Cryogenic tank and manufacturing process

Abstract

The invention relates to a cryogenic tank and its manufacturing method configured to store a liquefied gas at a cryogenic temperature preferably below -100°C, for example liquid nitrogen, the tank (1) being composed of a set of welded 201LN type austenitic stainless steel sheet(s), characterized in that the tank is work-hardened at a work-hardening rate of between 1% and 12% and preferably between 5% and 10%, i.e. the set of welded 201LN type austenitic stainless steel sheet(s) is work-hardened at a work-hardening rate of between 1% and 12% and preferably between 5% and 10%. Abstract figure: Fig. 1

Description

Title of the invention: Cryogenic tank and manufacturing method

[0001] The invention relates to a cryogenic tank and its manufacturing method.

[0002] The invention relates more particularly to a cryogenic tank configured to store a liquefied gas at a cryogenic temperature preferably below -100°C, for example liquid nitrogen, the tank being composed of a set of welded austenitic stainless steel sheet(s) of type 201LN.

[0003] The invention relates to fixed or mobile tanks for the storage or transport of cryogenic liquids (air gas, CO2, LNG, nitrogen, ethylene, hydrogen or helium for example).

[0004] It is known to improve the mechanical characteristics of steels by work hardening, that is to say by deformation beyond the plastic limit of the material. This work hardening is defined by standards (see for example “EN 13458-2”).

[0005] Generally the sealed tank is filled with water and is pressurized and “inflated” according to predefined cycles until it induces stresses greater than the elastic limit of the metal to increase the mechanical characteristics.

[0006] To date, only a limited number of alloys are authorized by the regulations for the transport and storage of cryogenic fluids such as hydrogen (six to date). Thus, for example, it is known to manufacture and use tanks made of alloy type 304N or 304LN.

[0007] It is desirable to be able to use other materials that are less expensive, lighter or allow tanks to be offered with improved performance.

[0008] This is not easy because the tank must have good mechanical strength at low temperature, good resilience and must not be subject to cracks, particularly in the welds or at the periphery of the welds.

[0009] An aim of the present invention is to overcome all or part of the drawbacks of the prior art noted above.

[0010] To this end, the tank according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the tank is work-hardened at a work-hardening rate of between 1% and 12% and preferably between 5% and 10%, that is to say that the assembly of welded 201LN type austenitic stainless steel sheet(s) is work-hardened at a work-hardening rate of between 1% and 12% and preferably between 5% and 10%.

[0011] Furthermore, embodiments of the invention may include one or more of the following features: - the tank is work-hardened at a work-hardening rate of between 5% and 7%, for example 6%, - the assembly of sheet metal(s) is work-hardened in the sealed assembled configuration of the tank by internally pressurizing the tank with an incompressible fluid, for example water, - the entire sheet(s) is work-hardened before assembly and welding, for example during a rolling operation, - the tank is made of austenitic stainless steel sheet(s) of type 201LN welded using a “butt” type weld with a pair of wires and a flux suitable for 201LN steel.

[0012] The invention also relates to a method for manufacturing a cryogenic tank configured to store a liquefied gas at a cryogenic temperature preferably below -100°C, for example liquid nitrogen, the method comprising a step of assembling and welding a set of austenitic stainless steel sheets of type 201LN by welding, a step of work hardening the sheets, the work hardening step being carried out prior to the assembly and welding step and / or after assembly and welding, the work hardening step being configured to cause deformation beyond the plastic range of the type 201LN steel, the work hardening rate being between 1% and 12% and preferably between 5% and 10%.

[0013] According to other possible particularities the work hardening rate is between 5% and 7%, for example 6%.

[0014] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0015] Other features and advantages will appear on reading the description below, given with reference to the figures in which: Brief description of the figures

[0016] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended drawings in which:

[0017] [Fig.l] is a schematic and partial view in longitudinal section of an example of a reservoir during work hardening,

[0018] [Fig.2] is a schematic representation of the breaking strength values ​​of austenitic stainless steel parts making up the tank according to the invention tested for four levels of work hardening respectively,

[0019] [Fig.3] is a schematic representation of the impact test resistance values ​​of raw austenitic stainless steel parts making up the tank, at weld level and at the periphery of the weld for four work hardening levels respectively,

[0020] [Fig.4] is a schematic representation of the resistance values ​​at a test of elastic limit of raw austenitic stainless steel parts making up the tank, at the weld and at the periphery of the weld for three levels of work hardening respectively. Detailed description

[0021] In all the figures, the same references refer to the same elements.

[0022] In this detailed description, the following embodiments are examples. Well that the description refers to one or more embodiments, this does not mean that the features apply only to a single embodiment. Single features of different embodiments may also be combined and / or interchanged to provide other embodiments.

[0023] [Fig.l] very schematically illustrates a cryogenic tank 1 configured to store a liquefied gas at a cryogenic temperature (preferably less than -100°C), for example liquid nitrogen.

[0024] Tank 1 is composed of a set of welded 201LN type austenitic stainless steel sheets.

[0025] The composition of type 201LN steel provides in particular a rate (in moles) of 7 to 19% of chromium and 3 to 9% of nickel. It also contains traces of manganese, phosphorus, sulphide and nitrogen. It has a relatively low carbon rate which makes it very resistant to corrosion.

[0026] This alloy has the advantage of a relatively low nickel content which makes it less expensive.

[0027] For example, the steel may have the following composition in molar percentage: Cr 16 to 18.5%, Mn 6.40 to 7.50%, Ni 4 to 5%, Cu less than 1%, Si < 0.75%, N 0.10 to 0.25%, P < 0.045%, C < 0.030%, S < 0.030% and the remainder in Iron.

[0028] For example, a sheet 2 forms a central cylindrical shell or tube closed at its ends by domes 3. The tank 1 can thus have a generally cylindrical shape.

[0029] All of the steel sheets making up the tank 1 are work-hardened at a work-hardening rate of between 1% and 12% and preferably between 5% and 10%, i.e. all of the welded 201LN type austenitic stainless steel sheets are work-hardened at a work-hardening rate of between 1% and 12% and preferably between 5% and 10%, for example between 5% and 7%, for example 6%.

[0030] The rate or degree of work hardening represents the reduction in relative dimension (thickness for example) obtained by deformation (pressurization and / or rolling for example). This reduction in section can be related to the initial dimension (before work hardening) for example.

[0031] Preferably, the work hardening is obtained by cold deformation (“cold stretching”).

[0032] Work hardening can be carried out conventionally by applying internal pressure to the tank 1 with an incompressible fluid, for example water (as shown diagrammatically by arrows in [Fig.l]). That is to say that the assembled / welded tank 1 is subjected to one or more determined cycles of pressurization / deformation by injecting into its closed and sealed internal volume (see for example standard EN 13458-2).

[0033] Of course, as a variant or in combination, the set of sheets making up the tank 1 can be work-hardened before assembly and welding, for example during sheet rolling operations.

[0034] The inventor has found that the use of this particular 201LN alloy combined with the aforementioned work hardening rate makes it possible to give the tank all the resistance characteristics, in particular resistance to cold, which are necessary for the storage and transport of cryogenic fluids. In particular, and as explained below, the invention even makes it possible to give the tank 1 mechanical resistance performance superior to the tanks currently used while reducing its cost.

[0035] [Fig.2] illustrates the values ​​of tensile breaking limits (Rm in N / mm2) measured on samples (test coupons) work-hardened respectively at 0%, 6%, 10 and 15% (from left to right) according to the EN ISO 4136 standard. It can be seen that the tensile breaking limit of the 201LN sample continues to increase with the work-hardening rate. These values ​​are similar to or higher than the results obtained for the known 304LN material, particularly in terms of resilience (see for example the EN 10028-7, EN 13458-2 Annex C and EN ISO 9016 / EN ISO 148-1 standards).

[0036] [Fig.3] illustrates the impact strength limit values ​​(impact test "I" J / cm2 according to EN 13458-2) measured on welded samples (test coupons) work-hardened respectively to 0%, 6%, 10 and 15% (from left to right). For each work-hardening rate, the three columns represent respectively from left to right the values ​​for i) an impact test at -196°C for the base material 201LN, ii) an impact test at -196°C for a sample of two portions of 201LN welded at the weld and iii) an impact test at -196°C for a sample of two portions of 201LN welded at the "ZAT".

[0037] The "HAZ" refers to the injunction between the weld and the 201LN part. This is the heat-affected zone surrounding the weld in which the temperature of the welding process, combined with the stresses of uneven heating and cooling, alters the heat-treating properties of the alloy.

[0038] It is noted that the results obtained are greater than 50J / cm2 provided for by the ISO 21009 standard. The resistance decreases beyond a work hardening of 10%, particularly at the weld.

[0039] [Fig.4] illustrates the values ​​of the elastic limit and tensile rupture on welded samples (test coupons) work-hardened respectively to 6%, 10 and 15% (according to standard EN 13458-2 and EN ISO 9016 / EN ISO 148-1).

[0040] For each work hardening rate, the three columns represent respectively from left to right: i) the tensile strength pressure level (Rm in MPa), ii) the 0.2% yield strength pressure value (in MPa), iii) the elongation limit in percentage.

[0041] These different tests illustrate that from 0% to 15% work hardening, there is an increase in the mechanical characteristics of the 201LN material in the base metal and the weld with the work hardening rate. On the other hand, between 10% and 15% work hardening, the value of the resilience in the weld (in the metal deposited by the weld and in the "ZAT" heat-affected zone) decreases significantly.

[0042] Thus, this alloy and the work hardening rates of 1% to 12% present advantages but the optimum is between 6% and 10% work hardening and preferably around 6%.

[0043] As shown diagrammatically in dotted lines in [Fig.l], the tank 1 may comprise an outer casing 4 around the wall composed of the work-hardened 201LN material to form a double-casing tank with thermal insulation (for example under vacuum) between the two casings.

[0044] The work-hardened material according to the invention allows plastic deformation without breaking and has satisfactory ductility. It is suitable for welding. This structure allows the tank to resist the propagation of cracks.

Claims

Claims

1. Cryogenic tank configured to store a liquefied gas at a cryogenic temperature preferably below -100°C, for example liquid nitrogen, the tank (1) being composed of a set of welded 201LN type austenitic stainless steel sheet(s), characterized in that the tank is work-hardened at a work-hardening rate of between 5% and 10%, i.e. the set of welded 201LN type austenitic stainless steel sheet(s) is work-hardened at a work-hardening rate of between 5% and 10%.

2. Tank according to claim 1, characterized in that it is work-hardened at a work-hardening rate of between 5% and 7%, for example 6%.

3. Tank according to claim 1 or 2, characterized in that the assembly of sheet(s) is work-hardened in the sealed assembled configuration of the tank by internally pressurizing the tank with an incompressible fluid, for example water.

4. Tank according to any one of claims 1 to 3, characterized in that the set of sheets is work-hardened before assembly and welding, for example during a rolling operation.

5. Tank according to any one of claims 1 to 4, characterized in that it is composed of sheet(s) of austenitic stainless steel of type 201LN welded via a “butt” type weld with a pair of wires and a flux suitable for 201LN steel.

6. Method for manufacturing a cryogenic tank (1) configured to store a liquefied gas at a cryogenic temperature preferably below -100°C, for example liquid nitrogen, the method comprising a step of assembling and welding a set of austenitic stainless steel sheets of type 201LN by welding, a step of work hardening the sheets, the work hardening step being carried out prior to the assembly and welding step and / or after assembly and welding, the work hardening step being configured to cause deformation beyond the plastic range of the type 201LN steel, the work hardening rate being between 5% and 10%.

7. Method according to claim 6, characterized in that the work hardening rate is between 5% and 7%, for example 6%.

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