Transcript Document

Securing the Best Performance Entitlement from
MFL Technology
Ian Mullin
GE Oil & Gas, PII Pipeline Solutions
• Introduction to Magnetiser Design
• Mechanical Review
• Required Saturation Fields
• Velocity Effects
• Pole Spacing
• Magnetiser Bar vs. Solid Body Bristle
Fundamental Magnetiser Designs
Magnetiser Bar
Solid Body Bristle
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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
[Extrados]
Discrimination
Sensors
[Intrados]
3 of 4 external defects
(20mm x 40%) visible.
No signal from defect
on bend extrados
SWEEP’S BRUSH
Main Corrosion
Sensors
MAGNETIZER BAR
POF are now considering including bend inspection performance in their required
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specification
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Required Saturation Field Levels
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.†
- Same vehicle used in half/full magnet build
- Same EXTERNAL defect detected and sized
- Same run speed
Operating below the ‘knee’ of the curve
• Sensitive to material variation,
stress/strain etc.
• Poor defect detection & sizing
Above the ‘knee’
• Pipe-steel is in saturation
• Sensitive only to metal loss and wall
thickness variation
• Defect sized exactly the same
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.
† ASTM,
“Standard Terminology of Symbols and Definitions Relating to Magnetic Testing”
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Eddy currents
• Faraday’s Law
Changing magnetic flux dB/dt induces electric current in conductor
• Lenz’s law
Current generated by changing magnetic field will produce a magnetic
field in opposition to that which generated it (induced field).
 
dB
dt
J  vC  B
ε = EMF
Regions of high
current density, J
J = Current Density
σ = Electrical Conductivity
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
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Velocity Effects
Axial 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 Spacing
Axial field levels measured 90% into pipe-wall (OUTER)
Axial field levels on outer pipewall 14mm WT at 2/3 from front pole
Axial field levels on outer pipewall 14mm WT at 2/3 from front bristle contact
220.0
220.0
230mm
190mm
150mm
110mm
200.0
230mm
190mm
150mm
110mm
200.0
180.0
160.0
160.0
140.0
140.0
120.0
120.0
-Hz (Oe)
-Hz (Oe)
180.0
pole-spacing
pole-spacing
pole-spacing
pole-spacing
100.0
100.0
80.0
80.0
60.0
60.0
40.0
40.0
20.0
20.0
0.0
pole-spacing
pole-spacing
pole-spacing
pole-spacing
0.0
0
0.5
1
1.5
Short Pole-Spacing
2
2.5
3
3.5
4
4.5
Speed (m/s)
5
0
• 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
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Speed (m/s)
Pole Spacing
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
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5
Inner/Outer Pipe-wall Fields
Direction of Motion
14mm WT 5m/s
-Hz (Oe)
Field levels are predominantly much higher on the
inner pipe-wall
200
230mm
110mm
230mm
110mm
180
Ideally the sensor should be placed in or around the
crossover point (red circles)
pole-spacing (Inner)
pole-spacing (Inner)
pole-spacing (Outer)
pole-spacing (Outer)
160
140
• Short pole-spacing
120
- optimum sensor positioning possible?
- large field gradients
- inner wall field levels can be over 2x outer wall
100
80
• Long pole-spacing
- room for optimum sensor positioning
- smaller field gradients
- inner wall field levels can still be over 2x outer wall
60
40
20
 Short pole-spacing 110mm 
Long pole-spacing 230mm


0
Axial distance along pipe
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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Magbar vs. Sweeps Brush 12mm
Magbar 12mm 0m/s
500
110mm pole-spacing
450
150mm pole-spacing
170mm pole-spacing
400
350
350
300
300
250
200
Axial Field (Oe)
0m/s
(static)
400
200
150
150
100
100
50
50
0
Axial distance along pipe
0
Axial distance along pipe
Sweeps Brush
Magbar
Sweeps 12mm 5m/s
320
Magbar 12mm 5m/s
320
110mm pole-spacing
300
150mm pole-spacing
280
300
90mm pole-spacing
110mm pole-spacing
150mm pole-spacing
260
280
260
240
240
220
220
200
200
180
160
140
Axial Field (Oe)
170mm pole-spacing
5m/s
250
180
160
140
120
120
100
100
80
80
60
60
40
40
20
20
0
Axial distance along pipe
90mm pole-spacing
110mm pole-spacing
150mm pole-spacing
0
Axial distance along pipe
Axial Field (Oe)
450
Axial Field (Oe)
Sweeps 12mm 0m/s
500
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Magbar vs. Sweeps Brush 18mm
Sweeps 18mm 0m/s
260
220
200
200
180
180
160
160
140
120
100
Axial Field (Oe)
0m/s
(static)
240
120
100
80
60
60
40
40
20
20
0
Axial distance along pipe
Sweeps Brush
Magbar
Magbar 18mm 5m/s
140
Sweeps 18mm 5m/s
140
130
130
120
120
110
110
100
100
90
90
80
70
60
Axial Field (Oe)
5m/s
140
80
0
Axial distance along pipe
110mm pole-spacing
150mm pole-spacing
170mm pole-spacing
80
70
60
50
50
40
40
30
30
20
20
10
10
0
Axial distance along pipe
Axial Field (Oe)
220
110mm pole-spacing
150mm pole-spacing
170mm pole-spacing
90mm pole-spacing
110mm pole-spacing
150mm pole-spacing
0
Axial distance along pipe
90mm pole-spacing
110mm pole-spacing
150mm pole-spacing
Axial Field (Oe)
240
Magbar 18mm 0m/s
260
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Magbar vs. Sweeps Brush
Axial Field (Oe)
12mm PS:150mm
18mm PS:150mm
22mm PS:150mm
12mm PS:170mm
18mm PS:170mm
22mm PS:170mm
360
340
320
300
12mm PS:90mm
18mm PS:90mm
22mm PS:90mm
M agbar
380
Axial Field (Oe)
12mm PS:110mm
18mm PS:110mm
22mm PS:110mm
Sweeps
380
360
12mm PS:110mm
18mm PS:110mm
22mm PS:110mm
12mm PS:150mm
18mm PS:150mm
22mm PS:150mm
340
320
300
280
280
260
260
240
240
220
220
200
200
180
180
160
160
140
140
120
120
100
100
80
80
60
60
40
40
20
20
0
0
0
1
2
3
4
Speed (m/s)
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
5
0
1
2
3
4
Speed (m/s)
5
Magbar
• Median pole spacing (110mm) shows poor speed stability
but high fields at low velocity
• Shorter pole-spacing gives:
- higher fields at low velocities
- less speed stability
• 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
- better speed stability
- less ‘peaky’ field profiles
• Longer pole-spacing gives:
- lower peak fields
- some improvement in speed stability
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Magnetiser & Sensor Lift-off
380
12mm LO:0mm
12mm LO:5mm
12mm LO:10mm
18mm LO:0mm
18mm LO:5mm
18mm LO:10mm
22mm LO:0mm
22mm LO:5mm
22mm LO:10mm
360
340
320
300
280
260
360
340
320
300
280
260
240
240
220
180
160
200
180
160
140
140
120
120
100
100
80
80
60
60
40
40
20
20
0
125
100
75
50
Negligible drop in pipe-wall field
at sensor position
25
0
-Hz (Oe)
220
-Hz (Oe)
200
150
12mm LO:0mm
12mm LO:5mm
12mm LO:10mm
18mm LO:0mm
18mm LO:5mm
18mm LO:10mm
22mm LO:0mm
22mm LO:5mm
22mm LO:10mm
400
380
0
-25
-50
-75
Z (mm)along pipe
Axial distance
-100
-125
-150
-175
-200
150
125
100
75
50
25
0
-25
-50
Axial distance
Z (mm) along pipe
Sensor will not measure drop
-75
-100
-125
-150
~15% drop in pipe-wall field
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Magnetics Review
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
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Thank you for listening
Questions?
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