Research on Nondestructive Examination of Bracket Welds of ITER In-Vessel Coils (IVC)

The ITER in-vessel coils are comprised of edge-localized mode (ELM) and vertical stabilization (VS) coils. There are 27 ELM coils and 2 VS coils. All the ELM and VS coils are supported by the clamped brackets bolted to the rails which are welded to the vacuum vessel wall. The in-vessel environment is severe, characterized by large transient electromagnetic fields, high radiation flux, and high temperature. Therefore, an appropriate nondestructive examination approach should be established and qualified. The difficulty in the development of the bracket weld nondestructive examination is the complex structure which brings space limit and various reflect echoes. Phased array ultrasonic test (PAUT) was studied and developed for nondestructive examination. In order to obtain the appropriate test parameters, CIVA simulation software was utilized to visualize the acoustic field distribution and coverage. The sensitivity of the PAUT method was also demonstrated by using machined defect provided by ITER Organization. Experiment results shows that all of reference defects can be detected with peak amplitude higher than 80% of FSH for both first leg and second leg.