JP2001354295A - Method for sealing fine hole and method for manufacturing container sealed by that method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of easily sealing a fine hole and a method for manufacturing a container sealed by that method. SOLUTION: A water absorbable polymer 9 is applied to an object 1 to be sealed along with a liquid penetrant 7 to penetrate into the fine hole 8 of the object 1 and swell the water absorbable polymer 9 in the hole 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filling small holes remaining in a filling object such as a container.

[0002]

2. Description of the Related Art In a low-temperature underground tank for storing a low-temperature liquid such as LNG (liquid natural gas), an ammonia leak test is particularly performed as a leak test at a welded portion.

In the ammonia leak test, a reagent for detecting ammonia (alkali) is sprayed on a welded portion of a membrane forming an inner shell of a low-temperature underground tank, and ammonia gas is injected into a heat insulating layer formed on the back side of the membrane. This is to check for gas leakage.

[0004] Thus, a small hole in the welded portion of the membrane can be easily found, and the hole is filled by welding.

[0005]

However, in the ammonia leak test, it is almost impossible to detect a hole having a diameter of 5 μm, and it has been very difficult to find a fine hole having a diameter of 5 μm or less.

In order to fill such micro holes, there is a technique of attaching a putty or an adhesive tape along the welding bead, but the length of the welding bead reaches 20,000 meters. Because it was very difficult.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a sealing method capable of easily filling a fine hole and a method for manufacturing a container sealed by the method.

[0008]

In order to achieve the above object, the present invention provides a method for applying a water-absorbing polymer to an object to be sealed together with a penetrating liquid to form a water-absorbing polymer in fine pores of the object to be sealed. And then swell the water-absorbing polymer in the pores.

[0009] The fine pores of the object to be plugged are closed by the swollen water-absorbing polymer and are easily plugged.

It is preferable that water containing a surfactant is introduced into the pores to swell the water-absorbing polymer in the pores.

The water-absorbing polymer is preferably made of a saponified vinyl acetate-acrylate copolymer or a starch-acrylic acid graft copolymer.

Further, it is preferable to use any of methanol, ethanol and butanol for the above-mentioned permeate.

When the object to be sealed is a low-temperature tank, a water-absorbing polymer may be applied together with a permeating liquid to a membrane weld of the low-temperature tank.

Further, a water-absorbing polymer is applied together with a penetrating liquid to a container in which fine pores remain, so that the water-absorbing polymer penetrates into the fine pores, and then the water-absorbing polymer in the pores is swollen. The container is manufactured by sealing.

Then, the water-absorbing polymer is applied to the welded portion of the membrane together with the penetrating liquid, so that the water-absorbing polymer penetrates into the fine pores in the joint, and then the water-absorbing polymer in the pores is swollen to form the eye. The cryogenic tank is manufactured by stopping.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 4, a low-temperature underground tank 1 which is both an object to be sealed and a container of LNG includes a concrete layer 2 forming an outer shell, a membrane 3 forming an inner shell, and a membrane 3. And a heat insulating layer 4 formed between the concrete layers 2.

The heat insulating layer 4 is made of urethane foam so that external heat is not transmitted to LNG in the tank 1.

As shown in FIGS. 5A and 5B, the membrane 3 is formed by bonding a stainless plate 5 having a thickness of several millimeters. The stainless plates 5 are bonded to each other by welding (butt welding or fillet welding).

The weld bead 6 is provided on the welded portion of the membrane 3.
a and 6b are formed, and small holes such as pinholes and cracks are easily formed in the weld beads 6a and 6b formed by hand, particularly in corners, due to uneven welding.

As shown in FIG. 4, when performing an ammonia leak test, a reagent (not shown) for detecting ammonia is sprayed on the welding beads 6a and 6b, and ammonia gas is injected into the heat insulating layer 4.

When ammonia reacts on the reagents on the welding beads 6a and 6b, welding is further performed on the reaction site to fill the holes in which the ammonia gas has leaked.

Fine pores of 5 μm or less which cannot be detected by the ammonia leak test (hereinafter referred to as micropores) are closed with a water-absorbing polymer described later.

First, a water-absorbing polymer is mixed with a permeate at a predetermined ratio. Then, as shown in FIG. 5, the water-absorbing polymer is applied along with the penetrating liquid by a brush or the like along the weld beads 6a and 6b which are joints of the membrane 3.

As the permeating liquid, methanol (methyl alcohol) is used. As the water absorbing polymer, a saponified vinyl acetate-acrylate copolymer having a particle size of 5 μm or less is used.

The saponified vinyl acetate-acrylate copolymer is obtained by copolymerizing vinyl acetate and methyl acrylate and saponifying with an alkali.
The saponified polymer is a copolymer of vinyl alcohol and sodium acrylate, and becomes a superabsorbent polymer without a crosslinking agent.

The main characteristics of the saponified vinyl acetate-acrylate copolymer are that the strength and water retention capacity at the time of water absorption are remarkably high, the water absorption rate is high, the stability with time is excellent, and it is almost harmless to the human body. It has a high water absorption even under pressure.

The saponified vinyl acetate-acrylate copolymer does not absorb alcohol such as methanol, and does not swell when mixed with methanol.

As shown in FIG. 1, the osmotic liquid 7 easily penetrates into the micropores 8 by osmotic pressure, and the water-absorbing polymer 9 penetrates into the micropores 8 together with the osmotic liquid 7.

Thereafter, as shown in FIG.
By applying water 10 to a and 6b, the water 10 is brought into contact with the water-absorbing polymer 9 in the micropores 8 to swell.

The water 10 applied to the welding beads 6a and 6b is
Use deionized distilled water. Further, a surfactant (not shown) is added to the water 10 in advance.

As the surfactant, sodium dioctyl sulfosuccinate, which is an anionic surfactant, is used.

The water 10 applied to the welding beads 6a, 6b
Can easily penetrate into the micropores 8 by osmotic pressure because the surface tension is weakened. As shown in FIG. 3, the water-absorbing polymer 9 in contact with the water 10 rapidly absorbs the water 10 and expands from several times to several tens times the original particle size in several seconds to become a gel. .

The water-absorbing polymer 9 comes into contact with the inner peripheral surface of the micropores 8 during the expansion process and is pressurized. However, the water-absorbing polymer 9 deforms and absorbs the water 10 even under pressure. Since the water-absorbing polymer 9 has high strength at the time of absorbing water, the micropores 8 can be closed in a liquid-tight manner.

When a low-temperature liquid such as LNG is stored in the low-temperature tank, the membrane 3 is cooled to about -160 degrees Celsius. Since the water 10 in the swollen water-absorbent polymer 9 becomes ice, the water 10 in the water-absorbent polymer 9 does not come off due to evaporation or the like, and the water-absorbent polymer 9 is completely fixed in the micropores 8. Is done.

The water-absorbing polymer 9, vinyl acetate-
Acrylic ester copolymer saponified, 150 degrees Celsius
Although it is weak at high temperatures exceeding, it is extremely stable at low temperatures, and is not exposed to ultraviolet light in the tank, so that the micropores 8 can be stably closed for a long period of time.

As described above, the weld beads 6a, 6
The water-absorbing polymer 9 is applied along with the penetrant 7 along the line b, so that the water-absorbing polymer 9 penetrates into the fine holes 8 in the welding beads 6a and 6b. Due to the swelling, the fine holes 8 that are difficult to detect can be easily closed, and the welding beads 6a and 6b reaching 20,000 meters can be quickly filled.

The water 10 containing the surfactant was added to the welding bead 6.
The water-absorbing polymer 9 in the micropores 8 can be extremely easily swelled because the water-absorbing polymer 9 in the micropores 8 is swelled by infiltrating into the micropores 8 by being applied to a and 6b.

Further, since a saponified vinyl acetate-acrylate copolymer is used as the water absorbing polymer 9,
The micropores 8 can be stably closed for a long time, and methanol can be used as the permeate 7.

Since methanol is used as the penetrating liquid 7, the water-absorbing polymer 9 can easily penetrate into the micropores 8.

In the present embodiment, the method for sealing the welded portion of the membrane of the LNG tank has been described.
It is not limited to this. For example, it may be a low-temperature tank containing liquid nitrogen, an LPG tank, or a water tank. Further, the above-described sealing method may be used for sealing an unsealed integrally formed container or an object to be sealed other than the container such as a lid of the container.

In this case, it is preferable to select an optimal water-absorbing polymer according to the container and the contents, and it is preferable to change the permeating liquid 7 in accordance with the selected water-absorbing polymer. Penetrant 7
Does not expand the water-absorbing polymer beyond the pores to be closed,
In addition, any material can be used as long as it can penetrate into the holes.

In the case of an integrally molded container, it is not always necessary to apply the penetrating liquid 7 mixed with the water-absorbing polymer 9 from the inside of the container, but may apply it from the outside of the container.

The water-absorbing polymer 9 may be, in addition to the above-mentioned saponified vinyl acetate-acrylate copolymer, starch-
Acrylic acid graft copolymer, saponified vinyl acetate-unsaturated dicarboxylic acid monomer copolymer, saponified starch-acrylonitrile graft copolymer, or composite fiber of acrylic fiber inner core and acrylate copolymer outer layer Other than these, other polyacrylates, isobutylene-maleic acid copolymers, polyethylene oxides, carboxymethyl celluloses, alginates and the like may be used.

The surfactant added to the water 10 is not limited to sodium dioctyl sulfosuccinate.
Other materials such as sodium butylnaphthalenesulfonate and a polyoxyethylene addition type nonionic surfactant may be used.

The permeating liquid 7 may be other alcohols such as ethanol (ethyl alcohol) and butanol (butyl alcohol) in addition to the above-mentioned methanol.

Then, it is not always necessary to apply the water-absorbing polymer 9 after mixing it with the penetrating liquid 7. It may be embedded in the hole 8.

[0048]

In summary, according to the present invention, the following excellent effects can be obtained.

(1) It is possible to close a fine hole which is difficult to detect.

(2) Fine holes can be easily closed in a short time.

[Brief description of the drawings]

FIG. 1 is a schematic view of a membrane and micropores showing a preferred embodiment of the present invention.

FIG. 2 is a schematic diagram of a membrane and micropores in a state where a water-absorbing polymer has penetrated into the micropores.

FIG. 3 is a schematic view of a membrane and a micropore in a state where a water-absorbing polymer has swollen in the micropore.

FIG. 4 is a side sectional view of a low-temperature underground tank.

FIG. 5 (a) is an enlarged perspective view of a main part of a butt weld of a low-temperature underground tank, and FIG. 5 (b) is an enlarged perspective view of a main part of a fillet weld of the low-temperature underground tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Low-temperature underground tank (object to be stopped) 3 Membrane 6a Weld bead (joint) 6b Weld bead (joint) 7 Penetrant 8 holes (micro holes) 9 Water-absorbing polymer 10 water

Claims (7)

[Claims] 1. A water-absorbing polymer is applied to an object to be filled together with a penetrating liquid to cause the water-absorbing polymer to penetrate into fine pores of the object to be filled, and then the water-absorbing polymer in the hole is swollen. A method of filling fine holes, characterized in that it is performed. 2. The method for filling fine pores according to claim 1, wherein water containing a surfactant is introduced into the pores to swell the water-absorbing polymer in the pores. 3. The method according to claim 1, wherein the water-absorbing polymer is a saponified vinyl acetate-acrylate copolymer or a starch-acrylic acid graft copolymer. 4. The method according to claim 1, wherein any one of methanol, ethanol, and butanol is used as the permeate. 5. The filling object is a low-temperature tank,
The method for sealing a low-temperature tank according to any one of claims 1 to 4, wherein a water-absorbing polymer is applied to a membrane weld of the low-temperature tank together with a penetrating liquid. 6. A water-absorbing polymer is applied together with a penetrating liquid to a container in which fine pores remain, so that the water-absorbing polymer penetrates into the fine pores, and then the water-absorbing polymer in the pores is swollen. A method for producing a container, comprising filling. 7. A water-absorbing polymer is applied to a welded portion of the membrane together with a penetrating liquid to infiltrate the water-absorbing polymer into fine pores in the joint, and thereafter, the water-absorbing polymer in the pores is swollen to form an eye. A method for manufacturing a low-temperature tank, comprising stopping.