becomes more base than stainless steel (passive).

For this reason, unless an abnormal condition occurs, use stainless steel! (passive) is not subject to electrolytic corrosion. However, if the operating conditions of the condenser 2 change and a part of the surface of the stainless steel becomes active due to special conditions, such as foreign matter in seawater, the stainless steel becomes more base. The phenomenon in which a natural potential difference occurs between the naval brass plate of the tube sheet 22 and the aluminum brass tube of the cooling tube 3, and in this case stainless steel undergoes electrolytic corrosion, will be explained with reference to FIG. In FIG. 15, it is assumed that a part of the ball collector 14 installed in the outlet circulating water pipe 10 is in an active state, and the other part is covered with a passive film. At this time, it is assumed that the area where the active state has appeared is in area A in the figure.

In this case, the electrical circuit runs from the outlet circulating water pipe 10 to the exposed stainless steel ball collector 14, and then to the cooling seawater 6.
The circuit passes through the condenser tube plate 22 and the cooling pipe 23, and then through the shell of the condenser 2. From the exposed portion of the ball collector 14 covered with the passive coating, the ball collector 14 passes through area A of the ball collector 14.

Tube plate 22. A corrosive current 24 flows into the cooling pipe 3, and in this case as well, the stainless steel ball collector 14 is electrolytically corroded mainly in the area A.

As a method of protecting equipment from electrolytic corrosion in the inlet and outlet water chambers 8 and 9 and the inlet and outlet circulating water pipes 7 and 10, a widely used method is to flow an anticorrosive current into the inlet and outlet water chambers 8 and 9. ing. On the other hand, in response to a similar phenomenon in the ball collector 14 and the like, it is also practiced to prevent electrolytic corrosion by flowing an appropriate anti-corrosion current in the vicinity thereof.

Hereinafter, specific methods of cathodic protection will be explained focusing on these measures. In FIG. 16, reference numeral 26 indicates an external power supply electrode, to which an electrolytic protection device for generating a corrosion protection current 27 is connected.

Furthermore, a reference electrode 29 is attached to the lower part of the outlet water chamber 9 to control the corrosion protection potential and current value. This reference electrode 29 is connected to the electrolytic protection device 28 via a potential control device 30. Although not shown here, the inlet water chamber 8
A similar device has also been installed to produce similar effects.

In the above configuration, the anti-corrosion current 27 flows from the external power supply electrode 26 to the condenser tube plate 22. Cooling pipe 3. Coating damage part 23a.

23b, and the corrosion current 24 (see FIG. 13) flowing from the damaged coating parts 23a and 23b is extinguished. Thereby, electrolytic corrosion of the damaged coating parts 23a and 23b can be prevented. Further, at this time, local corrosion of the tube sheet 22 and the cooling pipe 3 is also prevented.

Incidentally, the reference electrode 29 and the potential control device 30 are installed to control the potential and current value of the cathodic protection device 27, and detect the potential at the position where the reference electrode 29 is attached and feed it back to the cathode protection device 27. ing. Normally, when cathodic protection is applied, the natural potential of the metal is 200~
Corrosion protection of the metal is achieved by setting the voltage to the base side of about 250 mV. Generally, the natural potential of iron in seawater is approximately 450 to -650+*V, as shown in Figure 12.
It is about SCE, and the anticorrosion potential of iron is set from this.

Furthermore, the corrosion prevention effect increases as the surface is placed closer to the car, but coating materials such as rubber and tar epoxy resin applied to the steel surface for corrosion protection have the problem that if placed too close to the car, the surface deteriorates and peels off. There is, and it cannot be set very much on the car side. Therefore, normally -650 to -900mV S
Set in the CE range.

On the other hand, if a stainless steel ball collector 14 is provided in the path of the outlet circulating water pipe 10, it is necessary to prepare for electrolytic corrosion of the stainless steel. In this case, cathodic protection is performed centering on the ball collector 14 as follows.

That is, in FIG. 17, reference numeral 31 indicates an external power supply electrode, to which an electrolytic protection device 33 for generating a corrosion protection current 32 is connected. In addition, the outlet circulation water pipe 10
A reference electrode 34 for controlling the anti-corrosion potential and current value is attached to a location adjacent to the ball collector 14. This reference electrode 34 is connected to the electrolytic protection device 33 via a potential control device 35.
It is tied to

In the above configuration, the anticorrosion current is transmitted from the external power supply electrode 31 to the ball collector 14. Flows to the damaged film part 23, and the damaged film part 23
The more flowing corrosion current 24 (see FIG. 13) is extinguished. Thereby, electrolytic corrosion of the damaged coating portion 23 can be prevented. At the same time, localized corrosion such as pitting corrosion and crevice corrosion of the ball collector 14 as well as active corrosion are also prevented.

Note that the reference electrode 34 and the potential control device 35 are also installed here to control the current value of the cathodic protection device 33,
The potential at the position where the reference electrode 34 is attached is detected and fed back.

Next, how can we deal with corrosion in a condenser where the main parts of the condenser 2, which is conventionally made of brass-based materials, are made of titanium, a metal that is more harmful than brass? Explain what you are doing.

Generally, such a condenser made of titanium material is called an all-titanium condenser, but the configuration of the condenser, peripheral equipment, piping, instrumentation, etc. is as shown in Figure 11. There is no difference. A typical all-titanium condenser of this type is used in large-scale thermal power plants and nuclear power plants, and the tube sheet 22 and cooling pipes 3 are made of titanium material.

The tube plate 22 and the cooling pipe 3 made of titanium material have extremely excellent corrosion resistance, and as long as the corrosion caused by seawater itself is limited, these parts can be largely excluded. However, as mentioned above, metals other than titanium are used for other parts of the all-titanium condenser, and metals less base than titanium are also used for peripheral equipment, piping, and products. However, due to the potential difference between the titanium material and other metals, it is inevitable that electrolytic corrosion will occur on the side metal.

In addition to this, all-titanium condensers are shown in Figures 16 and 1.
It is not enough to simply deal with the electrolytic corrosion phenomenon described in Figure 7; there are problems that must be tackled from a different perspective. This is the problem of hydrogen embrittlement, which is a phenomenon specific to titanium materials. Hydrogen embrittlement is a phenomenon in which metal materials become brittle due to the absorption of hydrogen.
This is caused by the start of hydrogen absorption when polarization is made to the side of 00 mV S CE. Therefore, when preventing electrolytic corrosion by the method shown in FIGS. 16 and 17, the corrosion protection potential must be set to a potential at which the titanium material does not develop hydrogen embrittlement.

FIG. 18 shows a method of applying cathodic protection to an all-titanium condenser based on the above-mentioned points. In addition,
In the figure, the same parts as those shown in FIGS. 16 and 17 are designated by the same reference numerals.

In FIG. 18, reference numeral 36 indicates an external power supply electrode, to which an electrolytic protection device 38 for generating a corrosion protection current 37 is connected. Further, at the lower part of the outlet water chamber 9 and at the end of the outlet circulating water pipe 10 on the condenser 2 side, there is a reference pole 39a for controlling the anti-corrosion potential and the current value.

39b are provided respectively. These reference electrodes 39a
.

39b is a cathodic protection system via potential control devices 40a and 40b! ! 138 respectively. In addition, in the figure,
Reference numeral 41 indicates ground. Although not shown here, a similar device is also provided in the inlet water chamber 8, so that similar effects can be obtained.

In the configuration described in item 1, the anti-corrosion current 37 is connected to the external power supply electrode 36.
From the tube plate 22. Cooling pipe 3. Damaged coating parts 23a, 23b
Corrosion current 24 (see FIG. 13) flowing from the damaged coating parts 23a and 23b is extinguished. Here, the reference electrode 39a detects the potential at the lower part of the outlet water chamber 9 and returns it to the cathodic protection device 38, but the set potential in this case is -600 mVSCE in order to avoid hydrogen embrittlement of the titanium material. I try to eat more than I can.

On the other hand, the reference electrode 39a detects the potential near the outlet of the circulating water pipe 10 and returns it to the electrolytic protection device 38. In this case, the set potential is -650 to -900 mV for iron.
It is set to a certain degree.

Note that the method for dealing with the electrolytic corrosion phenomenon in the stainless steel ball collector 14 is the same as that described in FIG. 17.

(Problems to be Solved by the Invention) As described above, in the all-titanium condenser, the coating damage parts 23a, 23 that occur in the outlet water chamber 9 and the outlet circulation wood pipe lO.
Outlet circulating water pipe 10 to prevent electrolytic corrosion on the exposed steel surface of b.
An external power supply electrode 36 is provided at , from which a corrosion protection current 37 is applied.
For example, the water is directed toward the damaged coating 23a present in the outlet water chamber 9, but in this case, the external power supply electrode 3
6 extremely close to the outlet water chamber 9 side, the anti-corrosion current 37 flows into the damaged coating portion 23a, and at the same time, the anti-corrosion current 37 also flows into the tube plate 22 and the cooling pipe 3 which are not subject to corrosion protection.

When this loss current flows into the tube plate 22 and the cooling pipe 3,
Since the polarization characteristics of the titanium material vary depending on the magnitude of the current value, the titanium material exhibits a potential closer to the vehicle than the natural potential it exhibits in seawater. Therefore, the potential detected by the reference electrode 39a at the lower part of the outlet water chamber 9 is closer to the vehicle than the potential of about -600 mVSCE at which titanium material becomes hydrogen brittle, and the feedback signal from the reference electrode 39a is guided to the potential control device 40a. As a result, the corrosion protection potential of the cathodic protection device 38 is selectively controlled, and the corrosion protection current 37 output from the external power supply electrode 36 is limited.

but.

At this time, as a result of the corrosion prevention potential being limited to corrosion, it deviates from the corrosion prevention potential of iron, -650 to -900 mV S CE, and it becomes impossible to prevent electrolytic corrosion of the coating damage part 23a of the outlet water chamber 9. . Similarly, it is also no longer suitable to stop electrolytic corrosion of the damaged coating portion 23b of the outlet circulating water pipe 10 near the outlet water chamber 9.

As a countermeasure to this problem, it is conceivable to provide the external power supply electrode 36 at a location far away from the outlet water chamber 9.

In this case, the loss current flowing through the tube plate 22 and the cooling tube 3 is significantly smaller than in the above case, and the reference electrode 3
The detection potential of 9a is lower than the above-mentioned approximately -600 mV S CE, and hydrogen embrittlement of the titanium material does not occur. However, the fact that this detected potential is lowered means that when looking at the entire inside of the outlet water chamber 9, the potential is further lowered in areas far from the reference electrode 39a. The anti-corrosion current 37 will no longer flow.

At this time, suppose that the external power supply electrode 36 is moved far away from the outlet water chamber 9 and at the same time the corrosion protection potential of iron is -650 to -900 mV.
If it is possible to set SCE to the lower side,
This is relatively easy to deal with and is considered desirable.

However, if such a measure is taken in the vicinity of the outlet circulating water pipe 10 to which the external power supply electrode 36 is attached, there is a concern that the following problem will occur, and there is no possibility that it will actually be used. In other words, rubber is applied to the steel surface to prevent corrosion of outlet circulation wood pipes, etc.

Measures to prevent surface peeling of coating materials such as tar epoxy resin further increase corrosion protection potential and current values, making deterioration more likely, and there is a risk that these materials will peel off from the steel surface, which is a major problem. becomes.

In this way, the corrosion protection potential of iron is simply -650 to -900 mV.
It is not preferable to bring the SCE to a more base side because it causes inconvenience to the coating material.

On the other hand, as mentioned earlier, the conventional cathodic protection method, which lacks the necessary consideration for the installation location of the external power supply electrode 36, cannot be said to be truly useful for preventing electrolytic corrosion, and improvements are needed. ing.

Therefore, the purpose of the present invention is to suppress the hydrogen embrittlement of titanium materials used in heat exchangers, and also to reliably prevent the steel surface from being corroded due to galvanic corrosion even in the carbon steel parts used together with the titanium materials. An object of the present invention is to provide a method for cathodic protection of an all-titanium heat exchanger and an apparatus therefor.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention has a pair of water chambers connected to a heat exchanger body, and seawater as a refrigerant is passed through heat transfer tubes from one of the water chambers to the other. In this case, each heat exchanger tube and the tube plate supporting the heat exchanger tube are made of titanium material, and each water chamber and the piping device connected to the water chamber are made of titanium material, which is electrically less expensive than titanium material. In the cathodic protection method for all-titanium heat exchangers, which are manufactured using metal materials such as In order to maintain the anti-corrosion potential in each water chamber and each piping device by covering the area with a relatively robust insulating material, we suppressed the hydrogen embrittlement of the titanium material near the bottom of the tube plate in each water chamber. It is characterized by controlling the voltage and current values so as to maintain a possible potential, and a potential that is at least more base than the natural potential of iron in seawater near the boundary of the area covered by the insulating material in each piping device. shall be.

Further, the cathodic protection device for an all-titanium heat exchanger according to the present invention has a pair of water chambers connected to the heat exchanger, and uses titanium material together with the tube plate that supports the cold heat transfer tube, and each water chamber has a pair of water chambers connected to the heat exchanger. In an all-titanium heat exchanger manufactured using a metal material that is electrically more base than titanium material together with the piping equipment connected to the chamber, the entire area inside each water chamber and a certain area connected to the water chamber in each piping equipment. The area is covered with a relatively strong insulating material so that the electrical insulation of In addition to providing reference electrodes for the vicinity of the water chambers, external power supply electrodes are also provided at a certain distance from each of the water chambers so that the corrosion protection potential at these points can be maintained at a predetermined value. .

(Function) Figure 2 shows the potential distribution at the center of the outlet water chamber and the outlet circulation wood pipe determined by experiment and analysis. In the figure, the vertical axis shows the potential at the center of the pipe, and the horizontal axis shows the parts of the outlet water chamber 9 and the outlet circulating water pipe 10 shown above the graph. The potential distribution is determined by changing the positions of the external power supply electrodes 36 in the outlet circulation wood pipe 10 to maintain the same potential (
This is when the voltage value is controlled to maintain approximately -1000mV 5CE), and the outlet water chamber 9 and outlet circulation water pipe 10
The distribution curves (a), (b), and (c) are created by connecting the measured potentials in
). First, (a) shows the potential distribution when the mounting position of the external power supply electrode 36 is ideal. becomes the potential of CE,
Inside the outlet water chamber 9, the potential is greater than -500 mVSCE. In other words, the outlet circulating water pipe 1 exhibits a higher potential than approximately -770 mV S CE as the boundary point.
0 and the outlet water chamber 9 following it are in a region where the steel surface is easily attacked by electrolytic corrosion if appropriate measures are not taken. On the other hand, the area within the outlet circulating water pipe 10 exhibiting a potential less noble than about -770 mVSCE is an area where cathodic protection is effective, and there is little risk of electrolytic corrosion on the steel surface.

According to the above experiment and analysis results, the area where the steel surface has a potential of more than approximately -770 mV S CE, where there is a risk of being attacked by electrolytic corrosion, is constructed using a material with particularly excellent electrical insulation properties. Approximately - within the inner and outlet circulating water pipes 10
Cover areas exhibiting potentials nobler than 770 mVSCE.

On the other hand, a region exhibiting a potential less noble than about -770 mV S CE is coated with a material mainly having anticorrosion properties in consideration of suppressing corrosion of the steel surface. Note that since the expansion joint 19 installed in the outlet circulating water pipe 10 is originally made of an insulating material (such as rubber), it may be excluded from the scope of cathodic protection.

Next, (b) shows the potential distribution when the external power supply electrode 36 is closer to the outlet water chamber 9 side than in the case (a). (a
), the location showing a potential of about -770 mV is closer to the outlet water chamber 9 side. That is, the area where the cathodic protection effect is applied is closer to the outlet water chamber 9 side than in (a), and the area covered by the material having total electrical insulation properties is reduced. However, the potential inside the outlet water chamber 9 is -500 mVS
Compared to (a) where CE is cut, the potential is significantly closer to the base side, and the potential is -600 mV S, which is accompanied by hydrogen embrittlement of the titanium material.
When approaching CE, if the potential changes significantly due to dirt on the tube plate 22 and cooling pipe 3 and swings to the base side,
00mVSCE may be reached, and (b) has less margin than (a), so the risk of hydrogen embrittlement is higher.
It is difficult to adopt.

Further, in contrast to (b), the potential distribution when the external power supply electrode 36 is attached at a position further away from (a) is shown as (C). In comparison with (a), the potential in the outlet water chamber 9 in this case is further shifted to a potential that poses no problem with regard to the hydrogen embrittlement of the titanium material. However, when compared with (a), the potential inside the outlet circulating water pipe 10 is approximately -770 mVSCE at the location where the potential is at the outlet water chamber 9.
It looks further away from the sky. That is, due to the movement of the area over which the cathodic protection effect is applied, the area covered by the electrically insulating material expands, whereas the area covered by the anticorrosion material narrows. In this way, extending the area covered by the electrically insulating material, in other words, expanding the area where the effect of cathodic protection does not reach, must be done with greater care, taking into account possible damage to the coating material. Furthermore, there is a limit to the application of economically expensive insulating materials. In the end, the external power supply electrode 36 is not attached to the position showing the potential distribution in (C),
This will be arranged so that the covered area is shorter. However, as described above, when the potential distribution becomes as shown in (b), there is a growing concern about hydrogen embrittlement of the titanium material. Therefore, in (a) there are few areas that are not covered by cathodic protection,
Furthermore, it can be said that the potential distribution is such that hydrogen embrittlement of the titanium material does not occur.

On the other hand, in another experiment and analysis, the potential near the external power supply electrode 36 was changed from about -1000 mV S CE in the above experiment to about -
The potential distribution was measured by increasing the voltage to 1,500 mV S CE. This is the distribution curve shown by the dashed line in the figure. If we compare it with (a), it is clear that the area where the effect of cathodic protection extends is even wider than in (a), but simply increasing the potential setting will only cause more harm than good. . That is, the potential inside the outlet water chamber 9 is -600
mV S CE is approaching, and the risk of hydrogen embrittlement is increasing, and -10100OS C
Since it is set closer to the car than E, the insulating material is likely to peel off.

Therefore, the potential of the external power supply electrode 36 is approximately -1000m
It is desirable to set the upper limit to VscE.

In addition, the lower limit of the corrosion protection potential is the natural potential car of iron in seawater 4
50~-650mV SCE with te, approx.-650m
VS CE.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the interior of the outlet water chamber 9 is covered with an electrically insulating covering material, for example rubber 42 of a robust construction. A reference electrode 39a is attached to the lower part of the outlet water chamber 9, and its potential is set to be lower than -600 mV S CE, and a detection potential is applied to the cathodic protection device 38 to prevent hydrogen embrittlement of the titanium material. They are being sent back. Further, a region L2 of the outlet circulating water pipe 10 that is connected to the outlet water chamber 9 is also covered with a similar rubber 42. Usually, the expansion joint 19 is made of rubber, and there is no exposed steel surface in the region L2.

Further, the area other than L2 of the outlet circulation wood pipe 10 is covered with tar epoxy resin 43, which is a coating material having anti-corrosion properties, and a reference electrode 39b is installed at the boundary between the rubber 42 and this tar epoxy resin 43. ing. The set potential of the reference electrode 39b is closer to the vehicle than -770 mV S CE, and the detected potential is fed back to the electrolytic protection device 38 to prevent the steel surface from being corroded by electrolytic corrosion.

On the other hand, an external power supply electrode 36 controlled by the cathodic protection device 38 is installed at a distance of .
Therefore, the area covered by cathodic protection beams.

It becomes Ll by subtracting L2 from.

Below, L3 is approximately 4.8 m + the inner diameter of the outlet circulating water pipe 10 is 2.4 m, and the potential of the external power supply electrode 36 is approximately -1000 mV.
We will discuss the measurement results of the potential and current value in the lower part of the outlet water chamber and the potential distribution in the outlet circulation wood pipe in the case of SCE.

First, changes in the potential in the lower part of the outlet water chamber will be explained.

In FIG. 3, the vertical axis in the figure represents the potential at the center of the outlet circulating water pipe 10, and the horizontal axis represents the distance from the external power supply electrode 36 to the heat exchanger side.

When L3 is about 4.8 m (L, /D: 2), the potential up to about 4.8 mm away from the external power supply electrode 36 is shown as a curve (g), and the lower part of the inside of the outlet water chamber 9 It is understood that the potential of is on the more noble side than 1600 mV S CE. In this case, in the range from about 4.8 m to about 3.3 m, the potential becomes lower than 1600 mV S CE, and hydrogen embrittlement of the titanium material does not occur within this range.

By the way, in FIG. 3, curves (h) and (i) show cases where the beam is about 2.4 m and about 1.2 m. Note that these values are 1.0 times and 0.5 times the inner diameter of the outlet circulating water pipe 10.

The potential of curves (h) and (i) is -600 mV SC
Hydrogen embrittlement occurs in the titanium material because it is always on the less-base side than E. Therefore, the distance was set twice as far as the inner diameter (g
) should be the goal.

Next, changes in current value will be explained.

In FIG. 4, the vertical axis is the external power supply electrode 36.
The horizontal axis shows the distance from the heat exchanger to the external power supply electrode 36.

From FIG. 4, when the distance is greater than about 4.8 m, the current remains almost constant at a little less than 2 amperes. Moreover, when it becomes smaller than this, the current value increases rapidly.

Next, the potential distribution within the outlet circulating water pipe IO will be explained. Note that the conditions are the same as those in FIGS. 3 and 4, except that the potential of the external power supply electrode 36 is approximately -1500 mV S
The case of CE is also shown.

In FIG. 5, the vertical axis represents the potential at the center of the outlet circulating water pipe 10 on the heat exchanger side from the external power supply electrode 3G, and the horizontal axis represents the distance from the external power supply electrode 36 to the heat exchanger side. are shown respectively.

Curve (j) indicates that the potential of the external power supply electrode 36 is approximately -1000 m.
The potential distribution of the outlet circulating water pipe 10 in the case of VSCE is shown. Although it varies somewhat depending on the current value, within a distance of about 2.4 m from the external power supply electrode 36, the potential distribution becomes less noble than 1770 mV S CE, and the desired corrosion prevention result on the steel surface can be obtained. On the other hand, the part beyond this (the shaded part) is -77
The potential becomes nobler than 0 mVSCE, and no anticorrosion effect can be obtained.

In order to contrast with the curve (j), the potential distribution at the center of the outlet water chamber 9 and the outlet circulation wood tube 10 when the potential of the external power supply electrode 36 is about -1500 mV S CE is shown as the curve (k). It varies slightly depending on the current value, but within a distance of approximately 4.1 m from the external power supply electrode 36, 1770 mVS
The potential distribution is on the more base side than CE, and the anticorrosion effect extends over a wider range than the above potential, but this potential keeps the potential at the lower part of the outlet water chamber 9 at an appropriate value as shown in (g) in Figure 3. (about -
+000a+V S CE ) and cannot be relied upon.

Based on the above figures 3, 4, and 5, when the external power supply electrode 36 is installed at a position of about 4.8 m, the range in which corrosion protection can be obtained is about 2.4 m, so L ,=L
, -L□= 4.8-2.4 = 2.4, which is about 2
．． In this case, the area covered by the insulating material is 4 m or more.

Next, another embodiment of the present invention will be described.

In this embodiment, the potential of the external power supply electrode 36 is 1770 mVS.
It is held at about -700 mV, which is a more negative potential than CE.

This can be considered especially when it is desired to further increase the economical effect by setting the electric potential to a lower value than in the above embodiment to lower the current value, and by reducing the area covered by expensive rubber. That's the way to do it.

In FIG. 6, similarly to the above embodiment, the inside of the outlet water chamber 9 and the region L2 connected thereto are covered with rubber 42 having a robust structure, and there are no exposed parts of the steel surface at these locations. Note that the area L2 includes the expansion joint 19.

Further, the area other than L2 of the outlet circulation wood pipe 10 is covered with the tar epoxy resin 43. External power 'If! The X electrode 36 is installed at a position within this covered area, and Ll, which is obtained by subtracting L2 from L, is the area to be subjected to cathodic protection in this case.

Hereinafter, L is approximately 3.6 m, and the inner diameter of the outlet circulation wood pipe 10 is 2.
．． 4m, the potential of the external power supply electrode 36 is approximately -700mV S
The measurement results of the potential in the lower part of the outlet water chamber 9, the current value, and the potential distribution in the outlet circulating water pipe 10 in the case of CE will be explained.

First, changes in the potential in the lower part of the outlet water chamber will be explained with reference to FIG. In the figure, the vertical axis represents the potential at the center of the outlet circulating water pipe 10, and the horizontal axis represents the distance from the external power supply pole 36 to the heat exchanger side.

When L3 is about 3.6 m (L3/D clause 1.5), that is, the potential up to a distance of about 3.6 m from the external power supply electrode 36 is shown as curve (e), and in this case,
Since the potential at the lower part of the outlet water chamber 9 is lower than -600 mV S CE, hydrogen embrittlement of the titanium material does not occur.

In addition, the beams of songs a (m) and (n) are 0.5 m (L,
/D clause 0.2) and 0.24m (L, /D#0.1
) is shown. In either case - 600f
Hydrogen embrittlement occurs in the titanium material because it is closer to the car than the SCE. Therefore, it is necessary to separate them by a distance that is 1.5 times the inner diameter.

Next, changes in current value will be explained with reference to FIG. Note that here, the vertical axis indicates the current value from the external power supply electrode 36, and the horizontal axis indicates the distance from the heat exchanger to the external power supply electrode 36. As shown in FIG. 8, when the distance is greater than 3.6 m, the current remains almost constant at a little less than 0.2 ampere. Furthermore, as the distance becomes smaller, the current value increases rapidly.

Next, the potential distribution within the outlet circulating water pipe IO will be explained with reference to FIG.

In the figure, the vertical axis represents the potential at the center of the outlet circulating water pipe 10 on the side closer to the heat exchanger than the external power source electrode 36, and the horizontal axis represents the distance from the external power source electrode 36 to the heat exchanger side.

Curve (o) indicates that the potential of the external power supply electrode 36 is approximately -700 mV.
The potential distribution of the outlet circulating water pipe 10 in the case of SCE is shown. Although it varies somewhat depending on the current value, within a distance of about 1.7 m from the external power supply electrode 36, the potential distribution becomes about -650 mV S CE on the car side, and the corrosion protection of the steel surface becomes an area where there is almost no problem. On the other hand, the part exceeding this (the shaded part) becomes eroded from about -650 mV S CE and no anticorrosive effect can be obtained.

Based on the above figures 7, 8, and 9, when the external power supply electrode 36 is installed at a position of about 3.6 m, the range in which the anticorrosive effect can be obtained is about 1.7 m, so 12= L
, -L1=3.6-1.7=1.9, about 1.9
m or more is the area covered by the electrically insulating material in this case.

The set potential of the outlet circulation wood pipe 10 of this embodiment is at the limit of the natural potential of iron in seawater, and is 770 mVscE in the above embodiment.
Although the reliability will be somewhat impaired because the cost will be more wasted than the above, if economic efficiency is important, this embodiment makes it possible to obtain a corresponding effect.

Furthermore, a method different from each of the above embodiments will be explained with reference to FIG. In FIG. 10, the configuration of this embodiment is the sixth
Taking the method shown in the figure one step further, reference electrodes 44a, 44
b is changed from zinc material to steel material, and for its set potential,
This is the natural potential of iron in seawater. That is, when using steel reference electrodes, the reference electrodes 44a, 44
When the potential near b is lower than the natural potential of iron in seawater, the potential of the reference electrode itself is immediately detected and an anticorrosive current is applied. If this happens, it can be detected immediately and the anti-corrosion current can be reduced, which has the advantage of being able to accurately grasp the corrosion and anti-corrosion status of the steel surface. With reference electrodes made of ordinary zinc materials, there is some variation in the potential measured, and errors pose a problem. In the case of the reference electrode made of zinc material in the above embodiment, it is difficult to decide what value to set the potential.
Even when set to 0mV S CH, there is a time lag in the detection potential, and furthermore, there are variations in the natural potential of the zinc material and variations due to environmental conditions.

There are variations in the potential during zinc polarization, and errors in the measured potential must be taken into account, but the reference voltage of steel material +444a,
By using 44b, there is no need to worry about such errors.

〔Effect of the invention〕

As explained above, the present invention uses a relatively robust insulating material to maintain electrical insulation of the entire area inside each water chamber and a certain area connected to the water chamber in each piping device. In order to maintain the anti-corrosion potential in each water chamber and each piping device, we maintain a potential that can suppress the hydrogen embrittlement of the titanium material near the bottom of the tube plate in each water chamber, and insulating material in each piping device. Since the voltage and current values are controlled to maintain a potential on the car side that is at least higher than the natural potential in seawater near the boundary of the covered area, there is no risk of hydrogen embrittlement in titanium materials, and carbon steel This has the excellent effect of reliably preventing electrolytic corrosion of the parts made of the material.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the apparatus applied to the method of the present invention, FIG. 2 is a potential distribution diagram showing the state of potential distribution in the present invention, and FIG. 3 is an embodiment shown in FIG. 1. FIG. 4 is a characteristic diagram showing the change in electric potential at the lower part of the outlet chamber, FIG. 4 is a characteristic diagram showing changes in the current value, FIG. 6 is a configuration diagram showing another embodiment of the apparatus applied to the method of the present invention, FIG. 7 is a characteristic diagram showing changes in potential at the lower part of the outlet water chamber according to the embodiment shown in FIG. 6, and FIG. Figure 9 is a characteristic diagram showing the change in the current value, Figure 9 is a characteristic diagram showing the potential distribution state in the outlet circulating water pipe, Figure 1O is a configuration diagram showing still another embodiment of the present invention, and Figure 11 is a characteristic diagram showing the potential distribution state in the outlet circulating water pipe. A system configuration diagram showing a conventional condenser and piping equipment connected to it; FIG. 12 is a characteristic diagram showing the natural potential of various metals in seawater;
FIGS. 13, 14, and 15 are explanatory diagrams showing the electrolytic corrosion phenomenon in a condenser, and FIGS. 16, 17, and 18 are configurations showing an example of a conventional cathodic protection device in a condenser. It is a diagram. 2... Condenser 3... Cooling pipe 7... Inlet circulating water pipe 8... Inlet water chamber 9... Outlet water chamber
lO... Outlet circulating water pipe 22... Tube plate 26
．． 31.36...External power supply electrode 28, 33.38...
- Cathodic protection device 29, 34. 39a, 39b - Reference electrode 42...Rubber 43...Tar epoxy resin agent Patent attorney Nori Chika Ken Yudo Daishimaru Ken 1st figure From the Kawamachi equipment to the electric train K paralysis y I elephant (rs) 1 Nyayosu's distance *<rn> Figure 8? , Distance from the main gallery (m) Figure 9 Figure 11 Figure 12 Figure 131

Claims (4)

[Claims] (1) It has a pair of water chambers connected to the heat exchanger body, and is configured so that seawater as a refrigerant flows from one of the water chambers to the other through the heat exchanger tubes, and in this case, each of the heat exchanger tubes is made of titanium material together with the tube plate that supports the heat exchanger tube, and each of the water chambers and the piping devices connected to the water chambers are made of a metal material that is electrically less noble than titanium material. In the cathodic protection method for titanium heat exchangers, in order to maintain suitable electrical insulation of the entire area inside each water chamber and a certain area connected to the water chamber in each piping device, the area is covered with a relatively robust insulating material. In order to maintain the anti-corrosion potential in each of the water chambers and each piping device, a potential that can suppress the hydrogen embrittlement of the titanium material near the bottom of the tube plate in each of the water chambers is maintained, and each of the piping An all-titanium heat exchanger characterized in that the voltage and current values are controlled so as to maintain at least a potential on the more base side than the natural potential of iron in seawater near the boundary of a region covered by an insulating material in the device. Cathodic protection method. (2) The entire area inside each water chamber and an area approximately 2.4 m from the bottom of the water chamber in the piping equipment are coated with an insulating material, and in order to maintain the anticorrosive potential in each water chamber and the piping equipment, each A potential of approximately -600 mVSCE is applied near the bottom of the tube plate in the water chamber, and approximately -
2. The cathodic protection method for an all-titanium heat exchanger according to claim 1, wherein the voltage and current values are controlled so as to maintain a potential of 770 mVSCE. (3) It has a pair of water chambers connected to the heat exchanger body, and is configured to flow seawater as a refrigerant from one of the water chambers to the other through the heat exchanger tubes, and in this case, each of the heat exchanger tubes The tube plate supporting the heat exchanger tubes is made of titanium material, and each of the water chambers and the piping devices connected to the water chambers are made of a metal material that is electrically less noble than titanium material. In the heat exchanger, the area is covered with a relatively robust insulating material so that electrical insulation is suitably maintained over the entire area within each water chamber and a certain area connected to the water chamber in each piping device. , a reference electrode is provided near the bottom of the tube plate in each of the water chambers and near the boundary of the area covered by the insulating material in each of the piping devices, and the anticorrosion potential at these points is maintained at a predetermined value. A cathodic protection device for an all-titanium heat exchanger, characterized in that an external power supply electrode is provided at a certain distance from each of the water chambers. (4) The installation location of the external power supply electrode is approximately 4 from the bottom of each water chamber.
．． 4. The cathodic protection device for an all-titanium heat exchanger according to claim 3, wherein the device is installed in a piping system 8 meters apart.