Detection of Stress due to Corrosion through Passive Measurement and Analysis of Magnetic FieldsD Cowell1, S Staples2 , C Vo1, P Jarram3, B Varcoe2, S Freear1
1 School of Electronic and Electrical Engineering,2 School of Physics and Astronomy,
University of Leeds, UK
3 Speir Hunter Ltd,Long Bennington, Newark, UKBooth 429, CORROSION 2013
Information in this presentation is propriety to Speir Hunter Limited.Not to be disclosed without permission.
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Overview
• Motivation for remote stress measurement
• Stress Concentration Tomography (SCT)
• Magnetoelastic effects in steel
• Experimental measurement of stress-magnetisation
• Finite element modelling of stress
• Finite element modelling of stress-magnetisation
• Experimental magnetic field characterisation rig
• Prototype SCT instrumentation
• Initial field survey results
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Motivation
• Ageing global pipeline infrastructure
• Non-invasive, remote, pipeline integrity assessment
• Applicable to non-piggable pipelines
• Non-interruption of pipeline service
• No change to operating parameters
• Detection of stress not geometry
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Stress ConcentrationTomography (SCT)
• Analyse changes in magnetic field along the pipeline
• Reporting
• Location of abnormal stresses
• Metallurgical and mechanical conditions
• Maximum allowable operating pressure (MAOP)
• Safe operating term
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Stress ConcentrationTomography (SCT)
• Pipeline experiences stress
• Corrosion Anomaly
• Stress Corrosion and Metallurgical Defects
• Slippage
• Subsidence
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Stress ConcentrationTomography (SCT)
Defective section
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Defective section
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Defective section
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Length of
anomaly 1
Length of
Anomaly 2
Length of
anomaly 3
Pipeline
Magnetic field
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Magnetoelastic effects
Joule MagnetostrictionChange in sample dimension in the direction of the applied field
Villari EffectChange in magnetization due to applied stress
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Stress-magnetisation in carbon steel
2003 Jiles, Li, IEEE Trans. Mag, 39, 3037
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Experimental Investigation ofStress-Magnetisation in Carbon Steel
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Physical Composition [%wt] Mechanical Properties
C Si Mn Cr Ni OthersTensile
Strength[N/mm]
YieldPoint
[N/mm]
0.42 -0.50
0.17-0.37
0.50-0.80
<0.25 <0.25 <0.035 570 295
Stress-Magnetisation in Carbon SteelExperimental Setup
• 20 x 210 mm rectangular sample• #45 Carbon Steel• 3 axis fluxgate magnetometer• Cyclic force
• 0-10-0 kN• 0-250-0 MPa
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Stress-Magnetisation in Carbon SteelProcessed Experimental Results
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FE Modelling of Magnetic Scalar Potential in Stressed Steel Bar
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FE Modelling of Magnetic Scalar Potential in Stressed Steel Bar
FEM of the Magnetic Scalar Potential of the Steel Bar Stressed to 120 MPa
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Comparison betweenExperimental and FEM Results
Experiment image of field compared to model calculated image
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FEM of Cracked Steel Bar
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Magnetic detection ofStress Concentration Zones (SCZ)
Characteristic curves of Self Magnetic Flux Leakage(SMFL)
SCZ
Graphic adapted from: Wang, Z.D., et al., Quantitative study of metal magnetic memory signal versus local stress concentration. NDT & E International, 2010. 43(6): p. 513-518.
Magnetic detection of Stress Concentration Zones (SCZ)Methodology - Wang et al
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Magnetic detection of Stress Concentration Zones (SCZ)Instrumentation
ΔZ pk magnitude12.5 μT
ΔZ pk-pk length6 m
Magnetic detection of Stress Concentration Zones (SCZ)Analysis of Field Data
48” diameter Gas Pipe at 40 bar
ΔX pk magnitude3 μT
ΔX pk length6 m
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Summary
• Motivation for remote stress measurement
• Stress Concentration Tomography (SCT)
• Magnetoelastic effects in steel
• Experimental measurement
• Finite element modelling of stress
• Finite element modelling of stress induced magnetic field
• Experimental magnetic field characterisation rig
• Prototype SCT instrumentation
• Initial field survey results
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Thank you for your attention
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