Steam valve and steam turbine plant including the same

Abstract

To provide a steam valve capable of reducing an accumulation amount of oxidized scale per operating time of a steam turbine, which is formed in a sliding part, etc. of the steam valve, by using a simple configuration and a steam turbine plant using the steam valve.SOLUTION: A steam valve includes a steam inlet part 31, a steam outlet part 32 and a steam chamber 33. The steam valve also includes: a valve seat 70 having an opening part 34 communicating with the steam chamber 33 and provided in the vicinity of the steam outlet part 32 in the steam chamber 33 in a valve casing; a valve lid 40 installed on the valve casing 30 to close the opening part 34 and having a through hole 40a; a cylindrical bush 41 fitted to the through hole 40a; a valve rod 50 slidably penetrating through the bush; and a valve element 60 provided at one end of the valve rod 50 and disposed to enable abutment to the valve seat 70. A coating layer 51 formed through PVD is formed on the outer peripheral surface of the valve rod 50 sliding in the bush or the inner peripheral surface 41a of the bush 41.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a steam valve and a steam turbine plant including the same.

Background Art

[0002] The steam valve provided in a steam turbine plant has a function of shutting off the inflowing steam to the steam turbine and controlling the amount of steam. FIG. 9 is a longitudinal sectional view showing a conventional steam control valve used in a steam turbine plant.

[0003] In the steam control valve 200 shown in FIG. 9, a valve casing 218 is closed by a valve cover 213. A valve rod 210 is provided so as to penetrate the valve cover 213. A valve body 211 is provided at one end of the valve rod 210, and the other end of the valve rod 210 is connected to a hydraulic drive mechanism 215 supported by the valve cover 213. A bush 214 through which the valve rod 210 penetrates is provided in the through portion of the valve cover 213. The inner peripheral surface 214a of the bush 214 and the outer peripheral surface 210a of the valve rod 210 constitute a sliding surface.

[0004] The valve body 211 comes into contact with or separates from a valve seat 212 when the valve rod 210 is driven in the vertical direction by a hydraulic drive mechanism 215. Thereby, the flow rate of the steam flowing in from the steam inlet portion 216 and flowing out from the steam outlet portion 217 is adjusted.

[0005] In the steam control valve 200, the gap between the valve rod 210 and the bush 214 cannot be made zero in order to enable the valve rod 210 to move in the vertical direction. Therefore, a predetermined gap is provided between the outer peripheral surface 210a of the valve rod 210 and the inner peripheral surface 214a of the bush 214.

[0006] In a steam turbine driven by high-temperature steam, it is known that oxide scale gradually accumulates on the outer peripheral surface 210a of the valve rod 210 and the inner peripheral surface 214a of the bush 214 over time. When the gap between the valve rod 210 and the bush 214 is closed due to the accumulation of oxide scale, sticking of the valve rod 210 occurs.

[0007] When wear occurs on the valve stem 210 during the operation of the steam turbine, the control function of the steam flow rate flowing into the steam turbine and the steam cutoff function in case of emergency are impaired. Therefore, in order to prevent wear of the valve stem 210, it is essential to regularly disassemble and inspect the steam valve and remove the oxide scale deposited on the outer peripheral surface 210a of the valve stem 210 and the inner peripheral surface 214a of the bush 214.

[0008] Generally, the amount of oxide scale deposition increases in proportion to the operating time of the steam turbine. Therefore, the larger the gap between the valve stem 210 and the bush 214, the longer the time until wear of the valve stem 210 occurs.

[0009] However, if the gap between the valve stem 210 and the bush 214 is increased, problems such as the progress of wear of the sliding part due to radial runout of the valve stem 210, an increase in vibration, poor contact between the valve body 211 and the valve seat 212 due to misalignment of the valve stem 210, and a decrease in the thermal efficiency of the steam turbine plant due to steam leakage from the gap between the valve stem 210 and the bush 214 will occur.

[0010] Therefore, the gap between the valve stem 210 and the bush 214 needs to be appropriately set within a range where the above problems do not occur, and it is necessary to regularly remove the oxide scale in order to prevent wear of the valve stem 210.

[0011] On the other hand, in recent years, the need for a longer inspection interval in steam turbines has been increasing. However, as described above, in the steam valve, it is necessary to regularly remove the oxide scale. Therefore, in order to achieve a longer inspection interval, it is important to reduce the rate of oxide scale deposition.

[0012] Here, due to the cooling of the leaked steam or the like, a part of the leaked steam condenses, and oxide scale gradually accumulates in the gap between the valve stem 210 and the bush 214 over time. Therefore, in a conventional steam valve, studies have been made to further reduce the leaked steam from the gap between the valve stem 210 and the bush 214.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0014] However, in a conventional steam valve, in order to further reduce the leaked steam, the structure of the steam valve becomes complicated. That is, in a conventional steam valve, it has been difficult to reduce the amount of leaked steam from the gap between the valve stem and the bush with a simple configuration and suppress the amount of oxide scale deposition.

[0015] The problem to be solved by the present invention is to provide a steam valve capable of reducing the amount of oxide scale deposition per operating hour of a steam turbine formed in a sliding part or the like in a steam valve with a simple configuration, and a steam turbine plant including the same.

Means for Solving the Problems

[0016] The steam valve of the embodiment includes a steam inlet portion, a steam outlet portion, and a steam chamber, and has a valve casing having an opening communicating with the steam chamber, a valve seat provided in the vicinity of the steam outlet portion in the steam chamber within the valve casing, a valve cover installed on the valve casing so as to close the opening and having a through hole, a cylindrical bush fitted into the through hole, a valve rod slidably penetrating through the bush, and a valve body provided at one end of the valve rod and configured to be able to contact the valve seat. And a PVD coating layer is formed on the outer peripheral surface of the valve rod sliding within the bush or the inner peripheral surface of the bush.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0018] (First Embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0019] FIG. 1 is a diagram showing the system configuration of a steam turbine plant 1 including a steam valve according to the first embodiment. As shown in FIG. 1, the steam turbine plant 1 includes a boiler 10, a high-pressure turbine 11, an intermediate-pressure turbine 12, a low-pressure turbine 13, a condenser 14, and a feed water pump 15. The steam turbine plant 1 also includes a main steam stop valve 20, a steam control valve 21, a reheat steam stop valve 22, an intercept valve 23, a high-pressure turbine bypass valve 24, a low-pressure turbine bypass valve 25, and a check valve 26.

[0020] Here, examples of the steam valve according to the present embodiment include the main steam stop valve 20, the steam control valve 21, the reheat steam stop valve 22, the intercept valve 23, the high-pressure turbine bypass valve 24, the low-pressure turbine bypass valve 25, the check valve 26, etc. described above. That is, the configuration of the present embodiment can be applied to these valves.

[0021] The boiler 10 is provided with a superheater 10a and a reheater 10b. Note that the boiler 10 functions as a steam generation device. The high-pressure steam (main steam) generated in the superheater 10a passes through the main steam stop valve 20 and the steam control valve 21 interposed in the main steam pipe 120 and is supplied to the high-pressure turbine 11. The main steam supplied to the high-pressure turbine 11 flows while expanding inside the high-pressure turbine 11 to drive the high-pressure turbine 11.

[0022] The steam (low-temperature reheat steam) exhausted from the high-pressure turbine 11 is guided to the reheater 10b of the boiler 10 via the check valve 26 interposed in the low-temperature reheat steam pipe 121 and is heated (reheated) to become reheat steam. The reheat steam from the reheater 10b is supplied to the intermediate-pressure turbine 12 via the reheat steam stop valve 22 and the intercept valve 23 interposed in the high-temperature reheat steam pipe 122. The reheat steam supplied to the intermediate-pressure turbine 12 flows while expanding inside the intermediate-pressure turbine 12 to drive the intermediate-pressure turbine 12. The steam discharged from the intermediate-pressure turbine 12 flows through the crossover pipe 123 and flows into the low-pressure turbine 13 to drive the low-pressure turbine 13.

[0023] The steam discharged from the low-pressure turbine 13 is led to the condenser 14. The steam led to the condenser 14 is cooled and condensed within the condenser 14 and returned to water (condensate). The water (condensate) condensed in the condenser 14 is pressurized by a feed pump 15 interposed in a feed pipe 124 and led to a superheater 10a of a boiler 10. In the steam turbine plant 1, a steam-water circulation system (thermal cycle) is formed as described above.

[0024] Also, depending on the steam turbine plant 1, in order to improve the operating efficiency, a high-pressure turbine bypass pipe 125 connecting the inflow side of the main steam stop valve 22 and the inflow side of the reheater 10b is provided. A high-pressure turbine bypass valve 24 is provided in this high-pressure turbine bypass pipe 125. In this configuration, by opening the high-pressure turbine bypass valve 24, it becomes possible to bypass the main steam from the superheater 10a and operate the high-pressure turbine 11.

[0025] Also, depending on the steam turbine plant 1, a low-pressure turbine bypass pipe 126 connected between the outflow side of the reheater 10b and the condenser 14 is provided. A low-pressure turbine bypass valve 25 is provided in this low-pressure turbine bypass pipe 126. In this configuration, by opening the low-pressure turbine bypass valve 25, it becomes possible to bypass the reheated steam from the reheater 10b and operate bypassing the intermediate-pressure turbine 12 and the low-pressure turbine 13.

[0026] By providing the high-pressure turbine bypass pipe 125 and the low-pressure turbine bypass pipe 126 as described above, it is possible to perform the circulation operation of the steam turbine plant only with the boiler system regardless of the operation of the steam turbine.

[0027] Next, the configuration of the steam valve of the first embodiment will be described.

[0028] FIG. 2 is a diagram showing a longitudinal section of the steam valve of the first embodiment. FIG. 3 is a diagram showing an enlarged partial cross-section of the steam valve of the first embodiment. Here, the steam control valve 21 will be exemplified and described as the steam valve of the first embodiment.

[0029] As shown in FIG. 2, the steam control valve 21 includes a valve casing 30, a valve cover 40, a valve rod 50, and a valve body 60 , and a valve seat 70.

[0030] The valve casing 30 has a steam inlet 31 for introducing main steam from the boiler 10 and a steam outlet 32 for discharging steam. Here, an example is shown in which the steam outlet 32 is configured to guide the main steam flowing in horizontally from the steam inlet 31 vertically downward.

[0031] The upper surface of the valve casing 30 facing the steam outlet 32 has an opening 34 communicating with the steam chamber 33. This opening 34 is sealed by the valve cover 40, and a steam chamber 33 is formed inside the valve casing 30. The valve seat 70 is provided at the connection portion with the steam outlet 32 inside the valve casing 30. Here, the steam chamber 33 is a space formed inside the valve casing 30, downstream of the steam inlet 31 and upstream of the contact portion of the valve seat 70 that contacts the valve body 60.

[0032] A through hole 40a is formed in the central portion of the valve cover 40. A bush 41 is fitted into this through hole 40a. The bush 41 is composed of a cylindrical member having a through hole 42 in the central longitudinal direction. Note that the bush 41 is fitted into the through hole 40a of the valve cover 40 by cold fitting or the like.

[0033] The valve rod 50 is provided so as to penetrate the through hole 42 of the bush 41. A valve body 60 is provided at one end of the valve rod 50, and the other end of the valve rod 50 is connected to a hydraulic drive mechanism 80 supported by the valve cover 40. Note that the central axis of the bush 41 is located coaxially with the central axis of the valve rod 50.

[0034] As shown in FIG. 3, a coating layer 51 is formed on the outer peripheral surface 50a of the valve rod 50. The outer peripheral surface 51a of the coating layer 51 and the inner peripheral surface 41a of the bush 41 constitute a sliding surface. On the outer peripheral surface 50a of the valve rod 50, the coating layer 51 is formed at least in a portion that slides with the inner peripheral surface 41a of the bush 41.

[0035] Here, an example in which the coating layer 51 is formed on the outer peripheral surface 50a of the valve rod 50 is shown. The coating layer 51 may be formed on the inner peripheral surface 41a of the bush 41. That is, the coating layer 51 is formed on the outer peripheral surface 50a of the valve rod 50 or the inner peripheral surface 41a of the bush 41. Note that the peripheral surface on which the coating layer 51 is not formed is subjected to, for example, any one of nitriding treatment, chromizing treatment, stellite welding, chromium carbide spraying, etc., to impart oxidation resistance. A predetermined gap for the valve rod 50 to slide is provided between the outer peripheral surface 51a of the coating layer 51 and the inner peripheral surface 41a of the bush 41.

[0036] The valve body 60 comes into contact with or separates from the valve seat 70 when the valve rod 50 is driven in the vertical direction by the hydraulic drive mechanism 80. Thereby, the flow rate of the main steam flowing in from the steam inlet portion 31 and flowing out from the steam outlet portion 32 is adjusted. Note that the rotation speed of the high-pressure turbine 11 is controlled by adjusting the amount of steam flowing out from the steam outlet portion 32 by the steam control valve 21.

[0037] Next, the coating layer 51 will be described.

[0038] As shown in FIG. 3, a coating layer 51 is formed on the outer peripheral surface 50a of the valve rod 50. The coating layer 51 is formed by PVD (Physical Vapor Deposition) coating. The PVD coating process is a process of evaporating the substance forming the coating layer 51 by heating it to a high temperature and forming a solid film (coating layer 51) of the substance on the surface of the base material.

[0039] Thus, in this embodiment, a PVD coating process is performed on the surface of the base material that constitutes a predetermined structural part of the steam valve to form a coating layer 51. That is, without performing a diffusion hardening surface treatment such as nitriding treatment, the PVD coating process is directly performed on the surface of the base material that constitutes the structural part to form the coating layer 51.

[0040] Here, the PVD coating process is preferably performed at 600°C or lower in consideration of the influence of heat on the base material to which the process is applied. Note that the coating layer formed by performing the PVD coating process functions as a PVD coating layer.

[0041] The coating layer 51 is composed of a material that has excellent slidability and excellent oxidation resistance in a high-temperature environment. Examples of the substance that constitutes the coating layer 51 include Cr-based nitrides such as CrN (chromium nitride), and Ti-based nitrides such as TiAlN (titanium aluminum nitride). Among Cr-based nitrides and Ti-based nitrides, CrN and TiAlN are more suitable as the coating layer 51. Note that the substance that constitutes the coating layer 51 is not limited to this, and depending on the purpose of use of the steam valve, it may be composed of other substances that have excellent slidability and excellent oxidation resistance in a high-temperature environment.

[0042] The film thickness of the coating layer 51 is preferably 2 μm to 30 μm. By setting the film thickness of the coating layer 51 within this range, excellent oxidation resistance can be obtained. When the film thickness of the coating layer 51 is less than 2 μm, the construction time and cost are reduced, but surface defects such as pinholes may occur locally, and the oxidation resistance may be lost. When the film thickness of the coating layer 51 exceeds 30 μm, oxidation resistance can be obtained, but the construction time and cost for forming the coating layer 51 increase.

[0043] Here, the member with the PVD coating can easily remove only the PVD coating without affecting the base material constituting the member by demembranation in the electrolyte solution, that is, electrolytic demembranation. As a result, when the base material after removing the PVD coating is sound, the PVD coating can be applied again and used. That is, the coating layer 51 can be easily formed again.

[0044] Here, the oxidation rate on the surface of the coating layer 51 with the PVD coating is 0.4×10 -6 mm / h or less. In other words, the oxide scale deposited per unit time on the surface of the coating layer 51 is 0.4×10 -6 mm or less.

[0045] Note that the oxidation rate is the amount of thickening (deposition amount of the oxide scale) of the oxide scale deposited per unit time on the surface of the coating layer 51. The measurement method of the oxidation rate conforms to JIS Z2290 "Test Method for High Temperature Corrosion of Metallic Materials".

[0046] In the above oxidation rate range, it has excellent oxidation resistance characteristics and can reduce the deposition amount of the oxide scale per operating hour of the steam turbine. Therefore, the period of disassembly inspection in the steam valve can be made longer than the period of disassembly inspection in the conventional steam valve.

[0047] The coefficient of kinetic friction between the member on which the coating layer 51 is formed and the member that slides with the member on which the coating layer 51 is formed is 0.25 or more and 0.4 or less. The measurement method of the coefficient of kinetic friction conforms to JIS R1613 "Wear Test Method for Fine Ceramics by Ball-on-Disk Method".

[0048] In the above range of the coefficient of kinetic friction, good slidability with the coating layer 51 can be ensured without excessively inhibiting the force in the sliding direction from the hydraulic drive mechanism 80.

[0049] The hardness of the coating layer 51 is 2000 HV (Vickers hardness) or more. By setting the hardness of the coating layer 51 within the above range, a hardness difference can be created with the hardness of the member on the mating side that slides against the coating layer 51. Thereby, galling (sticking) can be prevented. Also, by setting the hardness of the coating layer 51 within the above range, the strength of the member provided with the coating layer 51 can be increased.

[0050] According to the steam valve of the first embodiment, with a simple configuration in which the sliding surface between the valve rod 50 and the bush 41 is provided with the coating layer 51, the deposition amount of oxide scale deposited on the outer peripheral surface 50a of the valve rod 50 and the inner peripheral surface 41a of the bush 41 per operating hour of the steam turbine can be reduced.

[0051] As a result, the allowable cumulative operating time until the gap in the sliding portion between the valve rod 50 and the bush 41 is closed becomes longer. Therefore, the disassembly inspection period in the steam valve of the first embodiment can be made longer than the disassembly inspection period in the conventional steam valve.

[0052] Also, according to the steam valve of the first embodiment, even when maintaining the gap between the conventional valve rod and the bush without widening the gap between the valve rod and the bush in order to lengthen the disassembly inspection period, the disassembly inspection period can be made longer than the conventional disassembly inspection period. Since the gap with the bush is not widened in this way, problems such as the progress of wear of the sliding portion due to radial runout of the valve rod, an increase in vibration, poor contact between the valve body and the valve seat due to misalignment of the valve rod, and a decrease in the thermal efficiency as a steam turbine plant due to steam leakage from the gap between the valve rod and the bush do not occur.

[0053] Furthermore, since the deposition amount of the oxide scale per operating hour of the steam turbine, i.e., the oxidation rate, can be reduced, for example, even if the gap between the valve stem 50 and the bush 41 is made smaller than the gap between the conventional valve stem and bush, the disassembly inspection period of the steam valve can be set longer than the disassembly inspection period of the conventional steam valve. Further, by making the gap between the valve stem 50 and the bush 41 smaller than the gap between the conventional valve stem and bush, steam leakage can be further suppressed. As a result, it is possible to suppress the formation of oxide scale that accumulates over time in the gap between the valve stem 50 and the bush due to the condensation of the leaked steam.

[0054] (Second Embodiment) FIG. 4 is a longitudinal sectional view of the steam valve according to the second embodiment. FIG. 5 is an enlarged sectional view of a part of the steam valve according to the second embodiment. Here, as in the first embodiment, the steam control valve 21A is exemplified and described as the steam valve. In the following embodiments, the same reference numerals are given to the same components as those in the first embodiment, and redundant descriptions are omitted or simplified.

[0055] As shown in FIG. 4, the steam control valve 21A according to the second embodiment includes a sleeve 90 at the end of the valve cover 40 on the steam chamber 33 side. The sleeve 90 is composed of a cylindrical member having a through hole 91 in the central longitudinal direction. One end of the sleeve 90 is connected to the end of the valve cover 40 on the steam chamber 33 side, and the other end side of the sleeve 90 extends toward the steam outlet portion 32 side. The central axis of the sleeve 90 is located coaxially with the central axis of the bush 41. Further, these central axes are located coaxially with the central axis of the valve stem 50.

[0056] The valve body 60A provided at one end of the valve rod 50 includes a columnar portion 61 connected to one end of the valve rod 50 and a hemispherical portion 62 that abuts against the valve seat 70. The columnar portion 61 penetrates through the through hole 91 of the sleeve 90. As shown in FIG. 5, a coating layer 63 is formed on the outer peripheral surface 61a of the columnar portion 61. The outer peripheral surface 63a of the coating layer 63 and the inner peripheral surface 90a of the sleeve 90 constitute a sliding surface. On the outer peripheral surface 61a of the columnar portion 61, the coating layer 63 is formed at least on the portion that slides with the inner peripheral surface 90a of the sleeve 90.

[0057] Here, an example in which the coating layer 63 is formed on the outer peripheral surface 61a of the columnar portion 61 is shown. The coating layer 63 may be formed on the inner peripheral surface 90a of the sleeve 90. That is, the coating layer 63 is formed on the outer peripheral surface 61a of the columnar portion 61 of the valve body 60A or the inner peripheral surface 90a of the sleeve 90. Note that the peripheral surface where the coating layer 63 is not formed is subjected to, for example, any one of nitriding treatment, chromizing treatment, stellite welding, chromium carbide spraying, etc., to impart oxidation resistance. There is a predetermined gap between the outer peripheral surface 63a of the coating layer 63 and the inner peripheral surface 90a of the sleeve 90 for the columnar portion 61 to slide.

[0058] In the steam control valve 21A, by forming a steam balance chamber between the sleeve 90 and the valve body 60A, the steam unbalance force due to the steam differential pressure before and after the valve body 60A can be reduced.

[0059] The coating layer 63 has the same configuration as the coating layer 51 in the first embodiment.

[0060] According to the steam valve of the second embodiment, with a simple configuration including the coating layer 63 on the sliding surface between the columnar portion 61 of the valve body 60A and the sleeve 90, the deposition amount of the oxide scale deposited on the outer peripheral surface 61 a of the columnar portion 61 and the inner peripheral surface 90a of the sleeve 90 per operating hour of the steam turbine can be reduced.

[0061] As a result, the allowable cumulative operating time until the gap in the sliding portion between the cylindrical portion 61 of the valve body 60A and the sleeve 90 is closed becomes longer. Therefore, the disassembly inspection period of the steam valve according to the second embodiment can be made longer than the disassembly inspection period of the conventional steam valve.

[0062] In addition, since the deposition amount of the oxide scale per operating time of the steam turbine, that is, the oxidation rate can be reduced, for example, even if the gap between the cylindrical portion 61 and the sleeve 90 is made smaller than the gap between the conventional cylindrical portion and the sleeve, the disassembly inspection period of the steam valve can be set longer than the disassembly inspection period of the conventional steam valve.

[0063] (Third Embodiment) FIG. 6 is a longitudinal sectional view of a steam valve according to the third embodiment. FIG. 7 is an enlarged sectional view showing a part of the steam valve according to the third embodiment. Here, as in the first embodiment, the steam pressure reducing valve 21B is exemplified and described as the steam valve.

[0064] As shown in FIG. 6, the steam pressure reducing valve 21B according to the third embodiment includes a seat ring 100. The seat ring 100 is fitted into the through hole 40a of the valve cover 40 on the steam chamber 33 side of the bush 41. The seat ring 100 is in contact with the bush 41 and is fitted into the through hole 40a.

[0065] As shown in FIG. 7, the seat ring 100 is composed of an annular member having a predetermined thickness. The valve rod 50 passes through the central cylindrical hole portion 101 of the seat ring 100. The central axis of the seat ring 100 is located coaxially with the central axis of the bush 41. Further, these central axes are located coaxially with the central axis of the valve rod 50.

[0066] The peripheral edge on the steam chamber 33 side along the circumferential direction of the hole portion 101 in the seat ring 100 includes, for example, a chamfered portion 101a that has been chamfered. The chamfered portion 101a is formed over the circumferential direction. The chamfered portion 101a has, for example, a C-chamfer.

[0067] The valve rod 50 includes a small-diameter portion 52 and a large-diameter portion 53 having a diameter larger than that of the small-diameter portion 52. A stepped portion 54 is provided at the boundary between the small-diameter portion 52 and the large-diameter portion 53. The small-diameter portion 52 penetrates through the bush 41 and the seat ring 100. The large-diameter portion 53 is located on the valve seat 70 side with respect to the seat ring 100. The diameter of the large-diameter portion 53 is set larger than the diameter of the hole portion 101. Further, a valve body 60 is provided at the end of the large-diameter portion 53 on the valve seat 70 side.

[0068] The stepped portion 54 is formed in a shape corresponding to the shape of the chamfered portion 101a of the seat ring 100. The stepped portion 54 is configured, for example, in a frustum shape having a side surface that inclines corresponding to the shape of the chamfered portion 101a. Note that the stepped portion 54 functions as a contact portion.

[0069] A coating layer 55 is formed on the outer peripheral surface 50a of the valve rod 50. The coating layer 55 is formed at least on the outer peripheral surface 50a that slides on the inner peripheral surface 41a of the bush 41, the inner peripheral surface 101b of the hole portion 101 in the seat ring 100, and the outer peripheral surface 50a of the stepped portion 54 that contacts the chamfered portion 101a. Note that the coating layer 55 may be formed across the outer peripheral surface 50a of the large-diameter portion 53 of the valve rod 50 as shown in FIG. 7.

[0070] The outer peripheral surface 55a of the coating layer 55 and the inner peripheral surface 41a of the bush 41 and the inner peripheral surface 101b of the hole portion 101 constitute a sliding surface. A predetermined gap is provided between the outer peripheral surface 55a of the coating layer 55 and the inner peripheral surface 41a of the bush 41 and the inner peripheral surface 101b of the hole portion 101 for the small-diameter portion 52 of the valve rod 50 to slide.

[0071] Here, an example in which the coating layer 55 is formed on the outer peripheral surface 50a of the valve stem 50 is shown. Instead of being formed on the outer peripheral surface 50a of the valve stem 50, the coating layer 55 may be formed on the inner peripheral surface 41a of the bush 41, the inner peripheral surface 101b of the hole portion 101, and the chamfered portion 101a. Note that, for the peripheral surface where the coating layer 55 is not formed, any one of, for example, nitriding treatment, chromizing treatment, stellite welding, chromium carbide spraying, etc. is performed to impart oxidation resistance.

[0072] Here, when the valve body 60 is fully opened, the stepped portion 54 of the valve stem 50 abuts against the chamfered portion 101a of the seat ring 100. For example, the steam control valve 21B is operated with the valve body 60 fully opened during the normal operation of the steam turbine plant. In the steam control valve 21B, the abutment between the stepped portion 54 and the chamfered portion 101a functions as a stopper that determines the fully opened position of the valve body 60.

[0073] In addition, since steam leaking into the gap between the inner peripheral surface 41a of the bush 41 and the inner peripheral surface 101b of the hole portion 101 and the small diameter portion 52 of the valve stem 50 is blocked, the efficiency of the steam turbine plant can be improved.

[0074] Note that the above-described abutting structure between the seat ring 100 and the valve stem 50 is an example and is not limited to the above-described structure. This abutting structure may be configured such that when the valve body 60 is in the fully opened position, a part of the seat ring 100 and a part of the valve stem 50 abut against each other to close the gap between the valve stem 50 and the hole portion 101 from the steam chamber 33 side. And it is sufficient that a coating layer is formed on the abutting portion.

[0075] The coating layer 55 has the same configuration as the coating layer 51 in the first embodiment.

[0076] According to the steam valve of the third embodiment, with a simple configuration including a coating layer 55 on the sliding surfaces between the small-diameter portion 52 of the valve rod 50, the inner peripheral surface 41a of the bush 41, and the inner peripheral surface 101b of the hole portion 101, it is possible to reduce the deposition amount of oxide scale deposited on the inner peripheral surface 41a of the bush 41 and the inner peripheral surface 101b of the hole portion 101 per operating hour of the steam turbine.

[0077] By providing a coating layer 55 on the contact surface between the stepped portion 54 of the valve rod 50 and the chamfered portion 101a of the seat ring 100, it is possible to reduce the deposition amount of oxide scale deposited on the stepped portion 54 of the valve rod 50 and the chamfered portion 101a of the seat ring 100 per operating hour of the steam turbine.

[0078] Also, by reducing the deposition amount of oxide scale on the contact surface between the stepped portion 54 and the chamfered portion 101a, it is possible to reduce the amount of leaked steam into the gap between the inner peripheral surface 41a of the bush 41 and the inner peripheral surface 101b of the hole portion 101, and the small-diameter portion 52 of the valve rod 50.

[0079] As a result, the allowable cumulative operating time until the gap in the sliding portion between the small-diameter portion 52 of the valve rod 50, the inner peripheral surface 41a of the bush 41, and the inner peripheral surface 101b of the hole portion 101 is closed becomes longer. Therefore, the disassembly inspection cycle of the steam valve in the third embodiment can be made longer than the disassembly inspection cycle of the conventional steam valve.

[0080] (Fourth Embodiment) FIG. 8 is a diagram showing an enlarged partial cross-section of the steam valve of the fourth embodiment. Here, in the steam valves of the first to third embodiments described above, a configuration is shown in which a coating layer is provided at the contact portion between the valve body 60 and the valve seat 70. Therefore, the configurations of the valve body 60 and the valve seat 70 will be mainly described.

[0081] As shown in Fig. 8, a coating layer 66 is formed on the hemispherical outer peripheral surface 65 of the valve body 60 that abuts against the valve seat 70. The coating layer 66 is formed at least on the portion of the outer peripheral surface 65 that abuts against the valve seat 70. In Fig. 8, an example is shown in which the coating layer 66 is formed on the entire outer peripheral surface 65 of the valve body 60.

[0082] Here, an example in which the coating layer 66 is formed on the outer peripheral surface 65 of the valve body 60 is shown. The coating layer 66 may be formed on the outer peripheral surface 70a of the valve seat 70 that abuts against the valve body 60. In this case, the coating layer 66 is formed at least on the portion of the outer peripheral surface 70a that abuts against the valve body 60. Note that the coating layer 66 may be formed on the entire outer peripheral surface 70a of the valve seat 70. The peripheral surface on which the coating layer 66 is not formed is subjected to, for example, any one of nitriding treatment, chromizing treatment, stellite welding, chromium carbide spraying, etc., to impart oxidation resistance.

[0083] The coating layer 66 has the same configuration as the coating layer 51 in the first embodiment.

[0084] Here, the valve body 60 shuts off the steam flowing into the steam turbine by abutting against the valve seat 70. Therefore, if there is a defect in the contact between the contact surfaces of the valve body 60 and the valve seat 70, the steam passes through the contact surface and flows into the steam turbine. When an abnormality occurs during the operation of the steam turbine, the steam valve is rapidly fully closed to cut off the steam flowing into the steam turbine and stop the steam turbine. Therefore, it is important to perform maintenance management so that the contact between the valve body 60 and the valve seat 70 is always in good condition.

[0085] Therefore, in the steam valve of the fourth embodiment, with a simple configuration including the coating layer 66 at the contact portion between the valve body 60 and the valve seat 70, it is possible to reduce the deposition amount per operating hour of the steam turbine of the oxidation scale deposited on the outer peripheral surface 65 of the valve body 60 and the outer peripheral surface 70a of the valve seat 70 at the contact portion.

[0086] As a result, poor contact of the contact surface between the valve body 60 and the valve seat 70 is suppressed, and the steam turbine can be properly stopped even in an emergency. In addition, the disassembly inspection cycle of the steam valve according to the fourth embodiment can be made longer than the disassembly inspection cycle of the conventional steam valve.

[0087] (Evaluation of Oxide Scale Deposition Amount and Oxidation Rate) Next, in order to show that the deposition amount of oxide scale can be reduced in the steam valve of the present embodiment, the evaluation of the oxide scale deposition amount and the oxidation rate was performed.

[0088] In this evaluation, three types of sample members (sample member 1 - sample member 3) were prepared. The base materials of all the sample members used the same high-temperature alloy and had the same shape and size.

[0089] For sample member 1, a PVD coating was applied to the surface of the cleaned base material to form a coating layer. The coating layer was formed by adsorbing the vaporized substance on the surface of the base material loaded in a vacuum chamber. Here, the coating layer was composed of TiAlN. The film thickness of the coating layer was 3 μm. The film thickness was adjusted by the time for adsorbing the vaporized substance on the surface of the base material.

[0090] For sample member 2, nitriding treatment was performed on the surface of the cleaned base material by the diffusion hardening method. A nitriding treatment layer was formed to a depth of about 50 μm from the surface of the base material.

[0091] Sample member 3 was the base material itself and did not have a coating layer or a surface treatment layer.

[0092] Note that sample member 1 corresponds to the present embodiment, and sample members 2 - 3 are comparative examples outside the scope of the present embodiment.

[0093] The above-described sample members were exposed to a steam atmosphere at 630°C for 9000 hours. Then, the thickening amount (oxide scale deposition amount) of each sample member was measured. The thickening amount was measured using a micrometer.

[0094] As the measurement result of the amount of thickening, with the amount of thickening of the sample member 2 being set as "1", the ratio of the amount of thickening (ratio of the amount of oxide scale deposition) was shown. When the ratio of the amount of thickening is greater than 1, it means that it is greater than the amount of thickening of the sample member 2, and when the ratio of the amount of thickening is less than 1, it means that it is less than the amount of thickening of the sample member 2.

[0095] The oxidation rate (mm / h) was calculated by dividing the amount of thickening of each sample member by 9000 hours of the exposure time.

[0096] Table 1 shows the results of the amount of oxide scale deposition and the oxidation rate.

[0097]

Table 1

[0098] As shown in Table 1, it can be seen that the ratio of the amount of thickening in the sample member 1 is clearly smaller than the ratios of the amount of thickening in the sample member 2 and the sample member 3. Also, it can be seen that the oxidation rate in the sample member 1 is clearly slower than the oxidation rates in the sample member 2 and the sample member 3.

[0099] Thus, it can be seen that the sample member 1 provided with the coating layer formed by PVD coating has excellent oxidation resistance and a small amount of oxide scale deposition and a small amount of oxide scale deposition per unit time.

[0100] Also, the oxidation rate in the sample member 1 according to the present embodiment is, for example, compared with the sample member 2 subjected to nitriding treatment employed in a conventional steam valve is also a value one digit smaller. From this result, in the steam valve of the present embodiment, for example, even if the gap between the valve stem and the bush is made smaller than the gap between the conventional valve stem and the bush, there is a possibility that the cycle of disassembling and inspecting the steam valve can be set longer than the cycle of disassembling and inspecting the conventional steam valve. Furthermore, in the steam valve of the present embodiment, it is found that by making the gap between the valve stem and the bush smaller than the gap between the conventional valve stem and the bush, leakage of steam can be more suppressed.

[0101] According to the embodiments described above, with a simple configuration, it is possible to reduce the deposition amount of oxidation scale per operating hour of the steam turbine formed on the sliding part and the like in the steam valve.

[0102] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0103] 1... steam turbine plant, 10... boiler, 10a... superheater, 10b... reheater, 11... high-pressure turbine, 12... intermediate-pressure turbine, 13... low-pressure turbine, 14... condenser, 15... feed water pump, 20... main steam stop valve, 21, 21A, 21B... steam control valves, 22... reheated steam stop valve, 23... intercept valve, 24... high-pressure turbine bypass valve, 25... low-pressure turbine bypass valve, 26... check valve, 30... valve casing, 31... steam inlet section, 32... steam outlet section, 33... steam chamber, 34... opening, 40... valve cover, 40a, 42, 91... through holes, 41... bush, 41a, 90a, 101b... inner peripheral surface, 50... valve rod, 50a, 51a, 55a, 61a, 63a, 65, 70a... outer peripheral surface, 51, 55, 63, 66... coating layers, 52... small-diameter section, 53... large-diameter section, 54... step section, 60, 60A... valve body, 61... cylindrical section, 62... hemispherical section, 70... valve seat, 80... hydraulic drive mechanism, 90... sleeve, 100... seat ring, 101... hole, 101a... chamfered section, 120... main steam pipe, 121... low-temperature reheated steam pipe, 122... high-temperature reheated steam pipe, 123... crossover pipe, 124... feed water pipe, 125... high-pressure turbine bypass pipe, 126... low-pressure turbine bypass pipe.

Claims

1. A steam valve comprising a steam inlet portion, a steam outlet portion, and a steam chamber, a valve casing having an opening communicating with the steam chamber, a valve seat provided in the vicinity of the steam outlet portion in the steam chamber within the valve casing, a valve lid installed on the valve casing so as to close the opening and having a through hole, a cylindrical bush fitted into the through hole, a valve rod slidably penetrating through the bush, and a valve body provided at one end of the valve rod and configured to be capable of contacting the valve seat, wherein a PVD coating layer is formed on an outer peripheral surface of the valve rod sliding within the bush or an inner peripheral surface of the bush.

2. The steam valve according to claim 1, further comprising a cylindrical sleeve having a central axis coaxial with a central axis of the bush on a side of the valve lid facing the steam chamber, wherein the valve body includes a cylindrical portion connected to one end of the valve rod and sliding on an inner peripheral surface of the sleeve, and a hemispherical portion provided so as to be capable of contacting the valve seat, and a PVD coating layer is formed on an outer peripheral surface of the cylindrical portion sliding within the sleeve or an inner peripheral surface of the sleeve.

3. The steam valve according to claim 1, further comprising a seat ring formed of an annular member fitted on a side of the through hole of the valve lid closer to the steam chamber than the bush and having a hole in the center, wherein the valve rod includes a contact portion configured to contact the seat ring so as to close a gap between the valve rod and the hole from the steam chamber side when the valve body is in a fully open position, and a PVD coating layer is formed on a contact surface of the contact portion with the seat ring or a contact surface of the seat ring with the contact portion.

4. The steam valve according to claim 1, wherein a PVD coating layer is formed on a contact surface of the valve body with the valve seat or a contact surface of the valve seat with the valve body.

5. A steam turbine plant comprising a steam generator, a steam turbine, a steam pipe for guiding steam generated in the steam generator to the steam turbine, and the steam valve according to any one of claims 1 to 4 interposed in the steam pipe.

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