JPS6018804B2 - Bolt cooling control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bolt gouling control device for a horizontal saddle bolt of a steam turbine high pressure casing.

In recent years, steam turbines have been increasing in capacity and output, and as a result, the steam temperature and pressure have also increased, placing severe conditions on the casing that encloses the steam passages. This is especially true for the high-pressure casing, which is the inlet for high-temperature, high-pressure steam. The structure of a conventional steam turbine high pressure casing section will be explained based on FIGS. 1 to 5.

Figure 1 shows the steam flow path of the high-pressure casing. High-temperature, high-pressure steam sent from the boiler is introduced from the main steam inlet 2 installed at the top of the medium-pressure outer casing 1, and is loaded into the high-pressure stage. is applied to rotate the rotor and flow into the high-pressure exhaust chamber 3.

The steam flowing into the high-pressure exhaust chamber 3 comes into direct contact with the high-medium pressure outer casing 1 and then returns to the boiler, where the steam becomes even hotter and enters the reheat steam inlet 4, which applies a load to the medium-pressure stage and the rotor. and flows into the medium pressure exhaust chamber 5. Here, the temperature of the high-medium Shonai casing 7 is extremely high because it is in direct contact with steam and is also enclosed in the in-cylinder pressureless casing 1. Both the high-medium pressure outer casing 1 and the high-medium pressure inner casing 7 are divided into an upper half and a lower half, and are fastened together at the horizontal flange 6 with large-mouth bolts.

FIG. 2 shows a plan view of the horizontal flange 6 portion.

The high-medium pressure outer casing 1 contains high-temperature and high-pressure steam, that is, high-pressure exhaust pressure P, and high-pressure exhaust temperature T. , reheat steam pressure P2
, reheat steam temperature L, medium pressure exhaust pressure P3, medium pressure exhaust temperature T
The high-medium pressure internal casing 7 is surrounded by a high-pressure exhaust chamber 3, a reheat steam chamber 4, and a medium-pressure exhaust chamber 5. Because it is in contact with steam from the butterbur, it is even hotter than the high-temperature Shonai casing 1.

These casings have so-called through bolts 8 which are attached vertically from both sides with nuts on the top and bottom of the horizontal flange in the horizontal flange part, and nuts only on the upper side.
The lower half is fastened with a so-called stud bolt 9, which has a female thread provided directly on the horizontal flange and is fastened to this. Since the temperature around the casing plugs of these bolts 8 and 9 is high, the bolts themselves also become high temperature, and in the process of fastening the high-pressure casing, the initial brazing force decreases due to creep.

Then, high-pressure steam leakage may occur, which could lead to a major accident. For this reason, in the secondary system, low-temperature steam is flowed from the middle of the turbine stage to lower the bolt temperature, which is called bolt cooling, so as to prevent the subsequent stress from decreasing. Second
In the figure, 10 is a bolt cooling pipe, and this bolt cooling pipe 1 connects the high pressure exhaust chamber 3 and the medium pressure exhaust chamber 5 to form a bolt cooling steam passage. A bolt cooling steam passage connecting the high pressure exhaust chamber 3 and the reheat steam inlet 4 is formed in the horizontal flange 6 .

In the above configuration, the high-pressure exhaust pressure P, is higher than the reheat steam pressure P2 and the intermediate-pressure exhaust pressure P3, and a natural flow occurs depending on the diameter of the bolt cooling pipe 10.

The high pressure exhaust chamber temperature T, is lower than the reheat steam temperature T2 and cools the joint bolt near the reheat steam temperature T2.

Similarly, in the high-temperature Shonai casing 7, steam from the high-pressure low-temperature stage is allowed to flow to lower the temperature of the high-temperature bolt. Figure 3 shows stud bolt 9 being cooled.
It is a sectional view of the part, and the upper half-horizontal flange 3 and the lower half-horizontal flange 4 are butted together at the horizontal recess surface 15, and the horizontal flange 14 is provided with a female thread.

Both flanges 13 and 14 are fastened together by stud bolts 9. The stud bolt 9 is provided with a bolt center hole 12, and the stud bolt 9 at the upper half-horizontal flange 13 is formed in a pongee shape, with a bolt hole gap 1.
6 is formed.

A bolt cooling pipe 10 provided on the upper semi-horizontal flange 13 is closed in this bolt hole gap 16. The low-temperature cooling steam that has passed through the bolt cooling pipe 10 flows into the bolt hole gap 16, flows around the bolt 9, and cools the bolt, which is at a high temperature.

Then, it flows through the pipe 10 to the next bolt hole gap 16. In the above configuration, the bolt is cooled and its creep strength is improved, but in the initial stage of vertical mounting of the bolt, the bolt is subjected to a large amount of tensile stress due to the difference in thermal expansion between the bolt, which has been cooled to a low temperature, and the horizontal flange, which is at a high temperature. It is dangerous to be exposed to force.

The process will be explained based on FIG. The upper half-horizontal flange 13 has an extremely high temperature, and if the height of the upper half-horizontal flange 13 is the limit, the amount of elongation 62 of the upper half-horizontal flange 13 alone is 62:
Q・T2・However, Q: Coefficient of linear expansion L: Reheated steam temperature.

On the other hand, the amount of elongation of the stud bolt 9 is 6. Since the temperature is low, 6,=Q・T3・However, L: Cooling temperature So: Flange height Q: Linear expansion coefficient.

Here, the flange elongation amount 62 is larger than the bolt elongation amount 6, and there is no thermal deformation due to the influence of temperature when both are fastened.

Therefore, the effect of tensile stress on the bolt is ^-6
, and the effect of compressive stress on the upper half-horizontal flange 13 is ・621^.

If the tensile stress of the bolt increases due to heat, it will be added to the initial tightening stress and become excessive, which will eventually cause the bolt to break or the thread to break.

Figure 5 generally shows the relationship between bolt stress S and time t, and shows the residual stress curve 1 due to simple bolt tension.
7 decreases with time t, and becomes a constant stress after a certain period of time.

At the initial stage, the master rupture curve 18 is set at a level of 62 or more, but there is a risk that the thermal WS force 6 is applied to this and the master rupture curve 18 becomes higher than the residual stress, causing the bolt to break. If the temperature between the bolt and the horizontal flange of the casing is known, the thermal stress can be estimated and consideration can be given to bolt breakage. SUMMARY OF THE INVENTION An object of the present invention is to provide a bolt cooling control device that solves the above-mentioned conventional problems and can perform stable tightening.

The present invention measures the temperature between the bolt and the horizontal flange of the casing, which has not been known until now, and when the temperature difference becomes large, the bolt is heated to reduce bolt tension stress. It is configured to automatically adjust and control the bolt tensile stress so that it does not decrease too much.

The present invention will be explained below based on an embodiment shown in FIGS. 6 to 8.

FIG. 6 shows an embodiment in which the horizontal bushing part in FIG. At the bolt hole gap 16 position of the flange 13,
A thermocouple 21 facing the thermocouple 20 is provided.

The temperature of both thermocouples 20 and 21 is configured to be measured by a thermometer 22 provided outside. This thermometer 22 is connected to a temperature determiner 23, and the temperature of both is determined by a bimetal or the like built into the temperature determiner 23. The temperature determiner 23 is a heater wire 25 inserted into a vertical hole 24 provided in the stud bolt 9, or a flow control valve 26 provided in the bolt cooling pipe 10.
are electrically connected to actuating motors 27 that actuate the respective actuators. In the above configuration, when the casing temperature sensed by the thermocouple 21 becomes too high than the bolt temperature sensed by the thermocouple 2, the temperature determiner 23 energizes the heater wire 25 and the stud bolt 9 temperature increases.

This reduces the difference in elongation with the flange and reduces the tensile stress on the bolt. Conversely, if the bolt temperature sensed by the thermocouple 20 becomes too high than the flange temperature sensed by the thermocouple 21,
If the bolt stretches a lot, the tightening force will decrease and there is a risk of steam leakage.

In this case, the operating motor 27 is operated by the temperature determiner 23, and the cooling steam flow rate control valve 26 is operated, thereby increasing the amount of steam.

This performs bolt cooling. By repeating this cycle, appropriate bolt tightening force is maintained. FIG. 7 is a graph showing the relationship between the bolt stress cycle and temperature, where t on the mechanical axis represents time, S on the vertical axis represents the bolt tensile stress, and Bt represents the temperature difference between the bolt and the flange.

In the figure, 28 is a cycle curve of the temperature difference between the bolt and the flange.

Now, at point A, where the bolt becomes too hot, the elongation of the bolt becomes greater than the elongation of the flange, and the bolt tensile stress decreases, resulting in point a on the bolt stress cycle curve 29.

Further, at point B, where the bolt temperature becomes too low, the elongation of the flange becomes greater than the elongation of the bolt, and the bolt tensile stress increases, reaching point b. Repeating this cycle results in C and c. Here, the bolt temperature upper limit 29 is determined by the bolt required tightening stress 33, and if the temperature rises any higher, the bolt will loosen and the steam inside the casing will flow out, so an upper limit of the bolt temperature is set. On the other hand, the lower limit of bolt temperature is 30
is determined by the bolt stress limit 32, and the lower limit of the bolt temperature is set because the bolt stress becomes high and the bolt breaks at a temperature below this limit. Bolt stress cycle curve 29
In other words, by controlling the fluctuation of the cycle curve 28 of the temperature difference between the bolt and the flange to be smaller, the thermal WS,
It is possible to keep the force component constant.

FIG. 8 is a graph corresponding to FIG. 5 and showing the effects of the present invention, in which t represents time and S represents bolt stress.

In FIG. 8, by suppressing the thermal eaves and sword swing 32 to a small value, the thermal eaves and force load curves 19 where thermal stress is added to the residual stress curves 17 are shortened from the initial vertical installation compared to those in FIG. Within this time, the stress is greatly reduced, and the bolt stress S can be safely managed.

As explained above, according to this embodiment, the bolt stress can be accurately determined by measuring the bolt temperature, and accidents such as bolt breakage can be prevented by controlling the temperature.
It is extremely useful for bolt safety management.

The present invention has been described above based on preferred embodiments, but according to the present invention, bolt tensile stress can be accurately controlled.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of steam flow in the high-pressure casing of a steam turbine, Figure 2 is an enlarged view of the horizontal flange of the high-pressure casing, Figure 3 is a sectional view of a conventional example, and Figure 4 is a conventional cooling bolt. Figure 5 is a bolt stress graph when thermal stress is added to residual stress, Figure 6 is a sectional view showing an embodiment of the present invention, and Figure 7 is a diagram showing the relationship between bolt stress cycle and temperature. A graph showing the relationship, FIG. 8, is a bolt stress graph corresponding to FIG. 5. 1... High-medium pressure outer casing, 7... High-medium Shonai casing, 9... Stud bolt, 10 """
Port cooling piping, 13... Upper half-horizontal flange, 14... Lower half-horizontal flange, 20, 21...
...Thermo cutlet, 22 ...Thermometer, 2
3... Temperature determiner, 25... Heater wire, 26... Flow rate control valve, 27... Operating motor. Figure 2 Figure 3 Figure 4 Figure 5 Figure 7 Figure 2

Claims (1)

[Claims] 1. A heater is provided on the tightening bolts that rigidly connect the divided steam turbine high-pressure casings to each other, and the casing is provided with a heater.
A bolt cooling steam passage having a flow rate adjustment mechanism is formed, and a detection mechanism for detecting the mutual temperature of the bolt and the casing is provided, and the detection mechanism includes a heater or a flow rate adjustment mechanism to reduce the temperature difference therebetween. A bolt cooling control device characterized by operating a bolt cooling control device.