RU2803103C2 - Sealed and heat-insulated tank - Google Patents

Abstract

FIELD: storage tanks.

SUBSTANCE: group of inventions relates to a sealed and heat-insulating tank for storage of liquefied gas. The tank has walls, each wall of the tank contains, in the direction of thickness, from the outer side to the inner side of the tank, a heat-insulating barrier (12) and a sealed membrane (14) supported by a heat-insulating barrier. The tank has a lower section and an upper section, while the upper section is higher than the lower section. The sealed membrane (14) contains, in the lower section of said tank, an austenitic stainless steel grade having a chemical composition by weight containing 16.0%≤Cr≤28.0%, 10.0%≤Ni≤27.0%, and 2.0%≤Mo≤8.0%, in which the austenitic stainless steel grade is the first steel grade. The sealed membrane (14) additionally contains a second steel grade in the upper section of the tank. The second steel grade is an austenitic stainless steel which has a chemical composition by weight containing 15%≤Cr≤20%, 1%≤Ni≤12%, 0<Mn≤10%.

EFFECT: prevention of corrosion.

18 cl, 4 dwg, 2 tbl

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0001] The invention relates to the field of sealed and thermally insulated tanks with membranes. In particular, the invention relates to the field of sealed and thermally insulated tanks for storing and/or transporting low temperature liquid or liquefied gas, such as tanks for transporting liquefied petroleum gas (also known as LPG) with a temperature of, for example, -50°C to 0°C. These tanks can be installed onshore or on a floating structure. In the case of a floating structure, the tank may be designed to transport liquefied gas or to receive liquefied gas to serve as fuel to propel the floating structure.

BACKGROUND OF THE ART

[0002] It has come to the attention of the applicant that the metal sheets forming the sealed membranes of a liquefied gas storage tank are prone to pitting. This is especially likely to occur when the tank is connected to a re-liquefaction system equipped with seawater exchangers and the seals on said exchangers fail.

[0003] Patent application FR1537850 describes a sealed membrane for a reservoir with good properties in terms of corrosion resistance and mechanical strength under conditions of use. The membrane consists of a sheet of austenitic stainless steel containing less than or equal to 0.03% carbon, less than or equal to 18% chromium, less than or equal to 10% nickel, and 0.12% to 0 nitrogen. .25%. Alternatively, austenitic stainless steel may contain less than or equal to 0.03% carbon, less than or equal to 17.5% chromium, less than or equal to 13% nickel, or less than or equal to 2.8% molybdenum. , and nitrogen content from 0.12% to 0.25%. These membranes can be used in liquefied gas transport tanks.

[0004] However, the moisture corrosion resistance of such a sealed membrane is not entirely satisfactory, especially in the presence of residual seawater.

SUMMARY OF THE INVENTION

[0005] The idea that forms the basis of the invention is to provide a sealed membrane for a sealed and thermally insulating tank that is not subject to corrosion by moisture, especially in the presence of residual seawater within the tank. Thus, one of the objects of the invention is to prevent corrosion of the sealed membrane.

[0006] To this end, the present invention relates to a sealed membrane for a liquefied gas tank, said sealed membrane comprising, at least in a lower portion of said tank, a grade of austenitic stainless steel having a chemical composition by weight comprising:

16.0 ≤ Cr ≤ 28.0%,

10.0 ≤ Ni ≤ 27.0%,

2.0 ≤ Mo ≤ 8.0%.

[0007] Thus, such a sealed membrane has better moisture corrosion resistance than the membrane of the above-mentioned document. In particular, the presence of molybdenum in the above proportions makes it possible to improve the corrosion resistance to moisture, in particular towards halides such as chloride ions present in seawater.

[0008] "Liquefied gas" means any substance that is in a vapor state under conditions of normal pressure and temperature, and which has been converted into a liquid state by lowering its temperature and/or increasing its pressure.

[0009] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade further comprises:

0 <Mn ≤ 4%.

[0010] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade further comprises:

0 <Cu ≤ 2%.

[0011] According to one embodiment, the chemical composition by weight 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%.

[0012] According to one embodiment, the chemical composition by weight 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%.

[0013] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade comprises:

17.0% ≤ Cr ≤ 19.0%,

12.5% ≤ Ni ≤ 15.0%,

2.00% ≤ Mo ≤ 3.00%,

0% < N ≤ 0.11%,

0% <Mn ≤ 2.00%.

[0014] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade comprises:

16.5% ≤ Cr ≤ 18.5%,

12.5% ≤ Ni ≤14.5%,

4.00% ≤ Mo ≤ 5.00%,

0.12% ≤ N ≤ 0.22%,

0% <Mn ≤ 2.00%.

[0015] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade comprises:

24.0% ≤ Cr ≤ 26.0%,

21.0% ≤ Ni ≤ 23.0%,

2.00% ≤ Mo ≤ 2.50%,

0.10% ≤ N ≤ 0.16%,

0% <Mn ≤ 2.00%.

[0016] According to one embodiment, the chemical composition by weight 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%.

[0017] According to one embodiment, the chemical composition by weight 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%.

[0018] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade comprises:

24.0% ≤ Cr ≤ 26.0%,

24.0% ≤ N≤27.0%,

4.7% ≤ Mo ≤ 5.7%,

0.17% ≤ N ≤ 0.25%,

0% <Mn ≤ 2.0%,

1.00% ≤ Cu ≤ 2.00%.

[0019] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade comprises:

19.5% ≤ Cr ≤20.5%,

17.5% ≤ Ni ≤18.5%,

6.0% ≤ Mo ≤ 7.0%,

0.18% ≤ N ≤ 0.25%,

0% <Mn ≤ 1.00%,

0.5% ≤ Cu ≤1.00%.

[0020] According to one embodiment, the chemical composition by weight of the austenitic stainless steel grade comprises:

19.0% ≤ Cr ≤21.0%,

24.0% ≤ Ni ≤ 26.0%,

6.0% ≤ Mo ≤ 7.0%,

0.15% ≤ N ≤ 0.25%,

0% <Mn ≤ 1.00%,

0.5% ≤ Cu ≤ 1.50%.

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

[0022] In one embodiment, the austenitic stainless steel grade has an elastic limit greater than or equal to 220 MPa.

[0023] According to one embodiment, the elastic limit of the austenitic stainless steel grade is less than 340 MPa and, for example, from 245 to 305 MPa.

[0024] In one embodiment, the steel grade has a pitting resistance equivalent value (PREN) greater than or equal to 24. PREN is a predictive measurement of the resistance of stainless steel to local pitting, depending on its chemical composition. The higher the PREN value, the more resistant the stainless steel is to local chloride pitting. The formula used to calculate the PREN of a steel grade is as follows:

PREN = 1 x % Cr + 3.3 x % Mo + 16 x % N.

[0025] According to one embodiment, the austenitic stainless steel grade is a first steel grade, wherein said membrane further comprises, at an upper portion of the vessel, a second steel grade.

[0026] Thus, the membrane contains a grade of steel that is resistant to pitting corrosion in areas prone to this phenomenon, namely the lower region of the tank, while the upper portion of the tank can be made from a second grade of steel that is less expensive and/or has better mechanical properties.

[0027] In one embodiment, the second steel grade is an austenitic stainless steel that has a chemical composition by weight containing:

15% ≤ Cr ≤ 20%,

1% ≤ Ni ≤ 12%,

0 <Mn ≤ 10%.

[0028] This second grade of steel is particularly preferred in that it exhibits mechanical properties, particularly at -60°C, that are better than those of the first grade of steel. In particular, the second grade of steel has a higher elastic limit, which means that it does not experience plastic deformation due to the effect of “splashing” of liquefied gas inside the tank. Moreover, this second grade of steel is also less expensive than the first.

[0029] According to one embodiment, the composition by weight of the second grade of steel contains

0 <Mo ≤ 1%

[0030] According to one embodiment, the composition by weight of the second grade of steel contains

1% ≤ Ni ≤ 8%.

[0031] According to one embodiment, the composition by weight of the second grade of steel contains

2% ≤ Mn ≤ 10%.

[0032] According to one embodiment, the composition by weight of the second grade of steel contains:

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%.

[0033] According to one embodiment, the composition by weight of the second grade of steel contains:

0% < C ≤ 0.030%,

0% <Mn ≤ 2.0%, second grade

0.10% ≤ N ≤ 0.20%,

16.5% ≤ Cr ≤ 18.5%,

6.0% ≤ Ni ≤ 8.0%.

[0034] According to one embodiment, the composition by weight of the second grade of steel contains:

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%.

[0035] In one embodiment, the second grade of steel has a tensile strength greater than or equal to 320 MPa, preferably greater than or equal to 370 MPa, and preferably greater than or equal to 400 MPa.

[0036] According to one embodiment, the membrane has a thickness of from 0.5 mm to 1.5 mm, for example on the order of 1.2 mm.

[0037] According to one embodiment, the reservoir has walls, wherein each reservoir wall includes, in a thickness direction from the outside to the inside of the reservoir, a thermal barrier and the aforementioned sealed membrane supported by the thermal barrier.

[0038] According to one embodiment, the bottom of the reservoir includes a wall of the bottom of the reservoir.

[0039] According to one embodiment, the reservoir has a generally polyhedral shape and includes, in addition to a bottom wall, a first cross wall, a second cross wall, a ceiling wall, bottom chamfered walls, and side walls; wherein the first and second transverse walls are connected to each other by a bottom wall, a ceiling wall, lower beveled walls and side walls; the lower part of the tank additionally contains lower beveled walls.

[0040] According to one embodiment, the bottom portion of the reservoir includes a bottom portion of the first and second transverse walls, said bottom portion extending between the bottom wall and the top edge of the lower beveled walls.

[0041] According to one embodiment, the top portion of the reservoir includes a ceiling wall, side walls, and at least a top portion of the first and second cross walls.

[0042] According to one embodiment, the thermal barrier is a main thermal barrier, and the sealed membrane is a main sealed membrane.

[0043] Such a tank may form part of an onshore storage facility, for example for LPG storage, or be installed on a floating structure, onshore or offshore, such as an LPG carrier ship, a floating gas regasification and storage unit (FSRU), remote floating production and storage unit (FPSO), and the like. Such a tank can also be used as a fuel tank in any type of transport vessel.

[0044] According to one embodiment, a transport vessel for transporting cold liquid or liquefied gas includes a double body and a tank, as described above, located in the double body.

[0045] According to one embodiment, the invention also provides a method of loading or unloading such a transport vessel in which a cold liquid product or liquefied gas is transported through insulated pipelines from or to a floating or onshore storage facility, to or from a tank of the transport vessel.

[0046] According to one embodiment, the invention also provides a transmission system for transferring a cold liquid product or liquefied gas, the system comprising the aforementioned transport vessel, insulated piping arranged to connect a tank mounted in the hull of the transport vessel to a floating or an onshore storage facility, and a pump for transferring a stream of cold liquid product or liquefied gas through insulated pipelines from a floating or onshore storage facility to the tank of a ship for transport or from a tank of a ship for transport to a floating or onshore storage facility.

BRIEF DESCRIPTION OF THE FIGURES

[0047] The invention will be better understood and other objects, details, features and advantages thereof will become more apparent from the following description of several specific embodiments of the invention, presented solely by non-limiting illustration with reference to the accompanying drawings.

[0048] FIG. 1 is a schematic detail view of a sealed and thermally insulated tank for containing liquefied gas according to the first embodiment.

[0049] FIG. 2 is a sectional perspective view of the wall of a sealed and thermally insulating reservoir supported by the support wall of FIG. 1.

[0050] FIG. 3 is a partial schematic view of a sealed and thermally insulated tank for containing liquefied gas according to the second embodiment.

[0051] FIG. 4 schematically shows, with a local section, a liquefied gas storage facility on a transport vessel and a terminal for loading/unloading a liquefied gas storage tank.

DESCRIPTION OF IMPLEMENTATION OPTIONS

[0052] Conventionally, the adjectives "upper" and "lower" are used to define the position of one element relative to another with respect to gravity on Earth.

[0053] With reference to FIG. 1 shows the rear part of a tank 1 designed to receive liquefied gas. The tank 1 rests on a support structure formed by the inner hull of the double-hulled transport vessel. The reservoir 1 has a generally polyhedral or prismatic shape. The reservoir 1 has a first transverse wall 2 and a second transverse wall 3, in this case octagonal in shape. In fig. 1, the first transverse wall 2 is only partially shown in order to demonstrate the interior of the tank 1. The transverse walls 2, 3 are cofferdam walls of the transport vessel, and extend transversely to the longitudinal direction of the transport vessel. The tank 1 also has a ceiling wall 4, a bottom wall 5, lower slanted stacks 6, side walls 7, and upper slanted walls 8. The ceiling wall 4, bottom wall 5, lower slanted walls 6, side walls 7, and upper slanted walls 8 extend in longitudinal direction of the transport vessel, connect the first and second transverse walls 2, 3 at the edges 9, and meet at the edges 10.

[0054] As shown schematically in FIG. 2, the first transverse wall 2 of the tank 1 has, sequentially from the outer side to the inner side, in the direction of the wall thickness, a thermal insulating barrier 12 containing insulating elements 13, a sealed membrane 14 supported by the insulating elements of a thermal insulating barrier 12. The sealed membrane 14 is designed to contact with a liquefied gas contained in a tank, such as liquefied petroleum gas containing butane, propane, propene or the like, and having an equilibrium temperature of -50°C to 0°C. The description given above for the first transverse wall is valid for the other walls 3, 4, 5, 6, 7, 8 of the tank.

[0055] The sealed membrane 14 can be manufactured in various ways. In the example shown, the sealed membrane 14 of the reservoir 1 contains a plurality of metal plates 15 placed adjacent to each other. These metal plates 15 are preferably rectangular in shape. The metal plates 15 are overlap welded together to provide a tight seal to the sealed membrane 14. Preferably, the metal plates 15 are made of stainless steel. The metal plates 15 have a thickness of less than 3 mm, preferably from 0.5 to 1.5 mm, for example about 1.2 mm.

[0056] In order to allow the sealed membrane to deform in response to various stresses that occur in the tank, in particular in response to thermal compression resulting from the liquefied gas charge in the tank, the metal plates 15 contain a plurality of corrugations 16 oriented inside the tank. More specifically, the sealed membrane 14 of the reservoir 1 includes a first row of corrugations 16 and a second row of corrugations 16 forming a regular rectangular pattern. Preferably, the corrugations 16 extend parallel to the edges of the rectangular metal plates 15. The distance between two successive corrugations 16 of a row of corrugations is from 300 to 800 mm, and, for example, of the order of 600 mm.

[0057] Such tank walls are described, in particular, in the application WO17064426.

[0058] According to the first embodiment, all metal plates of the sealing membrane contain the same grade of steel.

[0059] The steel grade used is an alloy that must have the following properties:

- it has a low coefficient of linear expansion, that is, low thermal expansion from ambient temperature to the liquefaction temperature T _L of the liquefied gas;

- it has a viscous-to-brittle transition temperature lower than the temperature of the liquefied gas to be stored, that is, below -50°C when the liquefied gas to be stored is liquefied petroleum gas; And

- it can be welded.

[0060] The steel grade used preferably has:

- linear expansion coefficient less than or equal to 17⋅10 ^-6 K ^-1 , preferably from 10⋅10 ^-6 K ^-1 to 17⋅10 ^-6 K ^-1 from -200 to 100°C;

- elastic limit greater than or equal to 220 MPa, which allows limiting the risk of membrane deformation under the influence of the splashing effect; And

- equivalent index of resistance to pitting corrosion greater than or equal to 24.

[0061] Preferably, the steel grade used has the following chemical composition by weight:

16.0% ≤ Cr ≤ 19.0%,

10.0% ≤ Ni ≤ 15.0%,

2.00% ≤ Mo ≤ 3.00%,

0% < N ≤ 0.11%,

0% <Mn ≤ 2.00%.

[0062] Particularly interesting is the steel grade 316L, number 1.4432, which has the following chemical composition by weight:

16.0% ≤ Cr ≤ 18.5%,

10.0% ≤ Ni ≤ 14.0%,

2.00% ≤ Mo ≤ 3.00%,

0% < N ≤ 0.11%,

0% <Mn ≤ 2.00%.

[0063] Preferably, steels having a tensile strength greater than or equal to 220 MPa are selected from 316L/1.4432 steels. This grade of steel also exhibits excellent corrosion resistance from moisture in the presence of halide ions. In fact, 316L steel grade has an equivalent pitting resistance rating greater than or equal to 24. Finally, this steel grade has a linear expansion coefficient of 16⋅10 ^-6 K ^-1 .

[0064] Alternatively, 316L steel grade number 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%,

0% <Mn ≤ 2.00%.

[0065] Preferably, steels having a tensile strength greater than or equal to 220 MPa are selected from 316L/1.4435 steels. This grade of steel also exhibits excellent corrosion resistance from moisture in the presence of halide ions. In fact, 316L steel grade has an equivalent pitting resistance rating greater than or equal to 25. Finally, this steel grade has a linear expansion coefficient of 16⋅10 ^-6 K ^-1 .

[0066] Other steel grades that can be used as an alternative to 316L steel, along with their elastic strength, are listed in Table 1.

[0067] According to the second embodiment shown in FIG. 3, The sealed membrane is made of composite material. Thus, the parts of the sealed membrane covering the bottom wall 5, the lower beveled walls 6 and the bottom part of the first and second transverse walls 2, 3 contain metal plates having a first grade of steel; these parts are shaded in Fig. 3. Other areas of the sealed membrane, e.g. the upper part contains metal plates made of the second grade of steel.

[0068] It is sufficient to use the first grade of steel, which is particularly resistant to corrosion in the lower part of the tank. Specifically, when the seal fails, seawater from the re-liquefaction system exchangers tends to flow into the LPG-filled tank and form ice chunks when in contact with the LPG. Pieces of ice fall to the bottom of the tank due to the higher density of solid seawater compared to LPG. This way, when the tank is emptied, chunks of ice remain at the bottom of the tank. Since the empty reservoir is at room temperature, the ice chunks will melt. Liquid seawater can then cause corrosion of the sealed membrane at the bottom of the tank.

[0069] The second grade of steel used has the following properties:

- it has a low coefficient of thermal expansion;

- it has a viscous-to-brittle transition temperature lower than the temperature of the liquefied gas to be stored, that is, below -50°C when the liquefied gas to be stored is liquefied petroleum gas; And

- it can be welded.

[0060] The second steel grade used preferably has:

- linear expansion coefficient less than or equal to 17⋅10 ^-6 K ^-1 , preferably from 10⋅10 ^-6 to 17⋅10 ^-6 K ^-1 from -200 to 100°C; And

- elastic limit greater than or equal to 320 MPa, preferably greater than or equal to 370 MPa, and preferably greater than or equal to 400 MPa.

[0071] Preferably, the second steel grade used is 204LN and has the following chemical composition by weight:

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%.

[0072] Preferably, steels having a tensile strength greater than or equal to 380 MPa are selected from 204LN steels. This elastic limit is higher than that of 316L steel. This gives the membrane at the top of the tank improved resistance to sloshing when sloshing levels can be very high. Finally, this grade of steel has a linear expansion coefficient of 10⋅10 ^-6 K ^-1 .

[0073] Other grades of steel that can be used as an alternative to 204LN steel, along with its elastic limit and its coefficient of linear expansion, are listed in Table 2.

[0074] The sealed membrane described above according to the first and second embodiments can also be used as the main sealed membrane in a double membrane liquefied gas storage tank. The wall of a double-membrane reservoir generally comprises a thermal insulating barrier, an auxiliary sealed membrane superimposed on the auxiliary thermal insulating barrier, the tank wall further comprising a main thermal insulating barrier disposed thereon, an auxiliary sealed membrane, and a main sealed membrane supported by said primary thermal insulating barrier.

[0075] With reference to FIG. 4, a cross-sectional view of the shipping vessel 70, shows a sealed and insulated tank 71 of a generally prismatic shape mounted in the double housing 72 of the shipping vessel. The tank wall 71 includes a main sealed barrier designed to contact the LPG contained in the tank, a secondary sealed barrier located between the main sealed barrier and the double hull 72 of the transport vessel, and two isolating barriers located, respectively, between the main sealed barrier and the secondary sealed barrier. barrier and between the auxiliary sealed barrier and the double housing 72.

[0076] In a known manner, loading/unloading lines 73 located on the upper deck of a shipping vessel may be connected via suitable connectors to a marine or port terminal for transferring LPG cargo from or to tank 71.

[0077] FIG. 4 shows an example of a marine terminal including a loading and unloading station 75, a subsea pipe 76, and a shore structure 77. The loading and unloading station 75 is a stationary shore structure containing a movable boom 74 and a tower 78 that supports the movable boom 74. The movable boom arm 74 holds a bundle of insulated flexible pipes 79, which can be connected to the loading/unloading pipeline 73. The adjustable movable boom 74 can be adjusted to fit all sizes of LPG carrier vessel. A connecting pipe (not shown) extends into the tower 78. The loading and unloading station 75 allows the transport vessel 70 to be loaded and unloaded from and to the shore facility 77. This structure contains tanks 80 for storing liquefied gas and connecting pipes 81 connected by an underwater pipe 76 to a loading and unloading station 75. The subsea pipe 76 allows the liquefied gas to be transferred between the loading and unloading station 75 and the shore facility 77 over a long distance, such as 5 km, which allows the transport vessel 70 to be kept a long distance from shore during loading and unloading operations.

[0078] To create the pressure necessary to transfer the liquefied gas, pumps are used on board the transport vessel 70 and/or pumps installed at the shore facility 77 and/or pumps installed at the loading and unloading station 75.

[0079] Although the invention has been described in connection with certain specific embodiments, it is clear that it is in no way limited to them, and that it includes all technological equivalents of the described means, as well as combinations thereof, if they fall within the scope of the invention.

[0080] The use of the verbs “comprise” or “include” and their conjugate forms does not exclude the presence of other elements or other steps in addition to those listed in the claims.

[0081] In the claims, any reference symbol within parentheses should not be interpreted as limiting the claims. (repeat in par. 0084 and 0085)

[0082] The technology described above for producing a tank having a single sealed membrane can be used in various types of storage tank, for example to create a double membrane liquid petroleum gas (LPG) tank on an onshore facility or on a floating structure such as a ship for transportation of LPG or the like. In this context, it can be considered that the sealed membrane shown in the previous figures is a secondary sealed membrane, and that the main seal barrier along with the main sealed membrane (not shown) still needs to be added to the secondary sealed membrane. Thus, this technology can also be applied to tanks that have multiple stacked sealed membranes and thermal barriers.

[0083] Although the invention has been described in connection with certain specific embodiments, it is clear that it is in no way limited thereto, and that it includes all technological equivalents of the means described, as well as combinations thereof, if they fall within the scope of the invention.

[0084] The use of the verbs “comprise” or “include” and their conjugate forms does not preclude the presence of other elements or other steps in addition to those listed in the claims.

[0085] In the claims, any reference symbol within parentheses should not be interpreted as limiting the claims.

[0086] [Table 1] Chemical composition of austenitic stainless steel showing spot corrosion resistance Steel designation % by weight Minimum elastic limit R _p0.2 (MPa) ASTM Symbol Number C Si Mn P S N Cr Cu Mo Nb Ni Other 316L X2CrNiMo17-12-3 1.4432 ≤0.030 ≤1.00 ≤2.00 ≤0.045 ≤0.015 ≤0.011 16.0÷18.5 - 2.00÷3.00 - 10.0÷14.0 - 220 316L X2CrNiMo18-14-3 1.4435 ≤0.030 ≤1.00 ≤2.00 ≤0.045 ≤0.015 ≤0.011 17.0÷19 - 2.00÷3.00 - 12.5÷15.0 - 220 317NL X2CrNiMoN17-13-5 1.4439 ≤0.030 ≤1.00 ≤2.00 ≤0.045 ≤0.015 0.12÷0.22 16.5÷18.5 - 4.00÷5.00 - 12.5÷14.5 - 270 310MoLN X1CrNiMoN25-22-2 1.4466 ≤0.020 ≤0.70 ≤2.00 ≤0.045 ≤0.010 0.10÷0.16 24.0÷26.0 - 2.00÷2.50 - 21.0÷23.0 - 250 316LNMo+ X2CrNiMoN17-13-3 1.4429 ≤0.030 ≤1.00 ≤2.00 ≤0.045 ≤0.015 0.12÷0.22 16.5÷18.5 - 2.50÷3.00 - 11.0÷14.0 - 280 - X2CrNiMoN18-12-4 1.4434 ≤0.030 ≤1.00 ≤2.00 ≤0.045 ≤0.015 0.10÷0.20 16.5÷19.5 - 3.0÷4.0 - 10.5÷14.0 - 270 N08932 X1CrNiMoCuN25-25-5 1.4537 ≤0.020 ≤0.70 ≤2.00 ≤0.030 ≤0.010 0.17÷0.25 24.0÷26.0 1.00÷2.00 4.7÷5.7 - 24.0÷27.0 - 290 F44 X1CrNiMoCuN20-18-7 1.4547 ≤0.020 ≤0.70 ≤1.00 ≤0.030 ≤0.010 0.18÷0.25 19.5÷20.5 0.50÷1.00 6.0÷7.0 - 17.5÷18.5 - 300 N08926 X1CrNiMoCuN25-20-7 1.4529 ≤0.020 ≤0.50 ≤1.00 ≤0.030 ≤0.010 0.15÷0.25 19.0÷21.0 0.50÷1.50 6.0÷7.0 - 24.0÷26.0 - 300

[0087] [Table 2] Chemical composition of austenitic stainless steel with high elastic limit Steel designation % by weight Elastic limit R _p0.2 (MPa) ASTM Symbol Number C Si Mn P S N Cr Cu Mo Nb Ni Other 204NL ≤0.1 ≤0.75 8.5÷10.0 ≤0.060 ≤0.005 ≤0.2 15.5÷16.5 1.5÷2.0 - - 1.0÷2.0 - 380 301L X2CrNiN18-7 1.4318 ≤0.03 ≤1.00 ≤2.00 ≤0.045 ≤0.015 0.10÷0.20 16.5÷18.5 - - - 6.0÷8.0 - 330 201NL X2CrMnNiN17-7-5 1.4371 ≤0.03 ≤1.00 6.0÷8.0 ≤0.045 ≤0.015 0.15÷0.20 16.0÷17.0 - - - 6.5÷5.5 - 320

Claims (45)

1. A sealed and thermally insulated liquefied gas storage tank, said tank having walls, each tank wall comprising, in a thickness direction from the outside to the inside of the tank, a thermal insulating barrier (12) and a sealed membrane (14) supported by the thermal insulating barrier, said tank has a lower section and an upper section, wherein the upper section is above the lower section, said sealed membrane (14) contains, in the lower section of said tank, a grade of austenitic stainless steel having a chemical composition by weight containing 16.0%≤Cr≤28.0%, 10.0%≤Ni≤27.0% and 2.0%≤Mo≤8.0%, wherein the austenitic stainless steel grade is a first steel grade, said sealed membrane (14) further comprises, in the upper portion of the tank, a second steel grade, wherein said second steel grade is an austenitic stainless steel which has a chemical composition by weight containing 15%≤Cr≤20%, 1%≤Ni≤12%, 0<Mn≤10%. 2. A sealed and heat-insulating tank according to claim 1, in which the chemical composition by weight of the first grade of austenitic stainless steel additionally contains 0<Mn≤4%. 3. A sealed and heat-insulating tank according to claim 1 or 2, in which the chemical composition by weight of the first grade of austenitic stainless steel additionally contains 0<Cu≤2%. 4. Sealed and heat-insulating tank according to any one of paragraphs. 1 and 2, in which the chemical composition by weight of the first grade of austenitic stainless steel contains 16.0≤Cr≤18.5%, 10.0%≤Ni≤14.0%, 2.00%≤Mo≤3.00%, 0<N%≤0.11%, 0<Mn≤2.00%. 5. Sealed and heat-insulating tank according to any one of paragraphs. 1 and 2, in which the chemical composition by weight of the first grade of austenitic stainless steel contains 17.0≤Cr≤19.0%, 12.5%≤Ni≤15.0%, 2.00%≤Mo≤3.00%, 0<N%≤0.11%, 0<Mn≤2.00%. 6. Sealed and heat-insulating tank according to one of paragraphs. 1-5, in which the chemical composition by weight of the first grade of austenitic stainless steel by carbon is less than or equal to 0.03%. 7. Sealed and heat-insulating tank according to one of paragraphs. 1-6, in which the first grade of austenitic stainless steel has an elastic limit greater than or equal to 220 MPa. 8. Sealed and heat-insulating tank according to one of paragraphs. 1-7, in which the first grade of steel has an equivalent resistance to pitting corrosion greater than or equal to 24. 9. Sealed and heat-insulating tank according to one of paragraphs. 1-8, in which the composition by weight of the second steel grade contains 1%≤Ni≤8%. 10. Sealed and heat-insulating tank according to one of paragraphs. 1-9, in which the composition by weight of the second grade of steel contains 2≤Mn≤10%. 11. Sealed and heat-insulating tank according to one of paragraphs. 1-10, in which the composition by weight of the second steel grade contains 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%. 12. Sealed and heat-insulating tank according to one of paragraphs. 1-11, 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 preferably greater than or equal to 400 MPa. 13. Sealed and heat-insulating tank according to one of paragraphs. 1-12, in which the lower part of the tank contains a wall (5) of the bottom of the tank. 14. The sealed and thermally insulated tank according to claim 13, wherein the tank has a generally polygonal shape and includes, in addition to the bottom wall (5), a first transverse wall (2), a second transverse wall (3), a ceiling wall (4) , lower beveled walls (6) and side walls (7, 8); wherein the first and second transverse walls are connected to each other by a bottom wall, a ceiling wall, bottom chamfered walls and side walls; in this case, the lower part of the tank additionally contains lower beveled walls. 15. The hermetic and thermally insulating tank according to claim 14, wherein the upper portion of the tank comprises a ceiling wall (4), side walls (7, 8) and at least a portion of the top of the first and second transverse walls (2, 3). 16. A vessel (70) for transporting a cold liquid product, comprising a housing (72) and a sealed and heat-insulating tank according to one of claims. 1-15, located in the housing. 17. A transmission system for transporting a cold liquid product, comprising a transport vessel (70) according to claim 16, insulated pipelines (73, 79, 76, 81) arranged to connect a sealed and thermally insulated tank (71) installed in the housing transport vessel to the floating or onshore storage vessel (77), and a pump for transferring the cold liquid product stream through insulated pipelines from the floating or onshore storage vessel to the tank of the transport vessel or from the tank of the transport vessel to the floating or shore storage vessel. 18. The method of loading or unloading a vessel (70) for transportation according to claim 16, in which the cold liquid product is transported through insulated pipelines (73, 79, 76, 81) from a floating or shore storage (77) into a sealed and thermally insulated tank of the vessel ( 71) for transportation or from the vessel's sealed and thermally insulated tank (71) for transportation to a floating or onshore storage facility (77).