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Detecting Flaws in Condenser TubingWelds With the DefHi® ProbeApplication Note
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2 © Eddyfi NDT Inc. 2009–2015
Seam-Welded Tube HX
Condensers using seam-welded tubes:
• Usually less expensive than conventional HX
• Have one major potential weakness: the weld along the axis of the tubes
Seam-welded tube HX use thin-walled, seam-welded tubes
made of:
• 304/316 stainless steels
• Titanium
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3 © Eddyfi NDT Inc. 2009–2015
The Challenge
Seam-welded tubes affected by defects along seams, which
are difficult to accurately size and characterize with standard
eddy current bobbin probes because:
• Average bobbin coil response is over 360°
• Weld defects cover only very small percentage of total tube wall
• Phase response to depth significantly different for pits and cracks
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4 © Eddyfi NDT Inc. 2009–2015
The Solution
The shortcomings of bobbin probes can be worked around
with a judicious combination of hardware and software.
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5 © Eddyfi NDT Inc. 2009–2015
The Solution
The DefHi® probe is specifically designed to
inspect non-ferromagnetic tubing. It combines:
• Eddy current testing (ECT) technology
• Multiplexed eddy current array (ECA)
DefHi array coils:
• Transmitter-receiver configuration
• Multiplexed
• Absolute signals
Multiplexing enables:
• Array coils to detect defects anywhere in tubes
• Estimating the axial length and radial extent of defects
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6 © Eddyfi NDT Inc. 2009–2015
The Solution
The Magnifi® software uses all the data generated by the
DefHi probe to:
• Reduce defect sizing and characterization constraints through C-scans
• Increase sizing accuracy by leveraging the probe’s coils
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7 © Eddyfi NDT Inc. 2009–2015
The Solution
304 stainless steel tube results:
• 25.4 mm (1 in) outside diameter
• 0.7 mm (0.028 in) thickness
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8 © Eddyfi NDT Inc. 2009–2015
The Solution
Bobbin signals can be compared to
previous inspections with conventional
bobbin probes.
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9 © Eddyfi NDT Inc. 2009–2015
The Solution
The DefHi’s array
coils show that the
tube has no
circumferential
defects (right-hand
scan) along the tube,
while the axial C-scan
(left-hand scan)
displays several
defects.
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10 © Eddyfi NDT Inc. 2009–2015
The Benefits
Compared to standard ECT bobbin probes, the DefHi can:
• Differentiate between defects occurring at the same axial location along the
tube length
• Thoroughly map welded tubes, to size and characterize individual defects.
• Easily display defects along the seam.
• In conjunction with Magnifi, accurately locate defects along a tube’s length.
The DefHi’s standard differential bobbin coil channel
displays reference signals that can be used to compare with
previous bobbin probe inspections.
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11 © Eddyfi NDT Inc. 2009–2015
The Benefits
Seeing is Believing — Personnel without extensive ECT
data analysis experience can look at C-scan data and have
confidence in the inspection results.