Maintenance management method for ships

Abstract

The invention relates to a method for managing the maintenance of a vessel comprising a sealed thermally insulated tank for transporting liquefied gas. The method comprises the following steps: determining 310 the current filling level of the tank; determining 320 the current movement state of the vessel; determining 330 a current sloshing index IBi according to the current filling level of the tank and the current movement state of the vessel, taking into account the position and geometry of the tank; integrating 340 the determined current sloshing index IBi to obtain a wear index IUi taking into account the history of the sloshing index. The wear index is then compared with a threshold value to indicate whether the tank needs to be inspected according to the result of the comparison.

Description

Technical Field

[0001] The present invention relates to a maintenance management method for a vessel comprising one or more tanks. The invention more particularly relates to the inspection and maintenance of sealed thermally insulated tanks for transporting liquefied gases. In this document, the term "vessel" refers to a device for transporting liquefied gases between two points on the earth or a floating unit for processing and / or storing one or more liquefied gases. Background Art

[0002] Sealed thermally insulated tanks are generally used for storing and / or transporting liquefied gases at low temperatures, such as tanks for transporting liquefied petroleum gas (LPG) at temperatures between, for example, -50°C and 0°C inclusive, or tanks for transporting liquefied natural gas (LNG) at about -162°C at atmospheric pressure. These tanks can be used to transport liquefied gases and / or receive liquefied gases as fuel for the propulsion of floating structures. Thus, a wide variety of liquefied gases can be envisaged, in particular methane, ethane, propane, butane or ethylene.

[0003] Ship tanks can be single or double seal membrane tanks that allow transportation at atmospheric pressure. The sealing membrane is usually made of thin sheet stainless steel or Invar. The membrane is usually in direct contact with the liquefied gas.

[0004] During its transport, the liquid contained in the tank is subject to various movements. In particular, the movement of the ship at sea, for example due to climatic conditions such as sea or wind conditions, causes agitation of the liquid in the tank. The agitation of the liquid, usually called "sloshing" (or sloshing in French), generates stresses on the tank wall, which may jeopardize the integrity of the tank.

[0005] These sloshing phenomena occur on ships transporting natural gas, hereinafter referred to as LNG, or on methane carriers, as well as on moored storage vessels known as FPSO (Floating Production Storage and Offloading) units, such as, for example, oil production platforms and natural gas liquefaction plants, often referred to as FLNG (Floating Liquefied Natural Gas) units or floating storage and regasification units (FSRU), i.e., more generally, floating production, storage and export support units. As soon as the liquefied gas cargo resonates with the excitations generated by even low-amplitude surges to which the ship is subjected, sloshing phenomena occur just as much in severe sea conditions as in practically calm sea conditions. In these resonant situations, the sloshing can become very violent, in particular rupturing on vertical walls or at corners, with the risk of damaging the liquefied gas sealing system or the insulation system present behind said sealing system.

[0006] Now, tank integrity is particularly important in the case of liquefied gas tanks, such as LNG tanks, since the liquids transported are of flammable or explosive nature and there is a risk of cold spots on the steel hull of the floating unit in the event of a leak.

[0007] US Patent 8,643,509 discloses a method for reducing the risks associated with sloshing of liquefied gas cargoes. In this document, the resonant frequency of the liquid in the tank is estimated based on the tank and its filling level. During transportation, the movement frequency of the ship is evaluated based on the climate and sea conditions and the ship's speed. The predicted movement frequency is also evaluated based on the route followed by the ship. If one of the movement frequencies is too close to the resonant frequency of the liquid in the tank, an alarm is issued to change the route and / or change the speed of the ship in order to avoid a dangerous situation.

[0008] Despite the provision of sloshing reduction measures, sloshing of the liquid in the tank, in particular due to resonance phenomena, may lead to local risks of deformation of the primary sealing membrane, damage to the infrastructure present in the primary space and / or the secondary space on which the primary sealing membrane rests, in particular objects falling from static equipment are prone to damage the primary sealing membrane in the short to medium term, or more generally, may lead to deformation of the primary sealing membrane exceeding its structural tolerance. Tank inspections are provided in the preventive maintenance of ships in order to verify the good condition of the tanks. However, tank inspections require complete emptying of the tanks, which may cause the ship to be fixed or the storage tanks of the floating unit to be unusable for a period of time. On ships with more than one tank, most of the tanks, or even all of the tanks, are subject to traditional inspections, which represents a very high cost of inactivity. Now, in most cases, the inspection may show no defects or no repairs forced by non-conformity, which also means that the inspection is redundant and the ship is fixed in vain. In fact, the cost of fixing the tanks, for example due to the inspection, affects the cost-effectiveness of the ship; in other words, the tank inspection causes a non-negligible risk of redundant fixing. Summary of the invention

[0009] One idea on which the present invention is based is to determine the potential risk level of damage to the tanks of a ship according to the conditions experienced by the tanks during their service life, and this potential risk level of damage to the tanks is similar to a "wear index" that represents the actual aging of the tanks. To this end, a liquid slosh index is determined according to the movement of the ship when the ship is sailing between two points or is stationary. This liquid slosh index is stored and integrated over time to obtain a wear index for the tanks. The wear index is then used to trigger a tank inspection and / or to determine the tank that is most likely to be damaged among all the tanks of the ship.

[0010] According to a first embodiment, the invention provides a method for managing the maintenance of a vessel comprising at least one sealed thermally insulated tank for transporting liquefied gas, the tank having a geometric shape and a position on the vessel. The method comprises the steps consisting of:

[0011] determine the current fill level of the tank,

[0012] Determine the current movement status of the vessel,

[0013] Taking into account the position and geometry of the tank, the current sloshing index is determined based on the current filling level of the tank and the current movement state of the vessel,

[0014] The determined current slosh index is integrated to obtain the wear index taking into account the history of the slosh index,

[0015] comparing the wear index with a first threshold value to indicate whether the tank needs to be inspected based on the result of the comparison,

[0016] Due to the use of the first threshold value, it is possible to decide whether to perform a tank inspection based on an objective criterion representing the possible wear of the tank. The first threshold value can be set in various ways. According to one embodiment, the first threshold value can be set in an absolute manner indicating a wear level above which the tank must be inspected. According to another embodiment, the first threshold value is a relative value indicating that one tank may have suffered greater wear than another tank.

[0017] The history of the slosh index relates for example to a record of the current slosh index of the liquid since commissioning of the vessel or since a recent repair of part or all of the tanks. Thus, the current slosh index of the liquid augmented with the wear index, is always available, which itself is derived from the previously measured / recorded current slosh index.

[0018] According to a preferred embodiment, the vessel comprises a plurality of tanks, a wear index is determined for each tank, and the first threshold value corresponds to the wear index of the other tanks in order to indicate that an inspection has to be performed on the tank having the highest wear index.

[0019] According to various embodiments, a method of the above-mentioned kind may have one or more of the following features.

[0020] Once a tank is indicated as one that has exceeded the first threshold, the indicated tank may be inspected.

[0021] After inspecting the tank corresponding to the highest wear index, if the inspected tank is damaged, it is determined that the next tank that must be inspected is the tank with the highest wear index among the remaining tanks. And so on, the inspection of the tanks is carried out in descending order of wear index until the tank inspection shows that there is no failure to force partial or complete repair.

[0022] Thanks to the method, after inspecting the tank, if the tank is not damaged, the inspection of the tank can be stopped.

[0023] The comparison of the wear index with the threshold value is performed during maintenance operations of the vessel.

[0024] According to a variant, determining the current movement state of the vessel comprises determining at least one of the following parameters: height of waves, period of waves, angle of attack of waves relative to the orientation of the vessel, speed of the vessel, vibrations of the vessel, measured movement of the vessel.

[0025] The measured movement of the vessel has to be understood as a measurement of one or more actual movements of the vessel.According to this variant, determining the measured movement of the vessel may comprise measuring accelerations in translation and rotation about three mutually perpendicular axes.

[0026] According to another variant, determining the current slosh index takes into account at least one of the following additional structural state parameters: number of thermal cycles the tank has been subjected to, elongation of the vessel, stiffness level of the hull, properties of the liquefied gas, filling level of the ballast tanks.

[0027] Determining the current slosh index preferably comprises determining the probability of tank degradation when the tank is subjected to current movement conditions of the vessel.

[0028] According to a specific embodiment, the current sloshing index can be obtained by reading a value in a multi-entry correspondence table, one entry corresponding to the tank filling and at least one entry corresponding to the current movement state of the vessel, the read value representing the degradation probability of the tank.

[0029] According to another embodiment, integrating the current shake index corresponds to summing up the current shake index, which is calculated successively during consecutive measuring cycles.

[0030] According to a second embodiment, the present invention also provides a system for managing the maintenance of a ship comprising at least one sealed thermally insulated tank for transporting liquefied gas. The system comprises at least one tank filling level sensor, a device for assessing the movement of the ship, a processing device and an alarm device. At least one tank filling level sensor is suitable for measuring the current filling level of at least one tank. The device for assessing the movement of the ship is suitable for determining the current movement state of the ship. The processing device is configured to: determine a current sloshing index according to the current filling level of the tank and the current movement state of the ship, taking into account the position and geometry of the tank; integrate the determined current sloshing index to obtain a wear index taking into account the history of the sloshing index; and compare the wear index with a first threshold value. The alarm device indicates whether at least one tank or each tank must be inspected according to the comparison result.

[0031] According to one embodiment, the device for assessing the movement of a vessel comprises a weather station that measures the height, frequency and direction of waves in the vessel's environment.

[0032] According to another embodiment, an apparatus for assessing movement of a vessel includes an accelerometer placed in the vessel.

[0033] In a preferred example, the processing means are partly located in a monitoring station on land and communicate with the vessel, for example by radio or other telecommunication means, to receive information relating to the current filling level of the at least one tank and the current movement status of the vessel.

[0034] In another example, a liquefied gas transport vessel includes a plurality of sealed thermally insulated tanks and a management system for each of the tanks thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be better understood and other objects, details, features and advantages of the present invention will become more apparent during the following description of particular embodiments of the invention given by way of non-limiting illustration only with reference to the accompanying drawings.

[0036] Figure 1 This is a schematic diagram of a liquefied gas transport ship.

[0037] Figure 2 Indicates integration into Figure 1 management system in ships,

[0038] Figure 3 represents a management system according to another embodiment,

[0039] Figure 4 is a flow chart representing a method for updating a wear index,

[0040] Figure 5 is a flow chart representing a method for managing maintenance of tanks of a vessel. DETAILED DESCRIPTION

[0041] Embodiments are described below with reference to a vessel comprising a double hull forming a support structure in which a plurality of sealed thermally insulated tanks are arranged. In such a support structure, the tanks have, for example, a polyhedral geometry, such as a prismatic shape.

[0042] Sealed thermally insulated tanks of this type are provided for the transport of liquefied gas, for example. Liquefied gas is stored and transported at low temperatures in tanks of this type, which necessitates thermal insulation of the tank walls in order to keep the liquefied gas at this temperature. It is therefore particularly important to maintain the integrity of the tank walls, including the thermally insulating space located under the sealing membrane, in order to maintain the sealing of the tank and prevent leakage of the liquefied gas from the tank on the one hand, and to prevent degradation of the thermal insulation properties of the tank on the other hand, in order to keep the gas in its liquefied form.

[0043] The sealed thermally insulated tank also comprises an insulating barrier which is anchored to the double hull of the vessel and carries at least one sealing membrane. and or other trademarks sold to produce this type of tank.

[0044] Figure 1 A vessel 1 comprising four sealed thermally insulated tanks 2 is illustrated. The four tanks 2 may have the same or different filling states. When the vessel 1 is at sea, it is subjected to many movements related to the navigation conditions. These movements of the vessel 1 are transmitted to the liquid contained in the tanks 3, 4, 5, 6, which are therefore subjected to movements in the tanks 3, 4, 5, 6. These movements of the liquid in the tanks 3, 4, 5, 6 generate impacts on the walls of the tanks 3, 4, 5, 6, which can damage the tanks immediately if they are too severe. In addition, repeated hammering at a high but non-destructive level on the walls of the tanks 3, 4, 5, 6 may cause degradation of the walls by fatigue wear. It is now important to maintain the integrity of the walls of the tanks 3, 4, 5, 6 in order to maintain the sealing and insulating properties of the tanks 3, 4, 5, 6.

[0045] It is known that in order to avoid critical navigation conditions, it is necessary to avoid liquid movements that expose the tank to direct risk of damage. In the case of damage related to wear of the hammered material, only regular inspections of the tank can detect the state of damage. In order to be able to enter the tank, the tank inspection requires the complete emptying of the tank. This type of operation is relatively lengthy and keeps the ship stationary for a long time. In order to optimize the tank inspection, the invention proposes to determine the tank wear index in order to decide the timing of this type of inspection.

[0046] The wear index of a ship's tanks must represent the risk of tank damage based on the impacts suffered related to the sloshing of the liquefied gas cargo. The risk of damage to a ship's cryogenic tanks can be expressed by the following formula:

[0047] [Mathematical function 1]

[0048] Risk = ∫∫ 罐 ∫ o T Prob(Pres(dS,t)>Res(dS)|nr(t),mvt(t)).dS.dt

[0049] in:

[0050] -nr(t) represents the filling level of the tank at time t,

[0051] -mvt(t) represents the movement of the tank at time t,

[0052] - Pres(dS, t) represents the pressure exerted on the unit surface area dS of the tank at time t,

[0053] -Res(dS) represents the strength per unit surface area dS of the tank,

[0054] - Prob(Pres(dS, t) > Res(dS) | nr(t), mvt(t)) represents the probability that the pressure per unit surface area is greater than its intensity, depending on the filling level of the tank and the movement of the tank,

[0055] -T is the period during which the risk of damage is incurred.

[0056] By applying the approximation of the above formula to the actual life conditions of the tank, a tank wear index can be generated. Thus, the wear index will give a value representing the probability of damage, based on what the tank will actually be subjected to.

[0057] Figure 2 An example management system 100 on board a vessel 1 is illustrated. The management system 100 comprises a central processor unit 110 connected to a plurality of onboard sensors 120, allowing different parameter measurements to be obtained. Thus, as a non-exhaustive example, the sensors 120 comprise at least one fill level sensor 121 for each tank, various vessel movement sensors 122 (tachometer, heading) and sea state sensors 123. The management system 100 also comprises a communication interface 130 enabling the central processor unit 110 to communicate with remote devices, for example to obtain meteorological data, vessel position data, etc.

[0058] The number and type of motion sensors 122 and sea state sensors 123 are up to the skilled person to choose to determine the motion experienced by the vessel and any measurement redundancy. In a preferred embodiment, the sea state sensors include a weather station that measures the height, frequency and direction of waves in the vessel's environment. Alternatively, the sea state may not be measured, but the exact position of the vessel is simply inferred from weather information. However, it is preferred to have some redundancy to resist failure of some sensors.

[0059] The management system 100 further comprises a human-machine interface 140. The human-machine interface 140 comprises a display device 41. The display device 41 enables the operator to obtain management information calculated by the system or measurement values ​​obtained by the sensor 120 or even the current shaking state.

[0060] The human-machine interface 140 also comprises acquisition means 42 which enable an operator to manually feed quantity values ​​to the central processing unit 110, typically supplying the central processing unit 110 with data which cannot be obtained by sensors because the vessel does not comprise the necessary sensors or the sensors are damaged. For example, in one embodiment, the acquisition means allow an operator to input information about wave heights based on visual observations.

[0061] The management system 100 comprises a database 150. The database 150 allows storing the measurements made while underway. According to a preferred embodiment, the database comprises some quantities obtained during measurement campaigns in the laboratory or on board a ship at sea.

[0062] Figure 3 An example of a management system 200 located on land and communicating with a vessel 1 is illustrated. The vessel includes a central processor unit 110, a sensor 120, and a communication interface 130. The management system 200 includes a central processor unit 210, a communication interface 230, a human-machine interface 240, and a database 250. The functions of the management system 200 are similar to those of the management system 100, except that information measured by the sensor 120 of the vessel 1 is sent to the management system 200 located on land through the communication interfaces 130 and 230. For example, the communication interface may use terrestrial or satellite radio data transmission.

[0063] Figure 4 An example of updating the wear index is illustrated in the flow chart. According to a first embodiment, the updating is fully implemented in the central processor unit 110 forming a single processing device. According to a second embodiment, the updating is performed partly in the central processor unit 110 and partly in the central processor unit 210, the combination forming a shared processing device. During a first step 310, the tank filling level sensor 121 of each tank 3, 4, 5, 6 of the vessel measures the liquid level in each tank to determine the current filling level of each tank i. Then, during a second step 320, the movement sensor 122 and the sea state sensor 123 send information to the central processor unit 110 to determine the current movement state of the vessel.

[0064] In order to simplify the calculations, the measurements are preferably made within a unit time interval, during which the measurement is considered stable. By way of example, a unit duration of one hour is suitable. Thus, the current fill level measurement can be an average measurement over one hour, which allows to neglect the influence of the movement of the liquid on the measurement. With regard to the current movement state of the vessel, the average measurement or the worst-case measurement within the unit duration can be considered. For example, if within the unit duration the sea state sensor measures a wave of 2 meters and a wave of 8 meters, the retained measurement will correspond to a wave of 8 meters. On the other hand, in case the frequency of the waves is taken into account, an average measurement may be suitable.

[0065] Once the measurements are completed, a current sloshing index IBi is calculated for each tank during a step 330. The current sloshing index IBi can be determined in various ways, taking into account the position and geometry of the tanks, from various measurements made on the filling level of the tanks and the current movement state of the vessel.

[0066] For example, the simplified first embodiment does not take into account the average filling level of the tank and the maximum height of the waves in one hour. According to this first embodiment, the correspondence table contained in the database 150 or 250 is used to determine the corresponding sloshing index IBi by means of a simple reading from the measurements made in the table. The correspondence table can be generated during a measurement campaign on a tank with a similar geometric profile and on which the number and force of the impacts of the liquid on the tank wall have been measured. These measurements are then placed in a correspondence table, such as the following Table 1:

[0067] [Table 1]

[0068]

[0069] Depending on the filling level and depending on the wave height, the value of the current sloshing index IB is directly read off, taking into account the geometry of the tank. Obviously, the larger the table, the more precise the current sloshing index IB. Furthermore, the table must correspond to each tank of the vessel, since the sloshing of the liquid depends inter alia on the shape of the tank and its position in the vessel.

[0070] The use of a single movement parameter, such as the height of the waves, is not sufficient to allow an accurate determination of the effect of the sloshing, but only allows a rough indication to be obtained. In fact, many other parameters can be used to determine the sloshing of the liquid, such as the frequency of the waves, the angle of attack of the waves on the vessel, the speed of the forward movement of the vessel. In addition, secondary parameters can also be added, such as the force and direction of the wind and the current. It is conceivable to use a corresponding table with more entries. It is also possible that the data in the table can also be processed before they are used. For example, the frequency of the waves, the angle of attack of the waves and the speed of the ship can be combined to the frequency of the waves acting on the ship, and thus allow these three parameters to be reduced to a single parameter, and thus reduce the size of the table while taking into account multiple parameters. Another possibility is to determine a plurality of tables, each of which gives partial sloshing indices, and to cluster these indices together, for example by multiplying the partial indices.

[0071] The use of a table also allows to take into account indirect causes of movement, such as vibrations of the ship, vibrations of the barge or simple vibrations of the tank, generated for example by the blades of the propulsion system or the ship's propeller. The amplitude and frequency of the vibrations can be two entries in the table obtained by repeated trials on tanks of similar size.

[0072] Another possibility is to actually measure the agitation of the ship by extracting the state of the ocean. The sensor 120 determines the measured movement of the ship, for example, by measuring the accelerations to which the ship is subjected on three perpendicular axes in terms of translation and rotation. In order to evaluate the movement of the ship, an inertial measurement unit can be advantageously used, which is composed of one or more accelerometers and / or one or more gyroscopes, such as mechanical gyroscopes, and / or one or more magnetometers. It is assumed that a plurality of measurement units (of the same type or two different types) are used, which are advantageously distributed on the ship in a manner that records accurate measurements of the movement of the ship. It should be noted that an IMU is sometimes referred to as an MRU (motion reference unit). Similarly, a correspondence table can be used, which has an entry for each of the measured values.

[0073] Alternatively, it is also possible to calculate the index representing the agitation of the liquid in the tank in a different way. For example, the resonant frequency of the liquid in the tank is calculated based on the liquid level and geometry of the tank. Then, the average oscillation frequency of the vessel is determined, for example, by measuring the average frequency and the average oscillation amplitude of the vessel using an accelerometer. The current sloshing index IBi may be proportional to the oscillation amplitude of the vessel and inversely proportional to the difference between the resonant frequency of the tank and the oscillation frequency of the vessel.

[0074] For determining the transient slosh index, it is also possible that additional structural state parameters that may have an influence on the tank damage risk may be taken into account. The tank is subject to large thermal variations, which cause it to lengthen and shorten. The thermal cycles to which the tank is subjected also have a wear effect that weakens it. The multiplication factor of the transient slosh index may take into account the number of thermal cycles, thereby indicating an increased risk of damage associated with sloshing depending on the number of thermal cycles. The thermal cycles may likewise be weighted according to the liquid content of the tank, the temperature of which may vary and thus cause the amplitude of the thermal cycles to vary.

[0075] Another additional parameter concerns the elongation of the vessel, in other words, the change in length of the floating structure. The vessel is made of metal and the changes in length occur according to the temperature of the sea and the sun. These changes in length are independent of the expansion of the membranes of the tank, which is related to the temperature of the liquefied gas. These expansion differences lead to supplementary stresses at the level of the membranes that can weaken the membranes more or less. Again, the introduction of a multiplication factor makes it possible to take these phenomena into account, for example by weighting the transient sloshing index by 10% in the event that the stresses caused by the elongation exceed a predetermined threshold.

[0076] It is also possible to consider the level of stiffness of the hull or the flexibility of the hull, especially when one or more tanks are mounted on a movable vessel. When the vessel is subjected to waves, it will twist more or less, depending on its position relative to the waves. The resulting deformations lead to stresses on the tanks, which must be taken into account when determining the transient sloshing index.

[0077] The properties of the cryogenic liquid being transported may influence the determination of the transient slosh index. The composition of the liquefied gas causes changes in its density and its flow properties, which can modify the effects related to slosh in a positive or negative way, or simply change the resonant frequency of the liquid in the tank. If the tank is used for more than one type of gas, additional parameters specific to the properties of the cryogenic liquid being transported must be considered when determining the transient slosh index.

[0078] The height of the liquid column in the ballast tank is another additional parameter that can be taken into account when calculating the transient sloshing index. On some ships, the ballast tanks can be in direct contact with the walls of the supporting tanks. The seawater in the ballast tanks is also subject to sloshing. However, depending on the filling of the ballast tanks, the sloshing phenomena in the tanks and in the ballast tanks can be amplified or dampened. Only the structure of the ship can determine the final result.

[0079] Once the current sloshing index IBi has been determined for each tank of the vessel during the unit duration, it is necessary to integrate it into the tank wear index IUi during step 340. For the sloshing index calculated during a given unit period, simply updating the sum of the current sloshing index IBi in the previously calculated wear index IUi is sufficient to determine a wear index IUi that takes into account the history of the sloshing index, for example since the commissioning of the vessel.

[0080] The sloshing index IBi and the wear index IUi are not single, since they relate to the probability of damage. Furthermore, the magnitude of these indices IBi and IUi depends on the accuracy of the calculations that one wishes to obtain. An experienced person can even determine the magnitudes to be used with these indices. For example, the current sloshing index IBi determined in one hour may be between 0 and 15, and the cumulative wear index IUi over a 30-year service life of the ship may be between 0 and 4 million inclusive.

[0081] According to the second embodiment, Figure 4 The flowchart in is partly executed on a land management system 200 in communication with the ship. According to this second embodiment, the ship 1 transmits all the information from the sensors 120 to the land station. Alternatively, the sloshing index IBi is calculated and stored in the ship during the voyage, and the wear index IUi is calculated only when the ship arrives in port, after transmitting the sloshing index IBi calculated for the entire duration of the voyage achieved by the ship.

[0082] The wear index IUi is calculated, which is used by the maintenance management system through Figure 54. The flowchart of FIG. 410 is used, which is an example used when arriving at the correct port. The flowchart includes steps performed by maintenance personnel and other steps performed by the management system 100 or 200. Depending on the degree of automation of maintenance, some steps can be performed by maintenance personnel or by the system. Step 410 restores the wear index IUi of all tanks on the ship. A first test 420 is performed to determine whether a tank inspection must be envisaged given the current date and the number of days the ship has completed at sea.

[0083] If no inspection is scheduled, a test 430 compares the wear index IUi with an inspection threshold SV corresponding to a high risk of damage that should not normally be reached before the inspection date. If one or more wear indices IUi reach the inspection threshold SV, it is necessary to indicate during a step 440 that a tank inspection must be carried out for each of the tanks that have reached the threshold SV, for example by activating a visual or sound alarm. The crew is thus informed that it is necessary to carry out a tank inspection for the tank or tanks concerned upon arrival at the port. If the threshold SV has not been exceeded, or after the step 440 has been carried out, the flowchart ends.

[0084] If the test 420 determines that a tank inspection is scheduled, a step 450 enables the tank with the highest wear index to be determined. To this end, each wear index IUi is compared with the wear indexes IUi of all other tanks to determine the tank with the highest wear index Max(IUi).

[0085] Once the highest wear index Max(IUi) has been determined, the management system marks the corresponding tank during a step 460 and only performs a check on this tank.

[0086] After the inspection of the tank, a new test 470 is carried out to determine whether another tank must be inspected. This test 470 consists in verifying whether the tank inspected is damaged. If the tank is not damaged, it is not necessary to inspect other tanks that have a lower risk of damage according to the wear index IUi. On the other hand, if the tank is damaged, it is necessary to carry out step 480.

[0087] Step 480 is equivalent to removing the wear index corresponding to the damaged tank that has just been inspected from the wear index of the ship, which is the tank with the highest wear index among the remaining tanks, before repeating step 450 to determine the next tank that must be inspected. If the tank itself is damaged, the tanks are inspected in descending order of wear index IUi.

[0088] If the inspection of a tank does not reveal any defects or any nonconformity that would necessitate at least one repair, no further tanks need to be inspected. This approach makes it possible to significantly reduce the number of tanks inspected. The number of tanks inspected is reduced to the number of damaged tanks plus one, which avoids emptying all tanks.

[0089] As mentioned above, the automation intensity can be greater or less. According to a relatively low automation embodiment, the management system 100 and 200 only stores the wear indicators IUi and compares them with each other and with the check threshold SV. The management system then displays the wear indicators IUi in descending order, with a visual (e.g. red / green) indicator indicating whether the threshold SV has been exceeded. In this configuration, only steps 410, 430 and 450 are performed by the management system 100 or 200, and Figure 5 The remainder of the flowchart is performed by the maintainer.

[0090] According to a highly automated implementation, the maintenance personnel only performs the inspection of steps 440 and 460 , and the inspection results are recorded in the system.

[0091] Alternatively, step 460 may also compare the wear index Max(IUi) with a minimum wear threshold below which no tank inspection is necessary. This makes it possible to omit unnecessary tank inspections.

[0092] Alternatively, test 430 and step 440 may be eliminated. In fact, the inspection threshold SV must be relatively high to avoid having to perform a tank inspection on every voyage. If the threshold is high, it may prove useless.

[0093] According to another variant, it can also be considered that no inspection date is required and, on the contrary, it can be considered that only an inspection threshold SV is used to trigger the inspection. In this case, the test 430 can indicate that the wear index IUi of multiple tanks is higher than the threshold SV. In order to avoid inspecting multiple tanks, step 440 can be replaced by a step corresponding to steps 450 and 480, so that only one tank is inspected if they are not damaged.

[0094] If the threshold value SV is reached and no tank is damaged, it is necessary to increase the threshold value SV to a new value input by the acquisition device 42 .

[0095] If the tank inspection concludes that the tank is damaged, the tank must be repaired immediately, or repaired during a subsequent port call but the tank will be considered out of service pending repair. Figure 5 When drawing the flow chart, failed tanks can be ignored.

[0096] As long as no repairs have been carried out on the tank, it is necessary to retain a wear index representing the wear of the tank since the construction of the ship. Once the tank has been repaired, the wear index may no longer represent the wear state of the tank and it is necessary to modify the index. If the tank repair consists in rebuilding almost all of the tank, the repaired tank may be considered new and it is therefore necessary to reset its wear index IUi to zero by the acquisition means 42. On the other hand, if a partial repair has been carried out on the tank and certain signs of wear considered minor have not led to repairs, the wear index may decrease or remain unchanged. In particular, if the repairs involve a minimal area of ​​the tank, the index remains unchanged.

[0097] Although the present invention has been described in conjunction with a number of specific embodiments, it is obvious that the present invention is by no means limited to these embodiments and covers the combination of means described within the scope of the present invention and all technical equivalents if the latter fall within the scope of the present invention.

[0098] Use of the verb "comprise" or "include" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim.

[0099] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A method for managing the maintenance of a vessel (1), said vessel comprising at least one sealed thermally insulated tank for transporting liquefied gas, said tank having a geometric shape and a position on said vessel, said method comprising the steps consisting of: determining (310) a current fill level of the tank, determining (320) a current movement state of the vessel, Taking into account the position and geometry of the tank, a current sloshing index IBi is determined (330) according to the current filling level of the tank and the current movement state of the vessel, wherein determining the current sloshing index (IBi) comprises determining a degradation probability of the tank when the tank is subjected to a current movement state of the vessel, wherein the current sloshing index (IBi) is obtained by reading a value in a multi-entry correspondence table, one entry corresponding to the filling of the tank, at least one entry corresponding to the current movement state of the vessel, and the read value represents the degradation probability of the tank, The determined current slosh index IBi is integrated (340) to obtain a wear index IUi taking into account the history of said slosh index, The wear index is compared with a first threshold value (430, 450) to indicate whether the tank needs to be inspected (440, 460) based on the result of the comparison.

2. The method according to claim 1, wherein: The vessel comprises a plurality of tanks (3, 4, 5, 6), wherein a wear index (IUi) is determined for each tank, and wherein the first threshold corresponds to the wear index (IUi) of the other tanks in order to indicate (460) that the tank with the highest wear index (Max(IUi)) must be inspected.

3. The method according to claim 1 or 2, wherein: Inspect the indicated tank.

4. The method according to claims 2 and 3, wherein: After inspecting the tank corresponding to the highest wear index (Max(IUi)), if the inspected tank is damaged, it is determined (480) that the next tank that must be inspected is the tank with the highest wear index among the remaining tanks.

5. The method according to claims 2 and 3, wherein: After inspecting a can, if the can is not damaged, the inspection of the can is stopped.

6. A method according to any one of the preceding claims, wherein: A comparison (450) of the wear index (IUi) with a threshold value is performed during a maintenance operation of the vessel.

7. A method according to any one of the preceding claims, wherein: Determining the current movement state of the vessel includes determining at least one of the following parameters: The height of the waves, The cycle of the waves, the angle of attack of the wave relative to the orientation of the vessel, the speed of the vessel, the vibration of the vessel, The measured movement of the vessel.

8. A method according to any one of the preceding claims, wherein: Determining the current sloshing index (IBi) takes into account at least one of the following additional structural state parameters: The number of thermal cycles to which the tank has been subjected, the elongation of the vessel, The stiffness level of the shell, The properties of the liquefied gas, Fill level of ballast tanks.

9. A method according to any one of the preceding claims, wherein: Integrating the current sway index (IBi) corresponds to summing up the current sway index, which is calculated successively during consecutive measurement cycles.

10. A system (100, 200) for managing the maintenance of a vessel comprising at least one sealed thermally insulated tank for transporting liquefied gas, the system comprising: at least one tank fill level sensor (121, 230) for measuring a current fill level of at least one tank, a device (122, 123, 130, 230) for evaluating the movement of the vessel, the device being capable of determining the current movement state of the vessel, The processing device (110, 210) is configured to: determining (330) a current sloshing index (IBi) based on a current filling level of the tank and a current movement state of the vessel, taking into account the position and geometry of the tank, wherein determining the current sloshing index (IBi) comprises determining a probability of degradation of the tank when the tank is subjected to the current movement state of the vessel, wherein the current sloshing index (IBi) is obtained by reading a value in a multi-entry correspondence table, one entry corresponding to the filling of the tank, at least one entry corresponding to the current movement state of the vessel, and the read value represents the probability of degradation of the tank, Integrating (340) the determined current sloshing index (IBi) to obtain a wear index (IUi) taking into account the history of the sloshing index, comparing the wear index to a first threshold value (430, 450), An alarm device (41) indicates whether an inspection (440, 460) of the at least one tank must be carried out based on the result of the comparison.

11. The system according to claim 10, wherein: The device (123) for assessing the movement of the vessel comprises a weather station which measures the height, frequency and direction of waves in the vessel's environment.

12. The system according to claim 10 or 11, wherein: The processing device is located partly in a monitoring station (200) on land and communicates with the vessel by radio to receive information related to the current filling level of the at least one tank and the current movement status of the vessel.

13. A ship for transporting liquefied gas comprising a plurality of sealed thermally insulated tanks, the ship comprising a management system (100) according to any one of claims 10 to 12 for each of the tanks of the ship.

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