JPS6246430B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The disclosed technology is in the field of technology for removing the welded sealing cover of a manhole provided on the top of a tank such as a flat bottom cylindrical cryogenic tank.

Therefore, when opening a manhole for construction or maintenance provided on the upper part of the tank body of the flat-bottomed cylindrical low-temperature tank for inspection, first remove the screwed top cover on the upper part of the cylindrical body, and then remove the screwed top cover from the upper part of the cylindrical body. This relates to a manhole opening method in which the hermetic lid, which has been welded and sealed, is removed by gas cutting.
In particular, a safety gas such as an inert gas is supplied between the lower lid screwed to the lower part of the cylinder and the above-mentioned sealing lid to fill the space through purge replacement of the stored gas, and simultaneously with this state, the upper lid This relates to a method for opening a tank manhole by removing the gas-tight lid, safely cutting off the gas-tight lid, and finally removing the lower lid.

As is well known, storage tanks, especially liquid storage tanks, have become larger in recent years, and are used periodically to check the fatigue of the structure over time due to internal pressure fluctuations and thermal behavior, as well as for internal inspections after major earthquakes. Open inspections are conducted irregularly.

To deal with this, manholes used during construction are used. For example, as shown in FIG. During the above-mentioned inspection, the manhole 3 is opened by discharging the stored liquid and then discharging the gas to allow personnel to enter and exit.

By the way, after the manhole 3 is constructed as shown in FIG. 2, bolts 6 are attached to the upper flange 5 of the cylinder body 4.
Although the upper lid 8 is tightly sealed via the nut 7, the stored gas inevitably leaks during operation over time.
Since there is a possibility that the gas may be diffused into the cold insulating material 9, a sealing lid 10 is welded 11 as a blind lid inside the cylindrical body 4, as shown in the figure, to reliably prevent gas leakage.

Therefore, when opening the inspection, it is necessary to remove the sealing lid 10 after removing the upper lid 8;
Gas cutting is usually used due to ease of handling and efficiency.

However, although gas purging is performed from inside the tank body 2 after draining the liquid as described above, there is a risk that residual gas may be present, and if such residual gas is unexpectedly present in the tank, there is a risk of explosion due to gas arc. One drawback was that it was extremely difficult to confirm the absence of residual gas.

In view of the problems associated with opening the manhole of the tank during inspection, the object of the present invention is to screw a lower cover to the lower part of the cylindrical sealing cover, and to create a gap between the sealing cover and the lower cover when opening the manhole. A safety gas such as an inert gas is supplied to the tank to release and replace the existing gas, and before and after that, the top cover is removed from the cylinder.
It is an object of the present invention to provide an excellent method for opening a manhole in a tank, in which the hermetic lid is opened by gas cutting without causing an explosion, and finally the lower lid is removed.

Next, a third embodiment of the present invention that meets the above objectives will be described.
The explanation will be as follows with reference to the drawings below. Note that the same reference numerals are used to describe the same parts as in FIGS. 1 and 2.

In FIG. 3, the target tank is a flat-bottomed cylindrical low-temperature tank as in FIG. A top cover 8 is fastened and fixed to the upper flange 5 through bolts 6 and nuts 7 while sealing.
Further, a sealing lid 10 as a blind sealing lid is welded to the intermediate setting portion via welding 11 as in the conventional embodiment.

According to the present invention, the cylindrical body 4 is connected to the lower end flange 12 via bolts 6 and nuts 7.
The lower lid 13 is similarly sealed from the inside and is fastened as a blind lid, and a gas discharge pipe 15 and a purge pipe are connected to the space 14 formed by the sealing lid 10 and the lower lid 13. A pipe 16 is provided, each passing through an outer tank 17 (shown lower than the top cover 8 for convenience of illustration) and connected to an inert gas source as a safety gas source (not shown) by pipes 20 with valves 18 and 19 interposed therein. It is connected to a recovery tank (not shown) via a valve 21 and a pipe 22, or is released to the atmosphere.

Note that 23 is a pressure equalizing pipe, which is connected to the inside of the inner tank 2 and the pipe 20 between the valves 18 and 19 through a valve 24.

In the manhole 3' having the above structure, after constructing the tank, the lower cover 13 is fastened and closed, the sealing cover 10 is attached and sealed by welding to the cylinder body 4, and finally the upper cover 8 is fastened and closed.
The outer tank manhole is also sealed, and when the tank is operated, the valves 19 and 21 are closed, the valves 18 and 24 are opened, and the gas in the inner tank 2 is released through the gas discharge pipe 15 through the pipes 23 and 20 to the sealing lid 10 and the lower lid 13. The space 14 between them is filled to equalize the pressure inside and outside the lower lid 13, so as to prevent leakage due to stress distortion of the lower lid 13.

Therefore, in order to inspect the inner tank 2 at a predetermined timing during tank operation, the valve 24 is closed, and the liquid stored in the inner tank 2 is taken out via a drain mechanism and exhaust gas mechanism (not shown), and the stored gas is purged. Next, the valve 19 is opened to supply inert gas into the space 14 through the gas discharge pipe 15 through the piping 20 and the valve 18, and the valve 21 is opened, and the gas inside the space 14 is supplied through the purge pipe 16 through the piping 22. The gas is discharged and replaced with the inert gas.

In this case, since the pressure has been equalized as described above, the lower lid 13 is not distorted, and no inert gas leaks into the inner tank 2.

When the space 14 is filled with inert gas in this way, the valves 18, 19, and 21 are closed, and the space 14 is filled with the inert gas.
The inside is made into an inert gas space, and then the outer tank manhole is opened, and then, as shown in FIG. Lid 10 and cylinder 4
Cut the weld 11 with.

At this time, it is also possible to cut the weld 11 while supplying and discharging inert gas without closing the valves 18, 19, and 21. In this case, the lower cover 13 and the cylindrical body 4, it is not necessary to have a structure that completely maintains airtightness.

Furthermore, in this case, even if the arc reaches the space 14, there is no risk of explosion because of the inert gas.

Finally, remove the cutting sealing lid 10 and remove the fifth
As shown in the figure, remove the bolts 6 and nuts 7 and remove the lower cover 13.
Remove it and open the manhole 3'.

Then, as shown by the arrow, material is removed from the manhole 3'.
After taking the device in and out and completing the prescribed inspection work, the lower cover 13 is tightened again with the bolts 6 and nuts 7, the sealing cover 10 is welded and sealed, and the upper cover 8 is assembled and returned to its original state.

It goes without saying that the embodiments of this invention are not limited to the above embodiments; for example, air replacement may be used instead of inert gas, the top cover may be removed before gas replacement, and pressure equalization may be performed. Various aspects can be adopted, such as omitting the means or making the lower cover two-tiered.

The target tank is not limited to a flat-bottom cylindrical low-temperature tank, but may also be a spherical tank, a gas tank, an oil tank, etc.

As described above, according to the present invention, in the method of opening a manhole provided at the top of a tank body, the welded sealing cover provided between the lower cover and the upper cover of the cylindrical body facing into the tank and the lower cover are By replacing the gas in the leak tank with safety gas such as inert gas during the process and filling it, basically, when opening the tank, even after purging the stored liquid gas, there will be no explosion at the bottom of the airtight lid. An excellent effect can be achieved in which a state in which sexual gases are not present can be realized.

Therefore, by removing the screw top cover before or after replacing the safety gas, not only is there no risk of explosion even if the gas in the sealing lid is immediately disconnected, but also the residual gas is removed from the manhole when the sealing cover is removed. It has the effect that there is no fear of it leaking out.

Further, since the screw-on lower cover can be removed after the sealing lid is cut, it is easy to remove it, and it is convenient that the cut sealing lid can be temporarily placed or supported.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of a tank, Fig. 2 is an explanatory diagram of a tank manhole based on the prior art, Fig. 3 and the following are explanatory diagrams of an embodiment of the present invention, Fig. 3 is an explanatory diagram of gas replacement, and Fig. 4 is an explanatory diagram of an embodiment of the present invention. The figure is an explanatory diagram of cutting the sealing lid, No. 5
The figure is an explanatory view of opening the lower lid. 1...tank, 2...framework, 3'...manhole, 4
... Cylindrical body, 8... Top lid, 11... Welding, 10... Sealing lid,
13...Lower lid.

Claims (1)

[Claims] 1. In a manhole opening method in which a top cover screwed onto the top of a cylindrical body of a manhole provided at the top of a tank body and facing into the tank is opened and a sealing cover welded inside the cylindrical body is opened by cutting gas, the above-mentioned sealing cover is The space between the cylindrical body and the lower lid screwed onto the lower part of the cylinder body is filled with safety gas, the upper lid is opened before and after that, the airtight lid is removed by cutting off the gas, and finally the lower lid is opened. A tank manhole opening method characterized by: