ET16.pdf

Cracks were selected on the basis of discontinuity

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cracks were selected on the basis of discontinuity orientations (longitudinal and transverse), joint shapes (butt, fillet and cruciform joints) and discontinuity locations (on weld face, weld toe and base metal and near access ports). In the study, manual eddy current test results showed an 87 percent agreement with magnetic particle test results. Subsequent eddy current test results with the test bed showed a 100 percent agreement with magnetic particle testing. Causes of improved reliability included fine tuning the initial recommended practice and using highly qualified eddy current inspectors. Computer assisted results showed 62 percent agreement with the magnetic particle test results and significant false alarms. One factor impairing the results was that the eddy current probes were difficult to apply at weld toes and small access ports. Eddy Current Testing of Transfer Casks Background Transfer cask shells (Fig. 13) fabricated from a specified alloy steel 24 are used for transferring transportable storage canisters containing spent nuclear fuel bundles. Transfer casks are required to be tested on a scheduled basis in accordance with ANSI N14.6. 17 Annual testing of special lifting devices such as a transfer cask can be a significant disruption to an operation that runs all day, every day. This disruption becomes even more severe if the components need to have paint stripped and reapplied for the purposes of inspecting the load bearing welds. Paint stripping is further exacerbated by the fact that a transfer cask is considered to be contaminated unless a significant effort is expended to prove otherwise. Previous annual testing resulted in out-of-service time for these components of about one month. Magnetic particle testing has been done on transfer cask load bearing welds, requiring removal of all paint in those areas. Although magnetic particle testing is ideal for detection of surface cracks on ferritic material, magnetic particle testing loses its sensitivity when applied through coatings thicker than 200 to 300 μm (0.008 to 0.012 in.). Eddy current testing obviates removal and reapplication of coatings. Ferritic Weld Trials A nuclear engineering firm was asked by a nuclear operator to explore eddy current testing to replace magnetic particle testing. The application was unique in that a procedure was specified to detect a 1.6 mm (0.063 in.) discontinuity. Previous written practices for inservice testing specified a minimum detectability of 6 mm (0.25 in.) long and 0.8 mm (0.03 in.) deep by nonvisual testing. Field and manufactured samples were used to qualify the technique but there was no reference standard for calibration or for validation of discontinuity size. A calibration block with an electric discharge machined notch measuring 1.6 mm (0.063 in.) in length, 0.51 mm (0.020 in.) in depth and 0.015 mm (0.006 in.) in width was used because it was already referenced in an applicable standard. 25 The written procedure was revised to reflect this sensitivity.
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  • Fall '19
  • Test, Magnetic Field, Nondestructive testing, electromagnetic testing

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