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Eddy Current Array Probes
for Crack Detection and Sizing
in Carbon Steel Welds
Middle East Steel Conference
Dubai, UAE
October 21-23, 2014
Presented by:
Keith Sinclair
Director of Sales, India, Middle East & Africa
M. Sirois, S. Parmentier, N. Decourcelle, M. Grenier
Eddyfi®
National Seminar & Exhibition on Non-Destructive Evaluation, NDE 2014, Pune, December 4-6, 2014 (NDE-India 2014)
Vol.20 No.6 (June 2015) - The e-Journal of Nondestructive Testing - ISSN 1435-4934www.ndt.net/?id=17843
CONFIDENTIAL
Content
1. What are Eddy Current Arrays?
2. Why Carbon Steel Welds?
3. Development Objectives
4. ECA design: configuration, lift-off, sizing…
5. Our solution
6. Trials on Welded Specimen
7. Towards a Solution
8. Conclusions
2 © Eddyfi NDT, Inc., 2014
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Slow raster scan
(single-probe,
conventional
ECT)
Conventional eddy current
testing of carbon steel
weld (single sensor/probe)
• Only basic signals available for interpretation (no imaging, no C-Scan)
• Limited data storage (traces are saved)
• Lots of manual scanning involved: time-consuming, dexterity required
• No reliable depth sizing possible
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1.What Are Eddy Current Arrays?
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• An eddy current array (ECA) is composed of several
individual coils, grouped together in one probe.
• The coils are excited in a specific sequence to eliminate
interference from mutual inductance (channel multiplexing).
• Arrays can be made flexible or shaped to any geometry.
• Software provides graphical display (2D and 3D C-scans).
1.What Are Eddy Current Arrays?
4
Fast single-pass
(ECA)
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Typical benefits:
Reduced Inspection Time
Improved Flaw Detection (POD)
More Intuitive Interpretation
Full Inspection Records
5
1.What Are Eddy Current Arrays?
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2.Why Carbon Steel Welds?
6
Abundant & Critical
cc cc
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Vulnerable & Challenging
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2.Why Carbon Steel Welds?
cc
cccc
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• Penetrant Testing / Magnetic Particle Testing
• Surface preparation required, coating removal required
• Long: pre-clean, application, dwell-time, developer, evaluation, cleaning…
• On-site, immediate interpretation required
• Crude reporting and record-keeping capabilities (ruler & picture)
• Environmental concerns related to the use of chemicals
• No depth sizing possible
8
2.Why Carbon Steel Welds?
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• Detect surface-breaking cracks in CS joints
• Length and depth sizing
• Accommodate weld crown in the ”as is” condition
• Lift-off tolerance: coating/paint up to 2-3mm (0.080”-0.120”)
• Maximize coverage and speed
• Leverage advanced imaging capabilities (C-Scan, 2D/3D)
The solution:
A dedicated probe leveraging eddy current array (ECA)
technology for the examination of carbon steel welds.
3.Development Objectives
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3.Development Objectives
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Lift
• Surprisingly, defects within a range
of 0.5mm to 15mm in depth were
easily distinguishable.
• However, defects signals curvature
could complicate depth sizing
using either vertical or horizontal
component of signals.
• As lift-off occurs during weld
scans, the operating point moves
along this hooked curve producing
significant phase changes.
…cannot be reached with a Transmit-Receive (TR)
configuration using pancake coils side-by-side:
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4.ECA Design:
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A specific Transmit-Receive (TR) configuration
• Defects at 90 degrees with lift-off
• All defects have the same phase shift
• Lift-off “flatness”
25kHz 100kHz 50kHz
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• Lift-off monitoring is possible:
lift-off curve using horizontal amplitude (50kHz)
3mm 2mm 1mm 0mm
4.ECA Design: Lift-Off Monitoring
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• By measuring the horizontal offset of the operating
point during scans, lift-off can be measured and
depth sizing then corrected
4.ECA Design: Lift-Off Monitoring
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4.ECA Design: Depth Sizing
1mm
2.5mm
5mm
10mm
• Note: EDM notches used
during these tests were 1mm,
2.5mm, 5mm, 10mm,
12.5mm, 15mm and 20mm
deep, all 25mm in length.
• Until 12.5mm in depth
(2:1 length/depth ratio) sizing
remains good. However, for
ratios under 2:1 (rarely the
case for real cracks), EC
would tend to use the shortest
path and to bypass notches in
surface rather than « diving »
under it.
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• Using the vertical component of the signals, depth
sizing is possible:
4.ECA Design: Depth Sizing
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• The idea here is to correct depth sizing depending on
lift-off variations.
• Based on the orthogonality between defects and lift off
signals, any horizontal offset might be considered as a
potential lift off causing a decrease in amplitude on a
given defect.
• From there, multiple depth curves need to be calibrated
with various lift-off values, i.e. 0mm, 1mm, 2mm and
3mm.
• Using these multiple depth curves, a 3D depth “plan”
could be plotted with depth vs. vertical amplitude
vs. lift-off.
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4.ECA Design: Depth Sizing
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4.ECA Design: Depth Sizing Correction
• Thus, using the following depth curves with lift-off at
0mm and 1mm…
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4.ECA Design: Depth Sizing Correction
• And these at 2mm and 3mm…
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• We can plot a 3D depth curve vs. lift-off:
4.ECA Design: Depth Sizing Correction
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• For example, here is a defect 5mm deep with 1mm of
lift-off:
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4.ECA Design: Depth Sizing Correction
Lift-off sizing Depth sizing
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• One of the receiving coils is used to size the length :
This defect is 7.7 mm long and has been
sized at 7.5 mm using the encoder.
4.ECA Design: Length Sizing
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Validating:
• EC behaviors around simulated defects
• Lift-off and impact on EC uniformity
• Aspect ratios of crack-like defects
• Coil optimization
Finite-Element Analysis (FEA) with COMSOL
0mm 1mm 5mm
10mm
4.ECA Design: Validation
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Finite-Element Analysis (FEA) with COMSOL
4.ECA Design: Validation
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5. Our Solution – “Sharck™”
© 2010 Eddyfi. All rights reserved.24
“Sharck™” contains the letters of
crack (what it is designed to detect !).
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5. Our Solution – “Sharck™”
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Patent-pending
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• Single-V, as welded
• Toe cracks and HAZ crack
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6.Trials on Welded Specimen
• Carbon Steel
• 9.5 mm (3/8”) thick
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6.Trials on Welded Specimen
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Flaw 1
Flaw 2
Flaw 3
Flaw 1
Flaw 2
Flaw 3
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6.Trials on Welded Specimen
• First step: lift-off monitoring
→ 0.2mm thus, the 0mm lift-off curve must be selected
Sizing Flaw #1
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6.Trials on Welded Specimen
• Second step: depth sizing with vertical amplitude
Sizing Flaw #1
→ 1.3mm depth (real depth is 1.25mm)
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6.Trials on Welded Specimen
• Third step: length sizing
Sizing Flaw #1
→ 3.5mm length, real length is 3.2mm
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6.Trials on Welded Specimen
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What’s next?During the upcoming months, a thorough validation of the
probe capabilities is taking place.
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• Performance demonstrations, assessment of limitations
• New software tools including:
3D depth curves
New filtering processes
Special measurement cursors
Auto-calibration feature
And more!
7.Towards a Solution…
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8.Conclusions
• An eddy current array technique has been developed
for the detection and sizing of surface-breaking
cracks in carbon steel welds;
• A transmit-receive, multiplexed array probe provides
adequate signals and even allows detecting
transverse cracks;
• Results are promising, and capabilities in terms of
tolerance to paint/coating (lift-off), length and depth
sizing are being investigated;
• Additional work remains to thoroughly assess the
capabilities and limitations of ECA technology in the
context of carbon steel welds.
33 © Eddyfi NDT, Inc., 2014