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Magnetic Flux Leakage (MFL) Inspection Limitations
API 2006 Storage Tank ConferencePresentation
Morris KlineGeneral Manager of Domestic Sales
HMT Inc.
All Limitations
• Technology
• Human (Training and experience)
• Physical
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Let’s Talk about the Physical Limitations
• Tank Bottom inspection preparation• Bottom Plate Lap Welds seams• Bottom Plate Shapes and Sizes (sketch plates)• Shell (corner weld) radius• Patch Pla tes• Tank Bottom Obstructions (columns / re-pads, internal
piping, etc.)• Edge Settlement• Uneven Bottom Plates – peaks and valleys• Thick Reinforced Coating• Thick Annular Plates• “Edge effect” of Magnetic field extends the non-scanned
areas• Magnet and Sensor location
Typical Full Sized MFL Scanner
Overall scanner width = 14”Bridge Width = 12”
OverallLength = 36”
Front to basesensor = 10”
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Bottom Plate Lap Weld Seams
Limitation Zone
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Sketch Plate Example
Another Sketch Plate Example
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Typical Patch Plate
Patch Plate near lap seam - hole
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Typical Column with repad
Floating Roof Leg Striker Pad
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Tank Bottom Obstructions
Potential Multiple Patch Plates
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Manual/Mini Scanner for Near Corner Weld
Solutions/Options
• Following an informed “risk assessment” – what are yourbest options:
– Do Nothing!!– Extensive Visual Exam (should already be standard)– Vacuum Box Testing (leak detection only)– ACFM Crack Detection / Magnet Particle Examination
(surface breaking crack-like indications only)– Helium Testing (leak detection only)– Manual Ultrasonic Scrubs (corrosion locator)
– Hand/ Mini MFL Scanner (corrosion locator)
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Vacuum Box Testing
ACFM Crack Detection Equipment
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Helium Testing - Equipment
Helium Testing – Weld Seam Scanning
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In Summary
• Be aware of Limitations• Make an informed risk assessment• Revise or develop a work scope for your inspection vendor
that addresses either:– All tanksor– Specific to particular tanks based upon tank
characteristics, risk analysis or tank condition