Application of Alternating Current Field Measurement for Determination of Surface Cracks and Welds in Steel Structures at Lift-off

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Authors
  1. Farrell, S.
  2. Lugg, M.
  3. Avery, K.
Corporate Authors
Defence Research and Development Canada, Atlantic Research Centre, Halifax NS (CAN);TSC Inspection Systems, Wolverton Mill MK (UK)
Abstract
Alternating Current Field Measurement (ACFM) is a novel technique for Non-destructive inspection (NDI) and sizing of surface breaking cracks on conductive surfaces. This document examines the precision and accuracy of the ACFM technique for inspection of simulated surface breaking geometrical defects (ex., cracks) and electromagnetic discontinuities (i.e., welding, excessive grinding or corrosion) in high strength, low permeability steel plates at lift-offs :S 30 mm. An off-the-shelf standard array probe was shown to be effective at measuring crack lengths with an accuracy of ± 6% and a precision of :S 4 % at 0 and 4.4 mm lift-offs. The specialized high lift-off probe exhibited a precision of :S 5 % and an accuracy that decreased with increase in lift-off from ± 5% (at 0 lift-off) to ± 9 % (at 19.4 mm lift-off). The high lift-off probe was capable of detecting and sizing welding at 30 mm lift-off. Investigations are underway to improve the accuracy of the high lift-off probe to quantify depth.
Keywords
surface cracks;HY80 steel;structural hull survey;defect detection;non-destructive inspection;pulsed eddy current;weld overlay
Report Number
DRDC-RDDC-2015-N093 — External Literature
Date of publication
01 Mar 2015
Number of Pages
34
DSTKIM No
CA041355
CANDIS No
802467
Format(s):
Electronic Document(PDF)

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