JPS58133405A - Welded turbine casing - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam turbine casing in which upper and lower half shell members and a flange member are welded together, and the present invention reduces the stress generated at the welded connection between these members. This invention relates to an ini turbine casing.

Conventionally, steam turbine casings have been manufactured by casting, but as the casing becomes larger in size, there is a limit to its manufacturing capacity or economic efficiency. In other words, since it is a one-piece structure made by casting, it is not possible to use different materials depending on the stress level of each part or to freely change the wall thickness of the cage jig. There were also unavoidable economic problems. Additionally, large-sized and thick structures have performance problems such as easy casting defects. Therefore, a welded casing has been considered in which the casing is divided into component parts according to the stress level and complexity of the shape, blocks of material for these component parts are manufactured separately, and the blocks are welded together. ing. In this case, since the welded joint is made of a different material from the block material, the welded joint must be selected at a location where the shearing force is as low as possible. That is, the selection of the position of the welded joint between each block material becomes a very important issue for the reliability of the welded casing.

An object of the present invention is to improve the reliability of the welded casing by locating the welded joint in a low stress area of the casing during turbine operation. It's about letting people know.

The %IIk of the present invention relates to the welded joint between the upper and lower half shell parts and the flange part, which is one of the 11 important welded joints in a welded turbine casing, and the welded joint is used to control the stress distribution of the turbine casing. Taking into consideration the condition, the reliability of the welded turbine casing is improved by locating it at the lowest stress part of the shell part and flange part.

An embodiment according to the present invention will be described below with reference to FIG. In Fig. 1, the symbol 1o indicates the turbine number'/7f'fr
The turbine casing 10 is made up of an upper half shell part 1, a lower half shell part 2, and a flange s3.4. First, the upper half 7 flange portion 3 and the lower half flange portion 4 are connected to each other by bolts or the like 5 so as to sufficiently withstand the pressure difference between the inside and outside.

Here, upper half shell parts 1 each being a separate block of material,
When joining the lower half shell portion 2 and the flanges 3 and 4 by welding, the position of the welded joint becomes a problem as described above. Therefore, as shown in FIG. 3, a cross section of the casing in the turbine axial direction was taken to examine the two-dimensional stress distribution state. The principal stress distribution determined by the finite element method is shown in FIG. 2. According to FIG. Therefore, the principal stress σ rapidly decreases and becomes an almost constant tensile stress. On the other hand, when moving below the shell part la, 2 m near the flange part where the maximum tensile stress occurs, the principal stress σ rapidly decreases, and furthermore, in the flange part 3.4,
It becomes compressive stress. Due to this stress distribution, as shown in Figure 3, the cuff and port tightening force 6 due to the difference in pressure between the inside and outside
It is produced by the synthesis of

Due to the cuff due to the pressure difference between the inside and outside of the casing, tensile stress is generated across the casing shell 4 part 1.2 and the entire surface of the flange parts 3 and 4, but due to the bolt tightening stress 6 applied to the horizontal surfaces 3 and 4 of the flange part 3, the flange part 3 .4 and the shell portion near the flange portion are subjected to compressive stress. Therefore, the stress distribution caused by both the cuff and the bolt tightening stress σ due to the difference in internal and external pressure is as shown in FIG.

The present invention aims to improve the reliability of the welded joint by specifying the location of the welded joint at a low stress location. As for the position of welding connection between the flange part and the shell part, the method is to connect the flange part at the horizontal planes 3a and 4g of the flange part as shown in Fig. 4, and the shell part where the stress σ is reduced to an almost constant value as shown in Fig. 5. 1b.

A possible method is to connect using 2bK. However, in the method shown in Figure 4, the maximum principal stress occurs in the area 1a.

2a is very close, and the method shown in Figure 5 produces tensile stress, although the stress is not particularly high, so it cannot be said that there is sufficient reliability.In other words, 1IIk is also reliable. The welding method is to connect the flange vertical surfaces 3b, 4b and the shell outer surfaces 1c, 2c as shown in FIG. Flange part 3.4 as shown in Figure 2
The overall compressive stress is low, especially on the shell side of the flange, so higher reliability can be expected. Furthermore, steel materials are generally more resistant to compressive stress than tensile stress, and a compressive stress field has the advantage that cracks are unlikely to propagate even if there are internal defects generated during welding.

Note that the present invention provides a highly reliable casing by specifying the welding joint surface, and the materials of the flange portion and the casing portion (casting, steel plate, forged steel, etc.) are not critical. Furthermore, the flange portion and the casing portion may be made of different materials.

As explained above, according to the present invention, if a weld connection is formed between the vertical surface of the flange and the outer surface of the upper or lower half of the casing, the flange and the upper or lower half can be welded together without impairing reliability. It becomes possible to weld and join the parts. Therefore, by employing a weldable casing, it is possible to improve reliability, reduce costs, etc., which could not be obtained with conventional cast structures.

[Brief explanation of drawings]

Figure 1 is a sectional view showing a conventional turbine casing, Figure 2 is a sectional view showing a conventional turbine casing;
The figure is a principal stress distribution diagram of the upper half of a conventional turbine casing, and Figure 3 is an explanatory diagram of the forces acting on the turbine casing.
Fig. 4 and Fig. #15 are schematic diagrams showing a conventional glue-bin casing welding method, and Fig. 6 is a schematic diagram of a casing showing the positions of welded joints of a turbine casing according to an embodiment of the present invention. ...Upper half shell part, 2...Lower half shell part, 3...Upper half flange part, 4...Lower half flange part, 5...Bolt, 6...Bolt tightening force, 7... Force due to pressure difference between inside and outside, 10... Turbine casing, 1
a... Upper half shell maximum principal stress generation part, 2a... Lower half shell maximum principal stress generation part, 3a... Upper half flange horizontal ffi, 4a... Lower half flange horizontal surface, lb... Upper The part where the stress decreases to a constant value in the half shell, 2b...
・The part where stress decreases to a constant value in the lower half shell, IC
... Upper half shell outer surface welding connection portion, 2C... Lower half shell outer surface welding connection portion, 3b... Upper half flange vertical surface welding connection portion, 4b... Lower half flange vertical surface contacting portion. 'Hl Figure 12 Figure 3 謬y! J4IiJ ￥5 Diagram

Claims (1)

[Claims] 1. In a turbine casing in which an upper half shell part, a lower half shell part, and a flange part are formed separately,
When the upper and lower half-shell parts &c# flange parts are welded and fixed to form one body, the welded joints are welded so that they are located between the ship surface of the flange and the outer surface of the upper and lower half-shells. Features a welded turbine casing.