Fatigue strength of PF-1 coil helium inlet with weld defects.

Abstract

Helium inlet (HI), used for supply of liquid helium into a superconductor, is a critical element of PF-1 coil of the fusion reactor ITER. The superconductor is placed into internal bore of a steel jacket. TIG welding without subsequent heat treatment is used for connection the HI to the jacket. Deviations from the established technology of welding may cause some crack-like defects. Therefore possibility of occurrence the through wall cracks and inlet leak under cyclic loading was evaluated.Calculations of growth of initial weld defects with various depths under cyclic loading were performed using Paris equation. It was obtained that critical size of initial defects, which can growth up to through wall after 30,000 cycles is about 1 mm.For experimental study a cyclic strength and tightness fatigue tests of full-scale 1.5 m length sample of helium inlet have been conducted in liquid nitrogen (77K). Visual control, leak testing, X-ray and liquid penetration inspections were performed after passing the given base test 30,000 cycles. Defects were not found by all used control methods. Reliability of the adopted welding technology was confirmed.