CN114729845A - LNG cargo tank testing method, marine structure applying LNG cargo tank testing method and liquid nitrogen supply system of marine structure - Google Patents

Abstract

The invention discloses an LNG cargo hold testing method, an ocean structure applying the method and a liquid nitrogen supply system of the ocean structure. The LNG cargo hold testing method designed by the embodiment of the invention comprises the following steps: after the LNG cargo hold of the FLNG is built, carrying out a first integrity test on a secondary screen wall of the LNG cargo hold; cooling the interior of the LNG cargo tank; and (c) performing a second integrity test on the secondary wall of the LNG cargo tank, the steps (a) through (c) being performed on the FLNG LNG cargo tank in a state where the FLNG is deployed onshore, and the step (b) being performed using any refrigerant other than LNG.

Description

LNG cargo tank testing method, marine structure applying LNG cargo tank testing method and liquid nitrogen supply system of marine structure

Technical Field

The invention relates to a LNG cargo hold testing method, an ocean structure applying the method and a liquid nitrogen supply system of the ocean structure.

Background

After the LNG cargo hold of the marine structure is built, a first integrity test of the secondary wall is performed onshore. Then, the marine structure moves to the Offshore location (offset), and LNG supplied from the LNG bunker or directly produced in the Offshore location is injected into the LNG cargo tank and subjected to cooling (Cool down) operation. After Cold Shock (Cold Shock) is generated by the cooling operation, a second integrity test is performed on the secondary wall of the LNG cargo tank.

Thus, after a first integrity test on the secondary wall on shore, the marine structure can only be moved offshore in order to perform a second integrity test on the secondary wall.

For example, FLNG (Floating Liquefied Natural Gas) which does not have self-propulsion capability in marine structures is difficult to receive LNG because it cannot be moved to an LNG port. Therefore, in a state where the FLNG is deployed in an offshore FLNG installation area, LNG is supplied by an LNG bunker or a method of direct production offshore.

However, the problem is that the approval process for the LNG cargo tank test operation after receiving LNG offshore is complicated and expensive. Furthermore, emergency situations offshore are difficult to deal with quickly.

In addition, for a ship with self-propulsion capability in a marine structure, after the first integrity test of the secondary barrier is completed, the ship leaves the shipbuilding factory under construction to drive into the LNG land terminal in order to receive the refrigerant LNG, and then the ship must return again in order to perform the LNG cargo tank test, which takes much time and is expensive.

Disclosure of Invention

The embodiment of the invention aims to provide an LNG cargo hold testing method, an ocean structure applying the method and a liquid nitrogen supply system of the ocean structure, and LNG cargo hold testing is carried out on the sea, so that the cost can be reduced, and the operation efficiency can be improved.

According to an aspect of the present invention, there is provided an LNG cargo tank test method including: after the LNG cargo hold of the FLNG is built, carrying out a first integrity test on a secondary screen wall of the LNG cargo hold; cooling the interior of the LNG cargo tank; and step (c) of performing a second integrity test on a secondary wall of the LNG cargo tank, wherein the steps (a) to (c) are performed on the LNG cargo tank of the FLNG in a state where the FLNG is deployed onshore, and the step (b) is performed using any one of refrigerants other than LNG.

According to another aspect of the present invention, there is provided an LNG cargo tank test method including: after an LNG cargo hold of a ship is built, carrying out a first integrity test on a secondary screen wall of the LNG cargo hold; after the step (b) is connected with the LNG cargo hold, performing a pipeline cold resistance test on a pipeline for executing LNG loading or unloading; cooling the interior of the LNG cargo tank; and (d) performing a second integrity test on a secondary wall of the LNG cargo tank, wherein the steps (a) to (d) are performed on the LNG cargo tank of the ship while the ship is docked on the shore, and the steps (b) and (c) are performed using liquid nitrogen.

The performing of the cooling operation may include spraying liquid nitrogen into the inside of the LNG cargo tank in a normal temperature state, and may also include controlling the temperature of the inside of the LNG cargo tank to be maintained at-158 ℃ ± 5 ℃ for a designated time.

After the cooling operation, a test process of filling liquid nitrogen into the LNG cargo tank on the shore, performing a pumping test on a pump inside the LNG cargo tank, and then unloading the liquid nitrogen inside the LNG cargo tank to another ship using a loading arm may be further included.

After the step of performing the second integrity test, the method may further include filling the LNG cargo tank with LNG, performing a pumping test on a pump inside the LNG cargo tank, and unloading the LNG inside the LNG cargo tank to another ship using a loading arm, in which in the case of the FLNG, the method may be performed at sea, and in the case of a ship having self-propulsion capability, the method may be performed at a land terminal.

According to another aspect of the invention, the method comprises the steps of (a) performing an LNG cargo tank main barrier integrity test; performing a first integrity test on a secondary wall of the LNG cargo tank; performing a pipeline cold resistance test on a pipeline connected with the LNG cargo tank; cooling the interior of the LNG cargo tank; step (e) heating operation for raising the internal temperature of the LNG cargo tank to normal temperature is carried out; step (f) discharging the fluid inside the LNG cargo tank, and performing visual inspection on the inside of the LNG cargo tank after injecting dry gas into the inside of the LNG cargo tank; and (g) performing a second integrity test on a secondary wall of the LNG cargo tank, wherein the steps (a) to (g) may be performed on the LNG cargo tank of a marine structure such as a ship in a state where the marine structure is placed on land.

The step (b) and the step (g) may be implemented by filling nitrogen gas in the lower side heat insulating layer of the sub-barrier and the upper side heat insulating layer of the sub-barrier, applying different pressures, measuring a pressure change value between the lower side heat insulating layer and the upper side heat insulating layer after a set certain time, and determining whether the sub-barrier is undamaged according to the measured value.

The step (d) may include a process of injecting a refrigerant into the LNG cargo tank to control the internal temperature of the LNG cargo tank to be maintained at-158 ℃ ± 5 ℃ for a set time.

The main barrier integrity test may include a process of coating an ammonia reaction substance on a welding portion of the main barrier, filling ammonia gas in a space between the main barrier and the sub barrier, and determining whether the main barrier is not damaged according to whether the ammonia reaction substance is discolored, and the pipe cold resistance test may include a process of flowing the refrigerant into the pipe and measuring whether contraction and expansion displacement amounts of the pipe are within an allowable range.

According to another aspect of the present invention, a marine structure to which an LNG cargo tank test method is applied may be provided.

According to another aspect of the present invention, there is provided a liquid nitrogen supply system for a marine structure, comprising a buffer tank for supplying liquid nitrogen to an LNG cargo tank of the marine structure placed on land in order to perform an LNG cargo tank test operation; and a control unit that adjusts the amount of liquid nitrogen injected into the LNG cargo tank so that the internal temperature of the LNG cargo tank is maintained within a set temperature range for a set time.

A tanker truck may be further included for receiving the liquefied nitrogen from the liquid nitrogen production section, moving to a dock where the buffer tank is provided, and supplying the liquefied nitrogen to the buffer tank.

The LNG cargo tank may further include a liquid nitrogen injection pipe connecting the buffer tank and the LNG cargo tank, an injection part injecting the liquid nitrogen supplied through the liquid nitrogen injection pipe into the LNG cargo tank to cool the LNG cargo tank, a control valve disposed in the liquid nitrogen injection pipe, and a temperature sensor measuring a temperature inside the LNG cargo tank, and the control part controls an opening and closing degree of the control valve according to the measured temperature value to adjust an amount of the liquid nitrogen injected into the LNG cargo tank by the injection part.

The control part may adjust the amount of liquid nitrogen sprayed into the LNG cargo tank so that the internal temperature of the LNG cargo tank is maintained at-158 ℃ ± 5 ℃.

The LNG cargo hold testing method, the marine structure applying the method and the liquid nitrogen supply system of the marine structure carry out all processes of LNG cargo hold testing on shore, so that cost can be saved and working efficiency can be improved. In particular, large test operations, which have been performed only offshore, can be performed onshore, making the operations simpler, more stable and more efficient, and also making it possible to end the project earlier.

The effects of the present invention are not limited to the above-mentioned various effects, and other effects not mentioned are easily known from the scope of claims by practitioners in the art.

Drawings

Fig. 1 is a flow chart of a process for testing an LNG cargo tank of a marine structure on land according to an embodiment of the present invention.

Fig. 2 is a schematic flow diagram of a process for testing the LNG cargo tank of the marine structure after the LNG cargo tank test shown in fig. 1.

FIG. 3 is a block schematic diagram of a liquid nitrogen supply system according to an embodiment of the present invention.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The present invention is not limited to the embodiments described below, and may be embodied in other forms. In order to more clearly explain the present invention, portions not related to the explanation are omitted in the drawings, and for convenience, the width, length, thickness, and the like of each member are exaggerated on the drawings. Like reference numerals refer to like elements throughout the specification.

Fig. 1 is a flowchart of a marine structure LNG cargo tank test process performed onshore according to an embodiment of the present invention.

Each test procedure of the LNG cargo tank shown in fig. 1 is performed on the LNG cargo tank of the marine structure in a state where the marine structure is placed on land.

The marine structure according to the embodiment of the present invention includes marine structures having an LNG cargo tank such as Floating Liquefied Natural Gas Facilities (FLNG) having no self-propulsion capability, Floating Storage Regasification Units (FSRU), Floating Storage regasification units (FSU), and marine structures having an LNG cargo tank such as Floating Storage units, and ships having an LNG transportation route having self-propulsion capability.

The term "onshore" as used in the embodiments of the present invention refers to land, including a dock (yard) representing a shipyard. That is, the use of "onshore" means a wider range than a dock. Performing LNG cargo compartment testing in a dock refers to performing LNG cargo compartment testing in a shipyard built into the marine structure, and performing LNG cargo compartment testing "on-shore" includes performing LNG cargo compartment testing in the dock (i.e., the shipyard) and other onshore locations in addition.

In the embodiments of the invention described below, although the entire process of testing the LNG cargo hold of the marine structure is described as being performed onshore, it may be performed in a "onshore" dock (i.e., a shipyard).

Referring to fig. 1, a main wall integrity TEST (PBGT, primary GLOBAL TEST) of a marine structure LNG cargo tank is first performed onshore (S201). The process (S201) may include a process of coating an ammonia reactant on a welding portion of the main panel, filling ammonia gas in a space between the main panel and the sub-panel, and determining whether the main panel is not damaged according to whether the ammonia reactant is discolored. For example, if a groove is formed at the welding position of the main screen wall, the ammonia reaction substance coated at the welding position of the main screen wall reacts with the ammonia gas filled between the main screen wall and the secondary screen wall and then changes color, and it can be determined that the main screen wall is damaged.

Then, a first time wall integrity TEST (SBTT) of the marine structure LNG cargo tank is performed onshore (S202). The process (S202) IS to fill nitrogen in a lower side heat Insulation layer (IS; Insulation Space) of the secondary screen wall and an upper side heat Insulation layer (IBS; Inter Barrier Space) of the secondary screen wall, apply different pressures respectively, measure a pressure change value between the lower side heat Insulation layer of the secondary screen wall and the upper side heat Insulation layer of the secondary screen wall after a set time, and judge whether the secondary screen wall IS not damaged according to the measured pressure change value. At this time, the pressure of the lower side heat insulating layer of the sub-barrier and the upper side heat insulating layer of the sub-barrier may be measured by a pressure gauge (not shown) installed in the space. For example, if the measured pressure of the lower side heat insulating layer of the sub-wall and the upper side heat insulating layer of the sub-wall is the same, it can be judged that the sub-wall is damaged.

Next, a pipeline cold resistance test is performed on the pipeline connected to the LNG cargo tank of the marine structure for LNG loading or unloading on shore (S203). This process (S203) may include a process of flowing refrigerant into the pipe and measuring the contraction and expansion displacement amounts of the pipe with a displacement meter (not shown). The refrigerant here may comprise liquid nitrogen. The pipeline may be a pipeline connected with a filling pipe and a discharge pipe of a pump tower for LNG loading or unloading, and a pipeline cold resistance test may be performed in a state where the pipeline is installed on a ship Deck (Deck). If the amount of displacement of contraction and expansion of the pipe measured using the displacement meter is within the allowable range, it can be judged as normal.

Next, the cooling operation is performed on the shore inside the cargo tank of the marine structure LNG (S204). This process (S204) may include using other refrigerants than LNG, and as with the pipeline cold tolerance test, liquid nitrogen may be used. Once the liquid nitrogen contacts the LNG cargo tank in a normal temperature state, most of the liquid nitrogen is immediately vaporized, thereby generating a convection phenomenon inside the LNG cargo tank. This process (S204) may include spraying liquid nitrogen into the inside of the LNG cargo tank in a normal temperature state while controlling the inside temperature of the LNG cargo tank to be maintained at-158 ℃ ± 5 ℃.

Next, a Warm-up operation (S205) of raising the temperature inside the LNG cargo tank of the marine structure to room temperature is performed on the shore. This process (S205) may include increasing the temperature of the inside of the LNG cargo tank by the heater (180, refer to fig. 3), and the fluid inside the LNG cargo tank is re-injected into the inside of the LNG cargo tank after being heated by the heater (180).

Then, the fluid in the LNG cargo tank of the marine structure is discharged on the shore, Dry Air (Dry Air) is injected into the LNG cargo tank, and the inside of the LNG cargo tank is visually inspected (S206). When the temperature in the LNG cargo tank is raised to normal temperature by the heater (180), most of the nitrogen remaining in the LNG cargo tank is in a gas state. Therefore, a worker must enter the inside of the LNG cargo tank to perform a visual inspection, discharge nitrogen gas inside the LNG cargo tank, and inject normal-temperature dry air (oxygen concentration of 20%) into the inside of the LNG cargo tank.

Next, a second secondary wall integrity test is performed on the marine structure LNG cargo hold onshore (S207). This process (S207) may include filling nitrogen gas in the lower side insulation layer of the sub-barrier and the upper side insulation layer of the sub-barrier, and applying different pressures, respectively, measuring a pressure change value between the lower side insulation layer and the upper side insulation layer after a set time has elapsed, and judging whether the sub-barrier is intact according to the measured pressure change value.

When the LNG cargo tank is of Mark-iii type, the main barrier uses not a welding process but an Adhesive (Adhesive) process, unlike the main barrier. As described above, the reason why the first and second tests for integrity of the barrier are performed is that after the first test for integrity of the barrier performed when the LNG cargo tank is constructed, liquefied gas is injected into the LNG cargo tank to perform a cooling operation, and the LNG cargo tank undergoes a rapid temperature change (hereinafter, referred to as Cold Shock).

That is, the first time of the wall integrity test process (S202) is performed under the condition that the LNG cargo tank construction work is finished, and the second time of the wall integrity test process (S207) is performed under the condition that the LNG cargo tank is subjected to cold shock. In the embodiment of the present invention, as described above, the inside of the LNG cargo tank is cooled by injecting liquid nitrogen during S204, but the inside temperature is maintained at-158 ℃ ± 5 ℃ for a set time (e.g., 22 hours) while cold shock is applied.

Thus, by the embodiment of the invention, various tests can be carried out on the LNG cargo hold of the marine structure on the shore, thereby reducing the cost and improving the working efficiency. In particular, large-scale test operations which need to be carried out offshore before being carried out onshore can improve the simplicity, stability and efficiency of the work and can also complete the engineering task in advance.

In addition, the test process (S201 to S207) of the LNG cargo tank of the marine structure may be performed in a dock (shipyard). That is, the above process (S201 to S207) can be performed in a shipyard where marine structures have been built onshore, and in this case, the movement of the marine structures is minimized, so that the cost can be reduced and the efficiency of the test work can be improved.

As shown in fig. 1, after the test operation of the LNG cargo tank is performed on the shore, a marine structure having no self-propulsion capability (e.g., FLNG) may be tested on the sea, and a marine structure having self-propulsion capability (e.g., LNG carrier) may be tested on the remaining LNG cargo tank at the terminal on the shore. The following description will be given by taking FLNG as an example of a marine structure without self-propulsion capability and an LNG carrier as an example of a marine structure with self-propulsion capability

Fig. 2 is a flow chart of a marine structure LNG cargo tank test process performed after the LNG cargo tank test shown in fig. 1.

Referring to fig. 2, the LNG cargo tank is filled with LNG, and a pump test is performed on a pump inside the LNG cargo tank (S208). For example, FLNG without self-propulsion capability, the present process is executed with the FLNG placed offshore (S208); the LNG carrier having self-propulsion capability performs the present process in a state where the LNG carrier is placed at an onshore terminal (S208).

In addition, in the FLNG example, after LNG is produced offshore, the produced LNG is filled into an LNG cargo tank, and a pump test is performed on a pump (not shown) disposed in the LNG cargo tank immediately. Additionally, as another example, the FLNG may be used to pump test pumps deployed within the cargo holds of LNG after receiving the LNG using the LNG bunker method.

In this case, the pump may be an LNG unloading pump installed in a pump tower, and the test may be performed in a state where the inside of the LNG cargo tank is filled with LNG.

Next, a test is performed to unload the LNG inside the LNG cargo tank to another LNG ship using the loading arm (S209). The process (S209) is also performed offshore for FLNG and onshore for LNG carriers.

In the LNG cargo tank test process (S208 to S209) of the marine structure, the test is performed using LNG, but in other examples, the test is not limited thereto, and the test may be performed using the refrigerant used in the cooling operation process (S204) instead of LNG.

In this case, the cooling process is performed (S204), and a pumping test and a loading arm test may be subsequently performed onshore, followed by the preheating operation (S205). In addition, the second screen integrity test process is performed (S207), and then a pumping test and a loading arm test may be performed onshore. At this time, the refrigerant is filled into the LNG cargo tank on the shore, a pump test is performed on the pump in the LNG cargo tank, and the refrigerant in the LNG cargo tank is unloaded to another LNG ship by using the loading arm to perform a test. Thus, pumping tests and loading arm tests can be performed onshore without the need to move offshore structures, including the FLNG.

Fig. 3 is a block diagram of a liquid nitrogen supply system according to an embodiment of the present invention.

Referring to fig. 3, a liquid nitrogen supply system according to an embodiment of the present invention supplies liquid nitrogen used in a test operation of an LNG cargo tank 101 of an offshore structure 100 shown in fig. 1 on shore.

Such a liquid nitrogen supply system may include: a tank car 110 that receives liquid nitrogen from a liquid nitrogen production section 105 that produces liquid nitrogen, transfers the liquid nitrogen to a buffer tank 120, and supplies the buffer tank 120 with the liquid nitrogen; a buffer tank 120 that supplies liquid nitrogen to the LNG cargo tank 101; and a control unit 130 for adjusting the amount of liquid nitrogen injected into the LNG cargo tank 101 so that the internal temperature of the LNG cargo tank 101 is maintained within a set temperature range for a set time.

In addition, the liquid nitrogen supply system may include a buffer tank 120; a liquid nitrogen injection pipe 140 connected to the LNG cargo tank 101; an injection part 150 injecting liquid nitrogen received through the liquid nitrogen injection pipe 140 into the LNG cargo tank 101; a control valve 160 disposed on the liquid nitrogen injection pipe 140; a temperature sensor 170 that measures the temperature inside the LNG cargo tank 101.

In addition, the liquid nitrogen supply System is provided with one or more Safety valves (193, Safety Valve) and Safety devices (193, Safety System) on the liquid nitrogen injection pipe 140 to cope with Emergency (Emergency) and Abnormal (Abnormal Condition).

The respective components will be specifically described below.

The liquid nitrogen producing section 105 may be prepared by an enterprise that specializes in gas management. The liquid nitrogen produced by the liquid nitrogen producing unit 105 is stored in the tank truck 110 and transported to the shore site where the marine structure 100 is located.

The buffer tank 120 may be configured as a mobile trailer type, and may receive liquid nitrogen from the tanker 110 and stably supply the liquid nitrogen to the LNG cargo hold 101 of the marine structure 100. Surge tank 120, like tanker truck 110, can be transported to the site of onshore marine structure 100. Although not shown, the buffer tank 120 may be equipped with a cryogenic pump, a vaporizer, a stirrer, and the like, and may transfer liquid nitrogen to the LNG cargo tank 101.

The control unit 130 controls the degree of opening and closing of the control valve 160 based on the temperature value measured by the temperature sensor 170 to adjust the amount of liquid nitrogen injected into the LNG cargo tank 101 by the injection unit 150. For example, the control part 130 may control the opening and closing degree of the control valve 160 to control the temperature inside the LNG cargo tank 101 within the range of-158 ℃ ± 5 ℃. Thereby, the internal temperature of the LNG cargo tank 101 can be maintained at approximately the LNG temperature level (about-163 ℃), and at the time of the LNG cargo tank test, the test work can be performed onshore using liquid nitrogen instead of LNG. That is, the liquid nitrogen is maintained at the LNG temperature level, so that the same effect as that of the cargo tank test using LNG can be achieved.

Specifically, in the cooling operation of the inside of the LNG cargo tank 101, if liquid nitrogen of about-195 ℃ is injected into the LNG cargo tank 101 in a normal temperature state, the temperature of the LNG cargo tank 101 is gradually lowered. Once the liquid nitrogen contacts the LNG cargo tank 101 at normal temperature, most of the liquid nitrogen is immediately vaporized, thereby generating a convection phenomenon in the LNG cargo tank 101. At this time, when adjusting the speed at which the temperature of the LNG cargo tank 101 is lowered according to the amount of liquid nitrogen injected, if the temperature of the LNG cargo tank 101 is excessively low, components of the LNG cargo tank 101 may be damaged, and thus the amount of liquid nitrogen injected may be adjusted at a preset speed.

After the liquid nitrogen is sprayed to the inner wall of the LNG cargo tank 101 in the normal temperature state, the temperature rises and the gas state can be immediately converted. If the cooling operation of the inside of the LNG cargo tank 101 in this state is continued, about-158 c may be reached, and the injection part 150 may stop the injection of the liquid nitrogen using this as a starting point. At this time, the control part 130 may close the control valve 160 according to the temperature value measured by the temperature sensor 170, thereby stopping the injection of liquid nitrogen through the injection part 150.

The control unit 130 may maintain the internal temperature fluctuation range of the LNG cargo tank 101 at-158 ℃ ± 5 ℃ for 22 hours according to the preset cargo tank cooling conditions. That is, after the injection of liquid nitrogen into the LNG cargo tank 101 is stopped, the temperature inside the LNG cargo tank 101 gradually rises as time passes, and the control part 130 opens the control valve 160 according to the temperature value measured by the temperature sensor 170 and gradually injects liquid nitrogen into the LNG cargo tank 101 through the injection part 150 little by little, and the temperature fluctuation range is maintained at-158 ℃ ± 5 ℃ for 22 hours according to the preset cargo cooling condition.

The liquid nitrogen injection pipe 140 is configured to supply liquid nitrogen supplied from the surge tank 120 to the LNG cargo tank 101, and can endure liquefied gas of an extremely low temperature. The liquid nitrogen injection pipe 140 may be transferred to the shore where the offshore structure 100 is located together with the buffer tank 120. The tank truck 110, the buffer tank 120 and the liquid nitrogen injection pipe 140 as described above may be configured to be movable so that the LNG cargo tank 101 test work of the marine structure 100 can be performed anywhere on the shore, i.e., not only at a shipyard but also at other places.

The injection part 150 may include a nozzle for injecting liquid nitrogen supplied through the liquid nitrogen injection pipe 140 into the inside of the LNG cargo tank 101.

And, a control valve 160 is disposed in the liquid nitrogen injection pipe 140 to adjust the flow rate of liquid nitrogen supplied to the LNG cargo tank 101.

The temperature sensor 170 measures the temperature inside the LNG cargo tank 101, which varies with the injection of liquid nitrogen, inside the LNG cargo tank 101.

The safety valve 193 and the safety device 195 can be used to cope with the protection of the supply equipment (liquid nitrogen supply system) under overpressure phenomenon or Emergency Condition (Emergency setup) and Abnormal Situation (Abnormal Condition) of the equipment due to the interruption of the liquid nitrogen supply.

One or more of the safety valve 193 and the safety device 195 may be disposed at one or more of the front and rear ends of the control valve 160 of the liquid nitrogen injection pipe 140.

The safety Valve 193 may include a "Pressure Reducing Valve (PRV) to cope with an overpressure phenomenon of the equipment and a" Pressure Vacuum Valve (PVV) to cope with a low Pressure (Vacuum) phenomenon.

Additionally, security device 195 may include one or more of warnings against abnormal conditions (Alarm), automatic provisioning, and interruptions.

For example, the overpressure phenomenon of the equipment may occur during the supply of liquid nitrogen to the cargo compartment (main line) using a conveying means such as a pump, and in the pipes and equipment which cannot supply liquid nitrogen to the cargo compartment (main line) in an emergency. Furthermore, the over-pressure phenomenon may be caused by a surging phenomenon (Surge) caused by sudden valve operation or driving changes during normal operation. In addition, in the case of long-term failure of the cargo hold (main line), overpressure phenomena may occur in the supply lines and outside the operating range of the respective plant, depending on the Vaporization phenomenon (Vaporization) of the liquid nitrogen in the supply plant.

In addition, the low pressure (vacuum) phenomenon may occur when the flow rate of the liquid nitrogen supply device to the main line exceeds the suppliable range, and may also occur when a transportation device such as a pump is operated in a state where liquid nitrogen is insufficient in the liquid nitrogen supply device.

In the embodiment of the present invention, the overpressure phenomenon and the low pressure (vacuum) phenomenon can be effectively coped with by the safety valve 193 and the safety device 195.

Thus, with the liquid nitrogen supply system according to the embodiment of the present invention, it is possible to replace LNG with liquid nitrogen and maintain the temperature level of LNG while being injected into the LNG cargo tank 101 of the offshore structure 100, so that it is possible to effectively perform a test work on the LNG cargo tank of the offshore structure 100 on shore.

The foregoing description has been given of specific embodiments only. However, the present invention is not limited to the above-described embodiments, and those having ordinary knowledge in the art to which the present invention pertains can be arbitrarily modified in various ways without departing from the core technical idea of the present invention described in the scope of the following claims.

Claims (14)

1. An LNG cargo tank testing method comprising:

after the LNG cargo hold of the FLNG is built, carrying out a first integrity test on a secondary screen wall of the LNG cargo hold;

cooling the inside of the LNG cargo tank; and

step (c) performing a second integrity test on a secondary wall of the LNG cargo tank,

the steps (a) to (c) are performed on an LNG cargo tank of the FLNG in a state where the FLNG is deployed onshore, and the step (b) is performed using any one refrigerant other than LNG.

2. An LNG cargo tank testing method comprising:

after an LNG cargo hold of a ship is built, carrying out a first integrity test on a secondary screen wall of the LNG cargo hold;

after the step (b) is connected with the LNG cargo hold, performing a pipeline cold resistance test on a pipeline for executing LNG loading or unloading;

cooling the interior of the LNG cargo tank; and

step (d) performing a second integrity test on the secondary wall of the LNG cargo tank,

the steps (a) to (d) are performed on an LNG cargo tank of the ship while the ship is docked on shore,

said steps (b) and (c) are carried out using liquid nitrogen.

3. An LNG cargo tank test method according to claim 1 or claim 2

The step of performing the cooling operation includes injecting liquid nitrogen into the inside of the LNG cargo tank in a normal temperature state, and also includes controlling the temperature of the inside of the LNG cargo tank to be maintained at-158 ℃ ± 5 ℃ for a designated time.

4. An LNG cargo tank test method according to claim 1 or claim 2,

further comprising filling liquid nitrogen into the inside of the LNG cargo tank on shore after the cooling operation, performing a pumping test on a pump inside the LNG cargo tank,

and then using a loading arm to unload the liquid nitrogen in the LNG cargo hold to a test process on other ships.

5. An LNG cargo tank test method according to claim 1 or claim 2,

after the step of performing the second integrity test, further comprising filling the LNG cargo tank with LNG, performing a pumping test on a pump inside the LNG cargo tank,

a test process for unloading the LNG inside the LNG cargo tank to another ship using a loading arm,

in the case of the FLNG, it can be performed at sea, and in the case of a vessel with self-propulsion capability, it can be performed at a land terminal.

6. An LNG cargo tank testing method comprising:

step (a), carrying out an integrity test on a main screen wall of the LNG cargo tank;

performing a first integrity test on a secondary wall of the LNG cargo tank;

performing a pipeline cold resistance test on a pipeline connected with the LNG cargo tank;

cooling the interior of the LNG cargo tank;

step (e) heating operation for raising the internal temperature of the LNG cargo tank to normal temperature is carried out;

step (f) discharging the fluid inside the LNG cargo tank, and performing visual inspection on the inside of the LNG cargo tank after injecting dry gas into the inside of the LNG cargo tank; and

step (g) performing a second integrity test on the secondary wall of the LNG cargo tank,

the steps (a) to (g) may be performed with respect to an LNG cargo tank of a marine structure such as a ship placed on land.

7. An LNG cargo tank test method according to claim 6:

the step (b) and the step (g) comprise filling nitrogen in the lower side heat-insulating layer of the secondary screen wall and the upper side heat-insulating layer of the secondary screen wall, and respectively applying different pressures,

measuring a pressure change value between the lower side heat-insulating layer and the upper side heat-insulating layer after a set certain time,

and judging whether the secondary screen wall is lossless or not according to the measured value.

8. An LNG cargo tank test method according to claim 6:

the step (d) includes a process of injecting a refrigerant into the LNG cargo tank to control the temperature inside the LNG cargo tank to be maintained at-158 ℃ ± 5 ℃ for a set time.

9. An LNG cargo tank test method according to claim 8:

the integrity test of the main screen wall comprises the process of coating an ammonia reaction substance on the welding part of the main screen wall, filling ammonia gas in the space between the main screen wall and the secondary screen wall, and judging whether the main screen wall is not damaged according to whether the ammonia reaction substance changes color or not,

the pipe cold resistance test may include a process of flowing the refrigerant into the pipe and measuring whether the contraction and expansion displacement amounts of the pipe are within an allowable range.

10. Marine structure to which the LNG cargo tank test method according to any one of claims 6 to 9 is applied.

11. A liquid nitrogen supply system for an offshore structure, comprising:

a buffer tank for supplying liquid nitrogen to the LNG cargo tank in order to perform a test operation of the LNG cargo tank of the marine structure placed on the land; and

and a control unit that adjusts the amount of liquid nitrogen injected into the LNG cargo tank so that the internal temperature of the LNG cargo tank is maintained within a set temperature range for a set time.

12. A liquid nitrogen supply system for a marine structure according to claim 11:

also included is a tanker for receiving liquefied nitrogen from the liquid nitrogen production section, moving to a dock where a buffer tank is provided, and supplying the buffer tank with the liquefied nitrogen.

13. A liquid nitrogen supply system for a marine structure according to claim 11:

and a liquid nitrogen injection pipe connecting the buffer tank and the LNG cargo tank,

injecting the liquid nitrogen supplied through the liquid nitrogen injection pipe into the inside of the LNG cargo tank to cool an injection part of the LNG cargo tank,

a control valve disposed in the liquid nitrogen injection pipe, and

a temperature sensor for measuring a temperature inside the LNG cargo tank,

the control part controls the opening and closing degree of the control valve according to the measured temperature value so as to adjust the amount of liquid nitrogen injected into the LNG cargo tank by the injection part.

14. A liquid nitrogen supply system for a marine structure according to claim 13:

the control unit adjusts the amount of liquid nitrogen injected into the LNG cargo tank so that the internal temperature of the LNG cargo tank is maintained at-158 ℃ ± 5 ℃.

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