Cryogenic tank and method for manufacturing it

Abstract

The present invention relates to a cryogenic tank configured for storing liquefied gas, such as liquid nitrogen, at cryogenic temperatures preferably below -100°C, and a method for manufacturing the same, wherein the tank (1) consists of a set of welded 201LN type austenitic stainless steel sheets, and the tank is work-hardened at a work-hardening rate of 1 to 12%, preferably 5 to 10%, that is, the set of welded 201LN type austenitic stainless steel sheets is work-hardened at a work-hardening rate of 1 to 12%, preferably 5 to 10%.

Description

Technical Field

[0001] The present invention relates to cryogenic containers and a method for manufacturing the same.

[0002] More specifically, the present invention relates to a cryogenic container configured to store a liquefied gas, such as liquid nitrogen, at a cryogenic temperature preferably below -100°C, the container consisting of a set of welded sheets of 201LN austenitic stainless steel.

[0003] The present invention relates to a fixed or movable container for storing or transporting cryogenic liquids (such as air gas, CO2, LNG, nitrogen, ethylene, hydrogen or helium).

[0004] It is a known practice to improve the mechanical properties of steel by work hardening, i.e., by deformation beyond the plastic limit of the material. This work hardening is defined by standard specifications (see, for example, "EN13458-2").

Background Art

[0005] Generally, until a stress beyond the elastic limit of the metal is induced and the mechanical properties are enhanced, the sealed container is filled with water and pressurized and "expanded" in a pre-defined cycle.

[0006] To date, regulations have permitted only a limited number of alloys (six to date) for the transport and storage of cryogenic liquids such as hydrogen. For example, it is a known practice to manufacture and use containers made of 304N or 304LN alloys.

Summary of the Invention

Problems to be Solved by the Invention

[0007] It is desirable to be able to use other materials that are low cost, lighter or that can impart improved performance quality to the container.

[0008] The container must have good mechanical strength and good resilience at low temperatures, and it must not be prone to cracking, especially at the welds or edges of the welds, which is not an easy task.

[0009] One object of the present invention is to overcome all or part of the above-mentioned drawbacks of the prior art. [Means for solving the problem]

[0010] For that purpose, in all other embodiments, the vessel according to the present invention, as defined in the general preface above, is essentially characterized in that the vessel is work-hardened to a work-hardening rate of 1 to 12%, preferably 5 to 10%, i.e., the set of welded sheets of 201LN austenitic stainless steel is work-hardened to a work-hardening rate of 1 to 12%, preferably 5 to 10%.

[0011] Furthermore, embodiments of the present invention have the following features: - The container is work-hardened to a rate of 5-7%, for example, 6%. - The set of sheets is work-hardened in a highly leaktight, pre-assembled structure by pressurizing the container with an incompressible fluid, such as water. - Before assembly and welding, for example during the rolling process, the sheet set is work-hardened. - The container consists of sheets of 201LN austenitic stainless steel welded by "butt" welding using wire pairs and flux designed for 201LN steel. It may have one or more of these.

[0012] The present invention also relates to a method for manufacturing a cryogenic container configured to store a liquefied gas, such as liquid nitrogen, at an extremely low temperature preferably below -100°C, the method comprising the steps of assembling and welding a set of sheets of 201LN austenitic stainless steel, and work hardening the sheets, the work hardening step being performed before and / or after the assembly and welding steps, the work hardening step being configured to produce deformation exceeding the plastic range of the 201LN steel, and the work hardening rate being 1 to 12%, preferably 5 to 10%.

[0013] According to other possible specific characteristics, the work hardening rate is 5-7%, for example, 6%.

[0014] The present invention may also relate to any alternative device or method that includes any combination of features exceeding or falling short of the claims.

[0015] Other specific features and advantages will become clear upon reading the following description, which is provided with reference to the drawings.

[0016] The present invention is provided merely as an example and will be better understood by reading the following description, which is accompanied by reference to the attached drawings. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 shows a schematic and partial view of a longitudinal cross-section of an example of a container undergoing work hardening. [Figure 2] Figure 2 shows a schematic diagram of the fracture strength values ​​of austenitic stainless steel components constituting the container according to the present invention, tested for each of the four levels of work hardening. [Figure 3] Figure 3 shows a schematic diagram of the impact resistance values ​​of the crude austenitic stainless steel components constituting the container at the weld or weld edge, for each of the four levels of work hardening. [Figure 4]FIG. 4 shows a schematic diagram of the values of the resistance to the elastic limit test of parts made of as - rolled austenitic stainless steel constituting the container at the welded part or the edge of the welded part, for each of the four levels of work hardening.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Throughout the drawings, the same reference numerals refer to the same components.

[0019] In this detailed description, the following embodiments are examples. In the description, one or more embodiments are referred to, but this does not mean that the features apply only to one embodiment. The individual features of different embodiments can also be combined and / or exchanged to provide other embodiments.

[0020] [FIG. 1] schematically illustrates a cryogenic container configured to store liquefied gas, such as liquid nitrogen, at cryogenic temperatures (preferably below - 100°C).

[0021] The container 1 consists of a set of welded sheets of 201LN austenitic stainless steel.

[0022] The composition of 201LN steel particularly includes chromium contents of 7 - 19% and nickel contents of 3 - 9% (molar). It also contains trace amounts of manganese, phosphorus, sulfur, and nitrogen. It has a relatively low carbon content, and thus is highly corrosion - resistant.

[0023] This alloy has the advantage of a relatively low nickel content, and thus the cost is reduced.

[0024] For example, the steel may have the following composition in mol%: Cr 16 - 18.5%, Mn 6.40 - 7.50%, Ni 4 - 5%, Cu less than 1%, Si ≤ 0.75%, N 0.10 - 0.25%, P ≤ 0.045%, C ≤ 0.030%, S ≤ 0.030%, and the remaining mol% of iron.

[0025] For example, sheet 2 forms a central cylindrical tube or shell, which is closed at its ends by dome 3. Thus, container 1 may have an overall cylindrical shape.

[0026] The set of steel sheets constituting the container 1 is work-hardened to a work-hardening rate of 1-12%, preferably 5-10%, that is, the set of welded sheets of 201LN austenitic stainless steel is work-hardened to a work-hardening rate of 1-12%, preferably 5-10%, for example 5-7%, for example 6%.

[0027] The work hardening rate or level represents the reduction in relative dimensions (e.g., thickness) obtained by deformation (e.g., pressurization and / or rolling). This reduction in cross-section can be expressed, for example, relative to the initial dimensions (before work hardening).

[0028] Work hardening is preferably achieved by cold stretching.

[0029] Work hardening can conventionally be carried out by pressurizing the container 1 with an incompressible fluid, such as water (schematically shown by arrows in Figure 1). That is, the assembled / welded container 1 is subjected to one or more specific cycles of pressurization / deformation by injection into its closed and sealed internal volume (see, for example, standard EN13458-2).

[0030] Naturally, as an alternative or in combination, the set of sheets constituting container 1 may be work-hardened before assembly and welding, for example, during the sheet rolling process.

[0031] The inventors have found that by using this particular 201LN alloy, which also possesses the aforementioned work hardening rate, it is possible to impart all strength properties, in particular, the low-temperature resistance necessary for the storage and transport of cryogenic liquids, to the container. In particular, and as described below, the present invention further enables the container 1 to have superior mechanical strength performance compared to currently used containers, while simultaneously reducing its cost.

[0032] [Figure 2] shows the tensile strength values ​​(N / mm²) measured for work-hardened samples (test coupons) at 0%, 6%, 10%, and 15% (from left to right), respectively, according to the standard EN ISO 4136. 2 This illustrates the Rm) in 201LN. It is noteworthy that the tensile strength of the sample made from 201LN does not stop increasing with the work hardening rate. These values ​​are similar to, or greater than, the results obtained with 304LN, which is particularly known in terms of resilience (see, for example, standards EN10028-7, EN13458-2 annex C, and EN ISO9016 / EN ISO148-1).

[0033] [Figure 3] shows the resilience limit values ​​(impact test "I" J / cm² in accordance with the EN13458-2 standard) measured for welded specimens (test coupons) work-hardened to 0%, 6%, 10%, and 15%, respectively (from left to right). 2 This illustrates the following. For each work hardening rate, the three columns, from left to right, represent, i) an impact test at -196°C on the 201LN base material, ii) an impact test at -196°C on two weld samples at the weld, and iii) an impact test at -196°C on two samples of 201LN welded at "HAZ".

[0034] "HAZ" refers to the joint between the weld and the 201LN component. It is the heat-affected zone around the weld where the alloy's heat treatment properties change due to the temperature of the welding process combined with irregular heating and cooling stresses.

[0035] The obtained result is 50 J / cm², as recognized by the standard ISO 21009. 2 It is noteworthy that this value exceeds [a certain threshold]. Strength decreases when work hardening exceeds 10%, especially in the welded area.

[0036] Figure 4 illustrates the elastic limit and fracture values ​​under tensile force (in accordance with standards EN13458-2 and EN ISO9016 / EN ISO148-1) for welded specimens (test coupons) work-hardened to 6%, 10%, and 15%, respectively.

[0037] For each work hardening rate, the three vertical bars, from left to right, represent, respectively: i) the pressure level of tensile strength (Rm in MPa), ii) the elastic limit pressure value at 0.2% (MPa), and iii) the elongation limit value (percentage).

[0038] These various tests illustrate that the mechanical properties of 201LN material in the base metal and weld are enhanced by the work hardening rate from 0% to 15%. However, between 10% and 15% work hardening, the resilience of the weld decreases significantly (in the metal welded and in the "HAZ" heat-affected zone).

[0039] Therefore, while this alloy and a work hardening rate of 1-12% have advantages, a work hardening rate of 6-10%, preferably around 6%, is optimal.

[0040] As schematically shown by the dashed lines in [Figure 1], the container 1 may include an outer jacket 4 around the wall made of work-hardened 201LN material such that a double-walled container with thermal insulation (e.g., under vacuum) is formed between the two jackets.

[0041] The work-hardening material according to the present invention is capable of plastic deformation without fracture and possesses sufficient ductility. It is weldable. This structure allows the container to withstand crack propagation.

Claims

1. A cryogenic container preferably configured to store liquefied gas, such as liquid nitrogen, at an extremely low temperature of less than -100°C, A cryogenic container characterized in that the container (1) consists of a set of welded sheets of 201LN austenitic stainless steel, and the container is work-hardened to a work-hardening rate of 5 to 10%, that is, the assembly of welded sheets of 201LN austenitic stainless steel is work-hardened to a work-hardening rate of 5 to 10%.

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

3. The container according to claim 1 or 2, characterized in that the set of sheets is work-hardened in the airtight assembly structure of the container by pressurizing the container with an incompressible fluid, such as water.

4. The container 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 rolling.

5. The container according to any one of claims 1 to 4, characterized in that it consists of sheets of 201LN austenitic stainless steel welded by "butt" welding using wire pairs and flux designed for 201LN steel.

6. A method for manufacturing a cryogenic container (1) preferably configured to store a liquefied gas, such as liquid nitrogen, at an extremely low temperature of less than -100°C, comprising the steps of: assembling and welding a set of sheets of 201LN austenitic stainless steel by welding; and work hardening the sheets, which is performed before and / or after the assembly and welding steps, and is configured to produce deformation exceeding the plastic range of the 201LN steel, with a work hardening rate of 5 to 10%.

7. The method according to claim 6, characterized in that the work hardening rate is 5 to 7%, for example, 6%.

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