Weld probe presentation- Given at COTEQ, Porto Galinhas, Brazil, June 2013
The Advantages of using
Eddy Current Technology
for Weld Inspection
by John Hansen
The Theory Behind Eddy
Eddy currents are created by using a coil to
induce an ac current into a conductive
The current is concentrated at the surface
and in ferrous material there is little or no
Changes in the impedance
with a simple coil are indicated
with lift-off giving a distinctly
different signal to a defect.
This for weld inspection makes
inspection very difficult. So
there has to be a better
History Of The WeldProbe
• 1966: Admiralty Materials Laboratory in the UK
develops the Amlec for ferrous weld inspection
(Hocking NDT License the technology) using a simple
• 1982: The Hocking WeldScan probe was developed by
John Calvert and John Hansen and others for use with
impedance plane eddy current instruments.
• 2000: Inspection procedure is standardised by BS
EN1711 eddy current examination of welds by complex
Why Use Eddy Current Probes
For Weld Inspection?
• MPI and Dye Penetrant inspection require the
removal of the coating before inspection, costing
both money and time.
• Eddy current probes allow welds to be efficiently
inspected for near-surface cracks.
• Eddy current can inspect welds through paint or
Why Use A Special Probe
For Weld Inspection?
By using a differential coil configuration, eddy
current weld probes:
• Allow inspection without the need to remove any
coating / paint
• Are in-sensitive to lift-off and variations in
material properties caused by the heat affected
zone unlike a simple absolute probe.
• A probe was designed with two orthogonal tangential
• The coils positioning and accuracy of manufacture is critical to
producing signals as required in the inspection procedure.
Scanning With An Eddy Current
• The active part of the probe is 3mm x 3mm.
• In order to scan the material, multiple scans need to performed. These are:
1. Zigzag scan of
the toe in the
along the length
of the toe
2. Scan of the weld
3. A sweep along the
What Makes The Weld Probe
• Minimal spurious signals caused by lift-off because of
• Sensitive to linear or near linear indications (e.g. cracks),
insensitive to symmetrical indications (e.g. holes and pits)
• Low lift-off sensitivity variation; 8 db per mm as compared
with the pencil probe at 40 db per mm.
• Directionality means that the defects in line with scan
give a positive indication and defects at right angle
give a negative indication with a null at + and - 45o.
• The probe has been
modeled and it shows an
extremely linear field in the
active area leading to good
sizing capability and
excellent lift off
• Widely used for weld inspection
where it replaces MPI due to not
needing to remove surface
• Readily applicable to
rope access inspection.
So further reducing the
cost of inspection
• Widely used in the nuclear NDT industry.
• Used for conventional manual inspection and also in
• Used for manual
inspection of defects in
rail and wheels.
• Axle inspection where
it has been shown to be
much more reliable
• Weld inspection on
chassis and bogeys.
• Steel framed buildings.
• Modern Art
• Overhead traffic lights.
• Amusement rides.
• Prison bars to detect saw cuts.
Equipment Used To Perform A
• Impedance Plane Display Eddy
Current Instrument (e.g. Vantage
• Weld probe.
• Paint probe to assess coating
thickness and compensate
calibration by means of shims.
• Test block with 2, 1 and 0.5mm
Notches and four 0.5mm shims.
• The technique has been widely accepted by various bodies including
BINDT-PCN, DNV and Lloyds Register.
• In 2000 BS EN1711 “Eddy current examination of welds by complex plane
analysis” was issued. Topics covered by this standard include:
• Equipment and Settings.
• Personnel Requirements.
• Calibration and Calibration Blocks.
• Acceptance Criteria and Weld Considerations.
• Scanning Methods.
• Coating Measurements.
• Testing Plans.
• Detectability of Flaws.
• Method Flow Diagrams.
• Non-acceptable Indications.
• Recording and Reporting of Inspections.
Weld Probe Specification
• Straight, 90deg Inline, 90deg Right Angle
• Diameters 11.0 (Small), 16 (Medium), 32mm (Large)
• Dis-connectable and integral probe cables
• Cable lengths from 1.5 to 50meters
• Frequency range 100, 20, 100-600kHz (Fe NFE)
• Minimal lift off signal, can find cracks though paint, oil
and conductive and nonconductive coatings
• Made from hard wearing PET
• Stainless steel and ceramic tips available on request
ETher NDE Weld Probes
Standard Bridge - Straight Standard Bridge – 90 Degree Inline
Standard Bridge – 90 Degree Transverse
Standard Disconnectable Weld Probes
Inline right angle
Advantages of EC NDT with
• Due to their size weld probes are much more suited to
difficult access inspections plus custom versions can be
used to further improve accessibility.
• The equipment is much more portable.
• There is a Euro Normstandardising the procedure for
application (BS EN 1711:2000)
• Weld probes are smaller
• Can apply to a vast range of applications
• Quick inspection time.
• Can inspect through paint or metallic coatings.
• Insensitive to Lift off in comparison with conventional
• Huge range of standard probes available.
Negatives of EC NDT with
• Sensitivity reduces with increasing coating
thickness 8dB/mm put procedure for
compensating for this.
• Not good at discriminating or classifying
defects beyond 5 mm depth in Ferrous
• Requires manual calibration on a test block.
• Standard probes will operate to 100oC and
there are special probes for use at up to 200oC
The WeldProbe provides a good alternative to MPI inspection as:
• It is not necessaryto remove the surface coating.
• Better suited for rope access inspectors.
• The probe is relatively easy to use so finds application in
• National standards, training courses with operator
certification and acceptance by certifying authorities mean
that the WeldProbe becomes a recognised solution.
• Mature technology with over 30 years of application