JPH04143403A - Steam valve - Google Patents

Abstract

PURPOSE:To thin the thickness of a requisite barrel part and relieve the thermal stress in equalizing the whole thickness by forming a valve body, constituting a pressure vessel, and an inlet member with steel forgings higher in hot strength than that of steel castings of the same chemical composition. CONSTITUTION:A valve body 21 consists of a valve upper-half body 21a, having the same barrel part thickness t1 in every spot and including a main valve 6, and a valve lower-half body 21b having the same barrel part thickness t2 in every spot and being situated downstream of the main valve 6. These valve half bodies 21a, 21b are solidly welded together via a weld zone W3. In addition, these bodies 21a, 21b are both manufactured by means of forging with molybdenum-vanadium steel excellent in material strength, whereas they are of the same thickness. Each inner surface of these bodies 21a, 21b is precisely shaped by means of machining. Thus, it is thinned in thickness as compared with the conventional one and, what is more, the whole thickness can be equalized, thus a thermal stress is made relievable.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is applicable to flow path control of high-temperature and high-pressure steam piping systems, such as the main steam pipe of a steam turbine and the reheat steam pipe. Concerning a preferred steam valve.

(Prior Art) In recent steam power stations, steam turbines based on the Rankine cycle and reheat regeneration cycles, which are modified to improve thermal efficiency, are often used.

The thermal efficiency of this steam power plant depends on the inlet steam pressure and steam temperature of the steam turbine, and the exhaust pressure, that is, the internal pressure of the condenser.The higher the inlet steam pressure or temperature, and the lower the exhaust pressure, the better the value. shows.

Nowadays, there is a strong demand for energy conservation, and there is a need to increase the inlet steam pressure and temperature of steam turbines, whether new or existing, to increase the thermal efficiency of steam power plants. Even in a supercritical pressure plant, the turbine inlet steam had to be limited to about 246 kg/Ci and 538° C. due to the heat resistance of the steam turbine's constituent materials and the main steam valve.

FIG. 3 shows an example of a conventional steam valve. This steam valve consists of a pressure vessel section 4 which is constructed by fixing an upper cover 2 to a valve body 1 with bolts 3, and a main body screwed into a valve stem 5. Valve 6, valve stem 5
The steam passage section 10 is composed of a guide piece 7 that holds the steam, a strainer 8 that traps foreign matter in the steam, and a valve seat 9 that is fixed to the valve body 1. In this case, an elbow 1a and a short pipe 1b for connecting to a steam pipe are integrated via a welded part WSW2.

Note that an actuator (
(not shown) is fixed to the valve body 1 with bolts 12 via a blanket 11, and the guide piece 7 is also fixed to the blanket 11 with bolts 13.

Steam flowing through a steam pipe (not shown) flows into the steam valve as shown by arrow A, passes through a flow path formed between the main valve 6 and valve seat 9, and flows out in arrow B. .

In the conventional steam valve configured as described above, the valve body 1
Chromium-molybdenum-vanadium cast steel products are widely used as materials for the elbow 1a, with the addition of chromium and molybdenum to increase high-temperature strength, and vanadium added to suppress the instability of the material surface caused by these additives. was.

Since the valve body 1 and the elbow 1a have complicated shapes as described above, the optimal method is to manufacture them by casting.

(Problem to be Solved by the Invention) However, because the conventional valve body 1 has a complicated shape, the wall thickness of each part becomes uneven due to its structure.As a result, when starting a steam turbine, etc. Due to the temperature difference that occurs between the inner and outer surfaces of the part, the generation of large thermal stresses is unavoidable.

Furthermore, if an attempt is made to increase the pressure and temperature of the steam at the inlet of the steam valve in order to improve the thermal efficiency of the power plant, there is a drawback that thermal stress increases even more.

Furthermore, the operating temperature limit of various materials used in current steam power plants is thought to be around 570°C.
Even if a material that can withstand even higher temperature and high pressure steam is developed in the near future, it will take a considerable amount of time to verify it, so users who are eager to improve the thermal efficiency of their power plants are looking for main steam that has excellent high temperature strength. It is expected that a considerable period of time will be required before various steam turbine equipment, including valves, can be put into practical use, and in the meantime, steam conditions will have to be set taking into account the operating temperature limit. There were drawbacks.

An object of the present invention is to eliminate the above-mentioned disadvantages and provide a steam valve that does not cause any problems even when the steam conditions become higher temperature and pressure.

[Structure of the invention]

(Means for Solving the Problems) As a means for achieving the above object, the present invention provides a valve body in which a main valve is pressurized and released, and a valve body which is welded to the inlet side of the valve body and which directs steam from a steam pipe to the valve body. In a steam valve in which a pressure vessel portion is formed from an inlet member that is guided into the steam valve, the valve body and the inlet member that constitute the pressure vessel portion are each made of forged steel, and the valve body includes a main valve. It consists of a valve upper body and a lower valve half body on the downstream side of the main valve, and is characterized in that the valve upper body and the lower valve half body are butted and welded together using a straight pipe portion of the same diameter. do.

(Function) In the steam valve according to the present invention, the valve body and the inlet member constituting the pressure vessel portion are made of a forged steel product that has higher high-temperature strength than a cast steel product of the same chemical composition. Therefore, the wall thickness can be made thinner than in the past, and the overall wall thickness can be made uniform, making it possible to alleviate thermal stress. Furthermore, since it is forged, there are no inherent defects in the valve body, making it possible to improve reliability.

Furthermore, since the valve body is composed of a benshi rod body containing the main valve and a lower valve half body on the downstream side of the main valve, it can be easily manufactured even in the case of a large steam valve. . Since the valve upper body and the lower valve half body are butt-welded using straight pipe portions having the same diameter, non-destructive inspection such as radiographic inspection can be easily performed, and the soundness of the structural welded portion can be confirmed.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a steam valve according to the present invention. In the figure, reference numeral 21 is a valve body, and this valve body 21 consists of an upper cover 2 and bolts 3 for fixing the upper cover 2 to the valve body 21. The valve body 21 also constitutes the pressure vessel section 4, and an inlet pipe 22 for connecting to a steam pipe (not shown) is integrated with the valve body 21 via a weld W1.

Inside the valve body 21, as shown in FIG. 1, there are a main valve 6 screwed into the valve stem 5, a guide piece 7 for holding the valve stem 5,
A strainer 8 for removing foreign matter from the steam and a valve seat 9 on which the main valve 6 is seated are incorporated, and a steam passage section 10 is constituted by these.

An actuator (not shown) for vertically operating the valve stem 5 is fixed to the valve body 21 with bolts 12 via a blanket 11, as shown in FIG. It is fixed to the blanket 11 by.

As shown in FIG. 1, the valve body 21 has an upper half body 21 that has the same body wall thickness t1 at each location and encloses the main valve 6.
a, and a lower valve half body 21b, which has the same body wall thickness t2 at each location and is located on the downstream side of the main valve 6, and the valve upper rod body 21a and the lower valve half body 21b are , weld W
3 and are welded together.

Further, the upper valve rod main body 21a and the lower valve half main body 21b are manufactured by forging chromium-molybdenum-vanadium steel, which has the same wall thickness and excellent material strength, and the inner surfaces of each main body 21a, 21b. is precisely shaped by machining. In addition, each main body 21a,
As shown in FIG. 1, a straight pipe portion 23a is located near the welded portion W3 of 21b in the axial direction around the center of the groove.
.

23b, respectively, so that the soundness of the welded structure can be easily confirmed by non-destructive testing such as radiation testing.

On the other hand, the inlet pipe 22 is constructed by using a pipe material made of the same material as a steam pipe (not shown), and having its tip integrally shaped to approximately 90 degrees by hot bending by forging. The welding groove thickness of No. 22 is set to t3. As shown in FIG. 1, this inlet pipe 22 is attached to the nozzle-shaped protrusion 24 of the valve upper rod body 21a at a welded portion W.
1 and are welded together.

Next, the operation of this embodiment will be explained.

The valve upper rod body 21a and the lower valve half body 21b that constitute the valve body 21 are manufactured by forging chromium-molybdenum-vanadium steel, and their inner surfaces have the same body wall thickness tt at each location.
, t2, and is precisely shaped by machining.

These side main bodies 21a, 21b each have straight pipe portions 23
After welding grooves are formed in a and 23b, butt welding is performed. Thereby, the side main body 21a.

21b are integrated via a weld W3. On this occasion,
The outer periphery of the welded portion W3 includes both straight pipe portions 23a, 23.
Since the weld is straight due to b, the soundness of the structural weld can be easily confirmed by non-destructive inspection such as radiographic inspection.

On the other hand, the inlet pipe 22 is made of a pipe material similar to that of a steam pipe (not shown), and the tip thereof is formed by hot bending by forging so that the welding groove thickness becomes t3.
It is integrally shaped to 0 degrees.

After that, the nozzle-shaped protrusion 24 of the valve upper rod body 21a
They are welded together through the welded portion W1.

By the way, the strength of the valve body 21 constituting the pressure vessel section 4 is a function of the inner diameter or outer diameter of the relevant body relative to the applied pressure, and as the diameter increases, the strength of the valve body 21 that constitutes the pressure vessel section 4 is approximately proportional to the strength of the body. Part thickness is required.

This thickness relationship will be explained below with reference to FIG. 2.

In FIG. 2, the horizontal axis is a function of the body wall thickness, and the vertical axis is a function of stress generated in the body. As mentioned above, the valve body 21
The body of the valve body is a function of the inner diameter or outer diameter. In the figure, line C indicates the characteristic of the body wall thickness with respect to the working pressure of the valve upper half body 21a. The thinner the wall thickness, the greater the generated stress. is high;
The thicker the wall, the lower the generated stress. Similarly, the line indicates the characteristic of the body wall thickness with respect to the applied pressure of the lower valve half body 21b, and the line is located below (inside) the line C by the amount of the smaller body size diameter.

Line E in Figure 2 shows the thermal stress characteristics generated in the body, and shows the change in the stress generated when the wall thickness of each body is changed while maintaining the same temperature difference between the inner and outer surfaces of the body. It is expressed. This line E represents that, for example, when an arbitrary temperature difference between the inner and outer surfaces acts on the body, the thicker the wall, the more the generated thermal stress increases.

By the way, there is an allowable limit line for the pressure resistance strength and thermal stress strength of the valve body 21, and in FIG. The line is indicated by line G.

In actual design, it must be designed to be inside each of these limit lines F and G. In other words, point J,
As long as it is within the ranges of K, L, and M, the body wall thickness of each main body 21a, 21b is 1. ．． 1. , can be set arbitrarily.

Here, for example, from the viewpoint of manufacturing cost, if the stress for the applied pressure is set to the same point H for both the valve upper body 21a and the valve lower half body 21b, the body wall thickness of the valve upper body 21a will be equal to the line C. tl from the intersection of the valve lower half body 2
The body thickness of 1b is t2 from the intersection with the wire. Therefore, the body wall thickness of the lower valve half body 21a is the same as that of the valve upper body 2.
It can be made thinner than the body wall thickness of 1a.

From an economic standpoint, it is desirable that the wall thicknesses of the body parts of the side bodies 21a and 21b be the same, and therefore, the thickness of the body part of the lower valve half body 21b is also normally set to tl. As a result, the stress generated in the lower valve half body 21b including the welded portion W3 can be brought to a point H' lower than the point H, as shown in FIG. Furthermore, even if the thickness of the body of the lower valve half body 21b is tl, it is within the thermal stress limit line 0, so there is no concern about thermal stress.

On the other hand, since the inlet pipe 22 is welded to the nozzle-shaped protrusion 24 of the valve body 21a, it becomes a welded joint of different materials, and the welding groove thickness t3 of this part is determined by the parts with low material strength. In other words, the body size of this portion calculated as a pressure vessel is clearly smaller than the body size of the valve upper half body 21a, so it does not exceed the body wall thickness t1 of the valve upper half body 21a.

This means that the wall thickness obtained for the largest dimension used in calculating the maximum outer diameter or inner diameter of the body wall thickness among the parts of each element constituting one pressure vessel can be used for all of the valve body parts. No matter what material is used for each component, it will not deviate from the purpose of the present invention, and materials can be used freely according to the special characteristics and usage of each component, if the standards are used for the dimensions of each component and each structure. This means that they can be combined.

Since the valve body 21 and the inlet pipe 22 constituting the pressure vessel section 4 are made of forged steel, the required body wall thickness can be made thinner than conventional products made of cast steel. By making the entire wall thickness uniform, thermal stress can be alleviated. Further, since it is forged, there are no inherent defects in the valve body 21, and reliability can be improved.

The valve body 21 also includes a valve upper body 21a and a lower valve half body 2.
1b, even when the valve body 21 is extremely heavy, such as a reheat steam valve, with an outer diameter of 3000 mm and a total length of 3500 mm, a single body (ingot) can be used. Unlike the case of manufacturing the valve body 21, the valve body 21 can be manufactured without being subject to equipment restrictions.

In addition, since the inlet pipe 22 is made of forged steel, there is no stress concentration even if repeated external force loads are applied from the steam pipe side, and the elbow 1a
There is no stress concentration at the weld W2 between the elbow 1a and the short pipe 1b, and there is no change in shape, unlike conventional products where stress tends to concentrate at the weld W2 between the elbow 1a and the short pipe 1b.

〔Effect of the invention〕

As explained above, in the present invention, the valve body and the inlet member are made of forged steel products that have higher high temperature strength than cast steel products with the same chemical composition, so the required body wall thickness can be reduced and the overall wall thickness can be reduced. Thermal stress can be alleviated by making the thickness uniform. Furthermore, since it is forged, there are no inherent defects in the valve body, improving the reliability of the steam valve and making maintenance and inspection easier.

Further, even if the inlet steam pressure or temperature of the steam valve increases, it is possible to sufficiently cope with the increase using the currently used composition materials.

Even if materials with better high-temperature strength appear as a result of future material development, an even more excellent steam valve can be obtained by applying the present invention.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a steam valve according to an embodiment of the present invention;
FIG. 2 is a graph showing the relationship between body wall thickness and stress, and FIG. 3 is a sectional view showing a conventional steam valve. 4... Pressure vessel part, 6... Main valve, 21... Valve body, 21a... Valve upper rod body, 21b... Valve lower half body,
22... Inlet pipe, 23 a, 23 b... Straight pipe section, Wl, W3... Welded section.

Claims (1)

[Claims] A steam valve in which a pressure vessel portion is constituted by a valve body in which a main valve is seated and seated, and an inlet member welded to the inlet side of the valve body to guide steam from a steam pipe into the valve body. The valve body and the inlet member constituting the part are each manufactured from forged steel products, and the valve body is composed of an upper valve half body containing the main valve, and a lower valve half body on the downstream side of the main valve, and A steam valve characterized in that an upper valve half body and a lower valve half body are butted and welded together using straight pipe portions of the same diameter.