JP6005436B2 - Light water reactor valve - Google Patents

Description

  Embodiments described herein relate generally to a light water reactor valve used in a light water reactor.

Conventionally, a built-up portion made of a Co-based alloy has been provided in a valve box of a light water reactor valve or a valve seat portion of a valve body for the purpose of imparting wear resistance and erosion resistance. However, since the built-up portion made of the Co-based alloy is in contact with the high-temperature high-pressure water of the light water reactor, Co is likely to be eluted from the surface into the reactor water. Further, the Co-base alloy is worn by sliding when the light water reactor valve is opened and closed, and this wear is easily mixed into the reactor water. These Cos enter the core and become Co ₆₀ , which circulates and adheres to pipes, turbines, and other equipment, and is considered to cause a decrease in the amount of exposure during the light water reactor plant regular inspection work.

  In order to reduce the amount of Co entering the reactor water, the use of a cobalt-free material containing no Co has been studied. For example, as a combination of a built-up portion of the valve seat portion on the valve box side and a built-up portion of the valve seat portion on the valve body side, a Cr-Ni-Fe-based Fe-based precipitation type alloy and a Cr-Nb-Mo-Ni-based alloy Combinations with Ni-based alloys have been studied (see, for example, Patent Document 1). However, for such materials, precipitation hardening heat treatment after welding of the overlay is extremely difficult.

  Further, as a combination of the built-up portion of the valve seat portion on the valve box side and the built-up portion of the valve seat portion on the valve body side, a combination of a Co-based alloy and a Ni-based alloy has been studied (for example, see Patent Document 2). ). According to such a thing, since one valve-seat part consists of Ni base alloy which is a cobalt free material, it is easy to suppress elution of Co. However, with regard to the combination of the Co-base alloy and the Ni-base alloy, the hardness of the Ni-base alloy is not necessarily small enough, so that the sliding wear of the Co-base alloy cannot be sufficiently suppressed. Easy to mix.

  Furthermore, in the case of a light water reactor valve already installed in a plant, the entire light water reactor valve including the valve box needs to be replaced in order to replace the built-up portion of the valve seat on the valve box side. In the case of complete replacement, a large work such as cutting and welding between the light water reactor valve and the pipe connected thereto may be required. For this reason, it is required to reduce the amount of exposure and improve safety without requiring a large work.

Japanese Patent Laid-Open No. 62-1837 JP-A-8-247302

  Embodiments of the present invention have been made to solve the above-described problems, and reduce the amount of Co eluting into the reactor water to improve safety and improve the wear resistance and the like of the light water reactor valve. For the purpose of provision.

  The light water reactor valve of the embodiment includes a valve box and a valve body disposed in the valve box. The valve box has a built-up portion made of a Co-based alloy on the valve seat surface. The valve body has a mass percentage display on the valve seat surface, Cr: 23.0-26.0%, Mo: 1.8-2.2%, Si: 3.1-3.5%, C : 1.10 to 1.35%, Ni: 3.7 to 5.0%, Mn: 4.0 to 5.0%, the balance being made of an Fe-based alloy having a chemical composition mainly composed of Fe, and Vickers It has a built-up part whose hardness Hv is 380-400.

  The valve for the light water reactor according to the embodiment has a built-up portion made of a Co-based alloy on the surface of one valve seat portion selected from the valve seat portion on the valve box side and the valve seat portion on the valve body side, and the other valve seat portion Has a built-up portion made of an Fe-based alloy having a predetermined composition and Vickers hardness Hv. According to such a combination of the built-up portions, it is possible to improve safety by reducing Co eluted in the reactor water, and to improve wear resistance and the like.

The partial cross section figure which shows one Embodiment of the valve for light water reactors. Sectional drawing which expands and shows the valve case and valve body in the valve for light water reactors. The figure which shows the relationship between the frequency | count of sliding and the amount of leaks in a sliding test. The figure which shows the relationship between the frequency | count of sliding in a sliding test, and a friction coefficient. The figure which shows the result of the test time and weight loss in an erosion test.

  Hereinafter, an embodiment of a light water reactor valve will be described with reference to the drawings.

FIG. 1 is a partial cross-sectional view showing a first embodiment of a light water reactor valve.
The light water reactor valve 10 includes, for example, a valve box 11, a valve body 12, a valve rod 13, a valve lid 14, a handle 15, a motor 16, and the like. The valve body 12 is slidably disposed inside the valve box 11. A handle 15 and a motor 16 are connected to the valve body 12 via a valve rod 13. In this light water reactor valve 10, the flow path in the valve box 11 can be opened and closed by moving the valve body 12 up and down via the valve rod 13 by the handle 15 and the motor 16.

  FIG. 2 is an enlarged cross-sectional view showing the valve box 11 and the valve body 12. On the surface of a pair of upper and lower annular valve seat portions of the valve box 11, a built-up portion 111 as a valve box sheet is provided in an annular shape. Here, in the light water reactor valve 10 of the present embodiment, a built-up portion 111 is provided on the inner surface of the annular member 112, and the annular member 112 provided with the built-up portion 111 is fixed inside the valve box 11. Yes. According to such a structure, compared with the case where the built-up portion 111 is provided directly inside the valve box 11, the formation of the built-up portion 111 is facilitated, so that the productivity of the valve box 11 can be improved. . Note that the built-up portion 111 is not necessarily formed on the annular member 112, and may be formed directly inside the valve box 11. In addition, on the surface of the valve seat portion of the valve body 12 facing the valve seat portion of the valve box 11, annular build-up portions 121 are provided as valve body seats, respectively.

  In the light water reactor valve 10 of the present embodiment, the built-up portion 111 of the valve box 11 is made of a Co-based alloy. Moreover, in the light water reactor valve 10 of this embodiment, the build-up part 121 of the valve body 12 is a mass percentage display, Cr: 23.0-26.0%, Mo: 1.8-2.2%, Si : 3.1-3.5%, C: 1.10-1.35%, Ni: 3.7-5.0%, Mn: 4.0-5.0%, the balance is mainly composed of Fe It is made of an Fe-based alloy having a composition and having a Vickers hardness Hv of 380 to 400.

  In the light water reactor valve 10 of the present embodiment, a combination of the built-up portion 111 of the valve box 11 and the built-up portion 121 of the valve body 12 is made of a Co-based alloy, a Fe-based material having a predetermined chemical composition and Vickers hardness Hv. By using a combination with the alloy, it is possible to wear the Fe-based alloy side mainly when the valve is opened and closed, thereby suppressing the wear of the Co-based alloy. Thereby, it is possible to suppress the wear of the Co-based alloy from being mixed into the reactor water, and to reduce the amount of exposure during the light water reactor plant regular inspection work or the like, thereby improving safety. Also, according to such a combination, the wear resistance and the like can be improved as in the case of the conventional combination of Co-based alloys.

  Furthermore, according to such a combination, it is possible to easily repair the light water reactor valve already installed in the light water reactor plant. That is, when the build-up part of the valve box and the build-up part of the valve body in the light water reactor valve already installed in the light water reactor plant is a combination of Co-based alloys, the build-up part of the valve box is left as it is, What is necessary is just to change only the build-up part of a valve body into the Fe-based alloy which has predetermined | prescribed chemical composition and Vickers hardness Hv.

  When exchanging the valve box, it is necessary to cut and disconnect the pipes connected to both sides of the valve box by welding or the like, so that a great deal of work is required. By leaving the configuration of the valve box as the conventional configuration, such a large amount of work can be eliminated. In addition, the valve body is generally periodically removed from the valve box for inspection, etc. Therefore, by remodeling the built-up part of the valve body in accordance with such inspection, special repairs are required. It is possible to eliminate the need for work such as simple disassembly.

Hereinafter, main chemical components of the Fe-based alloy will be described.
Cr is a component necessary for maintaining corrosion resistance. On the other hand, if the content is excessively large, wear resistance may be lowered. Therefore, the Cr content is in the range of 23.0 to 26.0%.

  Si is added to improve hardness and wear resistance. On the other hand, if the content is excessively large, weld cracks may occur. Therefore, the Si content is in the range of 3.1 to 3.5%.

  C is added for improving hardness and wear resistance and stabilizing austenite. On the other hand, if the content is excessively high, the weld cracking sensitivity may be increased. Therefore, the C content is in the range of 1.10 to 1.35%.

  Ni is added as an austenite stabilizing element, and an effect of improving weldability and the like is also observed. On the other hand, if the content is excessively large, the hardness and wear resistance may be lowered. Therefore, the Ni content is in the range of 3.7 to 5.0%.

  Mn is added as an austenite stabilizing element. On the other hand, when the content is excessively large, there is a risk that the weld cracking sensitivity is developed. Therefore, the Mn content is in the range of 4.0 to 5.0%.

  Fe-based alloys are expressed in mass percentage, Cr: 23.0 to 26.0%, Mo: 1.8 to 2.2%, Si: 3.1 to 3.5%, C: 1.10 to 1 .35%, Ni: 3.7 to 5.0%, Mn: 4.0 to 5.0%, B: 0 to 0.002% (excluding 0.002%), S: 0 to 0 0.01% (excluding 0.01%), P: 0 to 0.020% (excluding 0.020%), N: 0 to 0.18% (excluding 0.18%) ), And a chemical composition comprising the balance Fe and inevitable impurities.

  The Vickers hardness Hv of the Fe-based alloy part is 380 to 400. When the Vickers hardness Hv of the Fe-based alloy part is less than 380, the Fe-based alloy part tends to be excessively worn, and the wear resistance as a whole may be reduced. On the other hand, when the Vickers hardness Hv of the Fe-based alloy part exceeds 400, the Co-based alloy part is likely to be worn, and the wear of the Co-based alloy may be mixed into the reactor water. Further, when the Vickers hardness Hv of the Fe-based alloy part is out of the above range, there is a possibility that weld cracking or the like may occur when the Fe-based alloy part is formed.

  The build-up portion 121 of the valve body 12, that is, the build-up portion 121 made of an Fe-based alloy having a predetermined chemical composition and Vickers hardness Hv is formed on the surface of the valve seat portion of the valve body 12, for example. It can be obtained by overlaying using an alloy powder having a chemical composition. As the overlay construction, powder plasma welding (PTA welding) or hot isostatic pressing (HIP method) is particularly preferable. By applying such a method, one having a Vickers hardness Hv of 380 to 400 can be suitably obtained.

  On the other hand, the Co-based alloy is not particularly limited, and a Co-based alloy used for a built-up portion formed on the surface of the valve seat portion in a known light water reactor valve can be applied. As such a Co-based alloy, for example, what is called stellite can be used. Specifically, in terms of mass percentage, Cr: 25.0 to 32.0%, Mo: 0 to 1.0%, Si: 0 to 2.0%, C: 0.70 to 1.40%, Ni: 0 to 3.0%, Fe: 0 to 5.0%, Mn: 0 to 2.0%, W: 3.0 to 6.0%, Co group having a chemical composition mainly composed of Co. Alloys are preferred.

  The Co-based alloy is expressed in mass percentage, Cr: 25.0 to 32.0%, Mo: 0 to 1.0%, Si: 0 to 2.0%, C: 0.70 to 1.40%, Ni: 0 to 3.0%, Fe: 0 to 5.0%, Mn: 0 to 2.0%, W: 3.0 to 6.0%, S: 0 to 0.03%, P: 0 It is more preferable to have a chemical composition consisting of ˜0.03%, the balance Co and inevitable impurities.

  The formation method of the build-up part 111 of the valve box 11, that is, the build-up part 111 made of a Co-based alloy is not particularly limited, and the build-up part is formed on the surface of the valve seat part of the valve box 11 in a known light water reactor valve. Therefore, the forming method used for the purpose can be applied. For example, it can be obtained by performing overlaying on the surface of the valve seat portion of the valve box 11 using the alloy powder having the predetermined chemical composition as described above. As the overlay construction, for example, a gas overlay welding method is preferable. By applying such a method, a material having the above-mentioned Vickers hardness Hv can be suitably obtained.

Next, a second embodiment of the light water reactor valve 10 will be described.
The light water reactor valve 10 of the second embodiment is basically the same as that of the first embodiment except that the constituent material of the built-up portion 111 of the valve box 11 and the constituent material of the built-up portion 121 of the valve body 12 are replaced. The light water reactor valve 10 has the same configuration. That is, as shown in FIG. 1, it has a valve box 11, a valve body 12, a valve rod 13, a valve lid 14, a handle 15, a motor 16, and the like. Further, as shown in FIG. 2, the surface of the annular valve seat portion of the valve box 11 is annularly provided as a valve box seat, and the valve body 12 has a valve body on the surface of the valve seat portion. A built-up portion 121 as a sheet is provided.

  In the light water reactor valve 10 of the second embodiment, the built-up portion 111 of the valve box 11 is expressed by mass percentage, Cr: 23.0 to 26.0%, Mo: 1.8 to 2.2%, Si : 3.1-3.5%, C: 1.10-1.35%, Ni: 3.7-5.0%, Mn: 4.0-5.0%, the balance is mainly composed of Fe It is made of an Fe-based alloy having a composition and having a Vickers hardness Hv of 380 to 400. Moreover, in the light water reactor valve 10 of the second embodiment, the built-up portion 121 of the valve body 12 is made of a Co-based alloy.

  Even in such a combination, the wear of the Co-based alloy can be suppressed by mainly wearing the Fe-based alloy side when the valve is opened and closed. As a result, it is possible to suppress the wear of the Co-based alloy from being mixed into the reactor water, and to reduce the exposure amount during the light water reactor plant regular inspection work, etc., and to improve the safety. Also, according to such a combination, the wear resistance and the like can be improved as in the case of the conventional combination of Co-based alloys.

  The Fe-based alloy is expressed in terms of mass percentage, Cr: 23.0 to 26.0%, Mo: 1.8 to 2.2%, Si: 3.1 to 3.5%, C: 1.10. 1.35%, Ni: 3.7-5.0%, Mn: 4.0-5.0%, B: 0-0.002% (excluding 0.002%), S: 0 0.01% (excluding 0.01%), P: 0 to 0.020% (excluding 0.020%), N: 0 to 0.18% (excluding 0.18%) It is preferable to have a chemical composition consisting of the balance Fe and inevitable impurities.

  The Co-based alloy is not particularly limited, and a Co-based alloy used for a built-up portion formed on the surface of a valve seat portion in a known light water reactor valve can be applied. As such a Co-based alloy, for example, what is called stellite can be used. Specifically, in terms of mass percentage, Cr: 25.0 to 32.0%, Mo: 0 to 1.0%, Si: 0 to 2.0%, C: 0.70 to 1.40%, Ni: 0 to 3.0%, Fe: 0 to 5.0%, Mn: 0 to 2.0%, W: 3.0 to 6.0%, Co group having a chemical composition mainly composed of Co. Alloys are preferred.

  The Co-based alloy is expressed in mass percentage, Cr: 25.0 to 32.0%, Mo: 0 to 1.0%, Si: 0 to 2.0%, C: 0.70 to 1.40%, Ni: 0 to 3.0%, Fe: 0 to 5.0%, Mn: 0 to 2.0%, W: 3.0 to 6.0%, S: 0 to 0.03%, P: 0 It is more preferable to have a chemical composition consisting of ˜0.03%, the balance Co and inevitable impurities.

  For the built-up portion 111 of the valve box 11 in the second embodiment, that is, the built-up portion 111 made of an Fe-based alloy having a predetermined chemical composition and Vickers hardness Hv, for example, the surface of the valve seat portion of the valve box 11, Specifically, it can be obtained by overlaying the inner surface of the annular member 112 using an alloy powder having a predetermined chemical composition as described above. As the overlay construction, powder plasma welding (PTA welding) or hot isostatic pressing (HIP method) is particularly preferable. By applying such a method, one having a Vickers hardness Hv of 380 to 400 can be suitably obtained.

  Moreover, the formation method in particular of the build-up part 121 of the valve body 12 in 2nd Embodiment, ie, the build-up part 121 which consists of Co base alloys, is not restrict | limited, In the valve for a well-known light water reactor, the valve seat part of the valve body 12 is provided. A forming method used for forming a built-up portion on the surface can be applied. For example, it can be obtained by performing overlaying on the surface of the valve seat portion of the valve body 12 using the alloy powder having the predetermined chemical composition as described above. As the overlay construction, for example, a gas overlay welding method is preferable. By applying such a method, a material having the above-mentioned Vickers hardness Hv can be suitably obtained.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  Hereinafter, specific description will be given with reference to examples. The embodiments of the present invention are not limited to the following examples.

(Preparation of sliding test piece)
The following two types of sliding test pieces were prepared as the sliding test pieces.

[Sliding specimen 1]
As an Fe-based alloy, Cr: 25.1%, Mo: 2.1%, Si: 3.3%, C: 1.20%, Ni: 4.1%, Mn: 4.4 in terms of mass percentage %, N: 0.13, balance Fe and a chemical composition consisting of inevitable impurities were prepared. This Fe-based alloy was melted in a vacuum or in an inert gas environment, and then an Fe-based alloy powder was produced by a gas atomization method. The particle size of the Fe-based alloy powder is + 80 / -325 mesh. Using this Fe-based alloy powder, a 150 A sliding test piece was obtained by performing three-layer overlay welding on S25C generally used for valve bodies and valve seats by plasma powder overlay welding. 1 was made. In addition, the Vickers hardness Hv of the built-up portion made of the Fe-based alloy in the sliding test piece 1 was in the range of 380 to 400. The Vickers hardness Hv was measured with a load applied to the diamond assembly of 10 kg.

[Sliding specimen 2]
As a Co-based alloy, Cr: 28.0%, C: 1.00%, Ni: 3.0%, Fe: 3.0% or less, W: 4.0%, balance Co and inevitable in terms of mass percentage Those having a chemical composition consisting of mechanical impurities were prepared. This Co-based alloy was melted in a vacuum or an inert gas environment, and then a Co-based alloy powder was produced by a gas atomization method. The particle size of the Co-based alloy powder is + 80 / -325 mesh. Using this Co-based alloy powder, a 150A sliding test piece 2 was manufactured from three-layer overlay welding on S25C generally used for valve bodies and valve seats by gas deposition welding. did. In addition, the Vickers hardness Hv of the built-up portion made of the Fe-based alloy in the sliding test piece 1 was 448.

(Example 1, Comparative Example 1)
Using the above-mentioned sliding tests 1 and 2 in combinations as shown in Table 1, the sliding test is performed with a sliding test device, and the leakage amount, friction coefficient, and surface roughness during and after the test are determined. evaluated. Here, Example 1 uses the sliding test piece 1 (the build-up part is an Fe-based alloy) as the valve seat part of the valve body, and the sliding test piece 2 (the build-up) as the valve seat part of the valve box. In which the part is a Co-based alloy). Moreover, the comparative example 1 was set as the combination which uses the sliding test piece 2 (what a build-up part is a Co base alloy) as both the valve seat part of a valve body, and the valve seat part of a valve box. The sliding test conditions were as follows: surface pressure 200 MPa, sliding frequency (valve opening / closing frequency) 100 times, 288 ° C. saturated steam.

  FIG. 3 shows the relationship between the number of sliding times and the amount of leakage in the sliding test. It was confirmed that Example 1, which was a combination of an Fe-based alloy and a Co-based alloy, eventually had a leakage amount of 40 cc / min or less, and exhibited leakage characteristics equivalent to those of Comparative Example 1 which was a combination of Co-based alloys. It was.

  FIG. 4 shows the relationship between the number of sliding times and the friction coefficient in the sliding test. Example 1, which was a combination of an Fe-based alloy and a Co-based alloy, showed a friction coefficient almost equivalent to that of Comparative Example 1, which was a combination of Co-based alloys, and was found to have equivalent sliding characteristics.

  Furthermore, after the sliding test, an inspection for disassembly was performed, and the surface of the built-up portion of the sliding test piece was observed. As a result, in Example 1, the arithmetic average surface roughness Ra of the surface of the build-up portion of the slide test piece 1 (the build-up portion is an Fe-based alloy) is 0.6 μm or less. The arithmetic average surface roughness Ra of the surface of the built-up part 2 (the built-up part is a Co-based alloy) was 0.26 μm or less. On the other hand, in Comparative Example 1, the arithmetic average surface roughness Ra of the surface of the build-up portion of the sliding test piece 2 (the build-up portion is a Co-based alloy) was 1.00 μm or less.

  When the sliding test piece 1 (in which the build-up part is an Fe-based alloy) and the sliding test piece 2 (in which the build-up part is a Co-based alloy) are combined as in Example 1, the hardness of both Since there is a difference, the surface of the built-up portion made of the Fe-based alloy wears predominantly, and the wear of the surface of the built-up portion made of the Co-based alloy can be suppressed.

  Therefore, when the light water reactor valve of the embodiment is adopted as the valve of the system that goes into the furnace, it is possible to suppress the wear of the Co-based alloy from entering the furnace. As a result, the amount of exposure in the light water reactor plant, particularly the light water reactor plant regular inspection work caused by the valve seat portion, can be reduced, and the work time at the time of the regular inspection can be largely secured, thereby producing a safer nuclear power plant.

  Next, the plasma powder overlay welding method was performed in the same manner as the sliding test piece 1 to produce a Fe-based alloy test piece, and the erosion test piece 1 was produced by machining. Similarly to the sliding test piece 2, a Co-based alloy test piece was produced by gas welding, and an erosion test piece 2 was produced by machining. These erosion test pieces 1 and 2 were exposed to high-pressure flowing water to generate erosion, and the test time and the weight change of the test piece were evaluated. FIG. 5 shows the relationship between the test time and the change in weight (weight loss) at room temperature.

  Furthermore, a sliding test was carried out with a 600 A gate valve. The built-up portion of the valve body was welded and welded with an Fe-based alloy by the plasma powder build-up welding method in the same manner as the sliding test piece 1. The overlay portion of the valve box was overlay welded with a Co-based alloy by gas overlay welding in the same manner as the sliding test piece 2 described above. The sliding test was performed under the conditions of a differential pressure of 7.13 MPa, a sliding frequency of 50 times, and 288 ° C. saturated steam, using a sliding test apparatus. After the sliding test, a valve seat leakage test was conducted with normal temperature water at a test pressure of 8.62 MPa and a holding time of 3 minutes to confirm the presence or absence of leakage. As a result, it was confirmed that there was no leakage.

  DESCRIPTION OF SYMBOLS 10 ... Light water reactor valve, 11 ... Valve box, 12 ... Valve body, 13 ... Valve rod, 14 ... Valve cover, 15 ... Handle, 16 ... Motor, 111 ... Overlay part, 112 ... Ring member, 121 ... Overlay part

Claims (2)

A light water reactor valve having a valve box and a valve body disposed in the valve box,
The valve box has a built-up portion made of a Co-based alloy on the valve seat surface,
The valve body has a mass percentage display on the valve seat surface, Cr: 23.0-26.0%, Mo: 1.8-2.2%, Si: 3.1-3.5%, C : 1.10 to 1.35%, Ni: 3.7 to 5.0%, Mn: 4.0 to 5.0%, the balance being made of an Fe-based alloy having a chemical composition mainly composed of Fe, and Vickers A light water reactor valve having a built-up portion having a hardness Hv of 380 to 400.   The Co-based alloy is expressed by mass percentage, Cr: 25.0 to 32.0%, Mo: 0 to 1.0%, Si: 0 to 2.0%, C: 0.70 to 1.40% Ni: 0 to 3.0%, Fe: 0 to 5.0%, Mn: 0 to 2.0%, W: 3.0 to 6.0%, the balance having a chemical composition mainly composed of Co The light water reactor valve according to claim 1.

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