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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April 22, 2023
Magnetiser Bar
Solid Body Bristle
Fundamental Magnetiser Designs
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April 22, 2023
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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April 22, 2023
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 22, 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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April 22, 2023
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
dtdB
BvJ C
Regions of high current density,
J
ε = EMF J = Current Densityσ = Electrical Conductivity
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April 22, 2023
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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April 22, 2023
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April 22, 2023
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April 22, 2023
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April 22, 2023
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April 22, 2023
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April 22, 2023
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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230mm pole-spacing190mm pole-spacing150mm 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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April 22, 2023
Inner/Outer Pipe-wall Fields 14mm WT 5m/s
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Axial distance along pipe
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(Oe) 230mm pole-spacing (Inner)
110mm pole-spacing (Inner)230mm pole-spacing (Outer)110mm pole-spacing (Outer)
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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April 22, 2023
Sweeps 12mm 0m/s
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Magbar 12mm 0m/s
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Sweeps 12mm 5m/s
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Magbar 12mm 5m/s
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Sweeps Brush
Magbar
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Magbar vs. Sweeps Brush 12mm
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April 22, 2023
Sweeps 18mm 0m/s
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Magbar 18mm 0m/s
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Sweeps 18mm 5m/s
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Magbar 18mm 5m/s
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Magbar vs. Sweeps Brush 18mm
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April 22, 2023
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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12mm PS:110mm 12mm PS:150mm 12mm PS:170mm18mm PS:110mm 18mm PS:150mm 18mm PS:170mm22mm PS:110mm 22mm PS:150mm 22mm PS:170mm
M agbar
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12mm PS:90mm 12mm PS:110mm 12mm PS:150mm18mm PS:90mm 18mm PS:110mm 18mm PS:150mm22mm PS:90mm 22mm PS:110mm 22mm PS:150mm
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April 22, 2023
020
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-200-175-150-125-100-75-50-250255075100125150Z (mm)
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12mm LO:0mm12mm LO:5mm12mm LO:10mm18mm LO:0mm18mm LO:5mm18mm LO:10mm22mm LO:0mm22mm LO:5mm22mm LO:10mm
020406080100120140160180200220240260280300320340360380400
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12mm LO:0mm12mm LO:5mm12mm LO:10mm18mm LO:0mm18mm LO:5mm18mm LO:10mm22mm LO:0mm22mm LO:5mm22mm LO:10mm
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
19 /GE /
April 22, 2023
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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April 22, 2023
Thank you for listening
Questions?