Development of SQUID-based non-destructive evaluation system for detecting fatigue induced transformation of δ-ferrite to non-magnetic phases

A SQUID based NDE set up based on a precision XY scanner developed and used to evaluate the transformation of δ-ferrite to non-magnetic phases during fatigue in weldment samples has been described. The SQUID based NDE system comprises of a SQUID insert housed in a liquid helium cryostat, precision XY scanner for the sample movement and the data acquisition module to acquire the SQUID output signal with respect to the sample coordinates for flat plate as well as cylindrical samples. The system has been used to detect δ-ferrite content of virgin and fatigue tested austenitic stainless steel weldments.