Manufacturing and Assembly of ITER Cryostat - Welding Challenges and Experiences

The ITER Cryostat-the largest austenitic stainless steel vessel provides ultra-cool environment for the ITER Vacuum vessel and the Superconducting Magnets. It weighs ∼3500 t and measures up to ∼29 meters in diameter and ∼29 meters in height. Material of Construction is dual marked SS 304/304L and thickness varies from 25 mm to 200 mm.

The Design, manufacturing and inspection of the cryostat is as per ASME Section VIII Division 2 with supplementary requirement of ITER. Due to large number of penetrations and transportation limitation at Site calls for the segmentation which results in number of subassemblies. Massive amount of welding deposition is required to join these subassemblies to fabricate the segment.

ITER Specification for Cryostat demands stringent dimensional tolerance requirement (0.3% out of roundness) as compare to ASME. Other challenges are higher thickness weld joints in all position, space constraints, welding accessibility and stringent ITER vacuum requirements. Austenitic Stainless steel is prone to distortion due to low thermal conductivity and high coefficient of thermal expansion. This paper covers improvements done in the traditional welding process SAW, FCAW and to achieve dimension requirements and results are discussed. This paper also covers application NG Hot wire TIG for Site weld joints.

n order to simulate the job conditions, mockup of 40° segment on base section and 60#176; segment for lower cylinder segment was performed for Welding & NDE feasibility, Welding sequence establishment for dimensional achievement. This paper also highlights the Learnings acquired from the mockups and implementation during manufacturing.