Method for manufacturing a metal storage vessel

Abstract

The invention relates to a method for manufacturing a metal storage vessel, particularly suited for applications such as liquid hydrogen (LH2) storage. The method involves explosive welding to join dissimilar metal structures, followed by processing to achieve a refined, final shape. The method further includes differentiated welding processes to integrate the bimetal workpiece with vessel segments made of distinct materials. This approach enables the creation of a lightweight, robust, and leak-tight vessel, optimized for demanding operational conditions and advanced applications.

Description

Method for manufacturing a metal storage vesselTechnical field

[0001] The invention relates to a method for manufacturing a metal storage vessel, such as a liquid hydrogen (LH2) vessel. The invention also relates to a metal storage vessel of an aircraft and to an aircraft.Prior art

[0002] In the demanding field of cryogenic liquid hydrogen (LH2) storage for aerospace and aeronautic applications, manufacturers face significant challenges related to the extreme properties of LH2 and the structural requirements of storage vessels. One issue arises from the need to integrate stainless steel pipes into aluminum vessel walls. These pipes facilitate essential functions, such as filling the tank with LH2 before flight and extracting it during operation. However, the cryogenic temperatures of LH2 induce extreme thermomechanical stresses at the interface between the pipe and the vessel wall, necessitating a connection that is both durable and leak-tight to contain the highly volatile LH2. Existing approaches struggle to reliably manage these stresses, often compromising the performance and safety of the system.

[0003] Another challenge is related to the use of lightweight, high-strength aluminum alloys, such as aluminum-copper-lithium alloy (Al-Cu-Li), for the construction of LH2 vessels. These alloys are ideal for aerospace applications but require friction stir welding (FSW) due to their material properties. The FSW process involves the use of an internal anvil, which must later be removed through an access hole in the vessel. Closing this hole presents significant challenges, as FSW cannot be used for this final step. Thus, there is a need to develop an improved solution for manufacturing metal storage vessels.Disclosure of the invention

[0004] An objective of the invention is to provide a reliable, efficient, and durable method for manufacturing metal storage vessels, to address the challenges posed by extreme operating conditions.

[0005] The invention relates to a method for manufacturing a metal storage vessel, and comprising:• performing an explosive welding process to join a first structure comprising a first metal material, and a second structure comprising a second metal material, in order to obtain a preliminary-shaped bimetal workpiece;• processing the preliminary-shaped bimetal workpiece into a finally-shaped bimetal workpiece;• performing a first welding process to join the first structure of the finally- shaped bimetal workpiece with a first vessel segment, while the first vessel segment comprises the first material; and• performing a second welding process to join the second structure of the finally-shaped bimetal workpiece with a second vessel segment, while the second vessel segment comprises the second material.

[0006] The invention offers multiple advantages. The invention leverages explosive welding to address the challenges of joining dissimilar materials, such as stainless steel and aluminum, having significantly different physical and thermal properties. Explosive welding creates a metallurgical bond at the interface, ensuring good strength and durability while preserving the integrity of both materials. This technique is particularly advantageous in managing the extreme thermomechanical stresses induced by the cryogenic temperatures of liquid hydrogen, where traditional welding methods often fail. Following the explosive welding process, an appropriate welding technique is applied to each material based on its properties. For instance, friction stir welding (FSW) is used for aluminum segments, taking advantage of its suitability for high-strength aluminum alloys like Al-Cu-Li, while conventional or specialized welding techniques are employed for stainless steel components. This sequential and material-specific approach ensures optimalstructural integrity, leak-tightness, and performance, making the vessel capable of withstanding the demanding conditions of cryogenic hydrogen storage.

[0007] In the context of this document, the first material is preferably, distinct from the second material to address the specific functional and structural requirements of the metal storage vessel.

[0008] As used herein, the terms ‘first,’ and ‘second,’ are employed solely to distinguish between different elements and do not necessarily imply a particular order, sequence, or priority. Unless explicitly stated otherwise, the steps, features, or components described may be arranged, substituted, or performed in any suitable order according to the specific implementation.

[0009] In one embodiment, the method involves welding the first and second structures through an interlayer. This configuration ensures a high-quality metallurgical bond while minimizing intermetallic corrosion and reducing stress concentrations at the interface, especially when joining dissimilar materials like aluminum and stainless steel. The use of an interlayer enhances the durability and reliability of the joint under operational conditions.

[0010] In one embodiment, the step of processing the preliminary-shaped bimetal workpiece comprises a machining process. This allows for precise shaping and removal of surface irregularities, ensuring the workpiece achieves the exact dimensions and geometric tolerances required for its integration into the storage vessel. Machining also improves the surface finish for metal components.

[0011] In one embodiment, the first vessel segment comprises a tank dome segment.

[0012] In one embodiment, the second vessel segment comprises either a tank dome segment or a tank tube segment. A tank dome segment enables secure sealing and containment of the storage vessel, while a tank tube segment allows for efficient integration of piping systems, feed lines, or external connections. Both options enhance the modularity and functionality of the storage system, supporting a wide range of design configurations.

[0013] In one embodiment, the first material comprises an aluminum alloy. This provides a lightweight yet strong solution ideal for aerospace applications, whereweight savings directly improve fuel efficiency. Aluminum alloys also offer excellent corrosion resistance. The aluminum alloy is specifically an aluminum-copper-lithium alloy (Al-Cu-Li). This alloy delivers exceptional strength-to-weight performance, resistance to fatigue, and superior toughness, making it highly suited for the demanding conditions of LH2 storage.

[0014] In one embodiment, the first welding process comprises a friction stir welding (FSW) process. Advantageously, FSW process creates a solid-state bond with minimal heat-affected zones, preserving the material properties and producing a weld joint with high mechanical strength and fatigue resistance, essential for ensuring long-term reliability in cryogenic environments. Preferably, the FSW process is performed using a non-retractable pin. This simplifies the operation, reduces the risk of tool failure, and ensures uniform weld quality. Post-welding, the affected zones at the start and stop points of the weld could be finished by machining, leaving a flawless and durable joint. Indeed, at the start of welding, the pin could plunge abruptly into the material, leading to incomplete stirring and localized weaknesses, while at the end, the sudden retraction of the pin could leave a hole in the material. To mitigate these issues, precision machining could be applied to refine the weld region and remove inconsistencies,

[0015] In one embodiment, the second material comprises stainless steel, nickel, titanium, or an aluminum alloy. These materials provide strength, corrosion resistance, and compatibility with various welding processes, making them ideal for constructing components exposed to high pressures.

[0016] In one embodiment, the second welding process comprises a Tungsten Inert Gas (TIG) welding process. TIG welding delivers precise, clean, and defect-free joints with excellent control over the weld pool. It is particularly effective for welding stainless steel or other materials in critical applications where leak-tightness and mechanical robustness are important.

[0017] In one embodiment, the first structure comprises a metal plate, a metal disk, or a tube segment. These configurations allow the bimetal workpiece to be adapted to various structural roles, such as forming part of a tank dome or serving as a conduit for liquid hydrogen transfer.

[0018] In one embodiment, the second structure comprises a tube segment or a metal plate. These forms enable the integration of piping systems or the reinforcement of structural segments, providing modularity and flexibility in the design of metal storage vessels.

[0019] The invention also relates to a metal storage vessel for an aircraft, obtainable according to a method of any of the preceding embodiments. The metal storage vessel is preferably, a tank designed to contain LH2, providing a lightweight, robust, and leak-tight solution for cryogenic storage.

[0020] The invention further relates to an aircraft comprising the metal storage vessel.Brief description of the figures

[0021] Other characteristics and advantages of the present invention will appear on reading the following detailed description, for the understanding of which, it is referred to the attached figures where:- Figures 1A-1B illustrate exemplary structures of a metal storage vessel obtainable by the method according to the invention;- Figure 2 illustrates a flowchart of the method according to the invention; - Figures 3A-3C illustrate cross-sectional side-views of an exemplary first and second structures progressing through selected steps of the method, according an embodiment of the invention;- Figures 4A-4C illustrate cross-sectional side-views of another exemplary first and second structures progressing through selected steps of the method according an embodiment of the invention;- Figures 5A-5B illustrate perspective views of a first welding process for joining the first structure of the finally-shaped bimetal workpiece with a first vessel segment; and- Figures 6A-6B illustrate perspective views of a second welding process to join a second structure of the finally-shaped bimetal workpiece with a second vessel segment.

[0022] The drawings in the figures are not scaled. Similar elements can be assigned by similar references in the figures. In the framework of the present document, identical or analogous elements may have the same references. The presence of reference numbers in the drawings cannot be considered to be limiting, in particular if these numbers are indicated in the claims.Description of specific embodiments of the invention

[0023] Description of preferred embodiments of the present invention are hereafter described with references to figures, but the invention is not limited by these references. In particular, the drawings or figures described below are only schematic and are not limiting in any way.

[0024] Figures 1A and 1B illustrate two exemplary structures of a metal storage vessel 100, obtainable by the method according to the invention. Preferably, the metal vessel 100 is designed to store liquid hydrogen (LH2) for aerospace applications. LH2 plays an important role as a propellant in rocket propulsion systems, thanks to its high energy density and efficiency. Storing LH2 for such missions requires advanced tank designs that can withstand the extreme conditions of space, including cryogenic temperatures (-253°C), intense vibrations during launch, and the vacuum environment of space. The tank's lightweight construction is critical for reducing launch costs and maximizing payload capacity.

[0025] Figure 1A depicts a first configuration of the metal storage vessel 100, primarily consisting of a tank body 101 in the form of a cylindrical shell. This shell is preferably, made from a high-strength aluminum alloy, such as Al-Cu-Li, chosen for its lightweight and durable properties, which are crucial for reducing the overall mass in aircraft applications. The metal storage vessel 100 also includes a tank dome 106, which is geometrically optimized to uniformly distribute internal stresses under cryogenic pressures, minimizing risks of deformation or localized failure. Moreover, a key feature in this configuration is the inclusion of a pipe 102 that protrudes through the tank dome 106. Preferably, made of stainless steel, this pipe 102 may serve as an interface for LH2 transfer, enabling both filling prior to flight and extraction during operation. Given the extreme cryogenic conditions of LH2 (-253°C), the pipe’s 102 integration must account for thermal expansion differences between stainless steel and aluminum. Precise alignment and positioning are important to avoid stress concentration points and ensure long-term leak-tight and structural stability. While the pipe 102 is shown protruding through the tank dome 106 in this configuration, it could alternatively be positioned at another suitable location on the vessel 100 without compromising its functionality, provided that thermal expansion effects and structural considerations are properly managed.

[0026] Figure 1B shows another configuration of the metal storage vessel 100 during an intermediate manufacturing stage. It highlights a hole 103 located in the tank dome 106, which results from the friction stir welding (FSW) process that can be used to assemble the vessel’s 100 aluminum components. Indeed, the FSW process incorporates an internal anvil to stabilize the weld seam from within the vessel throughout the welding operation. After the welding process is complete, the anvil is removed, leaving behind the hole 103. To ensure the vessel’s structural integrity and leak-tightness, the hole 103 must be securely sealed in subsequent steps, for example, using the method described in this invention. This sealing process restores the uniform strength and durability of the tank dome 106, ensuring the metal storage vessel 100 can reliably contain LH2 under the high-pressure and cryogenic conditions required for aerospace applications. The metal storage vessel 100 is primarily designed for LH2 storage in aerospace and space exploration. Beyond aerospace, the vessel's 100 design principles make it highly adaptable for general use with compressed gases. Similar demands for lightweight construction, and resistance to pressure are shared by tanks used, for instance, for compressed natural gas (CNG), oxygen, nitrogen, and carbon dioxide (CO2).

[0027] Figure 2 illustrates a flowchart detailing the method for manufacturing a metal storage vessel designed for aerospace applications. The method begins with step a, where a first structure and a second structure, each made of different metal materials, are joined through explosive welding to create a preliminary-shaped bimetal workpiece. This step establishes a strong metallurgical bond between the structures, ensuring durability and compatibility for subsequent steps. Next, the preliminary-shaped bimetal workpiece undergoes step b, a processing step whereit is refined to achieve precise dimensions and a smooth surface finish, resulting in its transformation into the finally-shaped bimetal workpiece. In step c, a first welding process is performed to join the first structure of the finally-shaped bimetal workpiece with a first vessel segment, ensuring a robust and seamless connection. Finally, the method concludes with step d, where a second welding process bonds the second structure of the finally-shaped bimetal workpiece to a second vessel segment, completing the assembly.

[0028] Figures 3A to 3C provide cross-sectional side views illustrating the step-by-step progression of the first structure 11 , a metal disk, and the second structure 12, a tube segment, as processed according to the described method. The first structure 11 is made of a first metal material, such as aluminum, while the second structure 12 is made of a second metal material, such as stainless steel.

[0029] Figure 3A provides a view of the first step of the method where explosive welding is used to join the tube segment 12 to the metal disk 11 , forming a bimetal interface. The tube segment 12 is carefully positioned relative to the metal disk 11 with preferably, the help of a support 13 structure, which ensures alignment and prevents movement during the welding process. This support 13 structure is important as it maintains the precise orientation of the tube segment under the intense forces generated during explosive welding. Explosives 15 could strategically be placed inside the tube segment 12, creating a controlled detonation that causes the tube segment 12 to impact and bond with the metal disk 11. The welding process relies on the extremely high pressures and velocities produced by the detonation to create a metallurgical bond at the interface between the two structures (11,12) even if they have significantly different mechanical or thermal properties (e.g., stainless steel and aluminum). The explosive process can be automated to ensure precision and safety. In an industrial setup, the explosives 15 could carefully calculated and placed in predetermined positions within the tube segment. The process could be initiated remotely via an electronic trigger, ensuring controlled detonation. The parameters, such as the explosive mass, detonation velocity of the explosives, placement, and detonation sequence, are precisely defined based on the structures (11,12) being joined and the dimensions of thecomponents. To further improve bond quality and prevent intermetallic corrosion at the interface between the two structures (11,12), which is common when joining materials like, stainless steel and aluminum, a metallic interlayer (not shown) can be introduced. The interlayer, positioned between the tube segment and the metal disk, acts as a buffer to minimize chemical reactions and stress concentration at the weld zone. An interlayer such as pure aluminum (unalloyed aluminum with a minimum purity of 99%), titanium or niobium, can be used when welding stainless steel to aluminum because these materials are compatible with both and prevents the formation of brittle intermetallic phases. The interlayer can be integrated into the explosive welding process in two ways. In the same explosive welding operation, the interlayer is positioned between the tube segment 12 and the metal disk 11 during the initial setup. Upon detonation, the explosive force bonds all three layers simultaneously, creating a strong and uniform interface. This method is highly efficient as it reduces production time and simplifies the process, making it particularly suitable for smaller components or when production speed is critical. Alternatively, the interlayer can be integrated in a separate operation, where it is first bonded to one of the two structures (11,12) such as the metal disk 11 , through a preliminary explosive welding process. A subsequent explosive welding step then joins the tube segment to the already-bonded interlayer. This two-step approach offers greater control over the interface quality, ensuring precise bonding and alignment.

[0030] Figure 3B illustrates a preliminary-shaped bimetal workpiece 10 formed after the completion of the explosive welding step. At this stage, the two structure (11, 12), comprising the metal disk and the tube segment, are successfully bonded, forming a robust bimetallic interface. The explosion accelerates a metal material in such a way that it is slammed into the other metal material at high velocity, while the contacting surface expands over a wave-like front. In this wave front, a combination of high pressure and friction occurs, resulting in a metallic bond while the metals do not melt. This resulting interface is characteristic of explosive welding and provides a strong mechanical and metallurgical connection that can withstand significant thermal and mechanical stresses. However, to transition the preliminary-shaped bimetal workpiece 10 from its robust yet raw state into a fully functional component ready for integration, further refinement is required. This is achieved through a supplementary step, as illustrated in the following Figure 3C.

[0031] Figure 3C shows a finally-shaped bimetal workpiece 20 obtained after the preliminary-shaped workpiece 10 has undergone, preferably, a machining process to refine it to its final dimensions. The machining process can remove any excess material or irregularities from the preliminary-shaped workpiece 10, resulting in a smooth, precise, and functional structure. The bonded tube segment and metal disk now form a clean, streamlined bimetallic component ready for integration into a larger assembly, such as a liquid hydrogen vessel. For an LH2 storage vessel, the tube segment could serve as a feed pipe portion for filling or extracting liquid hydrogen, while the metal disk could act as a structural base or connector. Beyond machining, several processes can further be performed on the final-shaped bimetal workpiece 20, such as surface treatment to prevent corrosion, or heat treatment to improve the mechanical properties. Indeed, various heat treatment strategies can be applied. Stress relief treatment can be applied to reduce residual stresses from the explosive welding process, enhancing dimensional stability and minimizing the risk of deformation over time. Aging further enhances mechanical strength and hardness, ensuring the material meets the required performance standards for its intended use. Furthermore, solutionizing and quenching can be used to reinforce the metal, particularly when it has been welded in a softer condition than required, allowing it to develop the desired properties while ensuring long-term reliability.

[0032] Figures 4A to 4C illustrate cross-sectional side views showing the progression of structures (11 , 12), which correspond to two metal plates: a bottom plate 11 and a top plate 12, respectively. These figures are similar to the views depicted in Figures 3A to 3C.

[0033] Figure 4A illustrates the setup for the explosive welding process involving two metal plates (11,12), comprising a top plate 12 positioned above a bottom plate 11. In this configuration, explosives 15 could be strategically placed on the top plate 12 to generate the required high-velocity impact. Upon detonation, the explosive force drives the top plate 12 toward the bottom plate 11 , creating an intense collisionat the interface. The precise alignment of the plates (11,12) ensures that the resulting bond achieves optimal mechanical strength and leak-tightness while maintaining geometric accuracy.The bottom plate 11 could represent an aluminum structural panel, and the top plate 12 a stainless-steel reinforcement plate. The combination allows for a lightweight yet robust assembly capable of withstanding stresses encountered in cryogenic conditions. The positioning and quantity of explosives are calculated to ensure uniform bonding without causing distortion or defects.

[0034] Figure 4B shows a preliminary-shaped bimetal workpiece 10, formed by the metal plates after the explosive welding process. The detonation drives the top plate 12 into the bottom plate 11, creating a strong metallurgical bond at the interface. The energy of the explosion generates a wave-like pattern at the bond line, characteristic of explosive welding, which enhances the mechanical strength of the joint. At this stage, the metal plates remain in a preliminary state with visible deformations or irregularities caused by the explosive forces.

[0035] In Figure 4C, the preliminary-shaped bimetal workpiece 10 undergoes a processing stage to transform it into a finally-shaped bimetal workpiece 20, with a machining process being the preferred method. The machining process involves several steps to refine the preliminary-shaped bimetal workpiece 10 and prepare it for functional integration into the vessel assembly. In this embodiment, the finally-shaped bimetal workpiece 20 serves, for instance, as a portion of a dome segment for a LH2 storage vessel. To fulfill its role as part of the dome, the workpiece must be precisely machined into a curved shape that conforms to the overall geometry of the vessel. This precision could be achieved using advanced CNC milling or turning processes, which carefully shape the bonded bimetal workpiece into a smooth, dome-like segment with exact dimensions. The accuracy of the curvature is critical to ensuring uniform stress distribution across the dome and facilitating seamless assembly with adjacent dome segments. In this configuration, the finally-shaped bimetal workpiece 20 may undergo a drilling operation to include the hole 103, as illustrated in Figure 1B. As previously mentioned, the hole 103 serves as an access point for the anvil required during the FSW process. Once the FSWprocess is complete, the anvil must be removed through the hole 103, leaving the opening as a necessary byproduct of the welding operation. This hole 103 cannot be closed using the FSW process itself due to its reliance on internal support. Instead, the hole 103 can be closed using another welding process, as will be illustrated in the following figures (Figure 6A).

[0036] Figures 5A and 5B illustrate a first welding process according to the method, where the finally-shaped bimetal workpiece 20 is joined to a first vessel segment using, for instance, a friction stir welding (FSW). In both figures, the first vessel segment, designed as a tank dome segment 106', is made of a metal material, such as an aluminum alloy. The finally-shaped bimetal workpiece 20 comprises two bonded structures: a first structure 11, made of the first metal material (e.g., aluminum), and a second structure 12, made of a second metal material (e.g., stainless steel).

[0037] In Figure 5A, the finally-shaped bimetal workpiece 20, derived from Figure 4C, is preferably positioned to align its first structure 11 (aluminum) with the tank dome segment 106', also made of aluminum. The first welding process is performed preferably, by using a specialized FSW tool 18. This FSW tool 18 rotates (arrow 90) at high speed and traverses (arrow 91) along the weld line, creating a solid-state bond between the two aluminum components (11,106') Indeed, the FSW process begins with the rotation and traversal of the tool's 18 pin, which generates a combination of heat, friction and pressure. This heat softens the aluminum alloy without melting it, enabling the material to plastically deform and form a strong metallurgical bond due to friction between the first structure 11 and the tank dome segment 106'. This process creates a homogeneous and defect-free weld with high mechanical strength and excellent resistance to fatigue, qualities. When the FSW tool 18 passes, the seam of the two metal materials are stirred under a combination of high pressure and friction. The material does not melt and therefore the structure of the metal remains intact, which results into a robust and durable joint. This ensures reliability under extreme temperature variations and internal pressures typical of LH2 storage applications. In this process, a non-retractable pin is preferred for its efficiency and simplicity. The welding starts and stops leave areas where thematerial properties may be slightly altered due to the pin's movement. Preferably, these areas are subsequently removed by machining, ensuring the final joint is flawless and meets the required tolerances. Preferably, the FSW process is performed using a 5-axis machine, where all five axes are controlled simultaneously. This advanced control ensures precise tool positioning and consistent weld quality.

[0038] Figure 5B illustrates the first welding process performed on the finally-shaped bimetal workpiece 20, which originates from the configuration depicted in Figure 3C. As with Figure 5A, the FSW process is applied exclusively to the aluminum components, ensuring a robust and seamless bond. In this case, the second structure 12 (e.g., made of stainless steel) of the bimetal workpiece 20 remains unaffected during the FSW process, preserving its properties and ensuring compatibility for subsequent integrations, such as attaching stainless steel feed pipes or other components.

[0039] Figures 6A and 6B illustrate a second welding process, preferably a Tungsten Inert Gas (TIG) welding process, where the second structure 12 of the finally-shaped bimetal workpiece 20 is joined to a second vessel segment. This step follows the first welding process as illustrated in Figures 5A and 5B, ensuring seamless integration of the bimetal workpiece into the vessel assembly. The TIG welding process involves creating a focused, high-temperature arc between a nonconsumable tungsten electrode 33 and the second metal material of the second structure 12, all within an inert gas shield to prevent oxidation.

[0040] In Figure 6A, the finally-shaped bimetal workpiece 20, processed from Figure 5A, is aligned with a tank dome segment 32, which serves as the closing section of the storage dome. For instance, the second structure 12, made of stainless steel, is welded to a stainless-steel dome segment 32 using the TIG process. This dome segment 32 completes the structural enclosure of the metal storage vessel, ensuring a secure and robust seal to contain, for instance, LH2. The TIG welding process ensures generates a controlled arc that melts the joint edges of the stainless-steel components without excessive heat input, minimizing distortion and preserving material properties.

[0041] In Figure 6B, the finally-shaped bimetal workpiece 20, processed from Figure 5B, is joined to a tank tube segment 35, which serves as a conduit or a feed pipe of the metal storage vessel. The second structure 12 of the bimetal workpiece (e.g., made of stainless steel) is aligned with the tank tube segment 35, also made of stainless steel, and welded using the TIG process. This welding operation creates a strong and leak tight connection, enabling the tank tube segment 35 to function as a feed line, or a connection to external systems such as hydrogen supply lines or an external equipment.

[0042] The present invention has been described in relation to the specific embodiments which have a value that is purely illustrative and should not be considered to be limiting. The skilled person will notice that the invention is not limited to the examples that are illustrated and / or described here above.

[0043] To sum up, the invention relates to a method for manufacturing a metal storage vessel 100, particularly suited for applications such as liquid hydrogen (LH2) storage. The method involves explosive welding to join dissimilar metal structures (11,12) followed by processing to achieve a refined, final shape. The method further includes differentiated welding processes to integrate the finalshaped bimetal workpiece 20 with vessel segments made of distinct materials. This approach enables the creation of a lightweight, robust, and leak-tight vessel, optimized for demanding operational conditions and advanced applications.

Claims

Claims1. A method for manufacturing a metal storage vessel (100), and comprising:a. performing an explosive welding process to join a first structure (11) comprising a first metal material, and a second structure (12) comprising a second metal material, in order to obtain a preliminaryshaped bimetal workpiece (10);b. processing the preliminary-shaped bimetal workpiece (10) into a finally-shaped bimetal workpiece (20);c. performing a first welding process to join the first structure (11 ) of the finally-shaped bimetal workpiece (20) with a first vessel segment, while the first vessel segment comprises the first material; and d. performing a second welding process to join the second structure (12) of the finally-shaped bimetal workpiece (20) with a second vessel segment, while the second vessel segment comprises the second material.

2. The method according to the preceding claim, wherein the first and second structures (11,12) are welded through an interlayer.

3. The method according to any of the preceding claims, wherein the step (b) of processing the preliminary-shaped bimetal workpiece (10) comprises a machining process.

4. The method according to any of the preceding claims, wherein the first vessel segment comprises a tank dome segment (106’).

5. The method according to any of the preceding claims, wherein the second vessel segment comprises a tank dome segment (32) or a tank tube segment (35).

6. The method according to any of the preceding claims, wherein the first material comprises an aluminum alloy.

7. The method according to the preceding claim, wherein the aluminum alloy is aluminum-copper-lithium alloy (Al-Cu-Li).

8. The method according to any of the preceding claims, wherein the first welding process comprises a friction stir welding (FSW) process.

9. The method according to the preceding claim, wherein the FSW process is performed by a non-retractable pin.

10. The method according to the preceding claim, wherein a weld area where the FSW process starts and stops is finished by a machining process.11.The method according to any of the preceding claims, wherein the second material comprises stainless steel, nickel, titanium, or an aluminum alloy.

12. The method according to any of the preceding claims, wherein the second welding process comprises a Tungsten inert gas (TIG) welding process.

13. The method according to any of the preceding claims, wherein the first structure (11 ) comprises a metal plate, a metal disk or a tube segment, and wherein the second structure (12) comprises a tube segment or a metal plate.

14. A metal storage vessel (100) of an aircraft, obtainable according to a method of any of the preceding claims, preferably the metal vessel (100) comprising a liquid hydrogen (LH2) tank.- 17 -15. An aircraft comprising a metal storage vessel (100) according to the preceding claim.

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