Detection Keynote:Development of an Inspection Technology For Mechanical Damage

J. Bruce NestlerothBattelle

Testing of a tool in an operating pipelineDOT / PRCIPRCIMay

2008May2006

Design of a dual magnetization tool.Technology demonstration

DOT / PRCIBattelleMar

2005Sep2003

Summary of Research for Mechanical Damage That Included Battelle

Validation of decoupling and evaluation of circumferential MFL. Nonlinear harmonics and mechanical assessment.

GTI / DOTBattelle, SwRIJun

2003May2000

Magnetic properties of pipeline steels an Dual magnetization. Non linear harmonics and neural networks.

DOTBattelle, SwRI,Iowa State

Dec 1999

Sep1996

Feasibility of MFL to better characterize mechanical damage.GRIBattelle, SwRIMay

1996Oct

1994

OutcomesSponsorContractor(s)EndStart

Technology transferGTITuboscopeSep2003

Sep2001

Non Linear Harmonics (NLH)

• Developed by Southwest Research Institute SwRI®

• An electronic method for detecting surface stress/strain patterns

• Uses an alternating magnetic field (10kHz), making it sensitive to only surface strain changes

• Examines only a small area, requiring multiple sensors for complete coverage of pipe surface

• A current SwRI project with DOT is evaluating the ability of NLH to monitor changes in gouged dents as they are cyclically loaded to failure.

NLH signals reveal defect stress patterns on pipe inner surface

Defect stress pattern from FEA

Finite element stressanalysis confirms NLHsignals relate to stress

intense stress

intense signalNLH data from pressurized scan

Data Provided by SwRI

Technology demonstration at the Pipeline Simulation Facility

• DOT PHMSA and DOE NETL have conducted Technology Demonstrations in Sept 2004 and Jan 2006 examining:– Corrosion sensorsfor crawlers (3)– SCC (1) – MechanicalDamage (2)– Plastic pipe

• Blind tests• Industry observers

24” diameter mechanical

damagesamples

8” diameter corrosion samples

26”diameterSCC test samples

6”diameterplasticpipe

sample

Ultrasonic strain measurementsusing EMATs

• Pacific Northwest National Laboratory (PNNL) is developing an ultrasonic sensor system for detecting and characterizing pipeline stress and strain caused by denting and other deformation

• Ranks the severity of smooth dents based on ultrasonic measurements of the mechanical properties and the presence of plastic strain, rather than dent dimensions or wall thickness

• Strain is measurable for uniaxial deformation• Developing predictions of effective strain when the

damage is more complex than a simple uniaxialdeformation on deformed pipe

PNNL Ultrasonic strain measurements vs. effective strain from dimensional measurementsof deformed pipe

0%

1%

2%

3%

4%

5%

6%

7%

0% 1% 2% 3% 4% 5% 6% 7%Effective Strain (thickness ( L/L0 ) (%)

Ultr

ason

ic S

trai

n M

easu

rem

ent

(%)

EMAT Sensor

Motor for sensor rotation

Springs for smooth motion past dents

Dual Magnetization MFL Inspection for Mechanical Damage

• Inspection Goal:–Increase the probability of obtaining a measurable

signal from significant mechanical damage and properly differentiates these signals from other "anomalous" signals

–Function reliably under pipeline conditions

• Dual magnetization MFL technology–Can detect magnetic property variations due to

stress associated with dents and gouges–Is an extension of the most successfully used

pipeline inspection technology

Initial Result: Low magnetic fields are sensitive to stress and cold work

Magnetizing Field (H)

Mag

netiz

atio

n

Saturation, Ms

No Residual Stress

Compressive Residual StressPerpendicular to H-Field

-8 -6 -4 -2 0 2 4 6 8

Axi

al M

FL S

igna

l (G

auss

)

Distance (Inches)

-8 -6 -4 -2 0 2 4 6 8

Axi

al M

FL S

igna

l (G

auss

)

Distance (Inches)

9080

60

50

4030

70

70 Oersteds

110 Oersteds130120

100

90

80

110

70

Nominal MFL Tools

High Fields Mask Damage

Medium Fields Show Damage

Mechanical Damage MFL Tools

Data from the GRI Mechanical Damage Program

Dual Magnetization Approach

Dual magnetization level signal processing (decoupling)

1. MFL signals at high magnetization levels are almost entirely due to geometry changes (corrosion and removed metal)

2. MFL signals at low levels are due to both geometry and magnetic changes

3. The difference is due to magnetic changes - the most important components of mechanical damage

Extracting the Magnetic Component: Decoupling

Low MagnetizationSignal

Scaled Geometric Signal

SCALING FACTOR (SF)

MFL Signal due to Magnetic Changes

Only

High Magnetization Signal

Decoupling ExampleH

igh

Mag

netiz

atio

n

Low

Mag

netiz

atio

n

Dec

oupl

ed

ReroundHalo

Gouge Signal

• Extra metal near mechanical damage • A geometric change• Decoupling theory says that geometric changes cancel.

Concrete pier withConcrete pier withsteel plate on topsteel plate on top

Mechanical DamageMechanical DamageDefectsDefects

Demonstration that decoupling worksH

igh

Mag

netiz

atio

n

Low

Mag

netiz

atio

n

Mechanical Damage Revealed!!!

Dec

oupl

ed

ReroundHalo

Gouge Signal

Decoupling method was tested in a variety of pipe materials

High

Low Decoupled

The Most Recent Project:Design of a dual magnetization tool

• Prior projects established:– Theory– Signal processing– Functional in

pipeline materials

• Built and tested a prototype tool at the pipeline simulation facility

NSN

BrushesNS

Magnetic NullPivot point

-200

-150

-100

-50

0

50

100

-20 -15 -10 -5 0 5 10 15 20Axial Position (inches)

Mag

netiz

ing

Fiel

d (O

erst

ed)

HighLow

• Magnet bar split at the null point with a ball joint coupling for passing pipeline bends.

Articulating magnet bar

Prototype tool built and tested atBattelle’s Pipeline Simulation Facility

Dual Magnetization Summary

• Deformation tools have been used to assess dents in pipelines for years.

• Some newer commercial MFL tools incorporate deformation sensors to identify dents with missing metal.

• The dual field approach has the potential to augment current MFL technology to identify and provide additional information on dents that are the result of third party excavation.– The dual field method exposes areas of stress, re-

rounding and cold work.– In particular, the decoupled signal can expose a region of

cold work where the ductility of the steel has been exhausted and the re-rounding of the dent applies a tensile load to the anomaly.

Future project

• A PRCI project has been recommended for a DOT PHMSA award to start gaining field experience

• Pigging vendor will build a dual magnetization tool for use on an operating pipeline

• Pipelines have been designated for evaluation of dual magnetization technology

• Single magnetization MFL technology will be evaluated