JPH06235303A - Steam valve - Google Patents

Abstract

PURPOSE:To provide a steam valve which can be provided with excellent solid particle errosion-resistance while given high abrasion-resistance and high shock- resistance. CONSTITUTION:A hard metal layer 3 composed of cobalt-base hard alloy is formed over a bypass valve body 2 from a seat part to an outlet of steam. A metal layer coating part 8 is formed on a part excluding the seat part by using composite welding metal composed of 30% of chrome carbide and 70% of cobalt-base hard alloy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam valve used in a steam turbine plant, which has high wear resistance and high impact resistance, and which has excellent solid particle erosion resistance.

[0002]

It is known that steam valves used in steam turbine plants are damaged by solid particle erosion contained in superheated steam at 566 ° C or 538 ° C. In particular, such damage is remarkable in the bypass valve that controls the steam amount of the main steam stop valve. With this bypass valve, it is necessary to withstand the impact and abrasion when closing the valve body to the valve seat, so it is recommended to perform overlay welding using a cobalt-based hard alloy that has high hardness and appropriate ductility and toughness. It is common. Furthermore, the metal layer by overlay welding is spread over a wider area to protect the bypass valve from solid particle erosion.

That is, as shown in FIG. 3, the metal layer formed by build-up welding has a hard metal layer 3 formed on the surface of a bypass valve body 2 provided at the upper end of a valve rod 1.
The range of the hard metal layer 3 extends downward beyond the contact surface with the bypass valve seat 4 (hereinafter referred to as the seat portion). By the way, the steam goes straight to the bypass valve valve body 2 through the cap 5 as shown by an arrow in the figure, turns downward along the bypass valve valve body 2, and passes through the main valve valve body 6.
Reference numeral 7 indicates a main valve seat.

[0004]

By the way, in recent years, the erosion resistance of the composite weld metal in which the cobalt-based hard alloy contains 10 to 50% by weight of chromium carbide is about 2 to 3 as compared with the cobalt-based hard alloy. It is known to be twice as excellent, and its application to steam valves is being considered.

However, when the hard metal layer 3 is formed by using the composite weld metal containing this chromium carbide,
There are the following problems. That is, when chromium carbide is contained in the cobalt-based hard alloy, the hardness is increased, but the toughness is unavoidably deteriorated, and cracks are likely to occur when an impact force is applied. Further, the weldability is worse than that of a cobalt-based hard alloy, and when overlay welding is performed on a discontinuous material shape, stress cracking is likely to occur due to stress concentration. In addition, the thermal expansion coefficient of the weld metal decreases due to the inclusion of ceramics such as chrome carbide, and the thermal expansion difference with the valve material becomes larger than the conventional one against the thermal load that is brought to the steam valve, making it harder. Peeling or cracking of the metal layer 3 is likely to occur.

Therefore, the present invention solves the above-mentioned problems of the prior art and provides a steam valve capable of imparting excellent solid particle erosion resistance while having high wear resistance and high impact resistance. The purpose is to provide.

[0007]

To achieve the above object, the present invention provides a bypass valve in a main valve body below the bypass valve body so that steam passing through the main valve body is stopped by the bypass valve body. In a steam valve having a valve seat, a hard metal layer made of a cobalt-based hard alloy is formed along the steam outlet direction from the seat portion of the bypass valve body facing the bypass valve seat, and the hard metal except the seat portion is formed. It is characterized in that the layer portion is formed by stacking a metal layer coating portion made of a composite weld metal containing a cobalt-based hard alloy and chromium carbide.

[0008]

According to the present invention, a hard metal layer made of a cobalt-based hard alloy having both hardness and appropriate toughness is formed on the seat portion which receives a large impact force when the valve body is opened and closed. Impact resistance can be maintained. Further, except for the sheet portion, the portion where the boiler scale collides forms a metal layer coating portion using a composite weld metal containing chromium carbide, and thus solid particle erosion resistance can be greatly improved.

Further, since the metal layer coating portion of the composite weld metal containing chromium carbide is formed on the hard metal layer made of a cobalt-based hard alloy having excellent toughness, it is formed as a valve material. The thermal strain due to the difference in the coefficient of thermal expansion can be relaxed, and even when an impact force is applied, the hard metal layer acts as a cushioning material and can absorb the impact force. This can prevent cracks from occurring in the composite weld metal containing chromium carbide.

Similarly, the hard metal layer made of the cobalt-based hard alloy formed on the seat portion is also formed adjacent to the metal layer coating portion made of the composite weld metal, and the thermal strain generated in the valve axis direction is relaxed. There is a function to do. Furthermore, the cover part made of composite weld metal excludes the sheet part,
Weld cracking due to stress concentration can be suppressed, and sound build-up welding can be performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, a hard metal layer 3 made of a cobalt-based hard alloy is formed on the bypass valve body 2 along the steam outlet direction from the seat portion. This hard metal layer 3 is TIG
Weld by welding. The buildup thickness is 2 to 3 mm.

Further, in the portion where the hard metal layer 3 is formed, excluding the sheet portion, the metal layer coating portion 8 is formed by using a composite weld metal composed of 30% chromium carbide and 70% cobalt-based hard alloy. The metal layer coating portion 8 is built up by plasma powder welding.

FIG. 2 is an enlarged sectional view of the bypass valve body 2, and clearly shows that the metal layer coating portion 8 is formed so as to overlap the hard metal layer 3. Further, it is also clear that the metal layer coating portion 8 is formed at the collision portion of the boiler scale on the downstream side of the sheet portion.

In the steam valve thus constructed, the metal layer coating portion 8 is formed so as to be superposed on the hard metal layer 3 made of a cobalt-based hard alloy having excellent toughness, so that the thermal expansion with the valve element base material is increased. The thermal strain due to the difference in coefficient can be relaxed. Further, even when receiving an impact force, the hard metal layer 3 functions as a cushioning material and can absorb the impact force. This makes it possible to prevent cracks from occurring in the composite weld metal.

[0016]

As described above, according to the present invention, a hard metal layer made of a cobalt-based hard alloy is formed from the seat portion of the bypass valve body facing the bypass valve seat along the steam outlet direction, and the seat portion is excluded. Since a hard metal layer is formed by stacking a metal layer coating part made of a composite weld metal containing chromium carbide in a cobalt-based hard alloy, it has high wear resistance and high impact resistance, It is possible to impart excellent solid particle erosion resistance. Therefore, according to the present invention, there is an excellent effect that the life of the steam valve can be greatly extended.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a steam valve according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing a main part of the steam valve of FIG.

FIG. 3 is a sectional view showing an example of a conventional steam valve.

[Explanation of symbols]

 2 ... Bypass valve body 3 ... Hard metal layer 6 ... Main valve body 8 ... Metal layer coating

Claims (1)

[Claims] 1. A steam valve in which a bypass valve seat is provided in the main valve body below the bypass valve body so that steam passing through the main valve body is stopped by the bypass valve body.
A hard alloy layer made of a cobalt-based hard alloy is formed from a seat portion of the bypass valve body facing the bypass valve seat along a steam outlet direction, and a cobalt-based hard alloy is formed on the hard metal layer excluding the seat portion. A steam valve, characterized in that a metal layer coating portion made of a composite weld metal containing chromium carbide is stacked on the metal layer.