FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

1. INTRODUCTION
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The development of an advanced eddy current testing (ET) nondestructive
Inspection system for heat exchanger tubing in nuclear facilities and other
industries presents a challenging set of problems. For the operator the
inspection system must be reliable, easy to operate and maintain. For the
analyst the system must present the data to facilitate on—line analysis.
Stored data required for signal confirmation must be comprehensive and easily
retrievable. The system must enable the complete inspection to be done
quickly and reliably to reduce the overall downtime of the heat exchanger,
and yet provide the utility manager and control agencies a convenient means
by which the conclusions of the inspection can be verified. To provide a
method of monitoring a heat exchanger's tube performance and permit long
range planning of maintenance and replacement, a convenient method of
comparing collected data must be available. The R'Eddy Record system,
designed to meet these needs of the operator, analyst, utility manager and
control agencies, represents a significant advance in eddy current inspection
technology.
Eddy current inspection is focused on the collection and analysis of two
voltage signals, Vx and Vv, which together represent the impedance of the
eddy current coil and make up one channel of eddy current data. The Vx and
Vy signals respectively represent the XY cartesian mapping of coil
impedance and the Lissajous figure, Vx versus V„, represents the eddy
current impedance image or 'feature'. The measured coil impedance is a
function of frequency and the material environment surrounding the coil.
Conventional single and multifrequency eddy current instrumentation can
provide X and Y outputs at both single and multiple test frequencies,
frequency mixes, and provide a storage oscilloscope impedance image display.
Signal analysis of the eddy current data involves interpretation of the 2—D
image with the separate X and Y versus distance traces providing information
on signal direction within the image.
A rudimentary inspection would consist of manual probe insertion down a heat
exchanger tube. An operator would analyze the tube condition by visually
monitoring the oscilloscope impedance image. A single storage scope display
superimposes images, thus signals can be missed and/or misinterpreted. If
long terra data collection or hardcopy results were needed the data could be
put on FM analog tape and/or strip chart. On-line signal analysis is very
difficult and prone to errors in this type of inspection. Post inspection
analysis must then be accomplished. On large inspections, literally miles of
strip chart can be generated making data retrieval and record identification
cumbersome and difficult. Data playback from analog tape also presents the
same problems of retrieval, identification and feature display
superpositioning.
A logical extension to manual inspection and the CRNL forerunner to the
R'Eddy Record system was a motorized probe pusher/puller (probe drive) to
speed up data collection, and a separated feature playback display that
allowed an operator to display non-superimposed ET features on an analog XY