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

Magnetic Particle Inspection (MPI) Problems and Advantages

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

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)

The MagnaFORM™ Solution: Distinctive Benefits and Features

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

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

§ Maintains detection

No More Headaches Dealing with Lift-Off §  Flexible array probe helps ensure consistent contact

§ New dynamic lift-off compensation corrects sensitivity

Durable Inspection § Rugged construction (drop tested)

§ Wear face tested on a 22 km scan before it needed replacement

Ready to Inspect § Hand scanner or semi-automatic scanners

§ Suits pressure vessels and pipes

Motorized Scan

Accessible Technology § OmniScan® MX-based affordable solution

§ Easy-to-use dedicated “weld” software

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

The Power of Imaging §  Instant interpretation

§ Archive inspection files

§ Post-analysis is possible

How It Works

Basic Elements

Cart (MagnaFORM scanner)

Eddy current array probe

Encoder cable

Position encoder

Probe Close-Up

Detachable connector

Sensitive face

Pre-shaped “wedge”

Tool-Free Removal

1 2

3 4

Fits Most Pipes and Vessels

Flat

Large internal Smaller external

Large external

Flexible Sensor Array

16 + 16 sensors (two types)

Active circuitry

Eddy current sensors: multilayer PCB-etched coils

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

Two Eddy Current Sensor Types

Type 1 Crack detector

Type 2 Lift-off gage

0

1 2

Max

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

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

Powerful Combination

0

1 2

Max

(Raw) crack signal

Lift-off measurement

Dynamic lift-off compensation

Compensated crack signal

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

Independent Sensors

16 independent crack detectors

16 independent lift-off gages

16 independent dynamic lift-off compensated channels

+

=

MagnaFORM Scanner on a Weld

Flexible probe

Good contact

Increased lift-off

Weld Close-Up

Lift-off

Raw crack signal

Compensated crack signal

Watching the Weight

Before (no lift-off)

After (3 mm lift-off)

Maintains Sensitivity

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)

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)

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

MagnaFORM Sizing = Depth Evaluation

Selection cursor (when paused)

Depth reading

Selection length is taken

into account during the

sizing process

Sizing Demonstration

Results

#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

#1 — Weld Details

§  4 weld fillets on top

§ Width of weld ~ 1 in.

§ Rough surface

~ 1 in.

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

HAZ

Weld

#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

#2 — Painted Plate

§ Carbon steel plate; ~ 3/8 in. thick

§ Paint thickness ~ 0.003 in.

§  Induced / machined flaws in weld

#2 — Results Defect in toe Length = 25 mm, linear

Defect in crown Length = 12 mm, transverse

Simulated porosity (not detected)

#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

#3 — Drawing

#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

#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

#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

#4 — Magnetic Particle

Exterior Interior

#4 — Results (Exterior)

#4 — Results (Interior)

#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

#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

Sizing Results (All Applications)

Alternating current field measurement (ACFM)

MagnaFORM scanner

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)

Conclusion

Benefits §  Inspect through paint

§ Dynamic lift-off compensation

§ Single pass weld inspection

§ Stress corrosion cracking

§ Depth evaluation

§  Imaging and archiving

Thank you!