JP2010236385A - Steam valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam valve preventing occurrence of radial cracks at stellite padding part provided on a valve element or a valve seat. <P>SOLUTION: This steam valve has the stellite padding part 11 applied on a seat part 10 of at least one of the valve element 7 and the valve seat 6 in a circumference direction. The steam valve includes a slit part 12 disposed on the stellite padding part 11 in a circumference direction with interval and an embedded member 13 embedded in the slit part 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a steam valve used in a steam turbine or the like, and more particularly to a steam valve with enhanced thermal shock resistance and corrosion resistance of a valve body and a seat portion of a valve seat.

  For steam valves such as main steam control valves used in steam turbines, in order to prevent thermal shock due to inflow or outflow of high-temperature and high-pressure superheated steam, or damage due to wear such as erosion and corrosion, It is known to build-up a cobalt-based hard alloy (for example, a stellite material (trade name)) having impact properties and corrosion resistance and higher hardness than a valve base material. The inner surface of the valve seat of this steam valve is made of stellite and ceramics, and the functionally graded material whose content ratio changes continuously along the thickness direction is welded to reduce the generation of thermal stress. (For example, refer to Patent Document 1).

  This functionally gradient material has a stellite material content of 100% and a ceramic material content of 0% at the interface contacting the valve body, and gradually changes toward the weld surface. It is formed to have a content rate of 0% and a ceramic material content rate of 100%. For this reason, the linear expansion coefficient of the functionally gradient material is substantially equal to the linear expansion coefficient of the valve base material at the boundary surface in contact with the valve body.

JP-A-6-137108

  By the way, in order to improve the efficiency of the steam turbine, in recent years, the steam temperature has been increased. As the valve base material for the steam valve corresponding to this higher steam temperature, the strength is improved from Cr-Mo-V low alloy steel (chromium-molybdenum-vanadium low alloy steel) used as a conventional heat-resistant alloy steel. In order to improve oxidation resistance, steel materials with high Cr content such as 9Cr steel and 12Cr steel have been changed.

For this reason, the linear expansion coefficient of the Cr-Mo-V low alloy steel used in the past was about 13.0 × 10 ⁻⁶ / ° C., which is similar to that of the stellite material, whereas 9Cr steel and 12Cr The linear expansion coefficient of steel is about 9.2 to 10.5 × 10 ⁻⁶ / ° C., and the difference in linear expansion coefficient from the stellite material is increasing. In other words, in a steam valve using 9Cr steel or 12Cr steel as a base material, the difference in coefficient of linear expansion between the valve body and the stellite material welded to the seat portion of the valve seat becomes large. The welding residual stress generated by the tension between the stellite overlay on the seat and the valve base material is larger than the welding residual stress in the conventional steam valve using Cr-Mo-V low alloy steel as the base material. ing. In this welding residual stress, the stress on the circumferential direction side of the stellite build-up portion acts more than the stress on the radial direction side. In addition, an impact load at the time of the rapid closing of the steam valve and an applied stress such as a repeated thermal stress due to an operation cycle such as starting / stopping are superimposed on this welding residual stress. As a result, cracks are likely to occur in the radial direction of the stellite overlay.

  Furthermore, in a periodic inspection of a steam turbine plant that has been heated in recent years, it has been found that the frequency of occurrence of cracks in the radial direction of the stellite build-up portion of the steam valve is increased as compared with the conventional case.

  The present invention has been made on the basis of the above-mentioned matters, and its purpose is to reduce the residual welding stress in the circumferential direction of the stellite cladding portion applied to the valve body and the valve seat, and to prevent the occurrence of cracks. Is to provide.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a steam valve in which a stellite build-up part is constructed in a circumferential direction of at least one seat part of a valve body and a valve seat, and the circumferential direction of the stellite build-up part And a slit portion provided at intervals, and an embedded member embedded in the slit portion.

  In a second aspect based on the first aspect, the slit portion is formed by cutting the stellite build-up portion in the radial direction of the sheet portion.

  Further, according to a third aspect, in the first aspect, the slit portion is formed by cutting the stellite build-up portion with an inclination with respect to the radial direction of the sheet portion.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the embedded member has a linear expansion coefficient that is approximately between the linear expansion coefficient of the valve base material and the linear expansion coefficient of the stellite material. It shall be a member of.

  Furthermore, in a fifth aspect according to any one of the first to fourth aspects, the embedded member is build-up welded to the slit portion.

  According to the present invention, since the slit processing is performed in the radial direction of the stellite overlay portion applied to the valve body of the steam valve and the seat portion of the valve seat, the welding residual stress can be reduced. As a result, the occurrence of cracks in the stellite overlay can be prevented, and maintenance work for the stellite overlay can be reduced. In addition, the range of material selection for the valve base material and the stellite material can be expanded.

It is a longitudinal cross-sectional view which shows the inside of the adjustment valve for steam turbines which applied one Embodiment of the steam valve of this invention. It is a longitudinal cross-sectional view which shows the valve seat sheet | seat part in one Embodiment of the steam valve of this invention shown in FIG. It is a longitudinal cross-sectional view which expands and shows the A section of one Embodiment of the steam valve of this invention shown in FIG. It is a perspective view which shows the valve seat sheet | seat part in one Embodiment of the steam valve of this invention shown in FIG. It is a schematic diagram explaining the setting of the slit in one embodiment of the steam valve of the present invention.

Embodiments of the steam valve of the present invention will be described below with reference to the drawings.
1 to 3 show an embodiment of a steam valve of the present invention, and FIG. 1 is a longitudinal sectional view showing the inside of a steam turbine control valve to which an embodiment of the steam valve of the present invention is applied. FIG. 2 is a longitudinal sectional view showing a valve seat portion in the embodiment of the steam valve of the present invention shown in FIG. 1, and FIG. 3 is an enlarged view of part A of the embodiment of the steam valve of the present invention shown in FIG. It is a longitudinal cross-sectional view shown.

  In FIG. 1, a valve lid 2 is fastened to a valve body 1 of a steam valve with a bolt 3 to form a regulating valve casing 4 as a pressure vessel. In the casing 4, a valve body 7 that is brought into contact with and separated from the valve seat 6 via the valve rod 5 is disposed, and a strainer 8 that holds foreign matter in the steam is provided on the outer periphery of the valve body 7. . The valve stem 5 is held by a guide member 9, and a driving device (not shown) for operating the valve body 7 in the vertical direction is provided at the end thereof.

  The steam in the steam valve flows into the casing 4 from, for example, a steam pipe (not shown) as indicated by an arrow A, and the valve body 7 and the valve seat 6 formed by the upward movement of the valve body 7 shown in FIG. It flows out to the arrow B through the flow path between. A seat portion 10 is formed at the joint between the valve body 7 and the valve seat 6.

  2 and 3 are side views showing the seat portion 10 in the valve seat 6 of the steam valve. As shown in FIG. 3, the stellite build-up portion 11 is formed by overlay welding a stellite material, which is a cobalt-based corrosion-resistant heat-resistant alloy, over the entire circumference of the sheet portion 10 and adjusting the contact portion. Has been. Specific examples of the overlay welding method for such stellite materials include, for example, an oxygen acetylene method using a cobalt-based hard alloy welding wire, a TIG (Tungsten Inert Gas) method, a PTA (Plasma Transferred Arc) method, and a cobalt substrate alloy. There is a method of spraying powder. In the present embodiment, the stellite build-up portion 11 is formed by the PTA method. As described above, with the recent change in the steam valve base material, the difference in linear expansion coefficient between the stellite material and the valve base material increases, and the stellite build-up portion 11 applied to the valve body and the seat portion of the valve seat. The welding residual stress generated by the tension between the valve base metal and the valve base metal is larger than the welding residual stress in the conventional steam valve using Cr-Mo-V low alloy steel as the valve base material. As a result, cracks are likely to occur in the radial direction of the stellite overlay 11.

  Next, the manufacturing method of the stellite build-up part in one embodiment of the steam valve of the present invention will be described with reference to FIGS. 4 is a perspective view showing a valve seat portion in one embodiment of the steam valve of the present invention shown in FIG. 1, and FIG. 5 is a schematic diagram for explaining setting of slits in the embodiment of the steam valve of the present invention. is there. 4 and 5, the same reference numerals as those shown in FIGS. 1 to 3 are the same parts, and the detailed description thereof is omitted.

  First, as shown in FIG. 4, stellite build-up welding is performed on the valve seat portion 10 in the valve seat 6 of the steam valve, and the slit portion 12 is provided with a gap in the circumferential direction of the stellite build-up portion 11. The slit portion 12 is formed in the direction from the outer diameter portion to the inner diameter portion of the stellite build-up portion 11, and the depth is preferably cut to the extent that the valve base material is exposed. Further, the direction in which the slit portion 12 is formed is preferably parallel to the radial direction of the valve seat 6 in consideration of the flow of steam in the valve seat 6, but is inclined with respect to the radial direction. . By forming the slit portion 12 in this manner, it is possible to prevent the erosion of the slit build-up portion 11 due to the flow of steam.

  Next, in this slit portion 12, the slit portion is formed by using the embedded member 13, which is a member having a high ductility and a linear expansion coefficient approximately equal to the linear expansion coefficient of the valve base material and that of the stellite material. Overlay welding to fill The purpose of this overlay welding is to smooth the surface shape of the seat portion 10 of the valve seat 6 in order to reduce the turbulence of the steam flowing through the seat portion 10 of the valve seat 6. Therefore, the embedding member 13 embedded in the slit portion 12 does not need to ensure hardness compared to the stellite material. For example, the linear expansion coefficient of Inconel welding materials is approximately halfway between the linear expansion coefficient of valve base materials such as 9Cr steel and 12Cr steel, and the linear expansion coefficient of stellite materials. In the embodiment, use of these welding materials is preferable.

  Next, the surface of both the stellite build-up part 11 and the embedding member 13 embedded in the slit part 12 is smoothly formed and processed, and the final process for adjusting the contact part with the valve body 7 is performed.

  Since the stellite build-up part 11 is formed in this way, the seat part 10 of the valve seat 6 is covered with a hard stellite material, and it is possible to reduce welding residual stress while preventing erosion. It becomes.

Next, the setting of the slit part 12 formed in the stellite build-up part 11 is further demonstrated using FIG.
First, as shown in FIG. 5, the slit part 12 is formed by cutting the stellite build-up part 11 from the outer diameter part toward the inner diameter part. By cutting, the stellite build-up part 11 is independent without sandwiching the slit part 12. That is, as shown in FIG. 5, it is preferable to cut the slit portion 12 to the extent that the valve base material 14 is exposed at least in the form of dots or planes.

The direction of forming the slit portion 12 is preferably not obliquely parallel to the radial direction of the valve seat 6 as described above, but is obliquely processed with an inclination with respect to the radial direction. Shown in
In the stellite build-up part 11 shown in FIG. 5, when the gap between one slit part 12 and another slit part 12 is L, the gap L can be calculated according to the following formula.
L ≧ D × cosθ / sinθ (1)
Here, D is the width of the stellite buildup portion 11, and θ is the radial inclination angle of the slit portion 12 with respect to the inner diameter portion of the stellite buildup portion 11.

  The above-described formula (1) indicates that one slit portion 12 and the other slit portion 12 should be formed at an interval L that does not overlap in the radial direction of the stellite build-up portion 11. That is, the interval L can be increased in a range where the overlapping of the slit portions 12 and 12 does not occur. The value of the gap L is determined by the respective linear expansion coefficients of the valve base material, the stellite material, and the embedded member.

  On the other hand, the radial inclination angle θ of the slit portion 12 is preferably 60 ° or less in order to prevent erosion due to the flow of steam.

  According to the embodiment of the steam valve of the present invention described above, since the slit portion 12 is processed in the radial direction of the stellite build-up portion 11 applied to the valve body 7 of the steam valve and the seat portion 10 of the valve seat 6, Welding residual stress can be reduced. As a result, the occurrence of cracks in the stellite overlay 11 can be prevented. In addition, the range of material selection for the valve base material and the stellite material can be expanded.

  Further, according to the embodiment of the steam valve of the present invention, it is possible to reduce the residual stress of the stellite buildup portion 11 regardless of the combination of any valve base material and stellite material, and the stellite buildup portion. 11 can be prevented from occurring, and the maintenance work of the stellite overlay 11 can be reduced.

  Further, according to the embodiment of the steam valve of the present invention, the embedding member is a member having high ductility and a coefficient of linear expansion approximately equal to the linear expansion coefficient of the valve base material and the linear expansion coefficient of the stellite material. 13 is used for overlay welding to fill the slit portion, so that the seat portion 10 of the valve seat 6 of the steam valve is covered with a high-stiffness stellite material to prevent erosion and to prevent welding residual stress. Can be reduced.

  In the description of the present embodiment, the formation of the stellite buildup portion 11 in the seat portion 10 of the valve seat 6 of the steam valve has been described. For example, the stellite buildup portion 11 is provided only on the seat portion 10 of the valve body 7. The stellite build-up part 11 may be formed on both the seat part 10 of the valve seat 6 and the seat part 10 of the valve body 7.

DESCRIPTION OF SYMBOLS 1 Valve body 2 Valve lid 3 Bolt 4 Casing 5 Valve rod 6 Valve seat 7 Valve body 8 Strainer 9 Guide member 10 Seat part 11 Stellite overlay part 12 Slit part 13 Embedding member 14 Valve base material

Claims (5)

In the steam valve in which the stellite overlay is constructed in the circumferential direction of the seat part of at least one of the valve body and the valve seat,
A slit portion provided with an interval in the circumferential direction of the stellite overlay,
A steam valve comprising: an embedded member embedded in the slit portion. The steam valve according to claim 1,
The slit portion is formed by cutting the stellite build-up portion in the radial direction of the seat portion. The steam valve according to claim 1, wherein
The said slit part cuts and forms the said stellite build-up part with an inclination with respect to the radial direction of the said sheet | seat part. The steam valve characterized by the above-mentioned. The steam valve according to any one of claims 1 to 3,
The embedded member is a member whose linear expansion coefficient is a member having a value approximately in the middle of the linear expansion coefficient of the valve base material and the linear expansion coefficient of the stellite material. The steam valve according to any one of claims 1 to 4,
The said embedded member is build-up welded to the said slit part. The steam valve characterized by the above-mentioned.

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