JPS6187904A - Bolt cleaning method for steam turbine - Google Patents

Abstract

PURPOSE:To have efficient cooling of bolts used in a steam turbine having an external and an internal wheel chamber by using the extracted steam from the low-pressure side turbine wheel chamber for cooling the flange fastening bolts at the internal wheel chamber. CONSTITUTION:In this extra-high temp., high-pressure turbine in which an upper flange 2b and a lower flange 2c of the internal wheel chamber are fixed with bolts 18a and nuts 24, a flange 15 is provided at the external wheel chamber 2d so as to introduce cooling steam 22 to said lower flange 2c through a cooling pipe 14 connected to this flange 15. A cooling steam chamber 16 in communication with a bolt hole 21 through a cooling hole 16a is formed at th4e lower flange 2c, and a cooling 14 with its tip formed in a spherical surface 14a is inserted into this chamber 16. An adjust plug 14c with its inner surface formed in a stellate 14d is screwed fast at the open end edge of the steam chamber 16 so as to prevent wear of the contact part with the tip of the cooling 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a steam turbine casing, and more particularly to a steam turbine bolt cooling method for cooling bolts.

[Background of the invention]

As a method of cooling the bolts for tightening the upper and lower half flanges of the turbine casing, for example, as shown in Japanese Patent Laid-Open No. 54-79312, cooling holes are made in the flanges and the temperature difference between the bolts and the threaded portions of the flanges is determined. A known method is to reduce the thermal stress generated in the threaded portion by reducing the In this method, a steam supply pipe is installed on the flange, and one pipe is installed near the bolt thread.
The threaded part is cooled by opening more than one hole, and is discharged through a discharge pipe. Such a method is effective for a flange portion where the temperature is relatively low and there is no temperature difference between the compartments, and for a flange in an external compartment due to its structure. Super high temperature.

In the case of a high-pressure casing, the temperature of the internal casing reaches 650°C, so the material needs to be austenitic stainless steel. This material has a linear expansion coefficient approximately 1.5 times and thermal conductivity 1/1.5 times that of low-alloy steel, so it cools the upper and lower flanges evenly and minimizes the generation of thermal stress. It is necessary to limit it to IJs. In the conventional method, there is a pressure difference between the inlet and outlet of the cooling steam inside the vehicle, so natural circulation occurs due to the pressure difference, but it was not possible to cool areas where there was no pressure difference, and only the lower half flange and threaded parts The cooling caused thermal stress, which was thought to cause deformation of the upper and lower flanges of the passenger compartment. In addition, the structure was complicated to apply to the flange of the internal compartment, and the piping had to be welded, which caused structural problems.

[Purpose of the invention]

The purpose of the present invention is to provide a reliable turbine casing by effectively cooling horizontal joint flange bolts and flanges in an internal casing, extending the life of the bolts, and reducing thermal stress on the flange. be.

[Summary of the invention]

The temperature of the internal casing of an ultra-high-temperature, high-pressure turbine reaches 650°C, so heat-resistant steel is used for the bolts used to tighten the flange. However, current bolt materials can only be used up to about 570°C, making it necessary to cool the bolts more than ever before. Conventionally, exhaust steam was used as cooling steam, but the extremely high temperature
Since high-pressure turbines have no differential pressure between the cooling steam inlet and outlet, it is necessary to introduce steam at a lower temperature than the internal casing from the outside, let it flow into the bolt holes and cool it, and then return the cooled steam. I came. The cooling structure needed to be easy to assemble and disassemble, and the structure was designed so that problems would not occur due to differential expansion at the connection between the external compartment and internal compartment of the steam introduction section.

[Embodiments of the invention]

Embodiments of the present invention will be described based on FIGS. 1 to 4. FIG. 1 is a structural diagram. The upper half flange 2b and lower half flange 2C of the internal compartment are tightened with bolts 18a and nuts. In an ultra-high temperature turbine, the bolt 18a and the flange reach a temperature of 650°C.

Heat-resistant steel is used for the bolt material, but in order to use it under high temperature and high stress conditions, it is necessary to perform bolt cooling to lower the temperature of the entire bolt to reduce deterioration and extend its creep life. Therefore, the conventional internal compartment flange bolt 18a
To cool the bolt, steam having a lower temperature than the corresponding part is extracted from the stepped part, flows into the bolt hole 21, cools the bolt as it passes through the bolt hole one after another, and is discharged to the low pressure side. However, in the case of a high-temperature vehicle interior, this method loses its cooling effect because the temperature of the cooling steam itself is high. In order to be effective, it is necessary to flow a large amount of steam and to increase the pressure difference between the cooling steam inlet and outlet.

The present invention has the following structure in order to carry out effective ringing. A flange 15 is provided in the outer compartment 2d, and a cooling pipe 14 is connected thereto to guide cooling steam 22 to the lower half 2c of the inner compartment flange. This flange 15 is installed in the external compartment with a gasket 23 and tightening bolts 25. The lead pipe 11 extracts steam extracted from a casing 3 on the low pressure side (FIG. 2), which is different from the casing 2 of the turbine. Since this steam has a temperature necessary to cool the bolts in the internal casing of the ultra-high temperature and high pressure turbine 2, a sufficient cooling effect can be obtained. The steam after bolt cooling passes through the lead pipe 12 and is discharged to the bleed line of the high temperature turbine 4.

FIG. 3 is a diagram showing the cooling steam path of the ultra-high temperature turbine. It passes through the lead pipe 11 and the cooling pipe 14, is guided to the cooling steam chamber 16 in the internal compartment, passes through the bolt holes, and is discharged from the lead pipe 12. FIG. 4 is a plan view of the lower half compartment. Internal compartment 2C and external compartment 2d
Because a difference in expansion occurs as the temperature rises, the lead pipe 14 connecting the interior and exterior compartments has its pipe end welded to the flange 15 on the exterior compartment side 2d so that it can expand and contract only in the direction of the interior compartment 20. Leave the other end free.

A screw L4b is provided in this internal compartment 2c, into which an adjustment plug 14c is screwed. The inner surface of this plug and the outer surface of the lead pipe are overlaid with Stellite 14a and 14d, respectively, so that they have a structure that does not wear against contact with each other. By making the end part spherical, the sealing property of the cooling steam is maintained. The cooling steam that has entered the internal compartment 2C is collected in the steam chamber 16, passes through the cooling holes 16a and the bolt holes 21 as indicated by the arrows in the figure, and is cooled. Since the internal casing is used at high temperatures, stainless tIil steel is used as a heat-resistant steel, but this material has a heat transfer coefficient of 1/1.5 compared to low-alloy steel, which means that heat transfer is small. Therefore, when a turbine plant is started up, the thicker part of the flange remains colder than the rest, causing excessive thermal stress that can deform the casing or apply excessive force to the bolt. Therefore, by the method of the present invention, flange heating can also be performed at the time of startup. The thermal loss of the steam can also be minimized by returning the steam after use to the low-pressure turbine.

〔Effect of the invention〕

According to the present invention, in a double-structured casing consisting of an outer casing and an inner casing, extracted steam from the low-pressure side turbine casing is used to cool the flange tightening bolts in the inner casing. After use, the steam is returned to the lower-pressure bleed line in the low-pressure side compartment to effectively cool the bolt.

In addition, since the cooling steam is lower in pressure than the steam pressure inside the ultra-high temperature, high-pressure turbine casing, the bolt hole portion has a lower pressure than the pressure inside and outside the casing, which has the effect of recovering steam leaking to the outside from the flange horizontal joint surface.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a main part of an apparatus for carrying out the steam turbine bolt cooling method of the present invention, Fig. 2 is a plant system diagram of an ultra-high temperature and high pressure steam turbine carrying out the method of Fig. 1, and Fig. 3 is a FIG. 2 is a vertical cross-sectional view of a main part of the ultra-high temperature and high pressure steam turbine, and FIG. 4 is an exploded plan view of FIG. 3. 2a, 2d...External compartment, 2b, 2c...Internal compartment, 11.12...Lead pipe, 13a, 13b-exhaust Fig. 1 Fig. 20 32 40

Claims (1)

[Claims] 1. In a steam turbine with a double casing structure consisting of an inner casing and an outer casing, cooling steam extracted from the low-pressure side casing is sequentially passed through the tightening bolt holes of the inner casing flange of the high-temperature, high-pressure casing. After cooling the bolts and flanges, the steam is extracted from the high-temperature, high-pressure casing and returned to the low-pressure bleed line of the low-pressure side casing, cooling with steam at a lower pressure than the steam in the high-temperature, high-pressure casing. A steam turbine bolt cooling method characterized by performing cooling while recovering high-pressure steam in an internal casing that leaks outside from a horizontal joint surface.