Airtightness test method for liquid withdrawal nozzles on large liquid tanks

Abstract

To provide a large tank with a liquid extraction nozzle having a structure that allows an airtightness test to be done quickly and easily thereon without causing adverse effect on a main body base material due to heat.SOLUTION: A large liquid tank 1 with a liquid extraction nozzle 20 having an inner flange structure is provided, the liquid extraction nozzle 20 comprising a cylindrical short tube portion 21 penetrating through a side wall 1a of the large liquid tank 1 and having an inner flange 23 welded onto an end of the cylindrical short tube portion 21 inside the tank.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a large liquid tank having a liquid withdrawal nozzle with a flange structure on the inside of the tank, and a method for testing the airtightness of the liquid withdrawal nozzle. [Background technology]

[0002] In production plants such as petrochemical plants, nonferrous metal smelting plants, and pharmaceutical factories, generally, approximately cylindrical storage tanks are used for the temporary storage of liquids, such as liquid raw materials, auxiliary materials, liquid intermediate products, and final products. Liquids received in these storage tanks are withdrawn through a liquid withdrawal nozzle provided at the bottom of the storage tank's sidewall. When withdrawing liquid from the storage tank through this liquid withdrawal nozzle, the liquid typically passes through the nozzle at a speed of several meters per second, which can easily cause thinning of the liquid-contacting parts of the liquid withdrawal nozzle and the piping system connected to it. In particular, when the liquid in the storage tank is in a slurry state, significant thinning of the liquid-contacting parts can occur due to wear. Furthermore, when the liquid in the storage tank is strongly acidic or strongly alkaline, significant thinning of the liquid-contacting parts can occur due to corrosion.

[0003] If the thinning of the liquid-contacting parts progresses and a hole develops in the liquid-extraction nozzle, causing a leak, the liquid in the storage tank may leak out, causing personal injury and environmental damage, and in some cases, it may even lead to a shutdown of operations, resulting in significant economic losses. To prevent such a situation, storage tanks generally undergo leakage tests to confirm that there are no holes in the liquid-extraction nozzle during periodic inspections, as well as when they are newly constructed or remodeled.

[0004] The leak test for the liquid withdrawal nozzle can be performed, for example, by filling a storage tank with water while fully closing a valve installed in a piping system connected to the liquid withdrawal nozzle. However, this leak test method cannot properly check for leaks in tanks storing liquids with a higher specific gravity than water, such as sulfuric acid. This is because the pressure (head pressure) applied to the liquid withdrawal nozzle when the storage tank is filled with water does not reach the pressure applied to the liquid withdrawal nozzle when the storage tank is filled with sulfuric acid in actual operation, since the pressure applied to the liquid withdrawal nozzle is proportional to the specific gravity of the liquid. Therefore, it is possible to perform a leak test using sulfuric acid used in actual operation, but in this case, there is a risk of sulfuric acid leaking during the leak test.

[0005] An example of a method for detecting leaks by applying pressure to a liquid extraction nozzle during actual operation without risking leakage of the liquid used in the actual operation is an airtightness test. Patent Document 1, for example, discloses a technology for accurately detecting leaks in tanks and pipes without wasting time through an airtightness test. The technology in Patent Document 1 involves closing all openings leading to the tank and pipes under test to create an airtight system. In this state, the system is filled with an inert gas, such as nitrogen gas, to maintain a constant pressurized state, while measuring the pressure in the system with, for example, a manometer or a large Bourdon tube pressure gauge. If a leak is detected, the inert gas leaks from the system, causing the pressure in the system to decrease over time. The presence or absence of a leak can be determined by checking for this decrease in pressure.

[0006] Furthermore, Patent Document 2 discloses a technology for conducting an airtightness test by introducing nitrogen gas into an underground tank. Specifically, all but one of the multiple pipes connecting to the underground tank are closed, and nitrogen gas is introduced through the remaining pipe to maintain a pressurized state inside the underground tank, while a pressure sensor monitors the internal pressure of the underground tank. If a change occurs in the internal pressure of the underground tank, it is determined that a leak has occurred in the underground tank. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 1-203931 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-120414 Summary of the Invention [Problem to be solved by the invention]

[0008] By conducting a leak test using the airtightness testing methods described in Patent Documents 1 and 2, it is possible to properly check for leaks without the risk of liquid leaking during actual operation. However, when the equipment being tested is a large liquid tank, the airtightness testing method described above requires introducing nitrogen gas into the entire tank to create a pressurized state, which poses a problem in that the cost of nitrogen gas is excessive. Therefore, it is possible to conduct an airtightness test using nitrogen gas only on the liquid withdrawal nozzle, which is prone to leaks, rather than on the entire tank.

[0009] In general, in large liquid tanks, the liquid drain nozzle consists of a short cylindrical pipe with a flanged tip, which is welded to the lower part of the side wall that constitutes the tank body so that it protrudes outside the tank. This flanged liquid drain nozzle is generally connected to the drain line via a first valve such as a butterfly valve or ball valve, and closing this first valve can block communication between the inside of the tank and the drain line.

[0010] When conducting an airtightness test on only the liquid withdrawal nozzle with the above structure, the outer end of the liquid withdrawal nozzle can be easily closed with the first valve as described above, but the tank-side end of the liquid withdrawal nozzle cannot be closed from the outside of the tank because it is welded to the side wall of the tank. Therefore, it was necessary to first enter the tank and close the opening in the inner wall of the tank where the liquid withdrawal nozzle is welded by welding a curved iron plate along the inner wall surface of the tank.

[0011] As described above, in conventional large-sized liquid tanks, when airtightness testing only the liquid withdrawal nozzle, it is necessary to directly weld a steel plate or the like to the base material of the tank from the inside, which may adversely affect the base material due to heat during welding. Furthermore, each time an airtight test is conducted, it is necessary to weld the steel plate and remove the steel plate after the test, which poses a problem of taking a long time. The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a large-sized tank having a liquid withdrawal nozzle with a unique structure that allows airtightness testing of the liquid withdrawal nozzle of a large-sized liquid tank to be conducted easily and in a short time without adversely affecting the base material of the large-sized tank body due to heat, and a method for airtightness testing of the liquid withdrawal nozzle. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention Nitrogen filling jig teeth, Large liquid tanks have Liquid extraction nozzle Nitrogen filling jig for airtight testing The liquid withdrawal nozzle is made of a cylindrical short pipe portion that penetrates the side wall portion of the large liquid tank, and an inner flange is welded to the end of the cylindrical short pipe portion on the tank interior side. The nitrogen charging jig has a nitrogen gas introduction pipe with a shut-off valve, a pressure gauge, and a blind flange to which the introduction pipe and the pressure gauge are attached (excluding those having a member that blocks the inside of the nozzle), and the blind flange is directly fastened to the inner flange with bolts and nuts. It is characterized by:

[0013] The method for testing the airtightness of a liquid withdrawal nozzle according to the present invention includes the steps of: At the inner end of the tank Inner flange is welded 1. A method for testing the airtightness of a large liquid tank having a liquid outlet nozzle of the above structure, and these Blind flange with attached The blind flange of the nitrogen sealing jig havingwith bolts and nuts directly a step of fully closing a valve connected to the end of the liquid extraction nozzle on the outer side of the tank; a step of filling nitrogen gas into the liquid extraction nozzle from the nitrogen filling jig; and a step of fully closing the stop valve when the reading of the pressure gauge reaches a predetermined pressure and checking for the presence or absence of leakage. [Effects of the Invention]

[0014] According to the present invention, it is possible to easily conduct an airtightness test on a liquid discharge nozzle of a large liquid tank in a short time without adversely affecting the base material of the main body due to heat. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic flow diagram of a typical large liquid tank and a piping system connected thereto. [Figure 2] 1A is a cross-sectional view of a liquid withdrawal nozzle of a conventional large liquid tank, and FIG. 1B is a cross-sectional view showing the state during an airtightness test. [Figure 3] 1A is a cross-sectional view of a liquid discharge nozzle of a large liquid tank according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view showing the state during an airtightness test. [Figure 4] FIG. 4 is a cross-sectional view of an alternative example of the liquid withdrawal nozzle shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of a large liquid tank having a flange-structured liquid extraction nozzle of the present invention will be described in detail with reference to the drawings. As shown in Figure 1, the main body of a large liquid tank 1 is generally composed of a substantially cylindrical side wall 1a and a dome-shaped or conical ceiling 1b located above the side wall 1a. The ceiling 1b is provided with various nozzles, such as a nozzle for a supply line for the stored liquid, a nozzle for connecting equipment, a vent nozzle, and a nozzle for a return line for the liquid extracted from the liquid extraction nozzle (described later).

[0017] Meanwhile, a liquid extraction nozzle 2 for extracting the liquid from the large tank 1 is provided at the bottom of the side wall 1b. A first valve 3, such as a butterfly valve or a ball valve, is attached to this liquid extraction nozzle 2, and the flanges of the first valve 3 are fastened together with bolts and nuts. The liquid extraction nozzle 2 is connected to a liquid extraction line 4 via the first valve 3, and a liquid extraction pump 5 is provided on the liquid extraction line 4. In the large liquid tank 1 shown in Figure 1 above, the liquid extraction nozzle 2 surrounded by the dashed line has conventionally been of the structure shown in Figure 2(a). That is, the conventional liquid extraction nozzle 2 shown in Figure 2(a) is composed of a cylindrical short pipe portion 11, one end of which is welded to the side wall 1a, and an external flange 12, which is welded to the other end of the short pipe portion 11.

[0018] When checking for leaks from the liquid withdrawal nozzle 2, one possible test method is to fill the large liquid tank 1 with water while the first valve 3 is fully closed and visually check for leaks, but this test method does not allow for the application of appropriate pressure to perform a leak test on a storage tank for liquids with a higher specific gravity than water, such as sulfuric acid. Therefore, a nitrogen injection jig, as shown in Figure 2(b), was attached to the tank-side end of the liquid withdrawal nozzle 2, and tests were conducted to check for leaks while applying appropriate pressure using filled nitrogen gas.

[0019] That is, in a leak test for a liquid extraction nozzle 2 of a conventional structure, first, a circular iron plate 15 curved to fit the surface of the side wall 1a of the large tank 1 was directly welded to the opening where the liquid extraction nozzle 2 was attached, and the first valve 3 was fully closed to seal the liquid extraction nozzle 2. The iron plate 15 has an opening in the center, and an iron pipe 16 is attached to this opening so that it protrudes. A shut-off valve 17 is provided at the tip of this iron pipe 16, and a pressure gauge 18 is provided in the middle. The end of the shut-off valve 17 is provided with a connection port 19 to which the end of a flexible hose F for nitrogen gas supplied from a nitrogen gas supply source (not shown) is connected.

[0020] With this mechanism, nitrogen gas is introduced from the flexible hose F connected to the connection port 19 while the shut-off valve 17 is open, and when the reading on the pressure gauge 18 reaches a predetermined pressure, the shut-off valve 17 is fully closed. After maintaining this state for a predetermined time, the presence or absence of a leak can be determined by checking whether the reading on the pressure gauge 18 has dropped below the predetermined pressure. This makes it possible to conduct a leak test while applying an appropriate pressure to the liquid extraction nozzle 2, taking into account the liquid to be handled in actual operation.

[0021] However, this conventional leak test method required welding a steel plate to the base material of the tank sidewall and removing the steel plate after each test, and also required penetrant testing after welding, which made the test extremely time-consuming and labor-intensive. Furthermore, welding the steel plate could have a detrimental effect on the base material due to heat, which could potentially be the starting point for corrosion. For this reason, the conventional leak test method described above could not be performed multiple times during tank inspection and maintenance.

[0022] In contrast, in an embodiment of the present invention, by using a liquid extraction nozzle 20 having the structure shown in Figure 3(a) in a large liquid tank 1, the problems associated with the conventional liquid extraction nozzle 2 described above do not occur. Specifically, the liquid extraction nozzle 20 of the large liquid tank 1 of the embodiment of the present invention consists of a cylindrical short pipe section 21 that penetrates the tank side wall section 1a. An outer flange 22 for flange connection to the first valve 3 is welded to the end of this short pipe section 21 on the outer side of the tank, and an inner flange 23 for connection to a blind flange equipped with a nitrogen charging jig, which will be described later, is welded to the end on the inner side of the tank.

[0023] This configuration makes it possible to conduct an airtightness test easily and quickly by the following procedure. First, a blind flange 24 is fastened to the inner flange 23 of the liquid withdrawal nozzle 20 with bolts and nuts 25. This blind flange 24 has an opening in the center, and an iron pipe 26 is attached to this opening so that it protrudes. A shut-off valve 27 is provided at the tip of this iron pipe 26, and a pressure gauge 28 is provided in the middle. The end of the shut-off valve 27 is provided with a connection port 29 to which the end of a flexible tube F for nitrogen gas supplied from a nitrogen gas supply source such as a nitrogen cylinder (not shown) is connected.

[0024] With the shut-off valve 27 open, nitrogen gas is introduced into the liquid extraction nozzle 20 through the flexible tube F connected to the connection port 29, and pressure is applied until the pressure gauge 28 indicates a predetermined pressure. Once the predetermined pressure is reached, the shut-off valve 27 is fully closed. This state is maintained for a predetermined time, and by checking whether the pressure gauge 28 indicates a drop below the predetermined pressure, a leak test can be performed under an appropriate pressure that takes into account the liquid handled in actual operation. Note that instead of or in addition to checking for a drop in pressure on the pressure gauge 28 as described above, a liquid such as soapy water may be applied to the liquid extraction nozzle 20 from the outside, and if bubbles are generated, it may be determined that a leak has occurred.

[0025] After the leak test is completed, the flexible tube F is removed from the connection port 29 and the shut-off valve 27 is opened to release the nitrogen gas filled in the liquid extraction nozzle 20. The bolts and nuts 25 are then removed to separate the blind flange 24 from the inner flange 23, completing the work. In this way, with the airtightness test method of the embodiment of the present invention, the airtightness test can be performed simply by attaching and detaching the blind flange 24 equipped with the nitrogen charging jig to and from the inner flange 23. This shortens the test time compared to conventional airtightness test methods that involve welding steel plates or the like, and also eliminates the adverse effects of heat during welding on the tank base material.

[0026] The above describes an embodiment of the present invention, and a method for testing the airtightness of a large liquid tank and its liquid withdrawal nozzle. However, the present invention is not limited to the above embodiment and can include various alternatives and modifications without departing from the spirit of the present invention. For example, the liquid withdrawal nozzle 20 described above has an integrated short pipe portion 21 that penetrates the side wall portion 1a of the large liquid tank 1. However, the present invention is not limited to this. For example, the liquid withdrawal nozzle 2 of an existing large liquid tank 1 may be modified to have a structure in which an additional short pipe portion 21b having an inner flange 23 is welded from the inside of the tank to the tank-side end of the short pipe portion 21a having an outer flange 22, as in the liquid withdrawal nozzle 120 shown in Figure 4. [Example]

[0027] A 12-inch liquid extraction nozzle 2 with a conventional structure attached to an existing large liquid tank 1 shown in Table 1 below was modified to create a liquid extraction nozzle 120 with the structure shown in Figure 4. That is, a cylindrical short pipe section 21b of the same shape was connected to the tank-side end of the existing cylindrical short pipe section 21a from inside the tank by welding. An internal flange 23 had been welded to this short pipe section 21b. At this time, the length from the inner wall surface of the tank to the flange surface of the internal flange 23 was 250 mm.

[0028] [Table 1]

[0029] An airtightness test was performed by fastening a blind flange 24 equipped with a nitrogen filling jig as shown in Figure 3(b) to the internal flange 23 of this liquid extraction nozzle 120 with bolts and nuts 25. Specifically, a flexible tube F for nitrogen gas was connected to the connection port 29, and the first valve 3 was fully closed. Then, nitrogen gas was filled into the liquid extraction nozzle 20 from the nitrogen filling jig of the blind flange 24. When the reading on the pressure gauge 28 reached a predetermined pressure, the shut-off valve 27 was fully closed and this state was maintained for 30 minutes. During this time, the reading on the pressure gauge 28 was read every 10 minutes to check whether the pressure had dropped from the predetermined pressure, and soapy water was sprayed on the liquid extraction nozzle 120 from the outside to check whether bubbles were formed.

[0030] For comparison, a large liquid tank 1 having a conventional liquid extraction nozzle 2 was welded to the side wall 1a of the tank with an iron plate 15 equipped with a nitrogen injection jig having the structure shown in Figure 2(b) instead of the blind flange 24, and a penetrant inspection was carried out. Thereafter, an airtightness test was carried out in the same manner as in the above example. In this comparative example, it was necessary to remove the iron plate after the airtightness test. The time required for the airtightness tests of the above example and comparative example is shown in Table 2 below.

[0031] [Table 2]

[0032] As shown in Table 2 above, the present invention was able to significantly reduce the time required for the airtightness test on the liquid withdrawal nozzle compared to the comparative example. Furthermore, in the example, there is no welding to the side wall 1a of the tank, so there is no need to worry about adverse effects from heat, and it has become possible to perform an airtightness test on just the liquid withdrawal nozzle every time regular maintenance is performed. [Explanation of symbols]

[0033] 1 Large liquid tank 1a Side wall part 1b Ceiling 2, 20, 120 Liquid extraction nozzle 3 First Valve 4. Liquid extraction line 5. Liquid extraction pump 11, 21, 21a, 21b Short pipe section 12, 22 External flange 15 Iron Plate 16, 26 Iron pipe 17, 27 Shut-off valve 18, 28 Pressure gauge 19, 29 Connection port 23 Internal flange 24 blind flange F Flexible tube

Claims

[Claim 1] 1. A method for testing the airtightness of a liquid discharge nozzle of a large liquid tank, the liquid discharge nozzle having an inner flange welded to the inside end of the tank, the method comprising the steps of: directly fastening the blind flange of a nitrogen filling jig, the blind flange having a pressure gauge and a shut-off valve attached to the inner flange, to the inner flange with bolts and nuts; fully closing a valve connected to the outside end of the liquid discharge nozzle; filling nitrogen gas into the liquid discharge nozzle from the nitrogen filling jig; and fully closing the shut-off valve when the pressure gauge indicates a predetermined pressure and checking for the presence or absence of leakage.

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