The use of eddy current array (ECA) technology has already been shown to increase the speed of inspections and the reliability of the surface inspection process. However, surface inspection of carbon steel welds used in pipelines and pressure vessels represents many challenges for this technology. The geometric shape of the weld crown, the paint thickness, the presence of crest and crowns, and the ferromagnetism of the carbon steel are constraints. New tools have recently been developed to help overcome these challenges. A new orthogonal-type ECA probe based on flexible printed circuit board (PCB) technology conforms to the shape of the weld to help ensure flaw detection. Dynamic lift-off compensation and depth sizing tools were then added to a modern flaw detector, resulting in a leading-edge solution that can potentially replace Magnetic Particle Inspection for carbon steel weld inspection. With these inspection tools, users can fully benefit from the portability, imaging, data archiving, and reporting capabilities of eddy current array instruments. In this paper, we review this new carbon weld inspection solution and present results that demonstrate the solution’s effectiveness for inspecting carbon steel welds. This presentation is technically advanced and is addressed to NDT operators and engineers.

1. Eddy Current Array Inspection of Carbon Steel Welds
with Dynamic Lift-Off Compensation and Depth Sizing
Product Management | Tommy Bourgelas
ASNT, Long Beach, October 2016

2. Magnetic Particle Inspection (MPI)
Problems and Advantages

3. Summary: MPI Positive Impacts
§ Very simple to use
§ Applicable to various parts or geometries
§ Widespread with many operators
§ Works well on bare metal (ferromagnetic)
§ Great sensitivity and resolution
§ Affordable direct cost

4. Summary: MPI Negative Impacts
§ Paint removal and re-application
– Chemicals and environmental concerns
– Bare metal à liability
– Downtime (entire process)
– Cost of entire process
§ No sizing
§ No easy archiving
§ Multiple passes required
§ False indications (rough surfaces)

5. The MagnaFORM™ Solution:
Distinctive Benefits and Features

6. No More Paint Removal
§ Eddy current sensors inspect through paint thickness up to 3 mm

7. Single Pass Scanning
§ Covers the heat-affected zone (HAZ), toe, crest, and crevices
§ Maintains detection

8. No More Headaches Dealing with Lift-Off
§ Flexible array probe helps ensure consistent contact
§ New dynamic lift-off compensation corrects sensitivity

9. Durable Inspection
§ Rugged construction (drop tested)
§ Wear face tested on a 22 km scan before it needed replacement

10. Ready to Inspect
§ Hand scanner or semi-automatic scanners
§ Suits pressure vessels and pipes

11. Motorized Scan

12. Accessible Technology
§ OmniScan® MX-based affordable solution
§ Easy-to-use dedicated “weld” software

13. Defect Depth Evaluation
§ Quickly evaluate the severity of defects for screening purposes

14. The Power of Imaging
§ Instant interpretation
§ Archive inspection files
§ Post-analysis is possible

15. How It Works

16. Basic Elements
Cart (MagnaFORM scanner)
Eddy current array probe
Encoder cable
Position encoder

17. Probe Close-Up
Detachable
connector
Sensitive face
Pre-shaped
“wedge”

18. Tool-Free Removal
1 2
3 4

19. Fits Most Pipes and Vessels
Flat
Large internal Smaller external
Large external

20. Flexible Sensor Array
16 + 16 sensors
(two types)
Active circuitry
Eddy current sensors:
multilayer PCB-etched coils

21. Eddy Current Technology
§ Characteristics:
– Magnetic coupling
– Great for surface inspection
§ Benefits:
– Inspect through paint
– Minimal surface preparation
– Suitable for metals, including
carbon steel
– Easy to use
Lift-off

22. Two Eddy Current Sensor Types
Type 1
Crack detector
Type 2
Lift-off gage
0
1 2
Max

23. Type 1 Sensor: Crack Detector
=
§ PCB equivalent to cross-wound coil
§ Ideal for carbon steel
§ Widely used in “weld ECT probes” (WeldScan
system)
§ Easily detects surface-breaking defects
§ Detects through paint, but is affected by lift-off
Crack signal

24. Type 2 Sensor: Lift-Off Gage
=
§ Eddy current sensor
§ PCB version of a “sliding probe”
§ Stable lift-off measurement
0
1 2
Max
Lift-off
measurement

25. Powerful Combination
0
1 2
Max
(Raw) crack
signal
Lift-off
measurement
Dynamic lift-off
compensation
Compensated
crack signal

26. Dynamic Lift-Off Compensation
§ Dynamic = real-time software processing
§ When lift-off is increased, the sensitivity of crack
detectors also increases
– No/minimal lift-off = normal gain
– More lift-off = more gain to crack detectors
§ Maintains uniform sensitivity independently from
lift-off

27. Independent Sensors
16 independent
crack detectors
16 independent
lift-off gages
16 independent
dynamic lift-off
compensated channels
+
=

28. MagnaFORM Scanner on a Weld
Flexible
probe
Good
contact
Increased
lift-off

29. Weld Close-Up
Lift-off
Raw crack
signal
Compensated
crack signal

30. Watching the Weight
Before
(no lift-off)
After (3 mm
lift-off)
Maintains Sensitivity

31. MagnaFORM Representation
Live
impedance
plane
Color palette
(uses vertical
amplitude)
Vertical
amplitude
C-scan view
(2D mapping)
Index axis
(probe
coverage)
Scan axis
(distance or
time)

32. Is Sizing Possible?
0.5 mm
1 mm
2 mm
3 mm
§ Depth of surface-breaking defects has a direct effect on amplitude
§ Other amplitude-affecting variables:
– Lift-off (main variable on rough surfaces/welds)
– Magnetic permeability
– Defect length (and shape)

33. How About the Toe of the Weld…?
0.5 mm
1 mm
2 mm
3 mm 3 mm
Dynamically compensated
sensitivity helps fix sizing
Reduced sensitivity
due to increased lift-
off (wrong sizing)
Probe profile

34. MagnaFORM Sizing = Depth Evaluation
Selection
cursor
(when paused)
Depth
reading
Selection
length is taken
into account
during the
sizing process

35. Sizing Demonstration

36. Results

37. #1 — Painted Pipe
§ Carbon steel pipe; ~ 6.5 in. OD × ~ 0.5 in. WT
§ Paint thickness: 0.007 in.
§ Machined flaws in and around the weld (electrical
discharge machining; EDM)
§ Known flaw sizes

38. #1 — Weld Details
§ 4 weld fillets on top
§ Width of weld ~ 1 in.
§ Rough surface
~ 1 in.

39. #1 — MagnaFORM Scan
Circumferential axis (360°)Coverage (~ 3 in.)
HAZ
Weld

40. #1 — Detection Through Paint
EDM in HAZ
Length = 18 mm
Depth = 3 mm
EDM in weld
center/crown
Length = 18 mm
Depth = 3 mm
Electrical discharge
machining (EDM) in toe
Length = 18 mm
Depth = 3 mm
EDM in crevice
Length = 18 mm
Depth = 3 mm
EDM in toe
Length = 18 mm
Depth = 3 mm

41. #2 — Painted Plate
§ Carbon steel plate; ~ 3/8 in. thick
§ Paint thickness ~ 0.003 in.
§ Induced / machined flaws in weld

42. #2 — Results
Defect in toe
Length = 25 mm,
linear
Defect in crown
Length = 12 mm,
transverse
Simulated
porosity
(not detected)

43. #3 — Rough Weld with Undercut
§ Carbon steel plate; 12 in. × 14 in., ~ 0.5 in. thick
§ No paint, but has a protective varnish
§ Induced flaws in weld
§ Flaws in undercut
§ Very rough weld, 4 filler passes

44. #3 — Drawing

45. #3 — Detection Results
7 – Crack in toe
Length = 15 mm,
Depth = 2 mm
5 – Crack in toe
Length = 10 mm, Depth = 2
mm
3 – Centerline crack
Length = 10 mm, Depth =
2 mm

46. #3 — Detection Results (cont’d)
8 – Undercut
Length = 25 mm, Depth
= 0.8 mm
6 – Crack in undercut
Length = 10 mm, Depth = 2 +0.8
mm
4 – Crack in undercut
Length = 10 mm, Depth = 2 + 0.8
mm

47. #4 — Long Defect
§ Carbon steel plate; ~ ¾ in. thick, large radius
§ No paint (previously removed for magnetic
penetrant)
§ Presence of continued long crack in toe

48. #4 — Magnetic Particle
Exterior Interior

49. #4 — Results (Exterior)

50. #4 — Results (Interior)

51. #7 — Stress Corrosion Cracking (SCC) with
Additional Corrosion
§ Carbon steel plate; ~3/8 in. thick
§ Significant corrosion
§ No paint, sandblasted to add defects
§ EDM added inside and outside corrosion

52. #7 — Results
EDM in corrosion
Length = 10 mm, Depth = 3
mm
(3x) EDM
Length = 10 mm, Depth = 1 /
3 / 5 mm
Corrosion was
mostly
cancelled and
compensated
for lift-off

53. Sizing Results (All Applications)
Alternating current
field measurement
(ACFM)
MagnaFORM scanner

54. Future Improvements
§ Comparable sizing to ACFM
§ Accuracy improvement in progress (future versions)
§ Improvements to correct for magnetic permeability
§ Looking for others to contribute to improvements
(samples, known defects, etc)

55. Conclusion

56. Benefits
§ Inspect through paint
§ Dynamic lift-off compensation
§ Single pass weld inspection
§ Stress corrosion cracking
§ Depth evaluation
§ Imaging and archiving

57. Thank you!