Pulsed Eddy Current Inspection of Wall Loss in Steam Generator Trefoil Broach Supports

Abstract

Inspection for corrosion in steam generator (SG) tube support structures is a significant component of monitoring SG condition, since support degradation can lead to SG tube flaws, and thereby further SG deterioration. A pulsed eddy current probe was developed to augment SG inspection at carbon steel trefoil broach supports. The probe demonstrated capability to measure far side wall loss as small as 20% of the original 2.7-mm-thick broach support ligament from within the Alloy 800 SG tube. A power law fit of the data was found to describe signal variation at later times under conditions of varying wall thickness and lift-off. The associated power law exponent varied linearly with wall thickness and was observed to be largely independent of lift-off and angular orientation of the probe, identifying it as a potential parameter for ligament wall thickness monitoring. Voltage response integrated over time also provided a low-noise means of measuring the wall loss when lift-off variation and misalignment were not present.