An investigation of pinch welds using HTS SQUIDs

• Published in: Superconductor science & technology Vol. 19; no. 5; pp. S251 - S256
• Main Authors: Carr, Chris, Espy, Michelle A, Urbaitis, Algis V, Kraus Jr, Robert H
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.05.2006
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/19/5/S18

To contain high-pressure gases inside a pressure vessel a seal is often made in a thin-walled tube, known as the stem tube, that connects the gas reservoir and the vessel. This seal can be achieved through the use of a resistance pinch weld that forms with only a limited amount of melting occurring. The lack of melting makes applying traditional post-weld nondestructive evaluation (NDE) techniques extremely difficult. The welds of interest here are made from 304L stainless steel (typically 3.8 mm diameter and 38 mm long) and have a non-uniform geometry that does not inherently lend itself to either eddy current or static field SQUID-based measurement techniques. We perform these NDE measurements with both the sample and the SQUID located inside local electromagnetic shielding. SQUID data are presented as individual time series traces for a set of welds that were fabricated using a broad range of fabrication parameters, and a comparison is made between the SQUID-based results and the known parameters. With the limited spatial resolution offered by our present SQUID system, it is not clear if weld quality can be evaluated from purely SQUID-based results.