DETECTION OF SURFACE CRACKS IN ALLOY 600 TUBING WITH AN AC MAGNETIC BRIDGE

摘要

SCC in alloy tubing produces sharp discontinuities in imaginary reluctance of sufficient magnitude to be detectable by the magnetic bridge. Incorporation of a magnetic bridge into a tube probe should eliminate the development of a large lift-off variation, as was encountered in this experiment. Such a probe might take the form of a bridge whose pole faces are surface riding on the tube ID, with motorized rotation, similar to the Motorized Rotating Pancake Coil (MRPC) type of ECT probe, which is in widespread use for tubing inspection. A smaller bridge with smaller pole faces would improve spatial resolution and would be valuable for characterizing SCC in alloy 600 and for estimating its effect on tubing integrity and residual strength. Also, a differential bridge arrangement might prove to be valuable for suppressing global material variations and enhancing crack detection and characterization.