KR101022860B1 - Tightness Testing Method for LNG Cargo Tank of GTT NO96 Membrane Type - Google Patents

Abstract

The present invention relates to a gas tightness inspection method required in the manufacturing step of the GTT NO96 membrane type LNG carrier cargo tank, by improving the existing LNG tank cargo tank leakage inspection process, if the overall inspection process time is shortened without impairing the existing inspection quality It also suggests ways to ensure that confidentiality checks are completed more quickly and systematically and accurately.

Leak test, Helium leak test, Fabrication test, LNG carrier, Insulation film

Description

Tightness Testing Method for LNG Cargo Tank of GTT NO96 Membrane Type

The present invention relates to a gas tightness inspection method required in the manufacturing step of the GTT NO96 membrane type LNG carrier cargo tank.

LNG carriers have a Moss type and a Membrane type depending on the type of tank (hereinafter referred to as 'cargo tank') that stores LNG (liquefied natural gas).

The Mohs type is made of thick aluminum with a round ball shape tank of about 40 meters in diameter and installed on the ship. In contrast, the membrane type does not make a separate tank, but rather constitutes a cargo tank inside the hull, insulates the outer surface of the cargo tank using insulation, and attaches a special metal plate to the insulating surface.

At this time, the membrane type has different insulation materials and structures depending on the type of special metal plate, and GTT NO96 using a thin plate made of Invar (Invar-alloy having a very small thermal expansion coefficient mainly composed of iron and nickel, hereinafter referred to as 'Invar'). It is divided into membrane type and MARK III membrane type using stainless steel sheet.

Cargo tanks are made of special materials such as aluminum, invar, stainless steel, etc., which are stored in cargo tanks in the form of cryogenic liquids due to the characteristics of LNG, and are used in cargo tank structures that are cooled to cryogenic temperatures due to sloshing. Repeatedly generates shock and fatigue stress, so that the cargo tank's structure is low temperature embrittlement and fatigue cracks, and there is a risk of causing a large accident due to the leakage of LNG, which is resistant to low temperature embrittlement at low temperatures and repeated fatigue It is made of a material resistant to stress.

LNG Cargo Tank is like [Figure 1] A cargo tank outer wall 50 is formed and formed as two insulation zones with a primary insulation film 20 and a secondary insulation film 30 therein, and each insulation zone has a structure in which insulation material 40 is included. have. Here, the insulation film (Membrane) is manufactured by assembling and welding a thin plate of Invar material.

The heat insulating material 40 is fabricated by manufacturing a certain size of glass fiber, perlite, urethane foam, etc., the cargo tank outer wall 50, the secondary heat insulating film 30, the secondary heat insulating film 30 and the primary heat insulating film ( 20) It serves to insulate between.

LNG carrier cargo tank to be inspected in the technical field of the present invention is characterized by the storage and transport of ultra-low temperature LNG of 162 ˚C liquefied by compressing high pressure in accordance with the change of cargo tank pressure according to the storage and unloading LNG Subject to structural stresses such as compression and expansion. LNG ship is a ship that carries LNG while operating in a rough ocean. LNG is transported in liquid state inside LNG cargo tank, and accordingly, sloshing is caused by the flow of liquid in LNG cargo tank. The fatigue is accumulated by applying an impact to the insulating film.

As a result, when the primary and secondary insulation structures are damaged or leakage occurs in the primary insulation film 20 and the secondary insulation film 30, vaporized LNG may be introduced into the insulation material and thus may be exploded.

This requires a long repair period, resulting in the cost of repairs and the financial burden of delaying ship operation (presumably hundreds of millions of losses per day of flight failure). For this reason, confidentiality inspection of LNG carrier cargo tanks is essential.

LNG tanker cargo tank inspection includes the Strength Test, Bearing Test, Mechanical Stressing Test, Helium Leak Test, and Global Test. Each test procedure is described as follows.

(a) Strength Test (hereinafter referred to as "Strength Test")

Visual inspection of the secondary or primary insulation membranes is carried out inside the LNG Cargo Tank with vacuum (approximately -800 mbar) formed using a leak tester (pressure adjustment and monitoring device) for the insulation area. The purpose of this step is to check the installation of cargo tank structure by giving the pressure load that the sloshing shock that occurs while storing and transporting liquid LNG inside cargo tank of LNG carrier affects the insulation structure. .

When carrying out the vacuum forming and pressurization of the insulation zone during the inspection stage after the primary insulation film is installed during the cargo tank production inspection, the pressure in the secondary insulation zone must be kept equal to or lower than that of the primary insulation zone. The reason is that when the pressure of the secondary insulation zone is greater than the pressure of the primary insulation zone, structural deformation of the insulation 40 and the secondary and primary insulation films 30 and 20 can be caused.

(b) Bearing Test (hereinafter referred to as Bearing Test)

Visual inspection is to be carried out with a vacuum of approximately -200 mbar in the adiabatic zone. The purpose of this step is to check whether the insulation film installed on the insulation is installed in accordance with the prescribed regulations and whether foreign matter is inserted.

If the strength test or bearing test finds any part of the insulation or membrane to be repaired, the repair should be performed after reducing the pressure in the short-range zone to atmospheric pressure.

(c) Mechanical Stressing Test (hereinafter referred to as `` mechanical stress test '')

The insulation area is injected (pressurized) from atmospheric pressure to +20 mbar using a leak tester (pressure adjustment and monitoring device), maintained for a specified time, and then reduced to + atmospheric pressure at +20 mbar three times. The purpose of this step is to accumulate fatigue stress in the vulnerable welds that were not found during the installation of the thermal insulation film so that the vulnerable parts are damaged in advance and protrude.

(d) Helium Leak Test (hereinafter referred to as `` Helium Leak Test '')

After forming a vacuum up to about -600 mbar in the adiabatic zone, the helium gas is injected (pressurized) to +20 mbar using the cargo tank internal helium gas injection line 10 as shown in FIG. 10%), the helium leakage test is carried out using a helium leak detector and a leak detector (Auto Carriage) on the welded part of the insulation film and the seals associated with the insulation area.

The secondary insulation leak tightness test is performed by 100% helium leak test on the welded part, and the primary insulation film helium leak test is performed by 200% test, ie, twice helium leak test.

(e) Global Test (hereinafter referred to as 'Global Test')

After the helium leak test, a global test, a field of pressure change testing, is conducted to verify the overall tightness of the insulation.

Temperature sensors are installed inside and outside of the cargo tank and connected to the leak tester (pressure adjustment and monitoring device) .Then, vacuum is built up to about -800 mbar in the insulated area, and the gas flow and the uniform pressure inside the insulated area are maintained. In order to have a stabilization time of about 12 hours. After that, the pressure in the insulation zone and the atmosphere and the temperature inside and outside the cargo tank are monitored for about 24 hours.

Analyze the monitored pressure and temperature values to verify that the pressure change values meet the specified limits. If the specified value is exceeded, identify the cause and take corrective action, then re-run the global test. The limits of the specified pressure change value shall satisfy the following formula for the pressure change value for the 10-hour period during which the temperature value is stable among the measured 24 hours.

△ P (allowable pressure change value, mbar) ≤ 0.8 (constant) / insulation thickness (meter)

* Insulation thickness in secondary insulation zone = 0.30 meter

* Insulation thickness in primary insulation zone = 0.27 meter

The airtight inspection step of LNG carrier cargo tank is mainly the airtightness inspection step after the installation of the second insulation film, the airtightness inspection step after the installation of the first insulation film, the liquidity inspection step of the liquid dome connecting the upper part of the pump tower and the cargo tank. Airtight inspection after sealing the part of the temporary access opening for the input of materials into the cargo tank. Here, the pump tower is installed inside the cargo tank as shown in FIG. 9 and is connected to the LNG carrier pipeline outside the tank to serve as storage and unloading of LNG, and a pump is installed at the bottom thereof.

In the secondary insulation film airtight inspection step, the outer wall 50 of the LNG cargo tank is manufactured as shown in FIG. 2, and the secondary insulation film 30 is assembled and welded after constructing the insulation 40 around the inner wall of the outer wall 50. Carry-on tanks are to be carried out according to the specified inspection procedures for cargo tanks. At this time, the section between the cargo tank outer wall 50 and the secondary insulation film 30 is called a secondary insulation zone.

When it is verified that there is no leakage in the secondary insulation zone, the insulation material 40 is reconstructed on the secondary insulation film 30, the primary insulation film 20 is assembled and welded, and then the primary insulation is made according to the determined cargo tank manufacturing inspection order. Membrane leak test steps are performed. At this time, the section between the secondary insulation film 30 and the primary insulation film 20 is called a primary insulation zone.

If the primary insulation zone is verified to be free of leaks, a leak test of the liquid dome that connects the top of the pump tower to the cargo tank and a leak test of the temporary entrance to the material into the cargo tank are carried out.

In the conventional case, the secondary insulation sealing step is “strength test (S10) → bearing test (S20) → defect repair (S30) → corrector bearing test (S25) → mechanical stressing test (S40) → helium gas injection ( S55) → helium leak test (S50) → leak repair (S65) → leak repair (S60) → helium inlet and concentration test (S70) → global test (S80).

6 is a flow chart of the inspection process of the conventional (before improvement) secondary insulation film airtight inspection step. In this flowchart, the scale on the horizontal axis is the number of days required for the inspection, and the vertical axis is the pressure value in the short-range zone.

In the conventional case, the secondary insulating film leak-tightness step is performed to form a vacuum (about -200 mbar) for the correction bearing test (S25) after the defect repair (S30) and dry to atmospheric pressure for the mechanical stress test (S40). Pressure operation process for injecting air or nitrogen is continuously performed (defect repair (S30) → correction bearing test (S25) → mechanical stressing test (S40)). The work takes time. In addition, in the conventional secondary insulation film hermetic inspection step, the process of pressurizing again after vacuum formation has been repeated many times throughout the operation.

Therefore, in this case, the procedure to be performed in the vacuum forming process (for example, the water bearing bearing test (S25), the global test (S80)) and the pressurization process (for example For example, if the mechanical stressing test (S40), helium leak test (S50)) can be proceeded together without being separated separately from each other to proceed continuously, the process of pressurizing again after the vacuum is formed. You will be able to reduce waste.

And, in the conventional case, the primary insulation film airtight inspection step is "strength test (S10) → bearing test (S20) → defect repair (S30) → corrector bearing test (S25) → mechanical stressing test (S40) → helium gas Injection (S55) → Helium leak test (S50) → Leakage repair (S65) → Secondary helium leak test (S58) → Helium inlet and concentration test (S70) → Global test (S80) ” lost.

7 shows an inspection process flow chart of the conventional (prior to improvement) primary insulation film hermetic inspection step. In this flowchart, the scale on the horizontal axis is the number of days required for the inspection, and the vertical axis is the pressure value in the short-range zone.

In the conventional case, the first insulation seal test step is performed to form a vacuum (about -200 mbar) for the correction bearing test (S25) after the defect repair (S30) and dry to atmospheric pressure for the mechanical stress test (S40). Pressure operation process for injecting air or nitrogen is continuously performed (defect repair (S30) → correction bearing test (S25) → mechanical stressing test (S40)). The work takes time.

In addition, after performing a helium leak test (S50) and immediately before performing a second helium leak test (S58), a leak repair (S65) procedure must be performed (helium leak test (S50) → leak repair (S65) → secondary helium). Leak test (S58)), such as after the pressurized discharge and the process of repeating the press again takes a considerable time. In addition, in the conventional primary insulation film hermetic inspection step, the process of pressurizing again after vacuum formation (discharge) is repeated many times throughout the operation.

Therefore, in this case, the procedures to be performed in the vacuum formation (emission) process in performing the primary insulation film tightness inspection step (for example, the correction bearing test (S25), the strength test (S10), the global test (S80)) and If the procedure to be performed in the pressurization process (for example, helium leak test (S50), secondary helium leak test (S58)) can be carried out together in succession instead of separately and separately, pressurizing again after vacuum formation This can reduce the waste of work time as the process is repeated.

On the other hand, since the heat insulating material 40 of the primary heat insulating zone is adhered to the secondary heat insulating film 30 without adhesive, it is attached and adhered to the outer wall 50 using the resin (adhesive) as in the second heat insulating zone. Compared to the method to be attached to), even if the strength of the stress test (S10) and the bearing test (S20) is significantly less and diarrhea occurs, only a simple welding repair occurs.

Therefore, unlike the case of the secondary insulation film hermetic inspection step, the first insulation film hermetic inspection step is less necessary to perform the strength test (S10) in advance at the beginning of the inspection, and separately to perform the defect repair (S30) procedure The efficiency is quite low. Therefore, in this case, the defect repair (S30) procedure may be omitted, and the strength test (S10) procedure may be placed later in the inspection, thereby reducing overall work time and increasing efficiency.

And, in the case of the conventional liquid dome airtight inspection step is "bearing test (S20) → defect repair (S30) → correction bearing test (S25) → helium leakage test (S50) → leak repair (S65) → leak repair inspection (S60) → helium inlet welding (S73) → helium inlet bearing test (S76) ”.

8 is a flow chart of the inspection process of the conventional (before improvement) liquid dome airtight inspection step. In this flowchart, the scale on the horizontal axis is the number of days required for the inspection, and the vertical axis is the pressure value in the short-range zone.

In the conventional liquid dome inspection step, the process of forming a vacuum (about -200 mbar) for the bearing test (S20) and reducing the pressure to atmospheric pressure for the defect repair (S30) and the correction bearing test (S25) The process of forming vacuum again (about-200 mbar) and reducing the pressure back to atmospheric pressure for helium leak test (S50) is carried out continuously (bearing test (S20) → defect repair (S30) → correction) Bearing test (S25) → helium leak test (S50)), it takes a considerable time to repeat the process of pressing again (reduction to atmospheric pressure) after vacuum formation.

Therefore, in this case, in performing the liquid dome leak test step, the procedures to be performed in the vacuum forming process (for example, the bearing test (S20) and the helium inlet bearing test (S76)) are separated from each other without being separately separated. If it can be carried out continuously, it is possible to reduce the waste of working time as the process of repeated pressurization (reduction to atmospheric pressure) after the vacuum is formed.

On the other hand, since the liquid dome is a liquid dome insulating material consisting of a single insulating material independent of the primary and secondary insulating material 40 is attached by a fixing piece installed on the outer wall 50, the bearing test (S20) defects significantly less Even if it occurs, even if a defect occurs, the defect is enough to perform a simple welding repair.

Therefore, in the liquid dome leak test step, the need to perform a bearing test (S20) in advance at the beginning of the inspection is reduced, and separately performing a defect repair (S30) and corrector bearing test (S25) procedure is also very low efficiency. Therefore, in this case, by eliminating the defect repair (S30) and correction bearing test (S25) procedure and placing the bearing test (S20) procedure later in the inspection, it is possible to reduce the overall work time and increase efficiency.

As mentioned above, since the production inspection of each of the airtight inspection stages must be carried out in the LNG carrier cargo tank manufacturing process, it is necessary to improve the airtight inspection stage and production inspection procedures to cope with the faster manufacturing process on site.

The present invention has been proposed to solve the above problems, by improving the existing LNG tank cargo tank airtight inspection process to reduce the overall inspection process time and faster and systematically without compromising the existing inspection quality Its purpose is to provide a way to accurately complete a confidentiality test.

Other objects and advantages of the present invention will be described below, which are not limited to the matters set forth in the claims and the disclosure of the embodiments thereof, but also to the broader ranges by means and combinations within the range readily recited therefrom. Add that it will be included.

In order to achieve the above object, the present invention, the strength test (S10), bearing test (S20), defect repair (S30), helium gas injection (S55), mechanical stressing test (S40), helium leakage test (S50) Secondary insulation film airtight inspection step consisting of, in the order of the leak repair (S65), leak repair (S60), helium concentration test (S75), corrector bearing test (S25), global test (S80); Mechanical stressing test (S40), bearing test (S20), helium gas injection (S55), helium leak test (S50), secondary helium leak test (S58), leak repair (S65), leak repair test (S60) ), Helium concentration measurement test (S75), the correction bearing test (S25), the strength test (S10), the global heat test (S80) in the order of the first insulation film hermetic inspection step. And liquid dome in the order of helium leak test (S50), leak repair (S65), leak repair (S60), helium inlet welding (S73), bearing test (S20), helium inlet bearing test (S76). We present a method for leaktightness of GTT NO96 membrane type LNG Cargo Tank including leaktightness step.

The present invention improves the LNG cargo cargo tank confidentiality inspection process to shorten the overall inspection process time to be able to complete the confidentiality inspection in a quick and systematic manner without compromising the existing inspection quality.

The effect of shortening the inspection process is briefly described as follows. When inspecting one LNG carrier with four cargo tanks, approximately 20 inspectors are involved. If you shorten 1 day in the secondary insulation leak tightness step, 1.5 days in the primary insulation leak tightness step and 1 day in the Liquid Dome leak tightness test step, the total inspection process of 3.5 days will be shortened.

Arithmetic indications: (1) Shortening effect for one LNG carrier = 20 inspectors × 3.5 days × 4 cargo tanks = 280 persons / day, (2) Shortened amount for one LNG carrier = 280 persons / Day x 200,000 won / person / day = 56,000,000 won. As such, when the confidentiality inspection of one LNG carrier, the financial shortening effect of about KRW 56 million can be obtained, and the labor force of the shipyard used when manufacturing the LNG carrier is incomparably large, so the effect can be sufficiently estimated.

Other effects of the present invention, as well as those described in the above-described embodiments and claims of the present invention, as well as potential effects that may occur within the range that can be easily estimated therefrom and potential advantages that contribute to industrial development It will be added that it will be covered by a wider scope.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible, even if shown on different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the following will describe a preferred embodiment of the present invention, but the technical idea of the present invention is not limited thereto and may be variously modified and modified by those skilled in the art.

The present invention relates to a gas tightness inspection method required in the manufacturing step of the GTT NO96 membrane type LNG carrier cargo tank, by improving the existing LNG tank cargo tank leakage inspection process, if the overall inspection process time is shortened without impairing the existing inspection quality The present invention provides a method for completing the leak tightly and quickly and systematically and accurately. The present invention provides an improved secondary heat seal leak test step, a primary heat leak leak test step, and a liquid dome leak test step. It is made to include.

1. Secondary insulation film hermetic inspection according to the present invention

6 is a flow chart of the inspection process of the secondary insulation film airtight inspection step according to the present invention (after improvement). In this flowchart, the scale on the horizontal axis is the number of days required for the inspection, and the vertical axis is the pressure value in the short-range zone.

Secondary insulation film sealing step according to the present invention is "strength test (S10) → bearing test (S20) → defect repair (S30) → helium gas injection (S55) → mechanical stressing test (S40) → helium leakage test ( S50) → leak repair (S65) → leak repair (S60) → helium concentration test (S75) → correction bearing test (S25) → global test (S80) ”.

The secondary insulating film hermetic inspection step according to the present invention is to form a vacuum (about-200 mbar) for the correction bearing test (S25) after the defect repair (S30) in the conventional secondary insulation film hermetic inspection step (before improvement) The process and the pressure stress process for injecting dry air or nitrogen up to atmospheric pressure for mechanical stressing test (S40) have been improved continuously (by changing the work order), thereby eliminating the repetitive work process. It was shortened about 1 day.

That is, the present invention is a mechanical stressing test (S40) which is a procedure to be performed in the pressurization process and the correction bearing test (S25) and the global test (S80), which is a procedure to be performed in the vacuum forming process in performing the secondary insulation film tightness inspection. ) And helium leakage test (S50) is to reduce the waste of work time caused by repeated pressurization process after vacuum formation by allowing each one to proceed in succession instead of separately apart.

To this end, the secondary insulation film hermetic inspection step according to the present invention introduces a method of changing the operation time of some procedures differently from the conventional, specifically, for the defects of the strength test (S10) and the bearing test (S20) After the maintenance (S30), the bearing test (S25) for the correction part is performed just before the global test (S80) at about -800bmar vacuum state, and the helium gas injection (S55) immediately before the mechanical stress test (S40). Will be implemented.

On the other hand, in the secondary insulation film hermetic inspection step according to the present invention when the helium gas injection [Fig. 3] without using a helium gas injection line installed inside the cargo tank as shown in Figure 4 to form a vacuum inside the thermal insulation zone In order to inject dry air, gas pipes are used for nitrogen inspection of LNG carriers and airtight inspections installed on exhaust lines. As a result, it is possible to further shorten the time required for the process of welding and sealing the helium gas inlet 13 after the completion of the helium leakage inspection and the inspection process for the welded portion.

2. Primary insulation film hermetic inspection according to the present invention

At the bottom of FIG. 7 is a flow chart of the inspection process of the primary insulation film hermetic inspection step according to the present invention (after improvement). In this flowchart, the scale on the horizontal axis is the number of days required for the inspection, and the vertical axis is the pressure value in the short-range zone.

The primary insulation film leak test step according to the present invention is "mechanical stress test (S40) → bearing test (S20) → helium leak test (S50) → secondary helium leak test (S58) → leak repair (S65) → Leak repair department inspection (S60) → helium concentration test (S75) → hydraulic bearing test (S25) → strength test (S10) → global test (S80) ”.

The primary insulating film hermetic inspection step according to the present invention is to form a vacuum (about-200 mbar) for the correction bearing test (S25) after the defect repair (S30) in the conventional primary insulation film hermetic inspection step (before improvement) Improved the process and pressure operation process for injecting dry air or nitrogen to atmospheric pressure for the mechanical stress test (S40) continuously (change work order), while the second helium after the helium leak test (S50) By improving the flow of the leak repair (S65) immediately before performing the leak test (S58) (by changing the work order), the entire process of leak testing was shortened by about 1.5 days.

That is, the present invention should be made in the pressurization process with the correction bearing test (S25), the strength test (S10) and the global test (S80), which is a procedure to be performed in the vacuum formation (discharge) process in performing the primary insulation film tightness inspection. The helium leakage test (S50) and the secondary helium leak test (S58), which are to be performed separately, do not proceed separately, but can be carried out together in a continuous manner. It is reducing waste of work time.

To this end, in the first insulation film hermetic inspection step according to the present invention, when the strength test (S10), the correction bearing test (S25), the helium leak test (S50) and the second helium leak test (S58) It introduces a different change method.

Specifically, by conducting the strength test (S10) immediately before the global test (S80), the process of forming a vacuum to -800 mbar and injecting dry air and nitrogen gas is shortened. The test (S25) is performed after the helium leak test is completed to shorten the process of forming a vacuum to -200 mbar and injecting dry air and nitrogen gas again, and repairing the leaking part found in the helium leak test (S50). By performing the second helium leak test (S58) on the weld continuously without (S65), the pressure is reduced to atmospheric pressure for correction at + 20mb and the waiting time until the method of correcting the leak is determined by the supervisor such as the owner. It is shortening the process of injecting (pressurizing) the helium gas again for the second helium leak inspection (S58).

On the other hand, in the primary insulation film hermetic inspection step according to the present invention was improved by changing the order of the strength test (S10), unlike after the improvement of the secondary insulation film hermetic inspection step, this is the insulation material of the primary insulation zone (40) Since the adhesive is adhered to the secondary heat insulating film 30 without adhesive, it is attached to the outer wall 50 by using a resin (adhesive) as in the second heat insulating zone. S10) and bearing test (S20) Significantly less defects and even if a diarrhea defect occurs only a defect enough to perform a simple welding repair, the first insulation film airtight stage of the second insulation film airtight inspection stage Unlike the case, it is less necessary to perform the strength test (S10) in advance at the beginning of the inspection, and the separate defect repair (S30) procedure is also very low in efficiency. Therefore, to reduce the defect compensation (S30) is omitted and the procedure Strength testing (S10) the overall operation time of the waste by providing a procedure to check reviews with improved efficiency.

On the other hand, in the first insulation film airtight inspection step according to the present invention when the helium gas injection as shown in Figure 3 without using a helium gas injection line installed inside the cargo tank as shown in Figure 5 to form a vacuum inside the thermal insulation zone In order to inject dry air, gas pipes are used for nitrogen inspection of LNG carriers and airtight inspections installed on exhaust lines. As a result, it is possible to further shorten the time required for the process of welding and sealing the helium gas inlet 13 after the completion of the helium leakage inspection and the inspection process for the welded portion.

3. Liquid dome leak test according to the present invention

8 is a flow chart of the inspection process of the liquid dome airtight inspection step according to the present invention (after improvement). In this flowchart, the scale on the horizontal axis is the number of days required for the inspection, and the vertical axis is the pressure value in the short-range zone.

Liquid dome leak test step according to the present invention "Helium leak test (S50) → leak repair (S65) → leak repair (S60) → helium inlet welding (S73) → bearing test (S20) → helium inlet bearing test (S76) ”.

Liquid dome tightness inspection step according to the present invention is a process for forming a vacuum (about -200 mbar) for the bearing test (S20) in the conventional liquid dome tightness inspection step (before improvement) and pressure to atmospheric pressure for defect repair (S30) The process of reducing the pressure, forming the vacuum again for the correction bearing test (S25) (about -200 mbar), and reducing the pressure back to atmospheric pressure for the helium leak test (S50). By changing the work order, the repeated work process was eliminated to reduce the overall leak test process by about one day.

That is, in the present invention, the liquid test of the liquid dome may be carried out in a continuous manner without separately performing a bearing test (S20) and a helium inlet bearing test (S76), which are procedures to be performed in the vacuum forming process, separately from each other. By doing so, the process of pressurizing (reducing the pressure to atmospheric pressure) after vacuum formation is repeated, thereby reducing waste of work time.

To this end, the liquid dome airtight inspection step according to the present invention introduces a method for changing the timing of the bearing test (S20) and helium leakage test (S50) different from the conventional. Specifically, the helium leak test (S50) is carried out before the bearing test (S20), and the bearing test (S20) is carried out together with the helium inlet bearing test (S76) to form a vacuum to -200 mbar and reduce to atmospheric pressure. It is shortening the process.

Meanwhile, in the liquid dome airtight inspection step according to the present invention, unlike the conventional case, a defect repair (S30) and a correction bearing test (S25) procedure are omitted and a bearing test (S20) procedure is disposed at a later stage of inspection. Since the liquid insulator of the liquid dome is composed of one insulator independently of the primary and secondary insulators 40 and it is attached by a fixing piece installed on the outer wall 50, bearing defects (S20) are significantly less. This is because even if a defect occurs, it is enough to perform a simple welding repair.

The above description is merely illustrative of the technical idea of the present invention, and various modifications, changes, and substitutions may be made by those skilled in the art without departing from the essential characteristics of the present invention. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a cross-sectional view of the cargo tank insulation zone

2 Fig. 2 LNG Cargo Cargo Tank

[Figure 3] helium gas injection line inside the cargo tank before improvement

4 is the secondary insulation zone helium gas injection line after improvement

5 is the first insulation zone helium gas injection line after improvement

6 is a secondary insulation film airtight inspection step

7 is the primary insulation film airtight inspection step

[Figure 8] Liquid Dome leak test step

[Figure 9] LNG carrier cargo tank internal structure

<Description of Major Symbols in Drawing>

10: helium gas injection line P20: sealing plate

13: helium gas inlet P25: pump tower

15: ship outer wall P30: mastic

20: primary insulation film P35: liquid dome insulation film

30: secondary insulation film P40: vacuum pump

40: heat insulating material P50: helium gas

50: cargo tank outer wall P60: helium concentration measuring instrument

60: Ing-Zog P70: pressure measuring instrument

P10: Welding Line P80: Hose

P15: Sub Edition

Claims (3)

Strength test (S10), bearing test (S20), defect repair (S30), helium gas injection (S55), mechanical stress test (S40), helium leak test (S50), leak repair (S65), leak repair Secondary insulation film hermetic inspection step consisting of the inspection (S60), helium concentration measurement test (S75), corrector bearing test (S25), global test (S80) in order; Mechanical stressing test (S40), bearing test (S20), helium gas injection (S55), helium leak test (S50), secondary helium leak test (S58), leak repair (S65), leak repair test (S60) ), Helium concentration measurement test (S75), the correction bearing test (S25), the strength test (S10), the global heat test (S80) in the order of the first insulation film hermetic inspection step. And Liquid dome leak test in the order of helium leak test (S50), leak repair (S65), leak repair (S60), helium inlet welding (S73), bearing test (S20), helium inlet bearing test (S76) step Airtight inspection method of GTT NO96 membrane type LNG carrier cargo tank comprising a. The method of claim 1, In the second insulation leak tightness stage, A gas tightness inspection method for a GTT NO96 membrane type LNG tanker cargo tank, characterized in that helium gas is injected by using a gas pipe for the nitrogen injection of the LNG carrier and the gas tightness test installed in the exhaust line. The method of claim 1, In the first insulation leak tightness stage, A gas tightness inspection method for a GTT NO96 membrane type LNG tanker cargo tank, characterized in that helium gas is injected by using a gas pipe for the nitrogen injection of the LNG carrier and the gas tightness test installed in the exhaust line.

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