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