The Advantages of Eddy Current Array over Magnetic Particle and Penetrant Testing for Inspecting the Surface of Carbon Steel Welds

Product Management | Tommy Bourgelas OSSA, January 2017

Presenter: Tommy Bourgelas

Product Manager, eddy current and bond testing products

§  16+ years experience with eddy current technology

§ Has conducted numerous trainings and provides customer support

§ Contributed to the development of several applications (eddy current array (ECA), tube testing, bond testing (BT))

§ Works on product improvement, design, and definition

Agenda §  Industry problems

§ MagnaFORM™ solution

§ How it works

§ Results

§ Conclusion

Current Surface Inspection Methods (and Their Problems)

Magnetic Particle Inspection (MPI) § Globally preferred method for inspecting carbon steel welds

§ Surface-breaking defects

MPI Principles § Strong magnetic field magnetizes metal

§ Magnetic particles align in areas with discontinuities

Penetrant Testing (PT) § Alternative method to MPI — mostly applied on

complex shapes or non-ferromagnetic surfaces

§ Surface-breaking defects only

PT Principles § Paint must be stripped, and a thorough cleaning is needed before

inspection

§ Application of chemicals and dwell time

Source: mechjobs.in

Paint Pain: Removal and Re-Application § Paint needs to be removed to help ensure detection (before inspection)

§ Paint needs to be re-applied (after inspection)

Liability Concerns § Removing paint exposes bare metal

§ Accelerated corrosion rate, contamination, etc.

§ Compromised liability from the inspection itself

Environmental Impact § Paint removal requires chemicals

§ Growing environmental concerns about chemical agents

§ Chemical disposal adds to cost

Increased Costs § Paint removal and downtime are often disregarded costs

§  The entire process is much more costly than the inspection itself

Additional Limitations (MPI) § No depth sizing

§ No archiving

§ Multiple passes required

§  False indications on rough (corroded) surfaces

§ Significant repeated physical effort (holding the yoke)

Additional Limitations (PT) §  “Dirty cracks” prevent penetrant from entering

§  Tighter defects (such as early stress corrosion cracking (SCC)) are almost impossible to detect with visible dye

Summary: Positive Impacts of MPI and PT § Very simple to use

§ Applicable to various parts or geometries

§ Widely used by many operators

§ Well-suited for bare metal (ferromagnetic)

§ Great sensitivity and resolution (MPI)

§ Affordable direct cost

Summary: The Negative Impacts of MPI and PT § Paint removal and re-application

–  Chemicals and environmental concerns –  Bare metal à liability –  Downtime (entire process) –  Cost of entire process

§ No sizing capability

§ No easy archiving

§ Multiple passes required

§  Low performance on tight or dirty cracks (PT)

§ Potential for false indications (rough surfaces)

The MagnaFORM™ Solution Distinctive Benefits and Features

Paint Removal is History § Eddy current sensors inspect through up to 3 mm thick paint

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

§ Maintains detection

No More Lift-Off Headaches §  Flexible array probe maintains excellent 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 replacing

Ready to Inspect § Hand scanner or semi-automated scanners

§ Works well on pressure vessels and pipes

Motorized Scan

Accessible Technology § Affordable Solution that works with an

OmniScan® MX flaw detector

§ Easy-to-use dedicated “WELD” software

Defect Depth Evaluation § Quickly evaluate defect severity for screening purposes

The Power of Imaging §  Instant interpretation

§ Archive your inspection files

§ Post-inspection 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: Multi-Layer 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 –  Ease of 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 a cross-wound coil

§  Ideal for carbon steel

§ Widely used in “Weld ECT Probes” (such as WeldScan probes)

§ Easily detects surface-breaking defects

§ Detects through paint, but impacted 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

§  Increases the sensitivity of crack detectors when lift-off is increased

–  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

Close-Up of the Weld

Lift-Off

Raw Crack Signal

Compensated Crack Signal

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

§  The depth of surface-breaking defects has a direct effect on amplitude

§ Other variables that impact amplitude: –  Lift-off (primary 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

Sensitivity Dynamically Compensated 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 in the

Sizing Process

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 L = 18 mm Depth = 3 mm

EDM in Weld Center/Crown L = 18 mm Depth = 3 mm

EDM in Toe L = 18 mm Depth = 3 mm

EDM in Crevice L = 18 mm Depth = 3 mm

EDM in Toe L = 18 mm Depth = 3 mm

#2 — Painted Coupon

§ Carbon steel plate: ~ 3/8 in. thick

§ Paint thickness: ~ 0.003 in.

§  Induced / machined flaws in weld

Defect in Toe L = 25 mm, Linear

Defect in Crown L = 12 mm, Transverse

Simulated Porosity (Not Detected)

#2 — Results

#3 — Rough Weld with Undercut

§ Carbon steel plate, 12 in. × 14” in., ~ 0.5 in. thick

§ No paint, but a protective varnish

§  Induced flaws in the weld

§  Flaws in undercut

§ Very rough weld, 4 filler passes

#3 — Drawing

#3 — Detection Results 7 — Crack in Toe L = 15 mm, D = 2 mm

5 — Crack in Toe L = 10 mm, D = 2 mm

3 — Centerline Crack L = 10 mm, D = 2 mm

#3 — Detection Results (continued) 8 — Undercut L = 25 mm, D = 0.8 mm

6 — Crack in Undercut L = 10 mm, D = 2 +0.8 mm

4 — Crack in Undercut L = 10 mm, D = 2 + 0.8 mm

#4 — Long Defect

§ Carbon steel plate, ~ ¾ in. thick, large radius

§ No paint (previously removed for MP)

§ Presence of a continued long crack in the toe

#4 — Magnetic Particle

Exterior Interior

#4 — Results (Exterior)

#4 — Results (Interior)

#5 — Stress Corrosion Cracking (SCC)

§ Carbon steel plate, ~ 0.25 in. thick

§ No paint (previously removed for MP/PT)

§ Actual SCC (marked by hand after it was found with MP/PT)

#5 — SCC Results

#6 — Dense SCC

§ Carbon steel plate, ~ 3/8 in. thick

§ No paint (previously removed for MP/PT)

§ Actual SCC colonies all over

#6 — Wet MP Results

#7 — Dense SCC Using the MagnaFORM Probe

#7 — SCC with Corrosion

§ Carbon steel plate, ~3/8 in. thick

§ Significant corrosion

§ No paint, sandblasted to add defects

§ EDM added inside and outside the corrosion

#7 — Results EDM in Corrosion L = 10 mm, D = 3 mm

(3x) EDM L = 10 mm, D = 1 / 3 / 5 mm

Corrosion Mostly Cancelled and Compensated for Lift-Off

Conclusion

Benefits §  Inspect through paint

§ Dynamic lift-off compensation

§ Single pass weld inspection

§ Stress corrosion cracking

§ Depth evaluation

§  Imaging and archiving

Thank you! Questions?

www.olympus-ims.com