JP2014034711A - Connection structure in plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection structure in a plant which can ensure sealability in a connection between components and prevent crevice corrosion in the connection.SOLUTION: Stainless steel piping 6A mounted with a flange 20A at its end and stainless steel piping 6B mounted with a flange 20B at its end are connected by coupling the flanges 20A, 20B with a bolt 21 and a nut 22. A ring-shaped gasket 24, which is a seal member, and a ring-shaped oxo acid salt holding body 23 are sandwiched between the flanges 20A, 20B. The oxo acid salt holding body 23 is arranged inside the gasket 24 and integrated with the gasket 24. The oxo acid salt holding body 23 is configured by impregnating a ring-shaped rock wool with sodium molybdate.

Description

  The present invention relates to a connection structure of a plant, and in particular, a gap between components of a passive metal used in contact with seawater in a nuclear power plant, a thermal power plant, a seawater desalination plant, or a salt production plant. The present invention relates to a connection structure of a plant suitable for preventing corrosion.

  In a nuclear power plant, in order to remove some of the heat generated by the nuclear reaction of nuclear fuel materials and the decay heat of the nuclear fuel materials contained in the spent fuel assemblies stored in the fuel storage pool, Need to be continuously cooled. In addition, cooling is necessary to remove the generated heat during operation of auxiliary equipment such as an emergency diesel generator. Their cooling is accomplished by transferring heat to the coolant and circulating the coolant between the nuclear power plant and the heat dissipation source. Air and water are used as the coolant. Air or seawater is used as the final heat radiation source for cooling. In a boiling water nuclear power plant, as a system to cool by circulating seawater, circulating water system, auxiliary equipment cooling seawater system, turbine auxiliary equipment cooling seawater system, waste treatment building auxiliary equipment cooling seawater system, and residual heat removal equipment There are seawater systems.

  Generally, in plants that handle and store aqueous solutions containing seawater components, it is difficult to provide corrosion protection and anticorrosion coating by polymer resin lining on the surface of plant components. The constituent member may be manufactured using a passive metal represented by Passive metals are easily passivated, so the corrosion rate due to overall corrosion is small.However, when the passive film is destabilized by chloride ions contained in seawater, local corrosion occurs and the corrosion rate increases. May increase. In order to prevent unexpected local corrosion, it is necessary to take measures against local corrosion due to chloride ions contained in seawater.

  When stainless steel, which is a typical passive metal, is used in contact with seawater, crevice corrosion is one of the main forms of local corrosion of stainless steel. In the occurrence of crevice corrosion, (A) the protection of the passive film is reduced due to the intrusion of chloride ions into the gap, (B) the formation of an oxygen concentration cell in the gap, and (C) the pH drop in the gap. There are three factors.

In addition to the loss of protection of the passive film of stainless steel by chloride ions contained in seawater, the inside of the gap is selectively corroded by the formation of oxygen concentration cells inside and outside the gap. Since the metal ionized by corrosion is hydrolyzed by the formula (1), the concentration of H ⁺ is increased. That is, since the pH in the gap is lowered, the solubility of metal ions is increased and the dissolution of stainless steel is further facilitated.

M ^{n +} + mH ₂ O → M (OH) _n−m + mH ⁺ (1)
The most drastic measure to avoid crevice corrosion is to adopt a structure that eliminates crevice structure as much as possible in the plant. On the other hand, in a plant for storing or circulating a fluid, it may be difficult to eliminate a gap structure in a flange portion that connects pipes. When crevice corrosion progresses in the flange portion and liquid leakage occurs, it is conceivable to replace the member that has crevice corrosion in the flange portion. However, this replacement work may cause a period during which the original functions of the plant cannot be obtained and increase the running cost. Therefore, it is possible to maintain the soundness of the plant and extend the life of the plant. Therefore, measures to avoid crevice corrosion are necessary.

  The following techniques are known as techniques for avoiding crevice corrosion.

  Titanium or a titanium alloy is used as a typical seawater corrosion-resistant metal material. Titanium is also a passive metal, but its seawater resistance is superior to general-purpose stainless steel. Also by using a passive metal material whose components are adjusted for seawater, it is possible to avoid crevice corrosion in the gap formed in the connection part into which seawater flows. Japanese Patent Laid-Open No. 8-20845 describes an example of the passive metal material. This passive metal material is an alloy prepared such that (Cr + 3Mo + 10N) of the chemical components is 35% or more.

  Moreover, crevice corrosion can be suppressed by using the sacrificial anode widely used for suppressing corrosion on the entire surface of the component. Japanese Patent Application Laid-Open No. 2005-194624 describes an example in which a sacrificial anode is provided in a heat exchanger that uses seawater as a cooling medium, which is a stainless steel device. In the heat exchanger, flanges provided on the channel cover are attached to the flanges provided on both ends of the body, and a graphite-based sealing material is disposed between the opposing flanges to seal between these flanges. A sacrificial anode using an iron-based alloy, a magnesium-based alloy, an aluminum-based alloy, zinc, a zinc-based alloy, or the like is installed on the inner surface of the channel cover in contact with seawater.

  Crevice corrosion can also be avoided by mitigating the corrosive environment in the gap. Japanese Patent Application Laid-Open No. 61-73783 describes a technique in which a packing impregnated with nitrate ions is sandwiched between flanges in order to suppress pitting corrosion of components forming a gap. Japanese Patent Laid-Open No. 2-199372 describes that a stainless steel packing having a molybdenum alloy layer formed on a surface thereof is interposed between flanges connecting stainless steel components, for example, pipes. Molybdate ions eluted from the molybdenum alloy layer suppress crevice corrosion of the flange. In Japanese Patent Laid-Open No. 3-199385, a joint portion between an aluminum alloy and stainless steel is covered and sealed with a sealant or a coating agent containing a phosphate (ammonium salt of phosphoric acid) to prevent pitting corrosion at the joint portion. Techniques to do this are disclosed.

JP-A-8-20845 JP 2005-194624 A JP-A 61-73783 Japanese Patent Laid-Open No. 2-199372 JP-A-3-199385

Jin Yatsushiro and three others, “Inhibiting effect of various oxoacid salts on crevice corrosion of SUS304 stainless steel in 423K chloride aqueous solution”, Zairyo-to-Kankyo, 45, 131-137 (1996).

  Passive metal materials with components adjusted for titanium, titanium alloys, and seawater are more expensive than general-purpose stainless steel that is mass-produced. Moreover, since the passive metal material is subjected to component adjustment in order to enhance seawater corrosion resistance, other characteristics such as workability and machinability may be deteriorated.

  The sacrificial anode needs to be installed by electrically connecting the electrode material to the surface of the plant component that is subject to anticorrosion and contacting the seawater, and the workability in installing and replacing the electrode material is poor.

  The packing impregnated with nitrate ions encloses a minute space for holding nitrate ions inside the packing material. That is, since the nitrate ions are impregnated, the sealing performance of the packing may be lowered.

  Use of the above-mentioned packing impregnated with nitrate ions, use of stainless steel packing with a molybdenum alloy layer formed on the surface, and sealing of the joint with a sealant or coating agent containing phosphate (ammonium phosphate) In each method, existing standard seal members cannot be used, and there is a problem of low versatility with respect to various shapes of joints.

  The objective of this invention is providing the connection part structure of the plant which can ensure the sealing performance in the junction part of a structural member, and can prevent the crevice corrosion in the junction part.

  A feature of the present invention that achieves the above-described object is that a seal member disposed between connected passive metal components, and between the connected components on the inner side of the seal member. And an arranged oxoacid salt support.

  Since the seal member and the oxo acid salt holder different from the seal member are disposed between the passive metal components, the sealability between the components can be secured. By disposing the acid salt holder, crevice corrosion of the constituent members in the gap formed between the constituent members can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the sealing performance in the junction part of a structural member can be ensured, and the crevice corrosion in the junction part can be prevented.

It is a block diagram of the junction part of stainless steel piping to which the crevice corrosion suppression method of Example 1 which is one suitable Example of this invention was applied. It is a block diagram of the auxiliary | assistant cooling seawater system of the emergency diesel generator used for the nuclear power plant to which the crevice corrosion suppression method of Example 1 is applied. FIG. 2 is a front view of a seal member to which the oxoacid salt holder shown in FIG. 1 is attached. It is IV-IV sectional drawing of FIG. NaCl, it is a characteristic diagram showing the difference in effects on crevice corrosion of the stainless steel in each of Na ₂ SO ₄ and artificial seawater. It is a block diagram of the junction part of the piping made from stainless steel to which the crevice corrosion inhibitory method of Example 2 which is another Example of this invention was applied.

The inventors measured the corrosion gap repassivation potential for SUS304 steel, which is a type of stainless steel, using the method described in JIS G 0593. In this method, two large and small plate-like test pieces are overlapped to form an artificial gap, immersed in a test solution, and measured using a potential / current control measuring device called a potentiostat. First, after the electrode potential of the test piece is polarized in a noble direction to generate crevice corrosion, the crevice corrosion is grown by maintaining a constant current for a predetermined time. Subsequently, the potential is lowered stepwise, and the potential at which the current does not increase with time is determined. This potential when the current stops increasing is called the corrosion gap repassivation potential. If the corrosion gap is kept below the repassivation potential in the actual use state, crevice corrosion does not occur and can be used as an index value for operation management. The results of measuring this corrosion gap repassivation potential for SUS304 are shown in FIG. In seawater with a chloride ion concentration of 1000 ppm or more, the corrosion gap repassivation potential in the test piece is about 0. 0 than the result obtained by adjusting the Cl ^- concentration with NaCl as shown in JIS G 0582. It became 2V higher. On the other hand, when the Cl ⁻ concentration was adjusted to 200 ppm using a NaCl reagent, the result was in good agreement with the result shown in JIS G 0592. However, when the same measurement was performed using 271 ppm Na ₂ SO ₄ , no crevice corrosion occurred, and therefore no corrosion gap repassivation potential was observed.

  The crevice corrosion of stainless steel in a seawater environment is one of the three factors described above (deterioration of the protection of the passive film due to the ingress of chloride ions into the gap, formation of oxygen concentration cells, and decrease in the pH of the gap). It can be suppressed by avoiding this. Therefore, by supplying negative ions with the same negative charge as chloride ions into the gap and causing adsorption competition with chloride ions, the apparent chloride ion concentration is reduced, thereby protecting the passive film. Deterioration can be avoided. Moreover, the pH fall in a clearance can be suppressed by making an anion which has a buffering action of pH exist in a clearance.

The corrosion gap repassivation potential artificial seawater becomes about 0.2V higher, and Na ₂ reason for crevice corrosion did not occur at SO _4, the crevice corrosion inhibiting effect of Na ₂ SO ₄ is oxo acid salt (Jin Yatsushiro and three others, “Suppressing effect of various oxoacid salts on crevice corrosion of SUS304 stainless steel in 423K chloride aqueous solution”, Zairyo-to-Kankyo, 45, 131-137 (1996)). Think. This document describes that nitrates, phosphates, and molybdates as well as sulfates as oxoacid salts may have the same action.

However, when crevice corrosion of stainless steel is suppressed by adding oxo acid salt to the solution, components using other materials such as carbon steel due to reasons such as increased conductivity due to the added oxo acid salt It may cause adverse effects in areas other than the focused area, such as acceleration of corrosion. In addition, since it is necessary to continue adding the oxoacid salt to the solution, there is a problem that the economic burden is increased.
Therefore, the inventors have provided an oxoacid salt carrier impregnated with an oxoacid salt only in a gap where there is a concern about crevice corrosion at a joint of stainless steel used in contact with a solution containing a seawater component. We thought that it was effective to install. That is, the inventors hold oxo acid salt as a separate member from the sealing material without changing the shape and dimensions of the existing sealing material such as packing or gasket installed at the joint of the plant component. I came up with the idea that I should install my body. Here, the oxoacid salt carrier is a member made of a chemically stable solid material and having a spongy or asbestos-like form. The chemically stable solid substance is composed of at least one of glass fiber, carbon fiber, ceramic fiber, expanded graphite, polymer resin fiber, and rock wool. As the oxo acid salt, at least one of sulfate, nitrate, molybdate and phosphate is used.

  Examples of the present invention reflecting the above examination results will be described below.

  The connection part structure of the plant of Example 1 which is one suitable Example of this invention is demonstrated using FIG. 1 and FIG. The connection structure of the plant of the present embodiment is applied to an auxiliary equipment cooling seawater system for cooling an emergency diesel generator of a nuclear power plant. Specifically, the connection structure of the plant of this embodiment is applied to a connection part of a pipe through which seawater of an auxiliary machine cooling seawater system flows, that is, a flange connection part.

  First, the structure of the auxiliary cooling seawater system 2 for cooling an emergency diesel generator of a nuclear power plant to which the connection structure of the present embodiment is applied will be described below with reference to FIG.

  The auxiliary cooling seawater system 2 includes a seawater system 3 in which seawater flows, heat exchangers 4 and 12, and a freshwater system 11. The heat exchanger 4 has a plurality of heat transfer tubes 5 arranged in the body. The seawater system 3 includes a seawater supply pipe 6, a pump 7, and a seawater discharge pipe 9. The seawater supply pipe 6 is connected to one end of each of the plurality of heat transfer pipes 5, and the seawater discharge pipe 9 is connected to the other end of each of the plurality of heat transfer pipes 5. The seawater supply pipe 6 and the seawater discharge pipe 9 are made of stainless steel. A pump 7 and an on-off valve 8 are provided in the seawater supply pipe 6. An on-off valve 10 is provided in the seawater discharge pipe 9. The other end portions of the seawater supply pipe 6 and the seawater discharge pipe 9 extend to the sea and are arranged in the seawater 25.

  The fresh water system 11 has a fresh water supply pipe 17, a fresh water return pipe 14 and a pump 15. The fresh water supply pipe 17 has one end connected to the body of the heat exchanger 4 and the other end connected to one end of each of the plurality of heat transfer tubes 13 of the heat exchanger 12. The fresh water return pipe 14 has one end connected to the body of the heat exchanger 4 and the other end connected to the other end of each of the plurality of heat transfer tubes 13 of the heat exchanger 12. An on-off valve 18 is provided in the fresh water supply pipe 17. A pump 15 and an on-off valve 16 are provided in the fresh water return pipe 14. The fresh water supply pipe 17 and the fresh water return pipe 14 are connected to each other by a pipe provided with an on-off valve 19.

  The auxiliary cooling seawater system 2 is a system that removes heat generated by combustion of diesel fuel and transmitted to the structural members of the emergency diesel generator 1 when the emergency diesel generator 1 is operated. For this reason, the heat exchanger 12 is provided in the emergency diesel generator 1.

  When the emergency diesel generator 1 is operated, the on-off valves 8, 10, 16 and 18 are opened and the pumps 7 and 15 are driven. By driving the pump 15, fresh water (pure water) is supplied from the fresh water supply pipe 17, the heat transfer pipes 13 of the heat exchanger 12, the fresh water return pipe 14, and the heat exchanger 4 outside the heat transfer pipe 5 to the fuselage and fresh water. It circulates in a closed loop formed by the supply pipe 17. The heat generated by the operation of the emergency diesel generator 1 is removed by heating the cooling water (fresh water) flowing through the emergency diesel generator 1. This cooling water is cooled by the fresh water that flows in the body of the heat exchanger 12 outside the heat transfer tubes 13 and flows in the heat transfer tubes 13. The cooling water whose temperature has been lowered by cooling circulates in the structural member of the emergency diesel generator 1 toward the fuselage of the heat exchanger 12 for heat removal.

  The fresh water whose temperature has increased in each heat transfer tube 13 is supplied to the fuselage outside the heat transfer tube 5 of the heat exchanger 4 through the fresh water return tube 14 and cooled by seawater 25 flowing in each heat transfer tube 5. The Fresh water whose temperature has been reduced by cooling with seawater is supplied into each heat transfer tube 13 of the heat exchanger 12 through the fresh water supply tube 17.

  The seawater 25 whose pressure has been increased by driving the pump 7 is supplied into each heat transfer pipe 5 of the heat exchanger 4 through the seawater supply pipe 6. The seawater 25 flowing in each heat transfer tube 5 cools the fresh water flowing in the body of the heat exchanger 4. The seawater 25 whose temperature has risen due to the cooling of fresh water is discharged from each heat transfer pipe to the seawater discharge pipe 9 and is discharged to the sea through the seawater discharge pipe 9.

  In the seawater system 3 through which the seawater of the auxiliary cooling seawater system 2 flows, the connection part of the pump 7 and the seawater supply pipe 6, the connection part of the on-off valve 8 and the seawater supply pipe 6, the on-off valve 10 and the seawater discharge pipe 9 There are connecting portions, connecting portions between the plurality of pipes constituting the seawater supply pipe 6, and connecting portions between the plurality of pipes forming the seawater discharge pipe 9. The plurality of pipes constituting the seawater supply pipe 6 in the auxiliary cooling seawater system 2 used in the nuclear power plant, the plurality of pipes constituting the seawater discharge pipe 9, the pump 7 and the on-off valves 8 and 10 are respectively a nuclear power plant. It is a constituent member. For this reason, each above-mentioned connection part is a connection part of the structural members of a nuclear power plant.

  There are gaps formed in the connecting portions, and crevice corrosion may occur in the connecting portions due to the intrusion of seawater components into the gaps in the connecting portions. For this reason, the connection part structure of the plant of a present Example is applied to each above-mentioned connection part in the seawater system 3 of the auxiliary machine cooling seawater system 2. FIG. The connection part structure of the present embodiment will be specifically described with reference to FIG. The connection structure shown in FIG. 1 is applied to the seawater supply pipe 6. A stainless steel pipe 6A and a stainless steel pipe 6B constituting the seawater supply pipe 6 are connected. The connection structure of the stainless steel pipe 6A and the stainless steel pipe 6B includes a flange 20A provided at the end of the stainless steel pipe 6A and a flange 20B provided at the end of the stainless steel pipe 6B. A nut 24 is used for coupling, and a gasket 24 as a seal member and an oxoacid salt holder 23 are arranged between the flange 20A and the flange 20B. The gasket 24 and the oxoacid salt holder 23 are sandwiched between the flange 20A and the flange 20B. The flanges 20A and 20B are also made of stainless steel. The bolt 21 and the nut 22 are connecting members that connect the stainless steel pipe 6A and the stainless steel pipe 6B.

  As described above, the stainless steel pipe 6A provided with the flange 20A and the stainless steel pipe 6B provided with the flange 20B are constituent members of the nuclear power plant, and the flange 20A is a part of the stainless steel pipe 6A. The flange 20B is also a part of the stainless steel pipe 6B.

  The oxoacid salt holder 23 and the gasket 24 have a ring shape as shown in FIG. The oxo acid salt holder 23 is disposed inside the gasket 24, and the outer periphery of the oxo acid salt holder 23 is attached to the inner periphery of the gasket 24. For this reason, the oxoacid salt holder 23 and the gasket 24 are integrated. The oxoacid salt holding body 23 is configured by impregnating sodium molybdate into a rock wool formed in a ring shape. The oxo acid salt holder 23 may include any one or more of sulfate, nitrate, molybdate, and phosphate as the oxo acid salt.

  When connecting the stainless steel pipe 6A and the stainless steel pipe 6B, the gasket 24 and the oxoacid salt holding body 23 are sandwiched between the flange 20A and the flange 20B, and the bolt 21 and the nut 22 are tightened to a predetermined torque, thereby the flange 20A. And the flange 20B. As a result, the gap between the flange portion 20A and the flange portion 20B is narrowed, but the oxoacid salt holder 23 is deformed in accordance with the dimension of the gap, so that the inherent sealing property of the gasket 24 is not impaired.

  The connection part structure shown in FIG. 1 is another connection part in the seawater system 3, that is, a connection part between the pump 7 and the seawater supply pipe 6, a connection part between the on-off valve 8 and the seawater supply pipe 6, an on-off valve 10 and a seawater discharge pipe. 9, connection portions between a plurality of pipes constituting the seawater supply pipe 6, and connection portions between a plurality of pipes constituting the seawater discharge pipe 9.

  When the emergency diesel generator 1 is driven, the seawater 25 is supplied to the heat transfer pipe 5 of the heat exchanger 4 through the seawater supply pipe 6 as described above. A part of the seawater 25 enters a gap formed inside the oxoacid salt holder 23 between the flange 20A and the flange 20B. However, since the oxoacid salt holder 23 is disposed between the flange 20A and the flange 20B, the sodium molybdate impregnated in the oxoacid salt holder 23 is formed in the gap formed between the flange 20A and the flange 20B. The molybdate, which is an oxo acid salt, is present in the sea water in the gap. The oxoacid salt carrier 23 supplies molybdate ions having the same negative charge as chloride ions into the gap, and causes adsorption competition with the chloride ions, thereby destroying the passive film. By reducing the surface concentration of the product ions, it is possible to avoid a decrease in the protective properties of the passive film. Moreover, the pH fall in a clearance can be suppressed by making the molybdate ion which has a pH buffering effect exist in a clearance. For this reason, crevice corrosion in the surface which contacts seawater in a crevice of flange 20A and flange 20B by the action of molybdate can be controlled.

  According to the present embodiment, since the oxoacid salt holder 23 which is a member different from the gasket 24 which is a seal member is disposed between the flange 20A and the flange 20B which are joined to each other, the flange 20A and the flange 20B can be sufficiently secured, and further, by the action of molybdate eluted from the oxoacid salt holder 23 into the seawater in the gap formed between the flange 20A and the flange 20B, Generation | occurrence | production of the crevice corrosion in the flange 20A and the flange 20B can be suppressed. Since there is almost no flow of seawater in the gap, the molybdate eluted in the seawater in the gap is substantially present in the gap. Therefore, when the oxo acid salt is continuously added to the stainless steel pipe 6A (or the stainless steel pipe 6B), that is, the seawater 25 flowing in the seawater supply pipe 6 continuously throughout the operation period of the plant. Therefore, it becomes possible to suppress crevice corrosion.

  In this embodiment, an oxoacid salt holder 23 and a gasket 24 are used. For this reason, since the gasket 24 can be applied without changing the material, shape and dimensions of the existing sealing material, the versatility of the gasket 24 is high. Since an existing material can be used for the oxoacid salt holder, it can be manufactured and installed inexpensively and easily.

  In this embodiment, since the oxo acid salt holding body 23 and the gasket 24 are integrated, the operation of arranging the oxo acid salt holding body 23 and the gasket 24 between the flange 20A and the flange 20B can be easily performed. .

  The connection structure of the plant of Example 2, which is another example of the present invention, will be described with reference to FIG. The connection structure of the plant of this embodiment is also applied to an auxiliary cooling seawater system for cooling an emergency diesel generator of a nuclear power plant. Specifically, the connection structure of the plant of this embodiment is a connection structure that joins two stainless steel pipes using a union joint.

  The union joint has female connectors 31 </ b> A and 31 </ b> B and a cap nut 32. The female connectors 31A and 31B and the cap nut 32 are all made of stainless steel. The female connector 31A is attached to the end of the stainless steel pipe 30A with screws. The female connector 31B inserted into the cap nut 32 is attached to the end of the stainless steel pipe 30B with a screw with the cap nut 32 attached. The female connector 31A attached to the stainless steel pipe 30A and the female connector 31B attached to the stainless steel pipe 30B are arranged to face each other, and the cap nut 32 attached to the female connector 31B is formed on the outer peripheral surface of the female connector 31A. Engage with the threaded part. By tightening the cap nut 32, the female connector 31A and the female connector 31B are coupled, and as a result, the stainless steel pipe 30A and the stainless steel pipe 30B are coupled.

  The female connector 31A attached to the stainless steel pipe 30A is a part of the stainless steel pipe 30A that is a constituent member of the nuclear power plant. The female connector 31B attached to the stainless steel pipe 30B is a part of the stainless steel pipe 30B that is a constituent member of the nuclear power plant.

  Prior to tightening the cap nut 32, the oxoacid salt holder 23A and the gasket 24 are disposed between the female connector 31A and the female connector 31B. By tightening the cap nut 32 as described above, the oxoacid salt holder 23 and the gasket 24 are sandwiched between the female connector 31A and the female connector 31B. The ring-shaped oxoacid salt holding body 23A is configured by impregnating sodium tetrafluoride fibers with an ethylene tetrafluoride fiber formed into an annular filter paper shape. The oxoacid salt holder 23 </ b> A is also disposed inside the gasket 24 and is integrated with the gasket 24. The oxoacid salt support 23A may include any one or more of sulfate, nitrate, molybdate, and phosphate as the oxoacid salt.

  When the emergency diesel generator 1 is driven, the seawater 25 is supplied to the heat transfer pipe 5 of the heat exchanger 4 through the seawater supply pipe 6 as described above. At this time, a part of the seawater 25 enters between the female connector 31A and the female connector 31B in a gap formed inside the oxoacid salt holding body 23A. The crevice corrosion of the female connector 31A and the female connector 31B is suppressed by the action of nitrate eluted from the oxoacid salt holding body 23A into the seawater in the gap.

  In the present embodiment, each effect produced in the first embodiment can be obtained.

  Examples 1 and 2 described above are used in other passive metal components (for example, piping) that may come into contact with seawater in nuclear power plants, and in thermal power plants, seawater desalination plants, and salt production plants. It is used to prevent crevice corrosion of passive metal components used in contact with seawater.

  2 ... Auxiliary cooling seawater system, 3 ... Seawater system, 4,12 ... Heat exchanger, 6 ... Seawater supply pipe, 6A, 6B, 30A, 30B ... Stainless steel pipe, 9 ... Seawater discharge pipe, 11 ... Freshwater system, 23, 23A ... oxo acid salt holder, 24 ... gasket, 31A, 31B ... female connector, 32 ... cap nut.

Claims (4)

In the connection part structure of the plant that connects the constituent members that are made of passive metal and that are opposed to each other and made of passive metal,
A seal member disposed between the connected component members, and an oxoacid salt holder disposed between the connected component members inside the seal member. The connection structure of the plant.   2. The plant according to claim 1, wherein the seal member and the oxoacid salt holder have a ring shape, and the seal member and the oxoacid salt carrier disposed inside the seal member are integrated. Connection structure.   The plant connection structure according to claim 1 or 2, wherein the oxo acid salt carrier includes one or more oxo acid salts of sulfate, nitrate, molybdate, and phosphate.   4. The plant connection structure according to claim 3, wherein the oxo acid salt support is configured by applying the oxo acid salt to a spongy solid or an asbestos solid.

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