JPH06221103A - Steam turbine nozzle box - Google Patents

Abstract

PURPOSE:To assemble a steam turbine nozzle box in high accuracy, by welding even if the main body is made of cast steel. CONSTITUTION:After the cast steel main body 5 of a steam turbine nozzle box 4 and a forged steel nozzle block 9 are partly joined together by welding 23 by means of electron beam 22 the whole body is welded by welding member 24 superior in its strength. In this case, it is allowed if buttering welding or melting treatment 21 by radiation of electron beam may be applied beforehand in an electron beam welding position. Or in a structure for inter posing a forged steel reinforcing ring between the nozzle box main body 5 and the nozzle block 9, welding join among the reinforcing ring the nozzle box main body and the nozzle block are set to be jointed by welding respectively in the same way as the above-mentioned joint.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam turbine nozzle box, and more particularly to a welding joint between a nozzle box body and a nozzle block. However, the present invention is not limited to this, and can be applied to other metal processed products that require high precision and high strength.

[0002]

2. Description of the Related Art A nozzle box is usually provided at a steam inlet of a steam turbine, and high-temperature, high-pressure steam introduced into the turbine is jetted from the nozzle box to a moving blade to apply a rotational force to a rotor. I am trying to give.

Therefore, first, an example of the structure around the inlet of the steam turbine will be described with reference to FIG. 3. In a large capacity steam turbine using high-temperature and high-pressure steam 1, the inner casing 3 is usually inside the outer casing 2. The inner box 3 is provided with a nozzle box 4 inside. The nozzle box 4 includes a nozzle box body 5. An outer casing steam inlet pipe 6 welded to the outer casing 2 is inserted into the nozzle box body 5. A nozzle block 9 is welded to the tip of the nozzle box body 5 via a reinforcing ring 8 supporting a reinforcing rib 7.
Nozzle 11 is formed in this nozzle block 9. A seal ring 12 is provided at each of the penetration portion of the outer casing steam inlet pipe 6 into the inner casing 3 and the insertion portion of the nozzle box body 5.

In the above structure, the high-temperature, high-pressure steam (main steam) 1 flows into the turbine from the outer casing steam inlet pipe 6, passes through the inner casing 3, and communicates with the inside of the steam inlet pipe 6. It is once introduced into the main body 5 of the nozzle box 4.
The steam 1 is then ejected at high speed from a nozzle 11 of a nozzle block 9 provided at the tip of the nozzle box body 5 via a reinforcing ring 8 and hits a moving blade 14 implanted in a rotor 13. , Applies a rotational force to the rotor 13.

As described above, the nozzle box 4 is
Since it is located at the inlet of the steam turbine, it is exposed to the hottest steam 1 having the highest pressure. Therefore, the material used for the nozzle box body 5 is required to have sufficient high temperature strength and erosion resistance against creep and fatigue. In this case, as illustrated in FIG. 4, since the nozzle box 4 has a complicated structure and shape, a low alloy steel or 12Cr-based cast steel is usually selected as the material of the nozzle box body 5 in production. To be done. On the other hand, the material of the nozzle block 9 and the nozzle 11 is usually 12 due to its high temperature strength and erosion resistance, etc.
Forged steel of Cr-based steel is selected. Therefore, the nozzle box body 5 made of cast steel and the nozzle block 9 made of forged steel are
Usually, as described above, they are assembled by bolt fastening or welding with the reinforcing ring 8 interposed. In this case, the reinforcing ring 8 is usually made of forged steel.

A conventional example of nozzle box assembly by welding is disclosed in Japanese Utility Model Laid-Open No. 2-110201. In this conventional example, as shown in FIG. 5, a joint between a cast steel main body 5 of a steam turbine nozzle box 4 and a forged steel reinforcing ring 8 and the reinforcing ring 8 are provided.
At the joint between the nozzle block 9 and the forged steel nozzle block 9,
After the buttering welding 15 is performed in advance, the assembly is performed by electron beam welding 16.

[0007]

However, the conventional example shown in FIG. 5 has the following problems. That is, the buttering welding 15 needs to use a welding material with a small gas component in order to avoid a cavity defect when performing the electron beam welding 16, and a welding material containing nitrogen effective in high temperature strength cannot be applied. Is difficult to secure. On the other hand, when using a high-strength welding material containing a gas component such as nitrogen, which has excellent high-temperature strength, it is necessary to perform normal welding because cavity defects occur during electron beam welding. Since the amount of heat input is larger than that of the above, the accuracy of mounting the nozzle cannot be ensured and the turbine performance deteriorates. Further, in the electron beam welding, when the welding depth becomes large, it takes time for machining, and a welding defect due to misalignment or the like easily occurs.

Although the nozzle box may be made of forged steel instead of cast steel by design, as for the assembly of such a forged steel nozzle box, see, for example, Japanese Patent Laid-Open Publication No.
No. 0-69212, that is, the nozzle box main body is divided into several parts in the radial direction or the circumferential direction, and each divided part is manufactured by forging. It is already established that the parts are machined and then welded together to be assembled into one nozzle box.

The present invention has been made to solve the above-mentioned problems of the prior art, and even if the main body of the steam turbine nozzle box is made of cast steel, it can be assembled with high precision by welding. Intended to provide a box.

[0010]

In order to solve the above problems, the present invention relates to a steam turbine in which a nozzle box body made of cast steel is welded to a nozzle block made of forged steel directly or via a forged steel reinforcing ring. In the nozzle box,
A part of the welded joint between the nozzle box body and the nozzle block or the welded joint between the nozzle box body and the nozzle block and the reinforcing ring is welded by an electron beam.

[0011]

According to the above means, the accuracy of attaching the nozzle is ensured by the partial electron beam welding, and the welding material having a high strength containing the gas component can be applied by the ordinary welding thereafter. The strength of the entire joint can be improved. Further, since the penetration depth of the electron beam is small, the time required for machining and electron beam welding can be shortened.

Even if the electron beam welding position is subjected to buttering, the welding amount of buttering can be small.
If the buttering welding is not performed, the electron beam welding position is pre-irradiated with an electron beam to perform the melting process to remove the gas component at the joint portion. Occurrence of cavity defects during beam welding is avoided.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 (A), (B) and (C)
FIG. 3 is a diagram showing an embodiment of a steam turbine nozzle box according to the present invention in the order of joining steps with a nozzle block.

In this embodiment, in the steam turbine nozzle box 4, a part of the welded joint between the nozzle box body 5 made of cast steel and the nozzle block 9 made of forged steel is first shown in FIG.
As shown in (A) of No. 2, a portion 21 subjected to melting treatment for degassing by buttering welding or electron beam irradiation in vacuum is created. The thickness of this melting process is, for example, about 0.5 to 1.00 mm when the plate thickness of the nozzle box body 5 is 40 to 60 mm. Then, Figure 1
(B), the nozzle box body 5 and the nozzle block 9 are welded using the electron beam 22. Since the welding heat input is small and the welding depth is short, the welded portion 23 formed by the electron beam 22 hardly causes welding deformation (for example, a diameter of 1 m is deformed by 1 mm or more in the conventional example. In this embodiment, the deformation is 0.5 mm or less). Therefore, the nozzle box body 5 and the nozzle block 9 are joined with high accuracy. After that, as shown in FIG. 1C, the entire joint is welded with a welding material 24 containing a gas component and excellent in strength, for example, using a commercially available welding rod for spar 9Cr containing nitrogen.

Next, FIG. 2 is a sectional view showing another embodiment of the steam turbine nozzle box according to the present invention. This embodiment is applied to the steam turbine nozzle box 4 shown in FIG. 5, and the nozzle box body 5 made of cast steel is used.
The welded joint between the reinforcing ring 8 and the forged steel reinforcing ring 8 and the welded joint between the reinforcing ring 8 and the forged steel nozzle block 9 are shown in FIGS. 1A, 1B and 1C, respectively. Partially applied electron beam welds 2 joined in different order
3 and the high-strength welding material 24, it is possible to improve the strength of the joint as compared with the electron beam welding joint shown in FIG.

[0016]

As described above, the present invention relates to a steam turbine nozzle box in which a nozzle box body made of cast steel is welded and joined to a nozzle block made of forged steel directly or through a reinforcing ring made of forged steel. Since a part of the welding joint between the main body and the nozzle block or the welding joint between the nozzle box main body and the nozzle block and the reinforcing ring is made by the electron beam welding, the partial electron beam welding ensures the nozzle mounting accuracy. In addition, since the welding material having a high strength containing a gas component can be applied by the subsequent ordinary welding, the strength of the entire welded joint can be improved. Further, since the penetration depth of the electron beam is small, the time required for machining and electron beam welding can be shortened.

Even when the electron beam welding position is subjected to buttering, the welding amount of buttering can be small.
If the buttering welding is not performed, the electron beam welding position is pre-irradiated with an electron beam to perform the melting process to remove the gas component at the joint portion. Avoiding cavity defects during beam welding

[Brief description of drawings]

1 (A), (B) and (C) are views showing an embodiment of a steam turbine nozzle box according to the present invention in the order of joining steps with a nozzle block.

FIG. 2 is a sectional view showing another embodiment of the steam turbine nozzle box according to the present invention.

FIG. 3 is a cross-sectional view showing an example of the structure around the steam inlet part of the steam turbine of the present invention and the related art.

FIG. 4 is a diagram showing an appearance of a steam turbine nozzle box portion in FIG.

FIG. 5 is a sectional view showing a conventional steam turbine nozzle box.

[Explanation of symbols]

 4 Steam turbine nozzle box 5 Nozzle box body 7 Reinforcing rib 8 Reinforcing ring 9 Nozzle block 11 Nozzle 23 Electron beam welded portion 24 Welding material

Front Page Continuation (72) Inventor Masafumi Kazuhito 1-1, Atsunoura-machi, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries Ltd. Nagasaki Shipyard Co., Ltd.

Claims (2)

[Claims] 1. A steam turbine nozzle box in which a nozzle box body made of cast steel is welded to a nozzle block made of forged steel directly or through a reinforcing ring made of forged steel. A steam turbine nozzle box, wherein a part of the welded joint between the nozzle box body and the nozzle block and the reinforcing ring is welded by an electron beam. 2. A steam turbine nozzle box according to claim 1, wherein the electron beam welding position is previously subjected to buttering welding or melting treatment by irradiation with an electron beam.