Prevention of distortion in high thickness stainless steel fabricated components for ITER cryostat

Cryostat is a large stainless steel vessel providing vacuum environment to ITER Machine components. It houses and supports critical components like Vacuum Vessel and superconducting magnets. It measures up to ∼29 meters in diameter and ∼29 meters in height. For the entire vessel, material of construction is Dual marked SS 304/304L and thickness varies from 50 to 200 mm. ITER Cryostat is a large structure with complex shape with thickness ranging from 50 mm to 200 mm. In addition, being a large structure; manufacturing of ITER Cryostat in planned into modules at L and T Heavy Engineering, Hazira. Modules will be assembled at site in Cadarache, France. To achieve final dimensional tolerance after assembly of modules at site, it was critical to achieve stringent dimensional tolerance at module level which was a challenge considering size and complexity of the structures with varying thickness involved and material of construction prone to distortion. Hence, fabrication of modules within tolerance limit is a key to success. For this it was critical to decide welding process, welding methodology, fixturing arrangement and handling of components, which would be discussed in detail. This paper covers details of methods followed at plate and component stage to achieve dimensional tolerance in form of advanced welding technique, innovative fixturing arrangement and fabrication. (author)