Repairing and Welding Experience of LN2 Cryogenic Transfer Line of 80 K Distribution System of SST-1

The 80 K liquid nitrogen distribution system is one of the essential sub-systems of SST-1 cryogenics system. It consists of 80 K Thermal shields, current feeders system, integrated flow distribution and control system, pre-cooling heat exchanges and purifier of helium plant system. The maximum operating pressure of liquid nitrogen is 1.9 bar (a) from the source storage tanks. Preliminary, authors observed the frosting in one of the section of return LN₂ cryo line near the phase separator interface. Due to this problem, they were unable to collect the phase separated LN₂ in the sub-cooler back. Appropriate investigation of leaks, reason for the leaks identified. Welding protocols (ASME section IX) and replacement of Bellows (as per EJMA standards) were carried out under satisfying the flexibility criteria. The evacuation of transfer lines, insulation wrapping, welding and assembly in congested space and safety aspect at 12 m height were the challenges experienced during repairing task. Due to this activity, the huge amount of LN₂ fluid has been saved.

In this paper, authors will mainly focus on the identification of weld leaks, welding and repairing process, vacuum evacuation process, design of sealing set up, NDT testing of weld joints and helium leak testing at operating condition of cryogenic transfer lines after welding task.