JP3503565B2 - Valve and nuclear power plant using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve in which a corrosion-resistant and wear-resistant alloy is diffusion-bonded to a new sliding portion, and a nuclear power plant using the valve.

[0002]

2. Description of the Related Art Valves such as global valves, gate valves, butterfly valves, etc. are corrosion resistant to prevent erosion damage due to fluid near the valve seat during actual operation or to prevent galling during valve operation. Surface welding alloys such as high hardness cobalt (Co) based alloys, nickel (Ni) based alloys, and iron (Fe) based alloys having excellent wear resistance are used by being built up on the sliding portion of the valve.

However, in recent years, in turbine power generation equipment and the like, chemicals such as hydrogen peroxide water have been injected into the circulating water system to adjust the quality of circulating water, and the amount of dissolved oxygen downstream from the injection point of the chemicals. As a result, the valve seat surface of the valve is damaged by erosion and galling. This is because the eutectic carbide such as cobalt (Co) -based alloy that is built up on the sliding portion of the valve is selectively corroded and damaged. Following the corrosion damage of the eutectic carbide in the high-speed fluid, the base material part (matrix) of the cast structure may drop off and erosion may occur (“Thermal Nuclear Power Generation”: 30, Vol.
5, 67, "Damage to Machines": 1982, No. 2, 9
Page 0, and "Materials and Environment": Volume 47, No. 3,207
page).

Conventionally, erosion prevention is applied to the sliding parts of valves.
To prevent galling, high hardness Co-based alloys, Ni-based alloys, Fe-based alloys, etc. are overlaid as surface-welding alloys.

However, high-temperature, high-pressure water containing a large amount of dissolved oxygen
In a steam atmosphere, when using a valve or the like with a Co-based alloy built up, a mesh-like eutectic carbide that surrounds the base material (matrix) of the cast structure and the base material of the cast structure The eutectic carbide is selectively corroded, the surface roughness of the valve seat becomes remarkable, and the base material portion of the cast structure may easily fall off due to the flow. For this reason, there is a possibility that the leakage resistance of the valve may be deteriorated and that the control characteristic or the operating characteristic may be changed.

[0006] In nuclear power generation equipment, in sliding parts in contact with reactor water and valves of system equipment for supplying cooling water into the reactor, high hardness Co-based alloys etc. It is mixed in the system due to corrosion and erosion.

Carbon steel, structural alloy steel, low alloy steel, etc. are often used as the base metal for sliding parts of conventional valves. These carbon steel, structural alloy steel, low alloy steel, etc. When a surface-welding alloy such as Co-based alloy, Ni-based alloy, Fe-based alloy, etc. is built up on the surface, the surface of carbon steel, structural alloy steel and low-alloy steel undergoes rapid heating / cooling. Occurrence,
(2) Change in shape and dimension, (3) Decrease in fracture toughness and impact value,
(4) Corrosion resistance to various types of corrosion and deterioration of fatigue properties may occur.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a valve having improved corrosion resistance and erosion resistance of a sliding portion and a nuclear power plant using the valve.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to an alloy having a eutectic carbide on the sliding surface of a base material made of carbon steel mainly composed of ferrite and pearlite, structural alloy steel and low alloy steel. The above eutectic carbide is aggregated into a plurality of grains or a plurality of spheres to have a particle size of about 30 μm or less, preferably 10 μm
This valve is joined to a member made of a corrosion- and wear-resistant cobalt-based alloy, nickel-based alloy, or iron-based alloy with the following eutectic carbides in a discontinuous distribution. Cobalt-based alloy, by weight, C0.6-3%, Si2% or less, Cr25-32
%, W 15% or less, preferably 4 to 15%, Fe0 to 3
%, Ni 0 to 3%, Mo 0 to 6% are preferable. The nickel-based alloy is C1% or less by weight, preferably 0.2 to 0.5%, Si3 to 7% or less, and Cr7 to 18% by weight.
%, W3% or less, preferably 0.5 to 2%, and B3% or less are preferable. In addition, the Fe-based alloy, by weight,
C1.5 or less, preferably 0.3 to 1.0%, Si4% or less, preferably 0.5 to 3%, Cr15 to 27%, W3
% Or less, preferably 0.5 to 2% is preferable.

According to the present invention, the structure of the base metal in the sliding portion is made mainly of ferrite and pearlite by controlling the cooling rate after joining. The hardness is preferably about Hv100-250.

The alloy having the cast structure base material and the eutectic carbide is subjected to plastic working by forging or rolling or heat treatment to form a corrosion-resistant / wear-resistant alloy in which the eutectic carbide is discontinuously distributed by diffusion bonding. It is preferably joined to the sliding portion.

Furthermore, said diffusion bonding is liquid phase diffusion bonding in which an insert material having a melting point lower than that of the base material is inserted into the bonding interface to diffuse a melting point depressing element into the base material to promote solidification and bonding. Preferably, the insert material is by weight, S
i1-8%, B1-5%, preferably Si3-6%, B
Nickel-based alloy containing 2 to 4% or further Cr
Nickel-based alloys containing 5 to 20% are preferred.

Conventionally, as one method for discontinuing the eutectic carbide continuously distributed in the form of a mesh in the form of granules or spheres, plastic working such as forging / rolling and heat treatment of a surface welding alloy for overlay welding ( Annealing) or hot forging at high humidity
Although there is a method of performing hot rolling, the method is not limited to this.

The joining of the corrosion resistant and wear resistant alloy in which the eutectic carbide is discontinuous to the sliding portion can be easily realized by diffusion bonding, especially liquid phase diffusion bonding. In liquid phase diffusion bonding, an insert material having a melting point lower than that of the base material (non-bonding material) is inserted into the bonding interface, and the melting point depressing elements such as B, Si, P contained in the insert material during bonding (heating) Since the solidification / bonding is promoted by diffusing into the material, the pressing force at the time of bonding can be made smaller than the so-called solid phase diffusion bonding, and the deformation due to the bonding is also small. Further, good joining can be achieved even when the precision of mechanical heating of the joining surface is Rmax of about 20 μm. The present invention is to control the cooling rate to room temperature after diffusion bonding at high temperature. In the conventional method of overlaying a surface-welded alloy, the surface of the carbon steel of the sliding base metal, the structural alloy steel and the low alloy steel undergoes rapid heating / cooling, so that the microstructure of the overlay of the base metal The presence of martensite, bainite, etc. may cause problems such as generation of large residual stress, reduction in fracture toughness and impact value, and reduction in corrosion resistance and fatigue properties. On the other hand, in the present invention, the temperature-time curve after diffusion bonding, that is, the cooling curve, is the martensite in the continuous cooling transformation (CCT) diagram of the carbon steel, the structural alloy steel and the low alloy steel which are the base metal of the sliding portion. Alternatively, by controlling so as not to cross the region containing bainite, a microstructure mainly composed of ferrite and pearlite and a hardness of Hv 250 or less were realized, and the above problems were solved. If the hardness is Hv250 or less,
For example, the corrosion resistance and stress resistance of the base metal under the environment containing H ₂ S are greatly improved.

As a method of joining a base material (non-bonding material) through a liquid phase, brazing has been known from the past.
In brazing, the chemical bonding force and the physical adhesive force between the brazing material and the base material are mainly used, and the mutual diffusion between the brazing material and the base material is less than in the liquid phase diffusion bonding, Therefore, the liquid phase diffusion bonding is also excellent in the reliability of the bonding portion such as the bonding strength.

According to the present invention, by diffusion-bonding this to the sliding parts of various devices and valves, it is possible to suppress the corrosion damage of the eutectic carbide caused by the dissolved oxygen generated by the injection of hydrogen peroxide solution or the like. At the same time, to suppress the increase in frictional resistance of sliding parts of equipment and valves and the deterioration of leakage resistance due to roughness of valve seat surface, etc., to provide various equipment and valves excellent in impact resistance and maintenance performance. You can

Further, according to the present invention, a Co base or Ni having a granular or spherical eutectic carbide cut out from a plate material / bar material subjected to plastic working such as forging or rolling and heat treatment (annealing).
Diffusion bonding of corrosion resistant and wear resistant alloys such as base and Fe base to valve seats,
In particular, by liquid phase diffusion bonding, it is possible to provide a safety valve, a sluice valve, a sphere valve, and the like, which have reduced corrosion damage and erosion damage such as a valve seat caused by molten oxygen and have good impact resistance.

Further, according to the present invention, corrosion, erosion, and corrosion of Co-based alloys used in valves of nuclear power plants
By suppressing the scattering and diffusion of Co due to wear or the like, it is possible to provide a nuclear power plant with excellent maintainability.

In the Co-based corrosion resistant and wear resistant alloy of the present invention, plastic working such as forging and rolling, and subsequent heat treatment (annealing), etc.
Alternatively, by performing hot forging and hot rolling at high temperature, the eutectic carbides are discontinuously distributed in a granular or spherical shape in the base material of the cast structure, and the corrosion damage of the carbides due to dissolved oxygen comes into contact with the dissolved oxygen. It is limited only to the carbide on the surface, and the base material of the cast structure is less likely to fall off.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION [Example 1] 1050 to 1100
Eutectic carbide is granulated or spherical with a grain size of 30 μm or less by hot forging at ℃ or hot rolling at the same temperature 1.0 wt% C-30.0 wt% Cr-4.5 wt% W is included The high-hardness corrosion-resistant / wear-resistant Co-based alloy plate 3 was bonded to the valve body 1 and the valve body 2 of the sluice valve used in the dissolved oxygen atmosphere shown in FIG. 1 by liquid phase diffusion bonding. 1A is a sectional view of a gate valve body, FIG. 1B is a sectional view of a valve body 2, and FIG. 1C is a sectional view of a valve box 1. After cleaning the valve body / valve seat / valve box surface of the sluice valve, the joining insert material is placed on the valve seat surface of the valve body / valve box, and then the eutectic carbide is granulated or spherical on the material. The above-mentioned Co-C-Cr- in the shape of a ring plate having a thickness of about 7 mm
Liquid phase diffusion bonding was performed with W corrosion resistant and wear resistant alloy placed. The insert material with a thickness of about 40 μm used for joining is 7% by weight.
Cr-3 wt% Fe-4.5 wt% Si-3.2 wt% B
It is a Ni-based alloy containing Al and completely melts at about 1040 ° C.
Liquid-phase diffusion bonding conditions are: bonding temperature: 1100 ° C., holding time: 1 h, degree of vacuum: 1-2 × 10 ⁻⁴ Torr, pressure: about 8
It was set to 0 g / cm ² . In addition, cooling after joining is performed from 1100 ° C to 650 ° C at about 150 ° C / h, from 650 ° C to 425 ° C.
Approximately 100 ° C / h up to ° C, and air cooling below 425 ° C.
The material of the valve element / valve seat base metal was alloy steel forged steel SFVA F11A for high temperature pressure vessel, and the hardness when it was cooled to room temperature after joining was about Hv170.

When cross-sectional optical microscope observation was performed near the bonding interface after bonding, bonding defects such as voids in pinholes were scarcely observed, indicating a good bonding state.
The microstructure of the valve body / valve seat base metal SFVA F11A was mainly composed of ferrite and pearlite.
In the sluice valve produced by the method of the present invention, continuous corrosion generation of eutectic carbide due to dissolved oxygen is suppressed, and falling of the base material portion of the cast structure is suppressed, so that corrosion / erosion of the valve seat 1 is suppressed. The progress is suppressed, and the deterioration of the leakproof performance is prevented.

Example 2 Co-C-Cr produced by the same liquid phase diffusion bonding as in Example 1 and the subsequent cooling process.
-W alloy / SFVA F11A joint and Co on SFVA F11A
A V-notch impact test piece was cut out from each of the conventional Co-C-Cr-W / SFVA F11A overlays produced by overlay welding of a -C-Cr-W alloy by gas welding, and the joint or overlay was cut. We hit the shock value of base metal SFVA F11A near the part. The build-up conditions are preheating temperature: about 630 ° C., gas:
A mixed gas of oxygen and acetylene was used. The chemical composition of the overlay welding material used for gas welding is Co-1.0 wt% C-28.0 wt% Cr-4.0 wt% W. An impact test at 0 ° C. was performed on these samples. In the method of the present invention, the impact value is about 15 kgf · m, and the notch toughness of the base metal is good, whereas the conventional overlay welding by gas welding is about 5 kgf · m.
Notch toughness is inferior to m. Regarding the conventional method, a post-heat treatment similar to that performed in order to improve the performance of the welded portion in the welded joint portion and remove harmful effects such as welding residual stress was applied after the gas welding overlay. Also in this case, the impact value is still about 7 kgf · m, which is smaller than that of the method of the present invention, and it is clear that the present invention improves the impact resistance of the equipment and valves, especially the sliding parts thereof. In the present invention, in addition to mainly using ferrite and pearlite as the microstructure of the sliding part base metal made of carbon steel, structural alloy steel or low alloy steel, it is also important to set the hardness to Hv250 or less. Is one. When the hardness is Hv 250 or less, a sliding base metal having good corrosion resistance and stress corrosion resistance can be obtained even in an environment containing H ₂ S, for example.

Although the low melting point Ni-based alloy is used as the insert material in the above-mentioned first and second embodiments, Fe-based or Co-based low-melting point insert material can also be used. Further, the method of the present invention is applied not only to the sluice valve but also to sliding parts such as a check valve, a safety valve, a valve seat, etc., to reduce the leakage resistance, controllability and operating performance. Has the effect of suppressing the decrease of

[Embodiment 3] In this embodiment, 1050-1
1.1% by weight of high hardness of eutectic carbide having a grain size of 30 μm or less formed into particles or spheres by hot forging at 100 ° C.
A corrosion-resistant and wear-resistant Co-based alloy plate 3 containing 29.7% by weight Cr-4.5% by weight by liquid phase diffusion bonding in a dissolved oxygen atmosphere in a check valve valve box 1 and valve body 2. Joined to. The check valve body in this embodiment is made of the same base metal as in the first embodiment.

FIG. 2 is a vertical sectional view of the check valve.

The insert material used for joining was 7 wt% Cr
A Ni-based alloy containing -3 wt% Fe-4.5 wt% Si-3.2 wt% B, and its solidus temperature and liquidus temperature are about 970 ° C and about 1000 ° C, respectively. The liquid phase diffusion bonding conditions were a bonding temperature: 1090 ° C., a holding time: 1 h, a vacuum degree: 2 × 10 ⁻⁴ Torr, and a pressing force: 50 g / cm ² .

When the cross section of the bonding interface was observed after the bonding, bonding defects such as voids were scarcely observed and a good bonding state was shown.

Further, in the check valve produced in this example, continuous corrosion of eutectic carbide due to dissolved oxygen is suppressed, and the base material portion of the cast structure is prevented from falling off. Corrosion is suppressed, and deterioration of leak resistance is prevented.

In Example 2, a low melting point Ni-base alloy was used as the insert material, but a Fe-based or Co-based low-melting point insert material can also be used. Further, it is preferable that the insert material contains Cr which is effective for corrosion resistance, whereby the corrosion resistance of the joint portion, particularly the corrosion resistance of the joint portion in a high temperature / high pressure water / steam atmosphere containing a large amount of dissolved oxygen can be maintained.

[Embodiment 4] FIG. 3 is an example of a piping system diagram of a nuclear power plant in which the sluice valve and the check valve described in Embodiments 1 to 3 are used for a water supply system. Since these valves according to the present invention are present in a large number in the water supply system piping, illustration thereof is omitted.

The high-temperature high-pressure steam obtained in the reactor pressure vessel 14 is introduced into the high-pressure turbine 18 through the main steam pipe 15. Next, the exhaust steam from the high-pressure turbine 18 is introduced into the low-pressure turbine 19 to drive the generator 20. Exhaust steam from the high-pressure turbine 18 and the low-pressure turbine 19 passes through the gland steam condenser 26, and then passes through the water supply pump 30, the high-pressure water heater 31 and the water supply pipe 9 by the water supply valve system 6 having the valve of the present invention. Water is reciprocated in the reactor pressure vessel 14.

The present invention is effective in extending the life of the equipment and valves in the nuclear power plant, and can reduce the radiation exposure of workers in the plant.

Further, not only the sluice valve and the check valve of the present invention, but also the sliding portion of the valve seat portion such as a safety valve and an elliptic valve can be applied to reduce the leakage resistance, controllability and operation performance. It has the effect of suppressing the decrease.

By using the above valves in combination,
Corrosion and erosion of sliding parts such as valve seats of valves due to the influence of dissolved oxygen due to injection of hydrogen peroxide water for the purpose of water quality adjustment, which is performed in plant equipment such as turbine power generation equipment, can be suppressed, It is effective in improving the safety of plant equipment such as turbine power generation equipment.

Particularly, in a nuclear power generation facility, a eutectic carbide of a Co-based alloy such as a valve seat / cage of a system equipment for supplying cooling water to the sliding portion in contact with the reactor water and a system facility for supplying cooling water into the reactor is corroded and removed. In addition to suppressing the outflow / diffusion of Co in the eutectic carbide into the system, it is possible to suppress the fall of the base material part of the casting structure mainly composed of Co whose erosion resistance performance has deteriorated due to corrosion loss of the eutectic carbide. It is possible to remarkably reduce the radiation exposure of workers in the nuclear power plant.

[0036]

As described above, according to the apparatus and valve of the present invention, the sliding portion or valve seat portion of the valve is less rough due to the corrosion damage of the eutectic carbide due to the dissolved oxygen in the fluid, and the sliding The increase in frictional resistance at the valve seat and the valve seat portion and the prevention of leakage at the valve seat portion can be reliably maintained.

Further, in the nuclear power plant of the present invention, the life of the equipment and valves in the plant is extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a gate valve and an enlarged view of a valve seat portion.

FIG. 2 is a cross-sectional view of a check valve and an enlarged view of a valve seat portion.

FIG. 3 is a piping system diagram of a nuclear power plant using the valve of the present invention for a water supply system.

[Explanation of symbols]

1 ... Valve box, 2 ... Valve element, 3 ... Corrosion / wear resistant Co-based alloy plate,
5 ... Coolant purifying system heat exchanger, 6 ... Water supply valve system, 7 ... Water supply heater, 8 ... Recirculation system piping, 9 ... Water supply pipe, 10 ... Main condenser, 11 ... SLC tank, 12 ... SLC pump , 13 ...
Primary containment vessel, 14 ... Reactor pressure vessel, 15 ... Main steam pipe, 1
6 ... Water supply pipe, 17 ... Humidity analyzer, 18 ... High pressure turbine, 19 ... Low pressure turbine, 20 ... Generator, 21 ... Main transformer, 22 ... Exhaust pipe, 23 ... Off gas treatment system, 24 ... Air extractor , 25 ... Low-pressure condensate pump, 26 ... Grand steam condenser, 27 ... Condensate storage tank, 28 ... Condensate filtering device, 29 ...
Condensate demineralizer, 30 ... Feed pump, 31 ... High-pressure feed heater, 32 ... Control rod drive system, 33, 36 ... Heat exchanger, 34
… Filter desalting unit, 35… Cooling system for reactor isolation.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F16K 15/03 F22B 1/16 C F22B 1/16 C22C 19/03 K // C22C 19/03 19/07 K 19/07 38 / 00 302Z 38/00 302 B23K 103: 18 B23K 103: 18 G21D 1/00 V (72) Inventor Takahiko Kato 3-1-1 Sachimachi, Hitachi City, Ibaraki Hitachi Ltd. (72) Invention Person Yoshiteru Chiba 3-10-2 Benten-cho, Hitachi-shi, Ibaraki Hiritsu Kyowa Engineering Co., Ltd. (56) Reference JP 2003-48076 (JP, A) JP 2003-28315 (JP, A) JP 2003-183701 (JP, A) JP 2002-48264 (JP, A) JP 2001-288521 (JP, A) JP 2000-273573 (JP, A) JP 60-121088 (JP, A) Kaihei 8-193246 (JP, A ) JP-A-7-18365 (JP, A) JP-A-11-62503 (JP, A) JP-A-9-225681 (JP, A) JP-A-2-182854 (JP, A) International Publication 02/101204 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G21D 1/00 B23K 20/00 F16K 3/12 F16K 15/03 F22B 1/16 C22C 19/03 C22C 19/07 C22C 38/00 B23K 103: 18

Claims (6)

(57) [Claims] On the front surface of claim 1] ferrite and the substrate made of carbon steel or low alloy steel having mainly tissue pearlite has a eutectic carbide particle size of eutectic carbides is 30μm or less cobalt Base alloy, nickel base alloy or iron base alloy
A valve comprising members joined together. 2. The member according to claim 1, wherein the member is subjected to plastic working by hot forging or rolling, the eutectic carbide is discontinuously dispersed in a matrix , and diffusion bonding is applied to the base material. /> A valve characterized by being bonded to a surface. 3. The liquid phase diffusion bonding according to claim 2, wherein in the diffusion bonding, an insert material having a melting point lower than that of the base material is inserted into a bonding interface to diffuse a melting point depressing element into the base material to promote solidification / bonding. A valve characterized by being. 4. A nuclear power plant equipment is arranged to have a water supply valve consisting of carbon steel or low alloy steel having mainly tissue ferrite and pearlite in a circular system of nuclear reactor water, the front side of the valve A cobalt-based alloy having eutectic carbides and having a grain size of 30 μm or less,
A nuclear power plant in which members made of either a nickel-based alloy or an iron-based alloy are joined. 5. The member according to claim 4, wherein the member is subjected to plastic working by hot forging or rolling, the eutectic carbide is discontinuously dispersed in a matrix, and the member is formed by diffusion bonding. /> A nuclear power plant characterized by being bonded to a surface. 6. A front side of the water supply valve consisting of carbon steel or low alloy steel having a nuclear to ferrite and pearlite in contact with reactor water of the nuclear reactor plant in the main tissue, is the particle size 30μ
A nuclear power plant, wherein members made of any one of a cobalt-based alloy, a nickel-based alloy, and an iron-based alloy in which eutectic carbides of m or less are dispersed are joined by liquid phase diffusion bonding.