JP4154105B2 - Steam valve - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steam valve for controlling steam of a steam turbine, and more particularly to an improvement in a structure for attaching a steam valve body to a support member.
[0002]
[Prior art]
In a steam turbine of a thermal power plant, a steam valve disposed on the upstream side of the steam passage from the turbine casing is fixed via a fixing support mounting portion (supporting member). The support mounting portion includes a type that is directly welded to the steam valve valve body, that is, a casing, and a type that is fixed to the steam valve body by bolts.
[0003]
In the latter bolt-fixed type, as shown in FIGS. 5 and 6, a steam valve body 2 that houses a valve body (not shown) is provided with a mounting surface 3 parallel to the direction of the axis 2a. A screw hole 4 for a stud bolt is formed in the mounting surface 3.
[0004]
When fixing this type of steam valve 1, as shown in FIG. 7, a bracket 20 as the support mounting portion is fixed to the mounting surface 3 with bolts 21 and nuts 22. Is hangered.
[0005]
Under normal use conditions, high-temperature steam flows inside the steam valve main body 2, but the outer surface of the steam valve main body 2 is exposed to the atmosphere in the building. A temperature difference occurs on the outside, and as a result, thermal stress acts on the steam valve body 2. This thermal stress is compressive stress on the inner surface of the steam valve and tensile stress on the outer surface, but is higher than the stress acting on the flat portion of the mounting surface 3 due to stress concentration at the hole edge on the inlet side of the screw hole 4 of the mounting surface 3. Stress will act. This stress concentration causes cracks due to creep to progress over time at the hole edge of the screw hole 4, which may be a factor for shortening the life of the steam valve body 2.
[0006]
[Problems to be solved by the invention]
This invention is made | formed in view of the said actual condition, and it aims at suppressing the crack generation | occurrence | production of the hole edge of the screw hole of the attachment surface of a steam valve main body.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a steam valve for controlling steam of a steam turbine , wherein a mounting surface is provided outside a steam valve main body that accommodates the valve body, and the steam valve main body extends from the mounting surface. internal screw hole extending toward the inside are formed directly on the steam valve body, the steam valve body with a bolt screwed into the screw hole is fixed to the support member, in use, the steam valve body In the case where a tensile stress as a thermal stress is generated on the mounting surface due to a temperature difference generated between the inside and the outside of the steam valve main body due to high-temperature steam flowing therethrough, a counterbored hole is formed on the inlet side of the screw hole on the mounting surface. A steam valve is provided, wherein a contour of the counterbore hole includes a straight portion, and the straight portion is parallel to a main stress acting direction in the vicinity of the entrance of the counterbore hole.
[0008]
According to the present invention, since the counterbore hole is provided on the inlet side of the screw hole, the distance between the hole edge of the screw hole and the inner surface of the steam valve body can be reduced, and the hole edge of the screw hole and the steam valve can be reduced. The temperature difference with the inner surface of the main body can be reduced, and thereby the thermal stress acting on the hole edge of the screw hole can be reduced. Moreover, stress concentration can be reduced by providing counterbored holes. In particular, the cross-sectional contour of the counterbore hole includes a straight portion, and the straight portion is set substantially parallel to the main stress acting direction in the vicinity of the entrance of the counterbore hole. Becomes infinite and stress concentration can be minimized.
[0009]
The center position of the screw hole may be shifted from the center position of the counterbore hole along the main stress acting direction.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In the following description, the same members as those shown in FIGS. 5 to 7 for explaining the prior art are denoted by the same reference numerals.
[0011]
As shown in FIGS. 1 and 2, a plurality of screw holes 4 extending from the attachment surface 3 toward the inside of the steam valve body 2 are formed in the attachment surface 3 of the steam valve body 2. A counterbore 10 (or counterbore 10A) is formed on the inlet side of the screw hole 4, that is, on the mounting surface 3 side.
[0012]
As described in the section of the prior art, thermal stress acts on the steam valve main body 2 when the steam valve 1 is used. In this case, the thermal stress acts on a cylindrical object as shown in FIG. Can be outlined. In general, when a high-temperature and high-pressure fluid exists on the inner surface side of a cylindrical object as shown in the upper part of FIG. 3, the temperature gradient along the cross-section becomes as shown in the middle part of FIG. It is known that the thermal stress to be distributed has a distribution as shown in the lower graph of FIG. That is, the outer surface shows the highest tensile force, but the inner surface shows the highest compressive force.
[0013]
Therefore, by providing a counterbore hole 10 (10A) on the inlet side of the screw hole 4 of the mounting surface 21, the hole edge of the screw hole 4 is located inside the mounting surface 21 (corresponding to the cylindrical outer surface of the model of FIG. 4). Therefore, the stress value at the hole edge of the screw hole 4 is smaller than that without the counterbore 10 (10A). In addition, what is necessary is just to obtain | require the determination of the optimal value of the depth C (refer FIG.2 (b)) of the counterbore 10 (10A) experimentally and / or by numerical analysis.
[0014]
FIG. 2A is a diagram showing the details of the shape of the counterbore hole 10, and as shown in FIG. 2A, the hole edge of the counterbore hole 10 includes a pair of linear portions 11, 11 and these linear portions. 11 has an oval outline having a pair of semicircular portions 12 and 12 connecting both ends of the same. In the illustrated embodiment, the contour shape of the counterbore hole 10 is constant regardless of the distance in the depth direction from the hole edge of the counterbore hole 10.
[0015]
The direction of the straight portion 11 is parallel to the main stress acting direction Fm in the vicinity of the entrance of the counterbore hole 10. The principal stress acting direction Fm can be obtained experimentally or by numerical analysis.
[0016]
Each of the straight portions 11 has a length of B1 + B2. The dimensions B1 and B2 correspond to the distance from the point where a straight line passing through the center of the screw hole 4 and perpendicular to the cutting line IIb-IIb intersects each straight line part 11 to one end and the other end of each straight line part 11. It is. In the embodiment shown in FIG. 2, B1 = B2, and the center of the screw hole 4 and the center of the counterbore hole 10 coincide.
[0017]
As shown in FIG. 2A, the counterbore 10 is symmetric with respect to the cutting line IIb-IIb. The radii R1 and R2 of the semicircular portions 12 and 12 are the same, and the center of each semicircular portion 12 is a cutting line IIb-IIb and a straight line connecting ends corresponding to each other of the linear portions 11 and 11. Located on the intersection of The width dimension A of the counterbore 10 is twice the radius R1, R2 of the semicircular portions 12, 12. The direction of each straight line portion 11, 11 is the same as the direction of the tangent of each semicircular portion 12, 12 at the connection point between each straight line portion 11, 11 and each semicircular portion 12, 12. 11 and the semicircular portions 12 and 12 are smoothly connected, so that stress concentration is unlikely to occur at the connection point.
[0018]
By giving the above-mentioned geometric characteristics to the contour of the counterbore 10, the radius of curvature of the hole edge of the counterbore 10 with respect to the main stress acting direction Fm on the surface of the mounting surface 3 becomes infinite, resulting in stress concentration. Will be eased.
[0019]
As described above, in the present embodiment, the thermal stress acting on the hole edge of the screw hole 4 by providing the counterbore hole 10 on the inlet side of the screw hole 4 and shifting the position of the hole edge of the screw hole 4 inward. , And the straight portion 11 having the same direction as the main stress acting direction Fm is provided on the contour of the counterbore 10 to minimize stress concentration at the edge of the counterbore 10. For this reason, the possibility of damage near the hole edge of the screw hole 4 and the counterbore hole 10 hole edge can be greatly reduced.
[0020]
In FIG. 2, the dimensions B1 and B2 related to the straight line portion 11 are equal to each other, but the present invention is not limited to this, and the dimensions B1 and B2 may be different from each other (FIG. ) Refer to the counterbored hole 10A shown on the lower side). That is, the center position of the screw hole 4 may be shifted from the center position of the counterbore hole along the direction of the cutting line IIb-IIb, in other words, along the principal stress acting direction Fm. In this case, the same effect of reducing stress and stress concentration can be obtained.
[0021]
As shown in FIG. 4, bolts 21 are implanted in the respective screw holes 4 of the steam valve main body 2 configured as described above, and are attached to the brackets 20 by nuts 22 that are screwed into the respective bolts 21. . The bracket 20 is hangered in the building, whereby the steam valve 1 is fixed at a predetermined position.
[0022]
【The invention's effect】
As described above, according to the present invention, it is possible to effectively prevent damage to the edge of the screw hole on the mounting surface of the steam valve body.
[Brief description of the drawings]
FIG. 1 is a view showing an embodiment of a steam valve according to the present invention, in which FIG. 1 (a) is a front view of a mounting surface of the steam valve body, and FIG. 1 (b) is Ib− in FIG. Sectional drawing along an Ib cutting line.
2 is a view showing details of the shape of a counterbore hole and a screw hole shown in FIG. 1, in which FIG. 2 (a) is an enlarged view of a region IIa of FIG. 1 (a), and FIG. These are sectional drawings along the IIb-IIb cutting line in Drawing 2 (a).
FIG. 3 is a diagram for explaining thermal stress acting on a cylindrical object.
FIG. 4 is a view for explaining a method of attaching a steam valve.
5A and 5B are diagrams schematically illustrating a configuration of a steam valve main body, in which FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view taken along the line Vb-Vb in FIG. Figure.
6 is a view for explaining a mounting surface of a conventional steam valve body, in which FIG. 6 (a) is a front view of the mounting surface of the steam valve body viewed from the direction of arrow VIa in FIG. 5, and FIG. 6 (b). These are sectional drawings along the VIb-VIb cutting line in Fig.6 (a).
FIG. 7 is a view for explaining a conventional method of attaching a steam valve.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steam valve 2 Steam valve main body 3 Mounting surface 4 Screw hole 10 Counterbore hole 11 Straight part 20 Support member 21 Bolt Fm Main stress action direction

Claims (1)

A steam valve for controlling steam of a steam turbine , wherein a mounting surface is provided outside a steam valve main body that accommodates the valve body, and a screw hole extending from the mounting surface toward the inside of the steam valve main body has the steam valve The steam valve body is fixed to the support member using a bolt that is directly formed on the body and screwed into the screw hole, and when used, the steam valve body is heated by high-temperature steam flowing through the interior of the steam valve body. In the case where a tensile stress as a thermal stress is generated on the mounting surface due to a temperature difference generated between the inside and the outside,
A counterbore hole is provided on the inlet side of the screw hole on the mounting surface, the contour of the counterbore hole includes a straight line part, and the straight line part is parallel to the main stress acting direction in the vicinity of the inlet of the counterbore hole. A steam valve characterized by.

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