Securing the Best Performance Entitlement from MFL Technology

Ian MullinGE Oil & Gas, PII Pipeline Solutions

• Introduction to Magnetiser Design • Mechanical Review• Required Saturation Fields• Velocity Effects• Pole Spacing• Magnetiser Bar vs. Solid Body Bristle

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Magnetiser Bar

Solid Body Bristle

Fundamental Magnetiser Designs

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Mechanical Review Solid Core Bristle Design / “Sweep’s

Brush”

• Simple and robust• Maintains good coupling with pipe-wall at all times• Bristles absorb the impact of in pipe obstacles• Sensors contact intrados/extrados of bends• Predictable drag forces• Compressibility limited by solid core and poles

Magnetiser Bar / “Magbar” Design

• Possibility of extreme compressibility• Mechanically more complex design• Poles & sensors experience lift-off in bends• Large mass of magnetiser bar accelerated at pipeline obstacles• Large clamping forces

Solid core bristle design is mechanically more robust and suitable for most pipeline environments. Magnetiser bar designs can be more suitable for multi-diameter lines if compromises are made elsewhere.

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Magbar Issues with Bend Inspection

POF are now considering including bend inspection performance in their required specification

DiscriminationSensors

Main Corrosion Sensors

3 of 4 external defects (20mm x 40%) visible. No signal from defect on bend extrados

[Extrados]

[Intrados]

SWEEP’S BRUSH MAGNETIZER BAR

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April 18, 2023

- Same vehicle used in half/full magnet build- Same EXTERNAL defect detected and sized- Same run speed

• Defect sized exactly the same

Required Saturation Field Levels

† ASTM, “Standard Terminology of Symbols and Definitions Relating to Magnetic Testing”

Saturation - That degree of magnetization where a further increase in magnetization force produces no significant increase in the magnetic flux density (permeability) in a specimen.†

Above the ‘knee’ • Pipe-steel is in saturation• Sensitive only to metal loss and wall thickness variation

Operating below the ‘knee’ of the curve • Sensitive to material variation, stress/strain etc. • Poor defect detection & sizing

There are several sources of noise during inspection (magnetic, sensor, dynamics, electronics) and all of these must be addressed in order to obtain the best signal to

noise ratios. Designing solely to achieve the highest fields possible will result in a sub-optimal design.

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Eddy currents• Faraday’s Law

Changing magnetic flux dB/dt induces electric current in conductor

• Lenz’s lawCurrent generated by changing magnetic field will produce a magnetic field in opposition to that which generated it (induced field).

Result of pig moving through pipeline:

• Eddy currents generated in pipe (good electrical conductor) predominantly at points of pole contact

• Opposing induced fields attenuate field levels across the pipe-wall

• Field is concentrated onto inner pipe-wall

dt

dB BvJ C

Regions of high current density,

J

ε = EMF J = Current Densityσ = Electrical Conductivity

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Velocity EffectsAxial field (-Hz) contour plot for pipe section between poles

Low velocity (<2m/s):

• Axial field profile demonstrates good uniformity across wall thickness and axially across the sensor position

• High field levels at sensor position throughout the wall thickness

With increasing velocity:

• Axial fields attenuated across wall thickness

• Field levels drop on outer wall

• High fields migrate further toward rear bristle stack on inner wall

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Pole SpacingAxial field levels on outer pipewall 14mm WT at 2/3 from front pole

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Axial field levels on outer pipewall 14mm WT at 2/3 from front bristle contact

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Speed (m/s)

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230mm pole-spacing190mm pole-spacing

150mm pole-spacing110mm pole-spacing

Short Pole-Spacing• Poor performance across speed range (0-5m/s)• Very sensitive to sensor positioning – vibration of sensor during inspection will produce noise on data• Little room for sensor positioning• Very high fields possible at low velocity

Long Pole-Spacing• Field levels lower than short pole-spacing design• Maintains field levels from 0-5m/s• Relatively insensitive to sensor positioning –hence also less noise due to sensor vibration• More room for optimal positioning of sensor

Axial field levels measured 90% into pipe-wall (OUTER)

Pole Spacing

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Inner/Outer Pipe-wall Fields 14mm WT 5m/s

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Axial distance along pipe

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110mm pole-spacing (Inner)230mm pole-spacing (Outer)

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Short pole-spacing 110mm

Long pole-spacing 230mm

Field levels are predominantly much higher on the inner pipe-wall

Ideally the sensor should be placed in or around the crossover point (red circles)

• Short pole-spacing - optimum sensor positioning possible?- large field gradients - inner wall field levels can be over 2x outer wall

• Long pole-spacing- room for optimum sensor positioning- smaller field gradients- inner wall field levels can still be over 2x outer wall

Direction of Motion

When field levels are quoted for performance comparison it is crucial that they are OUTER wall levels, as these will be the minimum values (POF standards*). However, it is not possible to directly measure outer-wall fields on-board during an inspection run.

*Pipeline Operators Forum, “Specifications and Requirements for Intelligent Pig Inspection of Pipelines”

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Sweeps 12mm 0m/s

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Magbar 12mm 0m/s

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Sweeps 12mm 5m/s

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Sweeps Brush

Magbar

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Magbar vs. Sweeps Brush 12mm

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Sweeps 18mm 0m/s

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Magbar vs. Sweeps Brush 18mm

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Magbar vs. Sweeps Brush

Sweeps Brush• Median pole spacing (150mm) maintains field across full speed range in 12mm/18mm wall• In 22mm wall fields have collapsed beyond 3m/s

• Shorter pole-spacing gives: - higher fields at low velocities- less speed stability

• Longer pole-spacing gives:- lower peak fields- better speed stability- less ‘peaky’ field profiles

Magbar• Median pole spacing (110mm) shows poor speed stability but high fields at low velocity

• Shorter pole spacing gives:- higher fields at low velocities- variations in pole spacing has little influence on speed performance

• Longer pole-spacing gives:- lower peak fields- some improvement in speed stability

Sweeps

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M agbar

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12mm LO:0mm12mm LO:5mm12mm LO:10mm18mm LO:0mm18mm LO:5mm18mm LO:10mm22mm LO:0mm22mm LO:5mm22mm LO:10mm

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Axial distance along pipe Axial distance along pipe

Magnetiser & Sensor Lift-off

~15% drop in pipe-wall fieldNegligible drop in pipe-wall field at sensor position

Sensor will not measure drop

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Solid Core Bristle Design / “Sweep’s Brush” - Suits long pole-spacing

• Speed stable magnetic performance• Low sensitivity to lift-off• Uniform field profiles

• Lower peak field levels at low velocity relative to magbar

- Good in realistic pipeline environment across a range of speeds

Magnetiser Bar / “Magbar” Design - Suits shorter pole spacing

• High peak field levels at low velocity

• Poor magnetic performance at high speed• Sensitive to speed variations• ‘Peaky’ field profiles

- Good in ideal environment at low controlled speed

Magnetics Review

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Thank you for listening

Questions?