Eddy Current Inspection of Threaded Fasteners

Anti-seize lubricant commonly used on threaded fasteners makes it difficult to prepare surfaces adequately for magnetic particle and liquid penetrant testing. In high temperature applications, the lubricant forms a tenacious residue on the threaded fastener. An alternative surface examination technique requiring minimal surface preparation would reduce inspection cost and duration. Two types of threaded fasteners, reactor pressure vessel closure studs and turbine casing studs, have been targeted for investigation. Eddy current techniques requiring minimal surface preparation and capable of detecting flaws are being developed for these two applications. Other advantages of eddy current inspection over magnetic particle testing and liquid penetrant testing include the absence of consumable materials, capability to provide permanent digital records, and the potential for automation.