Abstract
We have developed a “traveling” superconducting quantum interference device (SQUID) magnetic imaging system for practical nondestructive testing (NDT). For years it has been widely acknowledged that DC-SQUID sensors are adversely affected by ambient noise (e.g., earth's magnetic field), therefore they are not effective when applied to sense large areas through self-propelling motion. We recently succeeded in developing an advanced SQUID magnetic imaging system in which the SQUID sensor continuously travels back and forth by itself over the surface of an object being tested without using magnetic shielding. Technically, the self-propelled scheme is useful to enlarge the available scanning area of SQUID-NDT without limitation. In order to demonstrate the capability, we represent data relating to the detection of ferromagnetism due to plastic deformation by tensile testing using type-304 austenitic stainless steel. We also found that the traveling SQUID system developed is useful for evaluating artificial internal cracks embedded in austenitic welds.
