This document discusses detecting flaws in condenser tubing welds using the DefHi probe. It notes that seam-welded condenser tubes are prone to defects along welds that are difficult to detect with standard bobbin probes. The DefHi probe uses eddy current testing and a multiplexed array coil configuration to better detect and characterize defects anywhere along tubes. Its software analyzes the multiple data signals to produce C-scans that accurately map defects, differentiating those in the same location or along welds. The DefHi provides advantages over bobbin probes for thoroughly inspecting welded tubes.

1. Detecting Flaws in Condenser Tubing
Welds With the DefHi® Probe
Application Note

2. 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
2 © Eddyfi NDT Inc. 2009–2015

3. 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
3 © Eddyfi NDT Inc. 2009–2015

4. The Solution
The shortcomings of bobbin probes can be worked around
with a judicious combination of hardware and software.
4 © Eddyfi NDT Inc. 2009–2015

5. 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
5 © Eddyfi NDT Inc. 2009–2015

6. 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
6 © Eddyfi NDT Inc. 2009–2015

7. The Solution
304 stainless steel tube results:
• 25.4 mm (1 in) outside diameter
• 0.7 mm (0.028 in) thickness
7 © Eddyfi NDT Inc. 2009–2015

8. The Solution
Bobbin signals can be compared to
previous inspections with conventional
bobbin probes.
8 © Eddyfi NDT Inc. 2009–2015

9. 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.
9 © Eddyfi NDT Inc. 2009–2015

10. 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.
10 © Eddyfi NDT Inc. 2009–2015

11. 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.
11 © Eddyfi NDT Inc. 2009–2015

12. www.eddyfi.com