JPS5915603A - Nozzle box for steam turbine - Google Patents

Abstract

PURPOSE:To prevent the generation of a crack due to a thermal effect of welding in a nozzle box, by constituting the nozzle box such that a steam introducing pipe and steam flow reducing parts are welded to the main unit of the nozzle box cut out of a forged material. CONSTITUTION:About 12% chrome forged steel is cut out of a forged material and a nozzle box main unit 36 is formed. A steam pipe 30 is mounted by welding in a welded part 48 while steam flow reducing parts 37a, 37b are mounted by welding in a welded part 42 to the nozzle box main unit 36. In this way, use of the 12-chrome forged steel can eliminate the generation of a crack in a nozzle box due to a thermal effect of welding as conventionally generated in case of using 12-chrome cast steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nozzle box used in a main steam introduction section of a steam turbine.

Figure 1 shows the system of an ultra-high-temperature, high-pressure turbine. The steam superheated to 350 Kg/cm'g-650C in the superheater 1 of the boiler is passed through the main steam stop valve 10. The flow rate is adjusted by a regulating valve 11 and guided to the ultra-high pressure section 2. The exhaust gas from the ultra-high pressure section 2 is led to the high pressure section 4 by a connecting pipe 3. The exhaust gas from the high pressure section is once returned to the boiler and heated to 566C in the reheater 5. The flow rate of the reheated steam is adjusted by the combination reheat valve 12, and the reheated steam is transferred to the medium pressure steam tank 6.
be guided by. The exhaust air from the medium pressure section is further expanded in the low pressure section 7 and discharged to the condenser 8. These turbine sections are connected to a single shaft.

The generator 9 is driven.

Next, FIG. 2 shows details of the ultra-high pressure section of the turbine to which the present invention is applied. The ultra-high pressure section 2 (Fig. 1) consists of an external compartment 14 and an internal southeast section 15. Nozzle box 16. The shaft glands 25, 26, 27 are similar to the main bearings 23, 24.

Steam enters main steam pipe 13, flexible vibe 1
7 and is guided to the nozzle box 16 by mechanical seals 18 and 19. The steam entering the nozzle box 16 is sped up by b1 and rotates 1t21. In the second and subsequent stages, the nozzle diaphragm 22 accelerates the steam. The steam that has finished expanding is exhausted from the exhaust pipe 28 and the auxiliary exhaust pipe 29.

A prior art nozzle box for this ultra-high pressure section is shown in FIG. In this case, the nozzle bomb, Cr
-Mo-V The steam inflow pipe 3o and the nozzle box body 36 are made of a casting method using low alloy steel and have an integral structure. Ahead of this is a wall 37a made of x2cr forged m,
37b are connected by welding 42, and further beyond that is the nozzle 4.
Space length with 5 in between - 38a and 38b is welded 43
．． They are connected by 44.

The flexible pipe 17 (Fig. 2) is connected to the steam inlet pipe 30.
It is inserted into the pipe 31 which has been processed into
This is done by a mechanical seal 19 (FIG. 2). There is a pipe 33 having a smaller diameter than the pipe 31 processed into the steam inflow pipe 3o, and the mechanical seal 19 is housed in the pipe wall 32 due to this difference in diameter.

The steam led into the nozzle box by the flexible pipe 17 is transferred to the pipe 31. The steam is guided through pipes 33 and 34 to a steam chamber 35 formed within a nozzle box body 36. From this, the steam is injected uniformly around the entire circumference of the ultra-high-pressure first-stage maple in the axial direction at one river speed by the nozzle 45. A fin 4o is provided to seal the top of the ultra-high pressure first stage blade, and a fin 44 is provided to seal the root of the blade.

In this nozzle box, a steam pipe 30 and a nozzle box body 36 made of cast steel are integrally cast. On the other hand, the nozzles 45 are precisely machined one by one and then inserted between the bases 38a and 38b and temporarily attached. At the same time, the steam condenser section is formed by walls 37a and 37b of 12cr forged steel.

It is reinforced in several places by ribs 39.

The structural welding of the nozzle box begins with welding 43 and 44 to the nozzle 4, which is temporarily attached to the base plates 38a and 38b.
5 is attached to the steam condensation sections 37a and 37b. after that,
Weld 42 and attach to the nozzle box body 36 to complete. Fin 4 ().

41 is made by welding 43 and 44 by cutting and overlaying.

When this nozzle box is viewed in the axial direction of the turbine, it appears as shown in FIG. In other words, Figure 3 is similar to the A-A cross section in Figure 4.
I'm right.

FIG. 4 shows only the -1 halves of the nozzle box divided into upper and lower halves, and the lower half is omitted.

Normally, the steam is 92 from the top and 2 from the bottom, total n1゛4
Since the steam is introduced into the steam turbine through two steam pipes, the nozzle box has two steam pipes (30a, 301) in the upper half.
Is required. These two steam pipes 30a and 30bfd are attached to a nozzle box main body 36 shaped like a half-split doughnut, and communicate with steam chambers 35a and 35b, respectively. This is a control valve 11 (
This is necessary in order to prevent the throttle losses of the control valves from influencing each other and to prevent a decrease in turbine thermal efficiency, since the control valves (Fig. 1) are normally closed separately. Steam room 35a.

35b is partitioned off by a wall 49 for this reason. Of course, the end of the nozzle box is closed, so
Nozzles cannot be installed all around the nozzle box (360°). The angle at which steam is ejected from the upper and lower halves is 345'. The remaining 15 degrees are these partitions! Used for 7@.

A lower half nozzle box similar to the above-mentioned upper half nozzle box is provided, and when installing the terpino, the rotor is sandwiched between the ports 14 provided on the flanges 46a and 46b.
74 and 47b are used to tighten the upper and lower halves, and the housing is housed in a high-pressure compartment (not shown).

Conventional nozzle boxes are made of low alloy@steel.

Therefore, it is impossible to completely eliminate the fine defects that occur in the cast material, and it is not possible to design a product that relies 100% on the inherent material strength of low alloy steel.

For this reason, it does not meet the strength required by a steam turbine for an ultra-supercritical pressure plant, which has ultra-ultra-high pressure and bulk steam conditions of 350 kg/2 g of rust and 650 C. Therefore, 12% chromium steel with higher strength is required, but in actual practice, 12% chromium steel is required.
Cast products made of chrome steel tend to crack in the weld heat-affected zone, making them undesirable for JX applications in important parts such as steam turbine nozzle boxes.

In a normal steam cooler of 246 Kg/cm'g-5387566°C, the steam flowing into the nozzle box is 24
6 Kg/Crn'g -538°C,
350 g/m'g-6501566°C steam turbine produces steam of 350 K g/crtr''·g-650C, and both square, ?)] and f are several orders of magnitude higher.

Therefore, a material with high high temperature strength such as 12Cr81ii is required, but 12Cr steel has poor casting properties and is prone to cracking.

The purpose of the present invention is to obtain 350 Kg/cMt-g-650G
One nozzle box of the steam turbine requires 12CR steel, and by making it using a forging method, it not only helps prevent cranking, but also increases high-temperature strength by about 30 yen, making it a highly reliable steam turbine. An object of the present invention is to provide a nozzle box for a turbine.

FIG. 5 shows the structure of a nozzle box that is an embodiment of the present invention. This figure corresponds to FIG. 2, which shows a structure according to the prior art.

In the 88 m type nozzle box, the steam pipe 30 is welded to the half donut-shaped nozzle box body 36.
Attached by 8. The rest of the structure is exactly the same as the prior art described above.

The feature of this forged nozzle box is that the steam pipe 30 has 12
Machined from cychrome forged steel. At the same time, the nozzle box body 36 is also machined from 12% chromium forged steel. Therefore, since the steam chamber 35 is machined by end milling, etc., the required volume of the steam chamber can be secured by increasing the axial length by 1-.

Regarding the structural welding of the nozzle box, the steam pipe 30 and
After the nozzle box 36 is joined by welding @1148, the procedure is exactly the same as that for a conventional nozzle box.

The features of the forged nozzle box according to the present invention are as follows:
Kg/crn!・g-650? In order to accommodate Z''s ultra-high pressure and high temperature steam, 12-tichrome steel, which has excellent high-temperature strength, was used for the entire nozzle box.

(Even in the conventional casting method, the steam condensation parts 37a, 37b
and nozzle 45, spacers 38a, 38
bll-1: i 2 rim i9J'jfi'MtJe
Use tea &. ) Furthermore, since the pipes 31, 33, 34 and the steam chamber 35 are formed by cutting out the inside of forged steel, the material strength is less likely to deteriorate due to the presence of minute internal defects, compared to conventional cast steel methods. Not only can this be prevented, but it also greatly contributes to the prevention of cracks, which tend to occur in the welding hot spots of 12 chromium cast steel.

Figure 6 shows the nozzle box viewed from the direction.

This figure corresponds to FIG.

Flange 46a for tightening the L half/lower half nozzle box,
46b is cut out from the nozzle box body U-6.

1. As explained in H, 350 Kg/Crn'g -6
In the 50° 1566C ultra high pressure high steam turbine,
The nozzle box requires 12% chromium alloy steel with high high temperature strength.

The following improvements were made in the present invention.

(1) The entire nozzle box is made of 12 chrome forged steel and has a JRJ-compatible structure.

(2) Forged steel materials not only prevent strength reduction due to minute internal defects in cast steel materials, but also have the ability to
The reliability of the nozzle box is improved because the paulownia wood also increases the strength of the paulownia by about 30 cm.

[Brief explanation of the drawing]

Figure 1 is a system diagram of an ultra-high-pressure, high-temperature steam turbine, Figure 2 is a cross-sectional view of the ultra-high-pressure section of the ultra-high-pressure, high-temperature steam turbine, Figure 3 is a cross-sectional view of a conventional nozzle box in the ultra-high pressure section, and Figure 4. 5 is a front view of a conventional nozzle box seen from the axial direction, FIG. 5 is a sectional view of a nozzle box which is an embodiment of the present invention in the ultra-high pressure section, and FIG. 6 is a front view of the nozzle box of the present invention seen from the axial direction. FIG. 35... Steam chamber, 30... Steam pipe, 36... Nozzle box main body, 48... Welded part, 45... Nozzle, 378° 37b... Steam condensation part. Figure 2 Figure 6

Claims (1)

[Claims] 1. In a nozzle box for a steam turbine, the nozzle box body carved from a forged piece and the steam introduction pipe are welded together, and the nozzle blade and the steam condenser part to which the nozzle blade is attached are attached to the mantle. A nozzle box for a steam turbine, characterized in that it is formed as a welded structure.