KR20100055163A - Method for airtight test of cargo tank - Google Patents

Abstract

PURPOSE: An airtight test method for a cargo tank is provided to accurately determine defects of primary and secondary barriers through a differential pressure test, a stress test and a gas reaction leak test. CONSTITUTION: An airtight test method for a cargo tank is as follows. Welding parts are successively inspected at the beginning of construction of a secondary barrier. While a primary barrier is constructed in the inspection-completed portion of the secondary barrier, the primary barrier under construction is inspected with naked eyes. A primary differential pressure test is carried out after the construction and inspection of the secondary barrier(S3). A stress test is carried out after construction of the primary barrier so that positive pressure is maintained in a primary space between the primary and secondary barriers and a detective portion is exposed(S4). The moisture of the primary space is removed and a gas reaction leak test is carried out. A secondary differential pressure test is carried out so that a secondary space between the secondary barrier and a hull and the primary space are kept in a vacuum state and detect of the primary barrier is detected(S6).

Description

Method of Airtightness Inspection of Cargo Depot {METHOD FOR AIRTIGHT TEST OF CARGO TANK}

The present invention relates to a cargo hold airtight inspection method, and more particularly to a cargo hold airtight inspection method that can increase the reliability of the air tightness in the cryogenic cargo hold is made of metal material of both primary and secondary barriers.

In general, liquefied natural gas (LNG) refers to a colorless, transparent cryogenic liquid whose natural gas, which contains methane as its main component, is cooled to -163 ° C and its volume is reduced to one hundredth.

As such liquefied natural gas has emerged as an energy resource, an efficient transportation method that can transport a large amount from the production base to the receiving site of the demand has been considered in order to use this gas as energy. LNG carriers have been shown.

LNG carriers are to be provided with cargo holds to store them for storage and transportation of liquefied liquefied natural gas at cryogenic conditions. At this time, the cargo hold is made of a material that can withstand ultra low temperatures, such as aluminum alloy, stainless steel, 36% nickel steel, etc., in order to store liquefied natural gas having a medium pressure higher than atmospheric pressure and a boiling temperature of minus -163 ° C. It must be manufactured, and the design to cope with thermal stress and heat shrinkage, and the installation of insulation structure to prevent heat intrusion are required.

1 is a cross-sectional view schematically showing a cargo hold structure of a conventional LNG carrier.

In the membrane-shaped cargo hold 10, generally, the secondary barrier 12 of the insulation panel, which is attached and fixed to the inside of the hull 1 by stud bolts (not shown), and is welded on the upper side of the secondary barrier 12. It is composed of the primary barrier 14 of the corrugation membrane (Corrugation Membrane) to be fixed to keep warm and sealed.

In order to check the gas leakage of the secondary barrier 12 in the structure of the cargo hold 10 as described above, as shown in FIG. 2, SBTT (Secondary Barrier Tightness Test) method has been used. Here, reference numeral 13 (shown in FIG. 1) denotes a space between the hull 1 and the secondary barrier 12 as an IS (Insulation Space), and reference numeral 15 (shown in FIG. 1) Inter Barrier Space (IBS) refers to the space between the secondary barrier 12 and the primary barrier 14.

In the SBT method, after the progress of the first and second preliminary tests 20 and 30, the process of the actual test 40 is performed, and in the first preliminary test 20, the IBS 15 is brought into an atmospheric pressure state. After maintaining the IS 13 in a vacuum state of about -530 mbar for about 4 hours, it stabilizes for about 1 hour and monitors the pressure change of the IS 13 every 5 hours or so.

In the second preliminary test 30, the IBS 15 is maintained at atmospheric pressure, and the IS 13 is maintained at about -530 mbar in a vacuum state for about 30 minutes, and then stabilized for about 1 hour and at about 5 hours. The pressure change of the IS 13 is monitored at a predetermined time.

In addition, the actual test 40 maintains the IBS 15 at atmospheric pressure and the IAS 13 at about -530 mbar in a vacuum state for about 30 minutes, and then stabilizes for about 1 hour and at a constant time at about 12 hours. The pressure change of the IS 13 is monitored.

When the test is complete, nitrogen is injected into the cargo hold and restored to atmospheric pressure.

On the other hand, if the pressure change rate of the IS 13 is large as a result of the monitoring, it can be determined that the secondary barrier 12 is defective, that is, the pressure change rate of the IS 13 is used as a criterion for monitoring. If the rate of change of pressure is larger than the reference value, it is determined that the secondary barrier 12 is defective, and if it is lower than that, the secondary barrier 12 is determined to be sound.

In addition, there is a gas reaction leakage test using ammonia as a primary barrier test.

In the gas reaction leak test on the primary barrier, ammonia gas is injected into the vacuum IBS (shown in Fig. 1), and the reaction paint is applied to the welded portion of the primary barrier (shown in Fig. 14). do. Therefore, in the defective welding part, the leaked ammonia and the paint react with each other to identify the leaking part through the reaction of the discolored paint.

However, the secondary barrier 12 of the insulation panel made of adhesive has a disadvantage in that the thin film structure becomes weak due to the cryogenic liquid as the use time passes, and the primary barrier 14 is made of Invar steel and nickel. In the case of alloy) steel, the thin film thickness always involves the risk of destruction due to the flow of liquid during operation. Moreover, the SBTT (Secondary Barrier Tightness Test) and the ammonia test method for checking the confidentiality of the primary and secondary barriers have problems of not finding a weak point because of the confidentiality based on the overall allowable range.

Therefore, due to these problems, membrane-type storage containers of relatively thick metal materials have been developed in recent years for both primary and secondary barriers. However, since there is no airtight inspection method for cargo holds in which primary and secondary barriers are metal, a new airtight method considering the reliability and economy is urgently needed.

In the present invention, it is possible to determine the presence or absence of defects in the primary and secondary barriers through the pressure test and the stress test and the gas reaction leakage test, which are repeatedly performed during or after the construction of the primary and secondary barriers. It is an object of the present invention to provide a method of airtight inspection of cargo holds which is capable of knowing the extent of area and size.

In order to achieve the above object, the present invention, in the airtight inspection method of the cargo hold, the step of sequentially inspecting the welding portion that proceeds at the same time as the start of construction of the secondary barrier, and the inspection completion site of the construction site of the secondary barrier primary Visually inspecting the primary barrier at the same time as the construction of the barrier proceeds, and performing the first pressure differential inspection after the completion of the construction and inspection of the secondary barrier, and the primary barrier and the completion of the construction of the primary barrier. By maintaining a positive pressure in the primary space between the secondary barriers to generate a stress on the welded portion of the primary barrier, the stress test is carried out to expose the defects, and the moisture in the primary space after the stress test is carried out. Removing and conducting a gas reaction leak test, and maintaining the secondary space between the primary space and the secondary barrier and the hull in a vacuum state to determine whether the primary barrier is defective. Provides an airtight test in the cargo hold comprises inspected.

As described above, according to the airtight inspection method of the cargo hold made of metal material in both the primary and secondary barriers, the pressure difference test and the stress test and the gas reaction leakage test are repeatedly performed during or after completion of the construction of the primary and secondary barriers. Through this, it is possible to determine whether the defects of the primary and secondary barriers are more reliable, and the degree of the defect occurrence region and the size thereof can be known. Moreover, when the secondary barrier construction is completed, the primary barrier construction is immediately performed, and at the same time, the inspection of the secondary barrier can be performed, so that the inspection time can be greatly shortened.

Hereinafter, the operating principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, when it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be made based on the contents throughout the specification.

3 is a configuration diagram for performing the airtight inspection method of the cargo hold in accordance with an embodiment of the present invention, Figure 4 is a flow chart of the airtight inspection method of the cargo hold according to an embodiment of the present invention.

The cargo hold 100 shown in FIG. 3 includes a secondary barrier 120 made of metal that is fixedly installed by a stud bolt (not shown) inside the hull 110, and a spacer (above) of the secondary barrier 120. It is composed of a primary barrier 130 in the form of a corrugation membrane that is supported by the (not shown). Here, by installing the secondary barrier 120 and the primary barrier 130, a secondary space 150 is formed between the hull 110 and the secondary barrier 120, and the secondary barrier 120 and 1 The primary space 140 is formed between the vehicle barriers 130.

In addition, an injection tube (not shown) installed in a liquid dome (not shown) or a gas dome (not shown) to supply nitrogen gas to the secondary space 150 and to inject a reaction gas into the primary space 140 according to the present invention. 164 is used, it is preferable that the injection pipe 164 is provided with a flow meter 162 that can check the injection amount of the gas and the gas supply unit 160 at the rear end.

In addition, the pressure gauge 170 is installed to check the pressure of the primary space 140 and the secondary space 150, and for making the interior of the primary space 140 and the secondary space 150 into a vacuum state. The vacuum pump 180 is connected to the primary space outlet 182 and the secondary space outlet 184.

Referring to the airtight inspection method of the cargo hold in accordance with an embodiment of the present invention configured as described above are as follows.

As shown in FIG. 4, a step (S1) of sequentially inspecting welds that proceed simultaneously with the start of construction of the secondary barrier (S1), and the construction of the primary barrier at the same time as the completion of the inspection of the construction of the secondary barrier are simultaneously performed. Visually inspecting the primary barrier being advanced and constructed (S2), and performing the first pressure difference inspection after the completion of the construction and inspection of the secondary barrier (S3), and the primary barrier after the completion of the construction of the primary barrier Maintaining a positive pressure in the primary space between the secondary barrier and the secondary barrier to generate a stress on the welded portion of the primary barrier so as to expose the defect site (S4), and the primary space after the stress test. Removing water and conducting a gas reaction leak test (S5) and maintaining a secondary space between the primary space and the secondary barrier and the hull in a vacuum state so that the primary barrier can be checked for defects. Performing the second pressure difference inspection (S6) It includes.

Here, in the step (S1) of sequentially inspecting the weld portion that proceeds simultaneously with the start of construction of the secondary barrier 120, the inspection of the weld portion is made through visual inspection and liquid penetrant examination.

For reference, the liquid penetrant inspection test applies a penetration solution to the welded area, and after a certain time, wipes and removes the applied penetration solution, and then applies a reaction material to the welded area. It penetrates and reacts to the reactants to determine whether it is defective.

In addition, the primary barrier 130 proceeds simultaneously to improve productivity to the site where the inspection is completed by visual inspection or liquid penetrant examination of the construction of the secondary barrier 120, and the primary barrier 130 is constructed. Is first visually inspected (step S2).

Next, when the inspection of the visual and liquid penetration test in accordance with the construction order of the secondary barrier 120 is completed, the first pressure difference inspection is performed on the constructed secondary barrier 120. (Step S3)

In the first pressure test, after the pressure in the secondary space is reached in a vacuum state of -100 mbar to -1000 mbarg, the pressure is stabilized between 1 hour and 2 hours and the pressure changes every 1 hour to 48 hours. Will be monitored.

At this time, the pressure increase rate obtained in the first pressure difference test is used as a reference value of the airtightness test of the secondary barrier 120 in the future.

That is, if the pressure increase rate obtained in the first pressure difference test is similar to the value obtained in the pressure difference test in the pressure difference test performed to determine whether the secondary barrier 120 leaks after a certain time of use of the cargo hold. It becomes the reference value which judges that confidentiality is maintained.

The first pressure difference inspection on the secondary barrier 120 is repeatedly performed until the construction of the primary barrier 130 is completed, thereby determining whether the secondary barrier 120 is damaged due to the construction of the primary barrier 130. You can check. Here, when the secondary barrier 120 is damaged by external factors during construction of the primary barrier 130, the pressure increase rate is increased according to the first pressure difference test, and thus whether the secondary barrier 120 is damaged by each part is known. It becomes possible.

In addition, after closing all the gas inlets and outlets so that the secondary space 150 is maintained in a vacuum state during the first pressure difference inspection, the pressure rise rate is obtained by obtaining a pressure rise value over time.

Next, when the construction of the primary barrier 130 is completed along with the construction of the secondary barrier 120, the positive pressure is maintained in the primary space 140 to generate stress on the welded portion of the primary barrier 130. A stress test is performed to expose the leaked part not found by the test (step S4).

The stress test on the primary barrier 130 preferably maintains the pressure in the primary space approximately 30 minutes to 5 hours under pressure of 5 mbar to 50 mbarg, then stabilizes the pressure between 10 minutes and 2 hours and then back to atmospheric pressure. By reducing the state, the stress change is monitored and repeated several times.

After the stress test, a gas reaction leakage test is performed (step S5).

For the gas reaction leakage test, first of all, the welding is not performed on a part of the primary barrier 140 to check whether the reaction gas is well filled in the construction of the primary barrier 130. Pipes (not shown) may be temporarily installed at the site, and the presence of the reaction gas may be confirmed through the pipe where the welding is not performed, that is, the installed pipe. At this time, the inlet of the pipe is a blocking means (not shown) is installed so as not to leak the reaction gas and at the same time can be checked whether the appropriate concentration is filled through a separate gas reaction device not shown.

In the step S5 of performing a gas reaction leak test, the first and second spaces 140 and 150 are repeatedly performed to be in a vacuum and atmospheric pressure state through the vacuum pump 180, and the gas supply unit 160 is injected. Nitrogen air is injected into the primary space 140 through the pipe 164 to remove moisture, and finally, through the gas supply unit 160 while the primary and secondary spaces 140 and 150 are in a vacuum state. The reaction space of helium or ammonia is injected into the secondary space 140, and nitrogen gas is injected into the secondary space 150, so that the gas reaction leakage test is performed while the positive pressure of the primary space 140 and the secondary space 150 is maintained. Is carried out.

Therefore, when the gas reaction leakage test is completed, the primary space 140 and the secondary space 150 are repeatedly performed to be in a vacuum and atmospheric pressure state by the vacuum pump 180, and the primary space 140 using nitrogen air. Reaction gas filled in the) is discharged to the primary space outlet 182. In addition, nitrogen gas may be present in the secondary space 150 without being discharged.

After the gas reaction leakage test is completed, the second pressure difference test is performed, and the second pressure difference test is performed after the re-welding of the unwelded portion and the found joint of the primary barrier 130 is performed. And the second pressure difference inspection is performed in real time until the end of the removal of the scaffold installed for the construction of the primary and secondary barriers 120 and 130 in the state where the secondary space 150 is maintained in a vacuum.

Through the second pressure test, it is finally confirmed whether there is a defect for each part of the primary barrier 130. (Step S6)

The conditions of the second pressure differential test preferably stabilize the pressure between 10 minutes and 2 hours after reaching the pressure of about -100 mbarg to -1000 mbarg, and change the pressure change every 1 hour to 48 hours. Will be monitored.

Therefore, in the present invention, the reliability of the airtightness of the primary and secondary barriers can be improved through the primary and secondary pressure difference test, the stress test and the gas reaction leakage test, and the secondary barrier through the pressure difference test on the secondary space after a certain period of use. It is possible to check periodically whether there is a leak and to check the leakage of the primary barrier through the pressure difference test on the secondary and primary spaces, and to reduce the inspection time.

What has been described above is just one preferred embodiment of the airtight inspection method of the cargo hold according to the present invention, the present invention is not limited to the above-described embodiment, the subject matter of the present invention as claimed in the following claims Without departing from the technical spirit of the present invention to the extent that any person of ordinary skill in the art to which the present invention pertains various modifications can be made.

1 is a cross-sectional view schematically showing the cargo hold structure of the LNG carrier according to the prior art,

2 is a flowchart of a method for checking whether a cargo hold is leaked according to the prior art;

3 is a block diagram for carrying out a method for checking the airtightness of the cargo hold in accordance with an embodiment of the present invention,

Figure 4 is a flow chart of the airtight inspection method of the cargo hold in accordance with an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: cargo hold 110: hull

120: secondary barrier 130: primary barrier

140: primary space 150: secondary space

160: gas supply unit 162: flow meter

164: injection tube 170: pressure gauge

180: vacuum pump 182: primary space outlet

184: secondary space outlet

Claims (9)

In the airtight inspection method of the cargo hold, Inspecting the welds that proceed simultaneously with the start of construction of the secondary barrier, A step of visually inspecting the primary barrier, in which construction of the primary barrier proceeds at the same time as the completion of the inspection, among the construction sites of the secondary barrier; Performing a first pressure difference inspection after completion of construction and inspection of the secondary barrier; After completion of the construction of the primary barrier by maintaining a positive pressure in the primary space between the primary barrier and the secondary barrier to generate a stress on the welded portion of the primary barrier, a stress test to expose the defect site Performing steps, Removing the moisture in the primary space after the stress test and conducting a gas reaction leakage test; Conducting a second pressure difference inspection to maintain the secondary space between the primary space and the secondary barrier and the hull in a vacuum state so as to determine whether the primary barrier is defective; Airtight inspection method of cargo hold comprising a. The method of claim 1, In the step of sequentially inspecting the welded portion that proceeds at the same time as the start of construction of the secondary barrier, Inspection of the weld portion is a cargo inspection method of the cargo hold made through visual inspection and liquid penetrant examination. The method of claim 1, In the step of performing the first pressure difference inspection, The pressure increase rate obtained in the first fork pressure inspection is the airtight inspection method of the cargo hold used as a reference value of the airtightness test of the secondary barrier in the future. The method of claim 1, In the step of performing the first pressure difference inspection, The first pressure inspection on the secondary barrier is repeatedly performed until the construction of the primary barrier is completed, so that the secondary barrier can be checked whether or not the secondary barrier is damaged due to the construction of the primary barrier. Method of inspection of cargo hold. The method of claim 1, In the step of performing the gas reaction leakage test, In order to check whether the reaction gas is filled in the primary space during the construction of the primary barrier for the gas reaction leakage inspection, welding is not performed on a portion of the reaction chamber. Airtightness inspection method of cargo hold to check existence. The method of claim 1, In the step of performing the gas reaction leakage test, The primary and secondary spaces are repeatedly subjected to vacuum and atmospheric pressure, nitrogen air is injected to remove moisture, and the reaction gas is injected into the primary space of the vacuum and nitrogen gas is injected into the secondary space of the vacuum to provide positive pressure. Airtight inspection method of the cargo hold in which the gas reaction leakage test is carried out in this state. The method according to claim 5 or 6, The reaction gas is a gas tight inspection method of the cargo hold is used helium or ammonia. The method of claim 1, After performing the gas reaction leakage test, And repeatedly conducting the primary and secondary spaces in a vacuum and atmospheric pressure state, and discharging the reaction gas filled in the primary space using nitrogen air. The method of claim 1, In the step of performing the second pressure difference inspection, After the re-welding of the unwelded portion and the found defect portion of the primary barrier is performed, the removal operation of the scaffold installed for the construction of the primary and secondary barriers is completed while the primary and secondary spaces are kept in vacuum. Airtight inspection method of the cargo hold is carried out in real time until the second forklift inspection.

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