Detecting Flaws in Condenser TubingWelds With the DefHi® ProbeApplication Note

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

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

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.

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

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

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

8 © Eddyfi NDT Inc. 2009–2015

The Solution

Bobbin signals can be compared to

previous inspections with conventional

bobbin probes.

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.

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.

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.

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