This paper describes the application of a SQUID susceptometer in nondestructive evaluation of steel pipes used in oil refmeries. Commonly used methods, such as ultrasound and eddy current techniques [ 11, normally need a very small liftoff distance between the pipe wall and the sensor, which would require removal of the thermal insulation protecting the pipe, thus increasing the costs related to the inspection.

SQUIDS have already proven to be able to perform nondestructive evaluation tasks without the need to remove such thermal insulation, having been successfully applied in electric current injection inspection of planar aluminum samples [2][3], with liftoff distances of up to 9 cm. So, SQUID systems open new frontiers for nondestructive evaluation with large liftoff of electrically conducting and ferromagnetic materials. Also, the development of high temperature SQUIDS, to which superconductivity occurs at liquid nitrogen temperatures, will further reduce the costs associated with the inspection by eliminating the need for cryogenic equipment to operate the SQUIDS with liquid Helium.

The next section describes the experimental setup used and the principle of operation of the SQUID susceptometer, followed by a description of the sample, which contains machined flaws, and the experimental results. Also, a comparison of these results with those from a commercial fmite element method software is discussed.