Eddy Current Crack Signals in Small Diameter Tubing

Abstract

Eddy current nondestructive testing methods are effective for the detection of cracks in conducting materials. However, to insure that the detection is reliable an accurate reference standard must be used in instrument calibration. Electrical-discharge-machined (EDM) notches have been used as a reference standard for fatigue cracks (1, 2). However, many researchers argue that an EDM notch gives a larger signal than an actual fatigue crack (3, 4) and thus cannot be used as an equivalent model. Much of the previous research on this topic was done with a probe over a flat block. This paper discusses the case of a probe inside a tube with cracks growing from the outer diameter. The focus of this investigation is to compare actual fatigue crack signals with signals from EDM notches and a finite element simulation.