JP5289325B2 - Soundness evaluation method for secondary barrier of liquefied gas tank - Google Patents

Description

  The present invention relates to a method for evaluating the soundness of a secondary barrier of a liquefied gas tank, which can evaluate the soundness of a secondary barrier of a liquefied gas tank of a ship in operation.

  As a method of transporting natural gas, which is attracting attention as a clean fuel, from the production area to the consumption area, there are a method of transporting natural gas in a gaseous state using a pipeline and a method of transporting natural gas in a liquid state by ship. Are known.

  In the case of transporting natural gas using a pipeline, high-pressure gas must be handled for long-distance transportation, and continuous maintenance and repair of the pipeline are necessary. Pipeline installation is also greatly affected by geopolitical issues.

  In recent years, in order to overcome such problems, a method of transporting natural gas using a ship has been widely used. In particular, construction of a liquefied natural gas transport ship capable of transporting natural gas in a liquid state has been facilitated by development of storage technology for cryogenic objects and construction technology for large ships. Therefore, the transportation of natural gas using ships is increasing more and more.

  Tanks used in liquefied natural gas transport ships are roughly classified into membrane tank systems and independent tank systems. Of the membrane tank system and the independent tank system, the membrane tank system has been more widely used in recent years.

  In the case of the membrane tank system, particularly the MARK 3 system, the tank is made of corrugated stainless steel having a thickness of 1.2 mm. Thereby, the primary barrier for storing the cryogenic liquefied gas is formed. If there is a problem with the primary barrier, liquefied natural gas will leak from the tank and damage the hull. In order to prevent this damage, a secondary barrier that isolates the cryogenic liquefied natural gas from the hull for a predetermined time is attached to the heat insulating space.

  When the ship is under construction, the integrity of the secondary barrier is evaluated by the secondary barrier hermetic test method. In the airtightness test method, the first heat insulating space is maintained at atmospheric pressure, the pressure in the second heat insulating space is reduced to −530 mbar, and then the time until the reduced pressure returns to atmospheric pressure is measured. Is. The hermetic test method uses the fact that pressure exchange takes place due to the porosity of the secondary barrier.

  However, the method can only be applied to a ship under construction, i.e. the method cannot be applied to a ship in operation. Therefore, there is a need for a method that can evaluate the soundness of the secondary barrier of a liquefied gas tank of a ship in operation.

  Therefore, the present invention has been made in view of the above circumstances, and its purpose is to evaluate the soundness of the secondary barrier of the liquefied gas tank of the ship in operation, and to evaluate the soundness of the secondary barrier of the liquefied gas tank Is to provide.

  According to one aspect of the present invention, (A) a step of observing the integrated automation system, and (B) a step of performing a first differential pressure test when an abnormality is observed by the observation in step (A), (C) As a result of the first differential pressure test in the step (B), when the pressure in the heat insulating space and the pressure in the space between the barrier walls are not equal to each other, or after both the pressures are equal to each other, the pressure reversal phenomenon When this occurs, a method for evaluating the soundness of the secondary barrier of the liquefied gas tank including the step of performing a second differential pressure test is provided.

  Preferably, in the evaluation method, (D) as a result of the second differential pressure test in the step (C), when the pressure in the heat insulation space and the pressure in the space between the barrier walls are equal to each other, the third difference The method further includes performing a pressure test.

  Preferably, the first differential pressure test includes: (a-1) checking the control valve and the pressure transmitter when the tank is in a steady state; and (b-1) leakage of the safety valve for the heat insulation space. (C-1) a step of switching the valve control mode from the automatic mode to the manual mode, and (d-1) a differential pressure between the heat insulation space and the space between the barrier walls. (E-1) closing the control valve, observing changes in pressure and recording process variables; (f-1) pressure in the heat insulation space and pressure in the space between the barriers And (g-1) when it is determined in step (f-1) that the pressure in the heat insulation space and the pressure in the space between the barrier walls are equal to each other, Pressure reversal after pressures are equal to each other And a step of elephant determining whether occurring.

  Preferably, the first differential pressure test further includes (h-1) when it is determined that the pressure reversal phenomenon has occurred in the step (g-1), the valve control mode is changed from the manual mode to the automatic mode. Switching to mode, checking for leak sites in the nitrogen pressurization system, and returning to step (c-1).

  Preferably, the second differential pressure test includes: (a-2) checking the control valve and the pressure transmitter when the tank is in a steady state; and (b-2) leakage of the safety valve for the heat insulation space. (C-2) a step of switching the valve control mode from the automatic mode to the manual mode, and (d-2) a differential pressure between the heat insulation space and the space between the barrier walls. (E-2) closing the control valve, closing manual valves arranged before and after the control valve, observing pressure changes, and recording process variables; -2) determining whether the pressure in the heat insulation space and the pressure in the space between the barrier walls are equal to each other.

  Preferably, the second differential pressure test further includes: (g-2) if it is determined in step (f-2) that the two pressures are not equal to each other, the test result of the first differential pressure test Comparing the test result of the second differential pressure test, and (h-2) if it is determined in step (g-2) that the test results are not the same, the valve control mode is set to Switching from the manual mode to the automatic mode, inspecting for leak sites in the nitrogen pressurization system, and returning to the step (c-2).

  Preferably, the third differential pressure test includes: (a-3) checking the control valve and the pressure transmitter when the tank is in a steady state; and (b-3) leakage of the safety valve for the insulated space. (C-3) a step of installing a name plate in a part of the nitrogen pressurization system, and (d-3) a step of switching the valve control mode from the automatic mode to the manual mode. And (e-3) a step of setting a differential pressure between the heat insulating space and the space between the barrier walls, and (f-3) a manual valve disposed before and after the control valve by closing the control valve. And observing the change in pressure and recording the process variable, and (g-3) determining whether the pressure in the heat insulation space and the pressure in the space between the barrier walls are equal to each other. .

  Preferably, the third differential pressure test further includes (h-3) a pressure reversal phenomenon after the pressures are equal to each other when the pressures are determined to be equal to each other in the step (g-3). And (i-3) when it is determined in step (h-3) that the pressure reversal phenomenon does not occur, the heat insulation space and the space between the barrier walls are isobaric. And (j-3) closing the control valve, closing manual valves disposed before and after the control valve, opening the control valve to exhaust gas from the heat insulating space, and (K-3) determining whether the pressure in the heat insulating space and the pressure in the inter-barrier space are equal to each other; (l-3) In step (k-3), the two pressures are equal to each other. If it is determined that the valve control mode is not correct, the step of switching the valve control mode from the manual mode to the automatic mode, (m-3) checking the leakage site of the nitrogen pressurization system, and returning to the step (d-3) Steps.

  Preferably, the third differential pressure test further includes a step of proceeding to step (l-3) when it is determined in step (h-3) that the pressure reversal phenomenon has occurred.

  Preferably, in the third differential pressure test, if it is determined in step (k-3) that the pressure in the heat insulation space and the pressure in the space between the barrier walls are not equal to each other, the airtight test for the secondary barrier wall The step of performing is included.

  Advantageous Effects of Invention According to the present invention, there is an effect that it is possible to provide a soundness evaluation method for a secondary barrier of a liquefied gas tank that can evaluate the soundness of a secondary barrier of a liquefied gas tank of a ship in operation.

It is a figure which shows the general | schematic block diagram of the liquefied gas tank to which the soundness evaluation method of the secondary barrier which concerns on one Embodiment of this invention was applied. It is a flowchart which shows the soundness evaluation method of the secondary barrier of the liquefied gas tank of FIG. It is a flowchart which shows the 1st differential pressure test process which concerns on one Embodiment of this invention. It is a flowchart which shows the 1st differential pressure test process which concerns on one Embodiment of this invention. It is a flowchart which shows the 2nd differential pressure test process which concerns on one Embodiment of this invention. It is a flowchart which shows the 2nd differential pressure test process which concerns on one Embodiment of this invention. It is a flowchart which shows the 3rd differential pressure test process which concerns on one Embodiment of this invention. It is a flowchart which shows the 3rd differential pressure test process which concerns on one Embodiment of this invention.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals shown in the drawings mean the same members.

  FIG. 1 shows a schematic block diagram of a liquefied gas tank to which a secondary barrier soundness evaluation method according to an embodiment of the present invention is applied.

  Referring to FIG. 1, the liquefied gas tank 10 includes a primary barrier 100 and a secondary barrier 200. The primary barrier 100 and the secondary barrier 200 form an inter-barrier space IBS and a heat insulating space IS. The inter-barrier space IBS and the heat insulation space IS are connected to a nitrogen pressurization system that supplies nitrogen to the inter-barrier space IBS and the heat insulation space IS through the nitrogen supply control valves 110 and 210. The inter-barrier space IBS and the heat insulation space IS are connected to the nitrogen exhaust control valves 120 and 220, and the gas in the inter-barrier space IBS and the heat insulation space IS is exhausted to the atmosphere via the nitrogen exhaust control valves 120 and 220. Is done. With such a configuration, the internal pressure of the inter-barrier space IBS and the heat insulating space IS is maintained. The manual valves 111, 112, 121, 122, 211, 212, 221, 222 are arranged before and after the control valves 110, 120, 210, 220. Pressure transmitters (PT) 130 and 230 for measuring internal pressures of the inter-barrier space IBS and the heat insulation space IS are provided in the inter-barrier space IBS and the heat insulation space IS. The heat insulation space IS is provided with a safety valve 240 for the heat insulation space IS.

  FIG. 2 is a flowchart showing a soundness evaluation method of the secondary barrier of the liquefied gas tank of FIG.

  Referring to FIG. 2, in order to evaluate the soundness of the secondary barrier 200 of the liquefied gas tank 10, first, an integrated automation system is observed (S100). It is determined whether an abnormality is observed through the observation (S110). When it is determined that the liquefied gas tank 10 is in a normal state, step S100 is performed again. If it is determined that an abnormality has been observed, a first differential pressure test is performed (S200). In the first differential pressure test, the pressure change is observed after setting the differential pressure between the heat insulating space IS and the inter-barrier space IBS. As a result of the observation, if it is determined that the pressure in the heat insulation space IS and the pressure in the inter-barrier space IBS are equal to each other and the pressure reversal phenomenon has occurred after the two pressures are equal to each other, Check and repeat the first differential pressure test. As a result of observation, if it is determined that the pressure in the heat insulation space IS and the pressure in the inter-barrier space IBS are not equal to each other, or that the pressure reversal phenomenon does not occur after the two pressures are equal to each other, the second differential pressure test (S400).

  In the second differential pressure test, a differential pressure is set between the heat insulation space IS and the inter-barrier space IBS, and then a change in pressure is observed. As a result of the observation, it is determined that the pressure in the heat insulation space IS and the pressure in the inter-barrier space IBS are not equal to each other, and the test result of the first differential pressure test and the test result of the second differential pressure test are the same. If so, the soundness of the secondary barrier 200 is confirmed. As a result of the observation, it is determined that the pressure in the heat insulation space IS and the pressure in the inter-barrier space IBS are not equal to each other, and the test result of the first differential pressure test and the test result of the second differential pressure test are not the same. If this happens, check the leakage site of the nitrogen pressurization system in the barrier and repeat the first differential pressure test. As a result of the observation, if it is determined that the pressure in the heat insulation space IS and the pressure in the inter-barrier space IBS are equal to each other, a third differential pressure test is performed (S600).

  In the third differential pressure test, the pressure change is observed after setting the differential pressure between the heat insulating space IS and the inter-barrier space IBS. As a result of the observation, if the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are not equal to each other, the soundness of the secondary barrier 200 is confirmed. As a result of the observation, if it is determined that the pressure in the heat insulation space IS and the pressure in the inter-barrier space IBS are equal to each other and the pressure reversal phenomenon has occurred after the two pressures are equal to each other, Check and repeat the differential pressure test. As a result of observation, when it is determined that the pressure reversal phenomenon does not occur after the two pressures are equal to each other, the pressure change is observed after setting the heat insulating space IS and the inter-barrier space IBS to the same pressure. As a result of the isobaric test, when it is determined that the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are equal to each other, an airtight test of the secondary barrier is performed. When it is determined that the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are not equal to each other, the leakage site of the nitrogen pressurization system is checked, and the differential pressure test is repeated.

  3 and 4 are flowcharts showing a first differential pressure test process according to an embodiment of the present invention.

  Referring to FIGS. 3 and 4, in the first differential pressure test, it is first determined whether or not the tank 10 is in a steady state (S201). When it is determined that the tank 10 is not in a steady state, the process waits until the tank 10 reaches a steady state (S202). When it is determined that the tank 10 is in a steady state, the control valves 110, 120, 210, 220 and the pressure transmitters 130, 230 are inspected (S203). Next, leakage of the safety valve 240 for the heat insulation space IS is confirmed (S204), and the valve control mode is switched from the automatic mode to the manual mode (S205). Next, a differential pressure is set between the heat insulating space IS and the inter-barrier space IBS (S206), and the control valves 110, 120, 210, and 220 are closed (S207). Next, the change in pressure is observed, and the process variable is recorded (S208). Next, it is determined whether or not the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are equal to each other (S209). If it is determined in step S209 that the pressures in both spaces IS and IBS are equal to each other, it is determined whether or not a pressure reversal phenomenon occurs after the two pressures are equal to each other (S210). When the pressure reversal phenomenon does not occur, the second differential pressure test is performed (S211). On the other hand, if the pressures in the spaces IS and IBS are not equal to each other in step S209, a second differential pressure test is performed (S211).

  When it is determined in step S210 that the pressure reversal phenomenon has occurred, the valve control mode is switched from the manual mode to the automatic mode (S212). Next, the leakage part of the nitrogen pressurization system is checked (S213). Thereafter, the test process proceeds to step S205.

  5 and 6 are flowcharts showing a second differential pressure test process according to an embodiment of the present invention.

  5 and 6, in the second differential pressure test, first, it is determined whether or not the tank 10 is in a steady state (S401). If the tank 10 is not in a steady state, the process waits until the tank 10 reaches a steady state (S402). When the tank 10 is in a steady state, the control valves 110, 120, 210, 220 and the pressure transmitters 130, 230 are inspected (S403). Next, leakage of the safety valve 240 for the heat insulation space IS is confirmed (S404), and the valve control mode is switched from the automatic mode to the manual mode (S405). Next, a differential pressure is set between the heat insulating space IS and the inter-barrier space IBS (S406), and the control valves 110, 120, 210, and 220 are closed (S407). Next, the manual valves 111, 112, 121, 122, 211, 212, 221, and 222 before and after the control valves 110, 120, 210, and 220 are closed (S408), the pressure change is observed, and the process variables are recorded. (S409). Next, it is determined whether or not the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are equal to each other (S410). When the pressures of both spaces IS and IBS are equal to each other, a third differential pressure test is performed (S411). If the pressures in the two spaces IS and IBS are not equal to each other, it is determined whether or not the test result of the first differential pressure test and the test result of the second differential pressure test are the same (S412). When the test results of the first and second differential pressure tests are the same, the soundness of the secondary barrier 200 is confirmed (S413). Otherwise, the valve control mode is switched from the manual mode to the automatic mode (S414). Next, the leakage site of the nitrogen pressurization system is checked (S415). Thereafter, the test process proceeds to step S405.

  7 and 8 are flowcharts showing a third differential pressure test process according to an embodiment of the present invention.

  7 and 8, in the third differential pressure test, first, it is determined whether or not the tank 10 is in a steady state (S601). If the tank 10 is not in a steady state, the process waits until the tank 10 reaches a steady state (S602). When the tank 10 is in a steady state, the control valves 110, 120, 210, 220 and the pressure transmitters 130, 230 are inspected (S603). Next, leakage of the safety valve 240 for the heat insulation space IS is confirmed (S604), and a name plate is installed in a part of the nitrogen pressurization system (S605). Next, the valve control mode is switched from the automatic mode to the manual mode (S606), and a differential pressure is set between the heat insulating space IS and the inter-barrier space IBS (S607). Next, the control valves 110, 120, 210, and 220 are closed (S608), and the manual valves 111, 112, 121, 122, 211, 212, 221, and 222 before and after the control valves 110, 120, 210, and 220 are closed. (S609). Next, the change in pressure is observed, and process variables are recorded (S610). Next, it is determined whether or not the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are equal to each other (S611). When the pressures of the two spaces IS and IBS are not equal to each other, the soundness of the secondary barrier 200 is confirmed (S612). If the pressures in both spaces IS and IBS are equal to each other, it is determined whether or not a pressure reversal phenomenon occurs (S613). When the pressure reversal phenomenon does not occur, the heat insulating space IS and the inter-barrier space IBS are set to the same pressure (S614). Next, the control valves 110, 120, 210, and 220 are closed (S615), and the manual valves 111, 112, 121, 122, 211, 212, 221, and 222 before and after the control valves 110, 120, 210, and 220 are closed. (S616). Next, only the exhaust control valve 220 for the heat insulation space IS is opened (S617), the change in pressure is observed, and the process variable is recorded (S618). Next, it is determined whether or not the pressure in the heat insulating space IS and the pressure in the inter-barrier space IBS are equal to each other (S619). If the pressures of the two spaces IS and IBS are not equal to each other, an airtight test of the secondary barrier 200 is performed (S620). If the pressures in both spaces IS and IBS are equal to each other, the valve control mode is switched from the manual mode to the automatic mode (S621).

  On the other hand, if it is determined in step S613 that the pressure reversal phenomenon has occurred, the test process proceeds to step S621, and the valve control mode is switched from the manual mode to the automatic mode. After step S621, the leakage site of the nitrogen pressurization system is checked (S622).

  In the soundness evaluation method for the secondary barrier 200 of the liquefied gas tank 10 according to the present invention, one step (for example, a step for checking a leakage site of the nitrogen pressurization system, etc.) or all steps are repeated depending on the request of a person skilled in the art. It goes without saying that it can be done.

  Although the present invention has been described with reference to an embodiment shown in the drawings, this is by way of example only, and one having ordinary skill in the art is defined in the claims. It will be understood that various modifications and changes can be made without departing from the scope of the invention as set forth.

Claims (7)

A method for evaluating the soundness of a secondary barrier of a liquefied gas tank,
The liquefied gas tank has an outer wall, the secondary barrier, and a primary barrier that is disposed inside the secondary barrier and accommodates liquefied gas therein, and is disposed between the outer wall and the secondary barrier. An insulation space is formed, and an inter-barrier space is formed between the secondary barrier and the primary barrier,
The method
(A) observing an integrated automation system that displays information about the health of the secondary barrier of the liquefied gas tank;
(B) when an abnormality is observed by the observation in step (A), performing a first differential pressure test;
(C) As a result of the first differential pressure test in the step (B), when the pressure in the heat insulation space and the pressure in the space between the barrier walls are not equal to each other, or after the both pressures are equal to each other, Performing a second differential pressure test when it is determined that the reverse phenomenon does not occur,
The first differential pressure test includes
(A-1) checking the control valve and the pressure transmitter when the tank is in a steady state;
(B-1) a step of confirming whether or not a leakage of the safety valve for the heat insulation space has occurred;
(C-1) switching the valve control mode from the automatic mode to the manual mode;
(D-1) setting a differential pressure between the heat insulating space and the space between the barriers;
(E-1) closing the control valve, observing a change in pressure, and recording the change in pressure;
(F-1) determining whether the pressure in the heat insulating space and the pressure in the inter-barrier space are equal to each other;
(G-1) When it is determined in step (f-1) that the pressure in the heat insulation space and the pressure in the space between the barrier walls are equal to each other, a pressure reversal phenomenon occurs after the two pressures are equal to each other. Determining whether or not
The second differential pressure test is
(A-2) checking the control valve and the pressure transmitter when the tank is in a steady state;
(B-2) a step of confirming whether a leakage of the safety valve for the heat insulation space has occurred;
(C-2) switching the valve control mode from the automatic mode to the manual mode;
(D-2) setting a differential pressure between the heat insulating space and the inter-barrier space;
(E-2) closing the control valve, closing manual valves arranged before and after the control valve, observing a change in pressure, and recording the change in pressure;
(F-2) The evaluation method characterized by including the step of determining whether the pressure of the said heat insulation space and the pressure of the said space between barrier walls are mutually equal. (D) As a result of the step of determining whether or not the pressure in the heat insulation space and the pressure in the inter-barrier space in the second differential pressure test in the step (C) are equal to each other, A step of performing a third differential pressure test when the pressure between the barrier walls is equal to each other;
The third differential pressure test is:
(A-3) checking the control valve and the pressure transmitter when the tank is in a steady state;
(B-3) a step of confirming whether a leakage of the safety valve for the heat insulation space has occurred;
(C-3) installing a nameplate in a part of the nitrogen pressurization system;
(D-3) switching the valve control mode from the automatic mode to the manual mode;
(E-3) setting a differential pressure between the heat insulating space and the space between the barriers;
(F-3) closing the control valve, closing manual valves arranged before and after the control valve, observing a change in pressure, and recording the change in pressure;
(G-3) The evaluation method of Claim 1 including the step which judges whether the pressure of the said heat insulation space and the pressure of the said inter-barrier space are mutually equal. The first differential pressure test includes
(H-1) If it is determined in step (g-1) that the pressure reversal phenomenon has occurred, the valve control mode is switched from the manual mode to the automatic mode, and the leakage part of the nitrogen pressurization system is checked. The evaluation method according to claim 1, further comprising a step of returning to step (c-1). The second differential pressure test is
(G-2) When it is determined in step (f-2) that the two pressures are not equal to each other, the test result of the first differential pressure test is compared with the test result of the second differential pressure test. And steps to
(H-2) When it is determined in step (g-2) that the two test results are not the same, the valve control mode is switched from the manual mode to the automatic mode, The evaluation method according to claim 1, further comprising the step of inspecting and returning to step (c-2). The third differential pressure test is:
(H-3) If it is determined in step (g-3) that the two pressures are equal to each other, determining whether a pressure reversal phenomenon occurs after the two pressures are equal to each other;
(I-3) when it is determined that the pressure reversal phenomenon does not occur in the step (h-3), the step of setting the heat insulating space and the space between the barrier walls to equal pressure;
(J-3) closing the control valve, closing the manual valve arranged before and after the control valve, opening the control valve to exhaust gas from the heat insulating space, and observing a change in pressure; Recording the change in pressure ;
(K-3) determining whether the pressure in the heat insulating space and the pressure in the inter-barrier space are equal to each other;
(L-3) when it is determined in step (k-3) that both pressures are equal to each other, the step of switching the valve control mode from the manual mode to the automatic mode;
The evaluation method according to claim 2, further comprising: (m-3) checking a leakage site of the nitrogen pressurization system and returning to the step (d-3). The third differential pressure test is:
6. The evaluation method according to claim 5, further comprising a step of proceeding to step (l-3) when it is determined in step (h-3) that the pressure reversal phenomenon has occurred. The third differential pressure test is:
The method further comprises a step of performing an airtight test on a secondary barrier when it is determined in step (k-3) that the pressure in the heat insulation space and the pressure in the space between the barrier walls are not equal to each other. 6. The evaluation method according to 6.

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