JPH05149106A - Steam turbine chamber - Google Patents

Abstract

PURPOSE:To improve reliability of a steam turbine by reducing thermal stress of a turbine chamber. CONSTITUTION:A high temperature part (A) positioned downstream from a medium pressure inlet part 21 is made of 12 chrome cast steel, and also a high pressure exhaust part 22 being a low temperature part (B) is made of low chrome cast steel. Both parts (A), and (B) are joined with each other by welding as shown by a reference numeral 23. Since the medium pressure inlet part 21 being the high temperature part (A) is made of 12 chrome cast steel, it is possible to reduce thermal stress of a turbine chamber by the difference between thermal expansion coefficients of materials.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a steam turbine casing.

[0002]

2. Description of the Related Art The interior of a high-to-intermediate-pressure portion of a steam turbine that has been already proposed has been manufactured using cast steel. And, in general, the cast steel casing is an integral casting made of the same material.

[0003]

However, in many cases, the steam temperature inside the steam turbine casing changes axially. However, when the temperature change in the casing axial direction is large, the thermal expansion difference causes a large amount of heat. Stress is generated.

For example, in the steam turbine casing as illustrated in FIG. 3, the metal temperature difference between the medium pressure inlet portion 1 and the high pressure exhaust portion 2 (temperature of the medium pressure inlet portion 1> high pressure exhaust portion 2). Temperature), the vehicle compartment of the medium pressure inlet portion 1 tends to become larger in diameter than the vehicle compartment of the high pressure exhaust portion 2 due to thermal expansion and pulls the vehicle compartment of the high pressure exhaust portion 2.

Therefore, a compressive stress is generated in the passenger compartment of the medium pressure inlet portion 1 and a tensile stress is generated in the passenger compartment of the high pressure exhaust portion 2. Now, this temperature difference is set to 200 ° C and a simple model is used for trial calculation. Assuming that the temperature in the axial direction suddenly changes in a stepwise manner, a compressive stress of about 30 kg / mm ² is applied to the passenger compartment of the medium pressure inlet 1 and about 30 kg / mm 2 to the passenger compartment of the high pressure exhaust portion 2 as shown below. A tensile stress of mm ² is generated.

That is, as shown in FIG. 4 to FIG.
Subscript 1 for inlet 1 and additional for high pressure exhaust 2.
It is shown as follows with the letter 2. Cabin metal temperature T₁, T₂  Average cabin diameter (when cold) d_1c, D_2c  Cabin thickness t₁, T₂  Cabin axial length l₁, L₂  Average vehicle compartment diameter in warm condition d_1h, D_2h  Even when the vehicle is warm, the interior of the vehicle remains cylindrical
Assumed to deform under the influence of minute
To do. Thermal stress in the passenger compartment σ₁, Σ₂(Σ₁Is compressive stress, σ₂Is
Tensile stress)

If the forces F ₁ and F ₂ that the adjacent portions exert on each other are F ₁ = σ ₁ × t ₁ × l ₁ × 2

[Equation 1] F ₂ = σ ₂ × t ₂ × l ₂ × 2

[Equation 2] Where E ₁ and E ₂ are the longitudinal elastic moduli of the vehicle interior material α ₁ and α ₂ are the thermal expansion coefficients of the vehicle interior material

Here, if F ₁ = F ₂ ,

[Equation 3]Since the same material is used, E₁= E₂, Α₁= Α₂， Also easy
Because it is simple, t₁= T₂, L₁= L₂, D_1c= D_2c, D_1h= D
_2hThen, from the above equation 3, d_1c(1 + α₁T₁) -D_1h= D_1h-D_1c(1 + α₁T₂) D_1c{2 + α₁(T₁+ T₂)} = 2d_1h   From the above formulaE₁= 2.1 x 10^FourKg / mm², Α₁= 1.3 x 10^-Five1 / ℃, T₁-T₂
Substituting = 200 ℃,σ₂= Σ₁= 27.3Kg / mm²

Due to this stress, the horizontal flange surface is deformed in the intermediate pressure inlet portion 1 and the flange bolt is yielded in the high pressure exhaust portion 2, which causes a problem of impairing the reliability of the steam turbine.

In FIG. 3, reference numeral 3 is an outer compartment, 4
Is a high-pressure interior compartment, 5 is a high-pressure dummy ring, 6 is a medium-pressure dummy ring,
7 is a rotor, 8 is a main steam inlet, 9 is a high pressure blade row, 10 is a medium pressure blade row, 11 is a high pressure exhaust port, 12 is a medium pressure exhaust port, 13 is a high temperature reheat steam inlet, and 14 and 15 are medium pressure. The bleed port and 16 are medium pressure exhaust ports, and these are not directly related to the gist of the present invention, and thus detailed description thereof will be omitted.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and provides a steam turbine casing in which the thermal stress in the casing is reduced to improve the reliability of the steam turbine. The purpose is to provide.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a steam turbine casing in which a low temperature portion is formed of low chromium cast steel and a high temperature portion is formed of 12 chromium cast steel. It is formed and then these two parts are joined by welding.

[0013]

According to the above means, the thermal stress in the steam turbine casing is reduced, so that the reliability of the steam turbine is improved. In addition, high temperature strength is high in the high temperature part of the turbine casing.
Since chrome cast steel is used, the strength margin of the high temperature part increases. Further, since the relatively inexpensive low chrome cast steel is used for the low temperature part of the turbine casing, it is possible to manufacture the entire casing at a lower cost than the 12 chrome cast steel while having the above-mentioned effects.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a steam turbine casing according to a first embodiment of the present invention. In this embodiment, the high temperature portion (the portion indicated by A) on the wake side from the intermediate pressure inlet portion 21 is formed of 12 chrome cast steel, and the portion of the high pressure exhaust portion 22 having the low temperature (the portion indicated by B) is formed. Is formed of low chrome cast steel, and these two portions A and B are joined by welding at the end portion near the medium pressure inlet portion 21 of the high pressure exhaust portion 22 as indicated by reference numeral 23.

In FIG. 1, other components, such as the outer casing 24, the high-pressure inner casing 25, the high-pressure dummy ring 26, the intermediate-pressure dummy ring 27, the rotor 28, the main steam inlet 29, the high-pressure blade row 30, and the intermediate pressure, are shown. Blade row 31, high pressure exhaust port 32, medium pressure exhaust port 3
3, the high-pressure reheated steam inlet 34, the medium-pressure extraction ports 35 and 36, and the medium-pressure exhaust port 37 are the same as the conventional configuration shown in FIG. 3, and are not directly related to the gist of the present invention. Detailed description is omitted.

The metal composition ratio applicable to the low chromium cast steel is 1 to 3% of chromium, and the conventional 1 chromium is 0.5%.
This includes molybdenum cast steel, 2.25 chrome 1 molybdenum cast steel, and the like. Further, the metal composition ratio applicable as 12 chrome cast steel is 9 to 12% of chromium. On the other hand, as a method of welding the intermediate pressure inlet portion 21 and the high pressure exhaust portion 22,
The submerged arc welding method or the metal inert gas welding method is adopted. In addition, the material of the welding rod used is the same as that of the casing material. That is, a low chromium welding rod (1 chromium 0.5 molybdenum etc.) or a 12 chromium welding rod (9 chromium 1 molybdenum etc.) may be used.

Next, the operation of this embodiment will be described.
Twelve medium pressure inlets 21 which are high temperature parts of the steam turbine casing
When manufactured from chrome cast steel, the thermal stress in the passenger compartment is reduced as follows due to the difference in the coefficient of thermal expansion of the materials when calculated by the simple model described above.

That is, in the above equation (3), E ₁ =
If E ₂ , t ₁ = t ₂ , l ₁ = l ₂ , d _1c = d _2c , d _1h = d _2h , then d _1c {2+ (α ₁ T ₁ + α ₂ T ₂ ) = 2d _1h Where α ₁ = 1.2 × 10 ^-5 1 / ° C, α ₂ = 1.3 × 10 ^-5 1 / ° C, T ₁
= 550 ° C and T ₂ = 350 ° C, Substituting the above equation with E ₁ = 2.1 × 10 ⁴ Kg / mm ² in the above equation ₁ , σ ₁ = 2.1 × 10 ⁴ × {1 + 1.2 × 550 × 10 ^-5 − (1 + 557.5 ×
10 ^-5 )} = 2.1 × 10 ⁴ × 102.5 × 10 ^-5 = 21.5Kg / mm ² Therefore, σ ₂ = σ ₁ = 21.5Kg / mm ² and conventional σ ₁ and σ ₂
The thermal stress is reduced compared to.

Next, FIG. 2 is a sectional view showing a steam turbine casing according to a second embodiment of the present invention. In the present embodiment, when the difference in the steam temperature in the vehicle compartment between the intermediate pressure inlet portion 21 and the intermediate pressure extraction portion 38 is large, a portion C on the downstream side of the intermediate pressure extraction portion 38 is used.
Is formed of low chrome cast steel in the same manner as the high-pressure exhaust part 22 shown in part E, and the medium pressure inlet part 2 made of 12-chrome cast steel shown in part D is formed.
The end portion close to 1 is welded. In this case, there are two welded portions 23A and 23B.
Also in this embodiment, the medium pressure inlet portion 21 and the medium pressure extraction portion 38
The thermal stress is reduced in the same manner as described above for the connection portion with and.

[0021]

As described above, according to the present invention, in the steam turbine casing, the low temperature portion is formed of low chromium cast steel, and the high temperature portion is formed of 12 chromium cast steel. With the structure in which both parts are joined by welding, the thermal stress in the passenger compartment can be reduced, so that the reliability of the steam turbine can be improved as compared with the conventional case. Further, since 12-chromium cast steel with high high temperature strength is used for the high temperature part of the turbine casing, the strength margin of the high temperature part can be increased, and at the same time, the low temperature low chromium cast steel for the low temperature part of the turbine casing is relatively low. Since it is used, it can be manufactured at a lower cost than the case where the entire passenger compartment is made of 12 chrome cast steel while having the above effects.

From the above, according to the present invention,
The excellent effect that a highly reliable steam turbine cabin can be provided is exhibited.

[Brief description of drawings]

FIG. 1 is a sectional view showing a steam turbine casing according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a steam turbine casing according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a conventional steam turbine casing.

FIG. 4 is an explanatory diagram of a simple model for calculating a thermal stress in a steam turbine casing.

FIG. 5 is an explanatory diagram of an intermediate pressure inlet portion in the simple model.

FIG. 6 is likewise an explanatory view of a high-pressure exhaust unit in the simple model.

[Explanation of symbols]

 21 Medium Pressure Inlet Part 22 High Pressure Exhaust Part 23 Welding Part 23A Welding Part 23B Welding Part 38 Medium Pressure Extraction Part A 12 Chrome Cast Steel Part B Low Chrome Cast Steel Part C Low Chrome Cast Steel Part D 12 Chrome Cast Steel Part Part E Part made of low chromium cast steel

Claims (1)

[Claims] 1. In a steam turbine casing, a low temperature portion is formed of low chrome cast steel, a high temperature portion is formed of 12 chrome cast steel, and both portions are joined by welding. The steam turbine compartment.