**2. Findings of literature review**

#### **2.1 Vacuum vessel configuration with developing method**

 The vacuum vessel has been developed for different applications according to the need of the achieved required vacuum range. For different material, many different methods are used for manufacture according to the type of base material used for the vacuum vessel. To develop a vacuum vessel, the following procedures have been used: arc welding methods like GTAW-Gas Tungsten Arc Welding, GMAW-Gas Metal Arc Welding, SAW -Submerge Arc Welding, MIEA-Modified Indirect Electric Arc welding and other non-convectional welding procedures such as Nd-YAG laser beam welding, FSW-Friction Stir Welding and Electron Beam welding.

#### *2.1.1 FSW-friction stir welding fabrication to develop vacuum vessel*

The friction stir welding process is shown in **Figure 1** and is an autogenous joining technique in the solid state and it uses an in-between non-consumable revolving tool with an appropriate geometry profiled shoulder and probe pin that is produced from a harder material than the workpiece material. The rotating tool is plunged into the weld joint and compelled to navigate the joint line, heating the adjoining segments by interfacial and internal friction between the tool and base material, thus producing a weld joint through extruding, forging and stirring the materials of the workpiece.

The benefits of FSW include the ability to join aluminum alloy materials, which are difficult to fusion weld, for example, 2XXX and 7XXX series aluminum alloys. Other benefits of the FSW process are that it is easy to weld any configuration even a long weld, there is low distortion with fine microscopic structure, excellent mechanical properties proven by fatigue, shear and tensile tests, no shielding gases and consumable fill up welding rods required [1].

 Dalder et al. [2] constructed a thick wall AA2219 material pressure vessel using a Bobbin tool friction stir welding (BTFSW). The whole research project was divided into two sections. The first section of research was focused on the development of the essential process to make defect-free circumferential weld joints between two 102 cm internal diameter hemispheres made from aluminum alloy AA2219 by means of BTFSW. The second section of the project involved signifying that the developed weld joint was essentially adequate for the intended service period. This literature work revealed that the spherical configuration vacuum vessel of aluminum alloy AA2219 was successfully welded by the bobbin friction stir welding. From closing out the circumferential weld, a keyhole is present due to bobbin tool retraction. Friction plug welding was used to close the hole with the same material as the pressure vessel.

#### *2.1.2 Fusion welding-TIG (tungsten inert gas) welding*

 Jadeja et al. [3] has been working on Limiter-based ADITYA tokamak, which was developed into the diverter designed ADITYA-U tokamak. The main feature of the ADITYA tokamak was that the rectangular cross-section of the vessel was

**Figure 1.**  *Principle of friction stir welding.* 

#### *A Review on Development and Fabrication Methodology for Vacuum Vessel from Aluminum Alloy DOI: http://dx.doi.org/10.5772/intechopen.81083*

 replaced by a circular cross-section to accommodate additional poloidal coils in the space between the wall of the vessel and toroidal field coil. The upgraded stainless steel SS304 L vacuum vessel has a spherical configuration developed by the manual operated TIG welding. To produce the joint in the section of the vessel and to join the nozzle and flanges attached to vacuum vessel outer surface, TIG welding was used to achieved ultra-high vacuum range of 1 × 10<sup>−</sup><sup>9</sup> mbar pressure in the chamber.

 Ishimaru [4] has recognized research work on the aluminum alloy vacuum vessel in achieving an ultimate pressure of 10<sup>−</sup>13 Torr. Vacuum beam chambers in accelerators generally require a complicated profile, having a distributed pump and heating and cooling structures. A complicated cross-section of the vessel was developed by an extrusion process using porthole dies. Aluminum alloy 6063-T6 provides superior performance during extrusion. The outer body and main chamber were developed by a special extrusion process and the three pieces of the main chamber were joined by tungsten inert gas (TIG) manual welding.

 Chen et al. [5] has focused his research work on the bending magnet of SRRC synchrotron light source developed from AA6061-T6. To develop a 35 mm thick vessel, the AA6061-T6 plate is first machined with NC machining in an ethyl alcohol vapor. Subsequent to machining, the two thick plates of the B-chamber were extruded to obtain an elliptical cross-section and after that chamber, TIG welding was used with no other chemical cleaning procedure. For long circumferential welding, the base material was preheated up to 70–80°C to prevent deformation. Then TIG welding was used for fabrication. After fabrication, at 150°C bakeout temperature, an ultimate vacuum pressure of 1 × 10<sup>−</sup>10 Torr and leak rate of 1 × 10−10 torr.l.s−1 was achieved.

 Reich et al. [6] has conducted his research work on the development of vacuum vessels of wendelstein 7-X in, which is the superconducting magnet system that is bounded among two toroidal formed vacuum vessels. Research work has established a manufacturing process adopted for fabrication. A one side (V) weld seam and double face (X) weld seam are filled and welded by TIG welding on stainless steel 316 LN ASTM. For the port, the opening is fabricated by water jet abrasive machining. During fusion welding the of vacuum vessel: weld distortion, backing out of vessel for higher temperature, non-uniform strength and quality of the weld are the problems faced during fabrication of vacuum vessel. Aluminium alloy can get oxide, warpage and distortion on the weld.

#### **2.2 Vacuum system material selection**

The general outline design of the vacuum structure is controlled by the kind of the progress involved and the ultimate vacuum pressure to be achieved in a specific application. The definite design outline will be influenced by the appropriateness and scope of the materials and accessible components obtainable and thus the particular choice of vacuum material is crucial for the performance and cost of the vacuum system to be optimized.

Vacuum vessel material selection criteria:


 The following are vacuum vessel materials which are most widely used.

	- • **304 L stainless steel:** a lower carbon variant of steel that is used for ultrahigh vacuum region requirement system.
	- **316 L stainless steel:** low carbon and magnetic stainless steel
	- **321 stainless steel**: preferred when low magnetic permeability is needed.

Chen et al. [6] developed and tested an aluminum vacuum chamber for bending magnet of the SRRC synchrotron light source. An aluminum alloy was chosen because it showed the minimum residual radioactivity among the available materials. Aluminum composites are generally utilized for the ultrahigh vacuum chambers because of their advantageous qualities such as great machinability, high thermal conductivity and low outgassing rate.


*A Review on Development and Fabrication Methodology for Vacuum Vessel from Aluminum Alloy DOI: http://dx.doi.org/10.5772/intechopen.81083* 


#### **Table 1.**

*Sealing mechanism selection [10].* 

tungsten is mechanically deformed or subjected to the extremely hightemperature region, it becomes brittle [9].

7.**Brass** is reliable for applications wherever a higher corrosion resisting ability and outgassing rate of 8 × 10<sup>−</sup><sup>7</sup> order is required. The outgassing rate of zinc can be controlled by nickel plating it. Adding zinc into brass may cause some difficulties for high and ultra-high vacuum region.

## *2.2.2 Flange and sealing mechanism material*

In a vacuum system, the selection of the sealing material between two contacting surfaces depends upon the flange type used. Following are the different sealing materials used (**Table 1**).
