FR3096432A1 - Waterproof membrane for storage tank - Google Patents

Abstract

The invention relates to a sealed membrane for a liquefied gas storage tank, said sealed membrane comprising, at least in a lower portion of said tank, an austenitic stainless steel grade having a chemical composition by mass comprising: 16.0% ≤ Cr ≤ 28.0%; 10.0% ≤ Ni ≤ 27.0%; and 2.0% ≤ Mo ≤ 8.0%. Figure to be published: Fig. 1

Description

Description Title of the invention: Waterproof Membrane for Storage Tank Technical field

The invention relates to the field of sealed tanks and thermally insulating membranes.

In particular, the invention relates to the field of sealed and thermally insulating tanks for the storage and/or transport of liquid at low temperature or of liquefied gas, such as tanks for the transport of Liquefied Petroleum Gas (also called LPG ) having for example a temperature between - 50°C and 0°C.

These tanks can be installed on land or on a floating structure.

In the case of a floating structure, the tank may be intended for the transport of liquefied gas or to receive liquefied gas serving as fuel for the propulsion of the floating structure.

Technology background

The Applicant has found that the sheets constituting the sealed membranes of a dc storage tank dc liquefied gas are likely to have points of pitting corrosion.

This is particularly likely to occur when the tank is associated with a re-liquefaction system equipped with seawater exchangers and the tightness of said exchangers is no longer ensured.

[0003] The patent application FR1537850 describes a sealed tank membrane having good corrosion resistance and mechanical strength properties under conditions of use.

The membrane is made of an austenitic stainless steel sheet comprising a carbon content less than or equal to 0.03%, a chromium content less than or equal to 18%, a nickel content less than or equal to 10%, and a nitrogen content between 0.12% and 0.25%.

Alternatively, the austenitic stainless steel may include a carbon content less than or equal to 0.03%, a chromium content less than or equal to 17.5%, a nickel content less than or equal to 13%, a molybdenum content less than or equal to 2.8%, and a nitrogen content of between 0.12% and 0.25%.

These membranes can be used in liquefied gas transport tanks.

[0004] However, the resistance to wet corrosion of such a waterproof membrane is not entirely satisfactory, in particular in the presence of seawater residues.

Abstract 100051 An idea underlying the invention is to provide a waterproof membrane for a waterproof and thermally insulating tank which is not subject to wet corrosion, in particular in the presence of seawater residues inside the tank. tank.

Thus one object of the invention is to prevent the waterproof membrane from being corroded.

To this end, the present invention relates to a sealed membrane for a liquefied gas storage tank 2, said sealed membrane comprising, at least in a lower portion of said tank, a grade of austenitic stainless steel having a chemical composition by mass comprising: - 16.0 < Cr < 28.0% - 10.0 < Ni < 27.0% - 2.0 < Mo < 8.0%.

[0007] Thus, such a waterproof membrane has better resistance to wet corrosion than the membrane of the aforementioned document.

In particular, the presence of molybdenum in the aforementioned proportions makes it possible to improve the resistance to wet corrosion, in particular with respect to halides such as the chloride ions present in seawater.

[0008] The term "liquefied gas" means any substance which is in the vapor state under normal pressure and temperature conditions and which has been placed in the liquid state by lowering its temperature and/or by increasing its temperature. pressure.

[0009] According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade further comprises: Oc Mn 54%.

[0010] According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade further comprises: - 0<Cu<2%.

According to one embodiment, the bulk chemical composition of the austenitic stainless steel grade comprises: - 16.0% < Cr < 19.0% - 10.0% < Ni < 15.0% - 2 .00% < Mo < 3.00% - 0% < N < 0.11% - 0% < Mn < 2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises: - 16.0% < Cr < 18.5% - 10.0% < Ni < 14.0% - 2 .00% < Mo < 3.00% - 0% < N < 0.11% - 0% < Mn < 2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises: - 17.0% <Cr <19.0% - 12.5% <Ni <15.0% 3 - 2.00%<Mo<3.00%-0%<N<0.11%-0%<Mn<2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises: - 16.5% < Cr < 18.5% - 12.5% < Ni < 14.5% - 4 .00% < Mn < 5.00% - 0.12% < N < 0.22% - 0% < Mn < 2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises: - 24.0% < Cr < 26.0% - 21.0% < Ni < 23.0% - 2 .00% < Mn < 2.50% - 0.10% < N < 0.16% - 0% < Mn < 2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises: - 16.5% < Cr < 18.5% - 11.0% < Ni < 14.0% - 2 .5% < Mo < 3.00% - 0.12% < N < 0.22% - 0% < Mn < 2.00%

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises - 16.5% < Cr < 19.5% - 10.5% < Ni < 14.0% - 3, 0% < Mo < 4.0% -0.1% < N < 0.2% - 0% < Mn < 2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises - 24.0% < Cr < 26.0% - 24.0% < Ni < 27.0% -4, 7% < Mo < 5.7% - 0.17% < N < 0.25% - 0% < Mn < 2.0% - 1.00% < Cu < 2.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises - 19.5% < Cr < 20.5% - 17.5% < Ni < 18.5% - 6, 0% < Mn < 7.0% - 0.18% < N < 0.25% - 0% < Mn < 1.00% -0.5% < Cu < 1.00%.

According to one embodiment, the chemical composition by mass of the austenitic stainless steel grade comprises - 19.0% < Cr < 21.0% - 24.0% < Ni < 26.0% - 6, 0% < Mn < 7.0% - 0.15% < N < 0.25% - 0% < Mn < 1.00% -0.5% < Cu < 1.50%.

[0021] According to one embodiment, the chemical composition by mass of the grade of austenitic stainless steel in carbon is less than or equal to 0.03%.

According to one embodiment, the austenitic stainless steel grade has an elastic limit greater than or equal to 220 MPa.

According to one embodiment, the elastic limit of the austenitic steel grade is less than 340 MPa and for example between 245 and 305 MPa.

[0024]According to one embodiment, the steel grade has an equivalent number of resistance to pitting greater than or equal to 24.

The Pitting Resistance Equivalent Number or PREN is a predictive measure of a stainless steel's resistance to localized pitting corrosion, based on its chemical composition.

The higher the PREN value, the more resistant the stainless steel is to localized chloride pitting corrosion.

A formula used to calculate the PREN of a steel grade is: PREN = 1 x %Cr + 3.3 x %Mo + 16 x %N.

According to one embodiment, the grade of austenitic stainless steel is a first grade of steel, said membrane further comprising, in an upper portion of the tank, a second grade of steel.

[0026] Thus, the membrane comprises a grade of steel offering resistance to pitting corrosion in the zones liable to be subjected to this phenomenon, namely the lower zone of the tank, while the upper portion of the tank is likely to be made with a second grade of steel that is less expensive and/or has better mechanical characteristics.

According to one embodiment, the second grade of steel is an austenitic stainless steel which has a chemical composition by mass comprising: - 15% <Cr <20% - 1% <Ni <12% - Oc Mn <10 %.

[0028] This second grade of steel is particularly advantageous in that it has mechanical properties, in particular at −60° C., that are better than the first grade of steel.

In particular, the second grade of steel has a higher elastic limit, which allows it not to undergo plastic deformations under the effect of the phenomena of "sloshing", that is to say the sloshing of the liquefied gas. inside the tank.

Furthermore, this second grade of steel is also less expensive than the first.

[0029] According to one embodiment, the mass composition of the second grade of steel comprises - 0 < Mo < 1%

[0030] According to one embodiment, the mass composition of the second steel grade comprises −1%<Ni<8%.

[0031] According to one embodiment, the composition by mass of the second grade of steel comprises −2% <Mn <10%.

According to one embodiment, the composition by mass of the second grade of steel comprises: - 0% <C <0.1% - 8.5% <Mn <10% -0% <N <0, 2% - 15.5% < Cr < 16.5% - 1.5% < Cu < 2.0% - 1.0% < Ni < 2.0%.

According to one embodiment, the composition by mass of the second grade of steel comprises: - 0% <C <0.030% - 0% <Mn <2.0% - 0.10% <N <0, 20% - 16.5% < Cr < 18.5% - 6.0% < Ni < 8.0%.

According to one embodiment, the composition by mass of the second grade 6 of steel comprises: - 0% <C <0.030% - 6.00% <Mn <8.0% -0.15% <N < 0.20% - 16.0% < Cr < 17.0% - 3.5% < Ni < 5.5% - 1.50% < W < 2.5%.

According to one embodiment, the second grade of steel has an elastic limit greater than or equal to 320 MPa, preferably greater than or equal to 370 MPa and advantageously greater than or equal to 400 MPa.

According to one embodiment, the membrane has a thickness of between 0.5 mm and 1.5 mm, for example of the order of 1.2 mm.

[0037] According to one embodiment, the tank has walls, each wall of the tank comprising, in the direction of the thickness, from the outside towards the inside of the tank, a thermally insulating barrier and an aforementioned sealed membrane supported by the thermally insulating barrier.

According to one embodiment, the lower part of the tank comprises a bottom wall of the tank.

According to one embodiment, the tank has a generally polyhedral shape and comprises, in addition to the bottom wall, a first transverse wall, a second transverse wall, a ceiling wall, lower bevel walls and side walls; the first and the second transverse walls being connected to each other by the bottom wall, the ceiling wall, the lower chamfer walls and the side walls; the bottom of the vessel further comprising the bottom chamfer walls.

According to one embodiment, the lower part of the tank comprises a lower portion of the first and of the second transverse wall, said lower portion extending between the bottom wall and an upper edge of the lower bevel walls.

According to one embodiment, the upper portion of the tank comprises the ceiling wall, the side walls and at least one upper portion of the first and second transverse walls.

According to one embodiment, the thermally insulating barrier is a primary thermally insulating barrier and the sealed membrane is a primary sealed membrane.

[0043] Such a tank can be part of an onshore storage facility, for example to store LPG or be installed in a floating, coastal or deep-water structure, in particular an LNG carrier, a floating storage and regasification unit. 7 station (FSRU), a floating production and remote storage unit (FPSO) and others.

Such a tank can also serve as a fuel tank in any type of ship.

[0044]According to one embodiment, a ship for transporting a cold liquid or a liquefied gas comprises a double hull and an aforementioned tank arranged in the double hull.

According to one embodiment, the invention also provides a method for loading or unloading such a ship, in which a cold liquid product or a liquefied gas is conveyed through insulated pipes from or to an installation floating or onshore storage to or from the vessel's tank.

[0046] According to one embodiment, the invention also provides a transfer system for a cold liquid product or a liquefied gas, the system comprising the aforementioned ship, insulated pipes arranged so as to connect the tank installed in the hull of the vessel to a floating or onshore storage facility and a pump for driving a flow of cold liquid product or liquefied gas through the insulated pipes from or to the floating or onshore storage facility to or from the vessel's tank.

Brief description of figures

The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given for illustrative purposes only. and non-limiting, with reference to the accompanying drawings.

[0048] [fig.1] FIG. I is a partial schematic view of a sealed and thermally insulating tank intended to contain a liquefied gas according to a first embodiment.

[0049] [fig.2] Figure 2 is a cutaway perspective view of a wall of a sealed and thermally insulating tank carried by a load-bearing wall of Figure I.

[0050] [fig.3] FIG. 3 is a partial schematic view of a sealed and thermally insulating tank intended to contain a liquefied gas according to a second embodiment.

[0051] [fig.4] Figure 4 is a cutaway schematic representation of a storage facility for a liquefied gas ship and a loading / unloading terminal of a tank of the storage facility a liquefied gas.

Description of the embodiments 100521 By convention, the adjectives “upper” and “lower” are used to define the relative position of one element with respect to another with respect to the earth's gravity field. 8

In connection with Figure 1, we observe the rear part of a tank 1 intended to receive a liquefied gas.

The tank 1 rests on a support structure formed by the inner hull of a double-hulled vessel.

The tank 1 has a generally polyhedral or prismatic shape.

The tank 1 has a first transverse wall 2 and a second transverse wall 3, here of octagonal shape.

In Figure 1, the first transverse wall 2 is only partially shown in order to allow visualization of the internal space of the tank 1.

The transverse walls 2, 3 are cofferdam walls of the ship and extend transversely to the longitudinal direction of the ship.

The tank 1 also has a ceiling wall 4, a bottom wall 5, lower chamfer walls 6, side walls 7 and upper chamfer walls 8.

The ceiling wall 4, the bottom wall 5, the lower chamfer walls 6, the side walls 7, and the upper chamfer walls 8 extend in the longitudinal direction of the ship, connecting the first and second transverse walls 2, 3 at edge level 9, and meet at edge level 10.

As shown schematically in Figure 2, the first transverse wall 2 of the tank 1 has successively, from the outside to the inside, in the direction of thickness of the walls, a thermally insulating barrier 12 comprising insulating elements 13, a waterproof membrane 14 resting on the insulating elements of the thermally insulating barrier 12.

The sealed membrane 14 is intended to be in contact with the liquefied gas contained in the tank such as liquefied petroleum gas comprising butane, propane, propene or other and having an equilibrium temperature between -50° C. and 0°C.

What has just been described for the first transverse wall is valid for the other walls 3, 4, 5, 6, 7, 8 of the tank

The waterproof membrane 14 can be made in different ways.

In the example shown, the sealed membrane 14 of the tank 1 comprises a plurality of metal plates 15 juxtaposed to each other.

These metal plates 15 are preferably rectangular in shape.

The metal plates 15 are overlap welded together in order to seal the waterproof membrane 14.

Preferably, the metal plates 15 are made of stainless steel.

The metal plates 15 have a thickness of less than 3 mm, advantageously between 0.5 and 1.5 mm, for example of the order of 1.2 mm

In order to allow the deformation of the sealed membrane in response to the various stresses undergone by the tank, in particular in response to the thermal contraction resulting from the loading of liquefied gas into the tank, the metal plates 15 comprise a plurality of undulations 16 facing the inside of the tank.

More particularly, the sealed membrane 14 of the tank 1 comprises a first series of undulations 16 and a second series of undulations 16 forming a regular rectangular pattern.

Preferably, the corrugations 16 develop parallel to the edges of the 9 rectangular metal plates 15.

The distance between two successive undulations 16 of a series of undulations is between 300 and 800 mm, and for example dc of the order of 600 mm.

Such vessel walls are described in particular in application W017064426.

According to a first embodiment, all the metal plates of the sealing membrane comprise the same grade of steel.

The steel grade used is an alloy which must have the following properties: it has a low coefficient of linear expansion, that is to say a low thermal expansion between room temperature and temperature TL. liquefaction of the liquefied gas; - it has a ductile-brittle transition temperature dc lower than the temperature of the liquefied gas to be stored, that is to say lower than -50° C. when the liquefied gas to be stored is Liquefied Petroleum Gas; and - it is weldable.

The steel grade used has dc preferably: - a coefficient dc linear expansion less than or equal to 17.106 K′, preferably between 10.10 6 K′ and 17.10 6 K′ between -200 and 100° C.; - an elastic limit greater than or equal to 220 MPa, cc which makes it possible to limit the risks of deformation of the membrane under the effect of the Sloshing phenomenon; and - an equivalent number of resistance to punctures greater than or equal to 24.

Preferably, the grade of steel used has the following chemical composition by mass: - 16.0% < Cr < 19.0% - 10.0% < Ni < 15.0% - 2.00% < Mo < 3.00% - 0% < N < 0.11% - 0% < Mn < 2.00 (fo.

A particularly interesting grade of steel is 316 L, with the numerical designation 1.4432, having the following chemical composition by mass: - 16.0% <Cr <18.5% -10.0% <Ni < 14.0% - 2.00% < Mo < 3.00% - 0% < N < 0.11% - 0% < Mn < 2.00 (fo.

Advantageously, among the 316L steels, of numerical designation 1.4432, steels having an elastic limit greater than or equal to 220 MPa are selected.

This steel grade also has excellent resistance to wet corrosion in the presence of halide ions.

Indeed, the 316L steel grade has an equivalent number of resistance to pitting greater than or equal to 24.

Finally, this steel grade has a linear expansion coefficient of 16.10-6

Alternatively, the 316L steel grade, with numerical designation 1.4435, may have the following composition: - 17.0%<Cr<19.0% - 12.5% <Ni <15.0% - 2.00% < Mo < 3.00% - 0%<N< 0.11% - O%<Mn < 2.00%

Advantageously, among the 316L steels, of numerical designation 1.4435, steels having an elastic limit greater than or equal to 220 MPa are selected.

This steel grade also has excellent resistance to wet corrosion in the presence of halide ions.

Indeed, the 316L steel grade has an equivalent number of resistance to pitting greater than or equal to 25.

Finally, this steel grade has a linear expansion coefficient of 16.10 6 K

[0066] Other grades of steel likely to be used as an alternative to 316L steel, together with their elastic limit, are grouped together in table 1.

According to a second embodiment shown in Figure 3, the waterproof membrane is made of composite material.

Thus the parts of the waterproof membrane covering the bottom wall 5, the lower bevel walls 6 and the lower part of the first and second transverse walls 2, 3, comprise metal plates having a first grade of steel, these parts are hatched in figure 3.

The other zones of the waterproof membrane, that is to say the upper part, comprise metal plates comprising a second grade of steel.

11 is sufficient to use the first steel grade particularly resistant to corrosion on the lower part of the tank.

Indeed, the sea water from the exchangers of the re-liquefaction system when the seal is no longer ensured, is likely to fall into the tank filled with LPG and form pieces of ice on contact with the LPG.

The pieces of ice fall to the bottom of the tank due to the greater density of seawater in the solid state compared to LPG.

Thus, when the tank is emptied, the pieces of ice remain at the bottom of the tank.

Because the emptied tank is at room temperature, the pieces of ice melt.

Liquid seawater can then corrode the waterproof membrane at the bottom of the tank.

The second grade of steel used has the following properties: it has a low coefficient of thermal expansion; - it has a brittle ductile transition temperature below the temperature of the liquefied gas to be stored, i.e. below -50°C when the liquefied gas to be stored is Liquefied Petroleum Gas and 11 - it is weldable .

The second grade of steel used preferably has: - a coefficient of linear expansion less than or equal to 17.10-6K-1, preferably between 10.10-6 and 17.10-6K-1 between -200 and 100°C ; and - an elastic limit greater than or equal to 320 MPa, preferably greater than or equal to 370 MPa and advantageously greater than or equal to 400 MPa.

[0071] Preferably, the second grade of steel used is 204LN and has the following chemical composition by mass: - 0% <C < 0.1% - 8.5% < Mn < 10% - 0% <N < 0.2% - 15.5% < Cr < 16.5% - 1.5% < Cu < 2.0% - 1.0% < Ni < 2.0%.

Advantageously, among the 204LN steels, steels having an elastic limit greater than or equal to 380 MPa are selected.

This elastic limit is higher than that of the 316L steel grade.

This gives the membrane in the upper part of the tank an improved resistance to sloshing, where the phenomenon of "sloshing" can be very important.

Finally, this steel grade has a linear expansion coefficient of 10.106 K

Other grades of steel likely to be used as an alternative to 204 LN steel with their elastic limit and their coefficient of linear expansion are grouped together in table 2.

[0074] The tight membrane described above according to the first and second embodiments can also be used as a primary tight membrane in double-membrane liquefied gas storage tanks.

A double membrane cell wall generally comprises a secondary thermally insulating barrier, a secondary sealed membrane deposited on the secondary thermally insulating barrier, the cell wall further comprising a primary thermally insulating barrier placed on the secondary sealed membrane and a primary sealed membrane carried by said primary thermally insulating barrier.

[0075] Referring to Figure 4, a cutaway view of a ship 70 shows a sealed and insulated tank 71 of generally prismatic shape mounted in the double hull 72 of the ship.

The tank 71 comprises a primary leaktight barrier intended to be in contact with the LPG contained in the tank, a secondary leaktight barrier arranged between the primary leaktight barrier and the double hull 72 of the ship, and two insulating barriers arranged respectively between the primary leaktight barrier and the secondary watertight barrier and between the secondary watertight barrier and the double hull 72. 12

In a manner known per se, loading/unloading pipes 73 arranged on the upper deck of the ship can be connected, by means of appropriate connectors, to a maritime or port terminal to transfer a cargo of LPG from or to the tank. 71.

[0077] Figure 4 shows an example of a maritime terminal comprising a loading and unloading station 75, an underwater pipe 76 and a shore installation 77.

The loading and unloading station 75 is a fixed offshore installation comprising a mobile arm 74 and a tower 78 which supports the mobile arm 74.

The mobile arm 74 carries a bundle of insulated flexible pipes 79 which can be connected to the loading/unloading pipes 73.

The adjustable mobile arm 74 adapts to all size LNG carriers.

A connecting pipe, not shown, extends inside tower 78.

The loading and unloading station 75 allows the loading and unloading of the ship 70 from or to the shore installation 77.

This comprises liquefied gas storage tanks 80 and connecting pipes 81 connected by the underwater pipe 76 to the loading and unloading station 75.

The underwater pipe 76 allows the transfer of the liquefied gas between the loading and unloading station 75 and the shore installation 77 over a long distance, for example 5 km, which makes it possible to keep the ship 70 at a great distance from the coast during loading and unloading operations.

To generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 70 and/or pumps fitted to the shore installation 77 and/or pumps fitted to the loading and unloading station are used. 75.

[0079] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0080] The use of the verb "to comprise", "to understand" or "to include" and of its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0081] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

The technique described above for making a tank having a single sealed membrane can also be used in different types of tanks, for example to form a double membrane tank for liquefied petroleum gas (LPG) in a land installation or in a floating structure such as an LNG carrier or other.

In this context, it can be considered that the waterproof membrane illustrated in the preceding figures is a secondary waterproof membrane, and that a primary insulating barrier as well as a primary waterproof membrane, not shown, must still be added to this secondary waterproof membrane. .

In this way, this technique can also be applied to tanks having a plurality of thermally insulating barriers and superimposed sealed membranes.

[0083] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0084] The use of the verb "to comprise", "to understand" or "to include" and of its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0085] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

[0086] [Tables 1] --cmpose'n eEuimiçue de. noxydaeE,s au,fin'tqu., nessan, .a COTTON'. puions 51.14 Qn(grja"n de Itier E..qs, 'OJ.Ieeupn , .1 P Y, an mass MU NI, NE Units Slastque jk1IEes,r1,01 0/Pa1 4060 >231,,,,,u 3 1 4430 ,,..O02 0 .35 0 .1 0.0 0.0.04r 0 3.010 COI 000 320 37> 3105.Eol_k 0.0.1 .7.2- 144E3 I 11525 ±3070 COCO ±0-043 ±10310 3.5240.10 24.55255 , 252 015LN t00+- 70_,, , 11.55342 .253. , 4507 ,C 020 .0 a 0.4f._;.0 "r> 1 515E :1.0 230 c 34.550 14357E I : 10357E ESfil > 10 .if 20 41000.4 , ,,,,,,,,,, , .45 _, 0 110 4E 00 251154L5E 41 4

[0087] [Tableaux2] 0,mpos2don q',e rl,u steels 10 yd,MSs a,,,'enhtiqsxtI possodene ne lisons d elaslinte ts,ge "2315 Desi nMiort d: fluer 1y,EdxEm'40.

Ntlff.,{pY , 31 fok^ 8 3 14 0 0th hl.) 140 5.8 42.0t0c.

L (10 0! 00. 00. ±0 ci 5444.5 5 0 050 5 5 0 110 0 a35 54.25 380 :Olt_ x2020000 7 24310 ±002 =1.00 0 11 4 0 20 1-374105 S fi 0 ,{h ICtuS 11:1;a 0 70 7072 17.53 - 330 14

Claims (1)

CLAIMS [Claim 1] Sealed membrane (14) for a liquefied gas storage tank, said sealed membrane comprising, at least in a lower portion of said tank, an austenitic stainless steel grade having a chemical composition by mass comprising: 16 .0% < Cr < 28.0%; 10.0% < Ni < 27.0%; and 2.0% < Mn < 8.0%. [Claim 2] A waterproof membrane (14) according to claim 1, wherein the bulk chemical composition of the austenitic stainless steel grade further comprises: 0 < Mn < 4%. [Claim 3] The seal membrane (14) according to claim 1 or 2, wherein the bulk chemical composition of the austenitic stainless steel grade further comprises: 0 < Cu < 2%. [Claim 4] Sealing membrane (14) according to one of Claims 1 to 2, in which the chemical composition by mass of the austenitic h-- oxidizable steel grade comprises: 16.0 < Cr < 18.0% 10 .0% < Ni < 14.0% 2.00% < Mo < 3.00% 0< N% < 0.11% 0< Mn < 2.00%. [Claim 5] Sealing membrane (14) according to one of Claims 1 to 2, in which the chemical composition by mass of the austenitic h-- oxidizable steel grade comprises: 17.0 < Cr < 19.0% 12 .5% < Ni < 15.0% 2.00% < Mo < 3.00% < N% < 0.11% 0< Mn < 2.00%. [Claim 6] Sealing membrane (14) according to one of Claims 1 to 5, in which the chemical composition by mass of the grade of austenitic stainless steel in carbon is less than or equal to 0.03%. [Claim 7] Sealing membrane (14) according to one of Claims 1 to 6, in which the austenitic stainless steel grade has a yield strength greater than or equal to 220 MPa. [Claim 8] The waterproof membrane (14) of one of claims 1 to 7, wherein the steel grade has an equivalent number of pitting resistance greater than or equal to 24. [Claim 9] The waterproof membrane (14) according to one of claims 1 to 8, wherein the grade of austenitic stainless steel is a first grade of steel, said membrane further comprising, in an upper portion of the tank, a second grade of steel. [Claim 10] A waterproof membrane (14) according to claim 9, wherein the second steel grade is an austenitic stainless steel which has a chemical composition by mass comprising: 15% < Cr < 20% 1% < Ni < 12% O c Mn < 10%. [Claim 11] Waterproof membrane (14) according to one of Claims 9 to 10, in which the composition by mass of the second grade of steel comprises: 1% < Ni < 8%. [Claim 12] Waterproof membrane (14) according to one of Claims 9 to 11, in which the composition by mass of the second grade of steel comprises: 2 < Mn < 10%. [Claim 13] Waterproof membrane (14) according to one of Claims 9 to 13, in which the composition by mass of the second grade of steel comprises: - 0% <C < 0.1% - 8.5% < Mn < 10% - 0% <N < 0.2% - 15.5% < Cr < 16.5% - 1.5% < Cu < 2.0% - 1.0% < Ni < 2.0% . [Claim 14] Waterproof membrane (14) according to one of Claims 9 to 13, in which the second grade of steel has an elastic limit greater than or equal to 320 MPa, preferably greater than or equal to 370 MPa and advantageously greater than or equals 400 MPa. [Claim 15] Sealed and thermally insulating tank for storing a liquefied gas, said tank comprising walls, each wall of the tank comprising, in the direction of the thickness, from the outside towards the inside of the tank, a 16 [Claim 16] [Claim 17] [Claim 18] [Claim 19] [Claim 20] [Claim 21] tuna-only insulating barrier (12), and a waterproof membrane (14), according to one of claims 1 to 14, supported by the thermally insulating barrier. Tank according to Claim 15, in which the lower part of the tank comprises a bottom wall (5) of the tank. Tank according to Claim 16, in which the tank has a general polyhedral shape and comprises, in addition to the bottom wall (5), a first transverse wall (2), a second transverse wall (3), a ceiling wall (4) , lower chamfer walls (6), side walls (7,8); the first and the second transverse walls being connected to each other by the bottom wall, the ceiling wall, the lower chamfer walls and the side walls; the bottom of the vessel further comprising the bottom chamfer walls. Tank according to Claim 17, in which the upper portion of the tank comprises the ceiling wall (4), the side walls (7,8) and at least an upper portion of the first and second transverse walls (2, 3). Vessel (70) for transporting a cold liquid product, the vessel comprising a hull (72) and a tank according to one of Claims 15 to 18 arranged in the hull. Method of loading or unloading a ship (70) according to claim 19, in which a cold liquid product is conveyed through insulated pipes (73, 79, 76, 81) from or to a floating or terrestrial storage installation ( 77) to or from the ship's tank (71). Transfer system for a cold liquid product, the system comprising a ship (70) according to claim 19, insulated pipes (73, 79, 76, 81) arranged to connect the tank (71) installed in the hull of the ship to a floating or onshore storage facility (77) and a pump for driving a flow of cold liquid product through the insulated pipes from or to the floating or onshore storage facility to or from the vessel's tank.