Sesión técnica, sala KM 19, Advances in detection and characterisation of metal loss in pipelines...

Copyright © TWI Ltd 2013

Advances in Detection and Characterisation of Metal Loss in

Pipelines Using Guided Wave Testing

Sean Fewell and Peter Mudge

TWI Ltd, Cambridge, UK

2nd International Conference and Exhibition on Logistics, Transportation and Hydrocarbon Distribution

León, Guanajuato, 20-22 November 2013


Outline

• Introduction to guided wave UT (GWT)

• International standards for GWT

• GWT pipeline inspection – current state of the art

• Flaw sizing using GWT

• New developments in GWT


Weld

Metal loss

Metal loss

FlangeGuided wavetransducers

Guided Wave

100% Coverage

Conventional UT Transducer

Pipe Cross-section

Guided wavetransducers

Weld

Metal loss

Metal loss

FlangeConventional UT

Transducer

Localised Inspection

Principles of GWT

Longitudinal Torsional Flexural


How GWT is Performed


Su

rfac

e C

on

dit

ion • Bare metal

• Smooth well bonded paint

• FBE

• Light pitting• Heavy pitting• Plastic, e.g.

PVC• Buried (earth

or sand)• Bitumen

coated• Concrete

coated

Geo

met

ry • Straight lengths

• Infrequent swept/pulled bends

• Attachments / brackets

• Branches

• Multiple bends

• Flanges

Co

nte

nts • Gas

• Low viscosity liquid

• High viscosity liquid

• Waxy or sludgy deposits

Long Range ~200m

Short Range ~20m or

less

Factors Affecting Performance


International Standards

• BS 9690:2011 Parts 1 and 2Guided Wave Testing

• ASTM E2775-11• US DoT PHMSA Guidelines (18 point checklist)

• ASME Section V Article 18 (Draft)• NACE TG 410

• API 570:2009, e.g. Paragraph 9.2.6 for buried piping inspection methods

• NACE RP 0502 Appendix B

• International Training and Certification:CSWIP & PCN


Test Data

• A-scans• A-maps• Active (true) focussing


Test Data – A-scans

Source: BS 9690-2


A-Maps to Complement A-scans

• Single wave mode transmitted

• Pipe features cause mode conversion

• The collection of reflected modes is analysed

• The inferred location and extent of features is presented on a map


GWT Test Data Example

High flexural signals at weld on A-scan and A-map


Category 1 response

Test Data – True Focussing

Category 3 response Category 2 response

Polar Plots

Semi-quantitative data using indication of circumferential extent to estimate severity


Test Method Incorporating Focussing

• Circumferential information obtained• Data displayed in more easily interpreted

manner• Operator needs to distinguish between:

– Areas of concern needing immediate attention– Areas to mark for inspection in the future– Areas of no significant problems

• This method provides semi-quantitative results

• An efficient classifier of defects


Focal response – Constant Area


Focal response – Constant Angle


Test Data – Focussing Example


GWT CapabilitiesCurrent State of the Art

• Rapid screening for in-service degradation• 100% coverage• Externally applied• Lines can be tested in-service• NPS 1.5” to 72”• Temperature up to 250°C (482°F)

– Standard set-up up to 125°C (257°F)

• Diagnostic length not a constant: 5 to 100m each side• Detects internal and external metal loss• Cross-section change ≥ 3%• Semi-quantitative assessment of flaw extent (focussing)• Longitudinal accuracy ~100mm

– Dependent on frequency and wave mode


Assessing Unpiggable Corroded Pipelines

Audit

• Identify high risk lines/segments/areas

• e.g. RBI

Screen• Identify corroded areas• e.g. Visual / GWT

Quantify

• Quantify corrosion damage• e.g. MUT / AUT / PAUT / Surface

Profiling

Assess

• FFS Assessment• e.g. ASME B31G / API 579-1/ASME

FFS-1

Decision• Run / Repair / Re-rate / Replace• Future inspection


Pipeline Inspection Using GWUT

• Screening / Detection– Visual– GWT

• Sizing– Pit gauging / laser profiling– UT / AUT– Phased Array UT

• CombinationVolumetric flaws:

Corrosion, erosion

Excavation orinsulation removal


Flaw Sizing Using GWT

Development Project Objectives:

• Integrate flaw sizing inspections with procedures for determining fitness-for-service

• Determine link between guided wave responses and flaw size

• Extend the flaw sizing method to cover a wider range of pipe diameters

• Establish the accuracy of these assessments through validation tests

Original R&D performed under TWI Core Research Programme

Further development funded by PRCI, EPRI, Shell UK

Modelling by Ruth Sanderson, TWI


Flaw Sizing R&D Approach

• Numerical modelling of GWT• Experimental validation tests• Initial TWI CRP study – 6” pipe• Further studies – range of pipe sizes and flaws• Flaws

– Saw cuts– ‘Quasi-real’ corrosion (stepped profile)– ‘Real’ corrosion (volumetric metal loss simulating more

representative corrosion profile)

• Flaw characteristics– Depth– Circumferential profile / angular extent– Axial extent

• Field validation (in-service pipelines)


Modelling Flaw Responses

Location of excitation

Flaw

Metal loss flaw in model of a 24” pipe


Initial Study Results: Real v. Predicted Depth

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Actual flaw depth, mm

Mea

sure

d fla

w de

pth,

mm

Part wall flaw

Through wall flaw

6” Schedule 40 pipeWT = 0.35” (7.11mm)

TWI Core Research Programme


Assessment of ‘Quasi-real’ Flaws

18° circumference50% wall thickness



7.5° circumference83% wall thickness

Concave profile Convex profile

Conical profileConical profile


Numerical Modelling Results – Flaw Depth

Pipe sizes 2” to 36”78 flaws studied


Experimental Validation and Procedure Development


Experimental Results – Flaw Depth


GWT Measurement of Flaw Depth

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6 7 8 9 10

Actual through wall extent, mm

Pre

dic

ted

th

rou

gh

w a

ll ex

ten

t, m

m

2" 70kHz

2" 140kHz

6" 27kHz

6" 50kHz

12" 70kHz

24" 70kHz

36" 27kHz

36" 50kHz

36" 70kHz

Errors caused by under-estimation of 7.5° flaw

Range of flaw sizes for a range of pipe diameters


‘Quasi-real’ Flaws – Flaw Depth

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12 14 16 18 20

Actual through wall extent, mm

Pre

dic

ted

th

rou

gh

w a

ll ex

ten

t, m

m

24" 70kHz

Error caused by over-estimation of 7.5° flaw

Depth

Range of flaw sizes for 24” pipe


0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12 14 16 18

Actual axial length, mm

Mea

sure

d a

xial

len

gth

, mm

Axial Sizing Results - Experimental

12” pipeexperimental results


Experimental Results – Fitness-For-Service

ASME B31G


Conclusions of Study

• Procedure demonstrated to be effective at determining depth and length of flaws for a range of pipe sizes

• Flaw sizing resolution sufficiently accurate for performing ASME B31G fitness-for-service assessments

• The maximum error was 1.1mm (0.043”) on flaw depth

• Narrow flaws (circumferentialextent) cannot currentlybe evaluated. Procedureenhancements showed thatthe limit may be 30circumferential extent


GWT Sizing – R&D Work Plan

Develop enhanced procedures for assessment of flaws down to 15

Test current and refined flaw sizing procedures on further samples & perform field validation tests

Guided wave inspection data suitable for use directly in FFS assessments


Quantitative GWT Field Validation

• Joint Industry Project being launched by TWI• Project will provide pipeline operators with data to define

performance of quantitative GWT for inaccessible lengths of pipelines, in particular cased road crossings

• Project aims to validate:– Flaw detection capability– Procedures for quantitative flaw sizing– Long-term performance (stability) of permanently installed

pipeline monitoring system

• Benefits– Confidence for operators to implement the technology– Justification to regulators for using the technology


Permanently Installed GWT

• Install in critical areas• Low profile (re-instate

insulation or close excavation over tool)

• Comparison of test data– Identify active corrosion– Trend metal loss over time

• Easily installed• Remains stable over time in

harsh environments


New Developments in GWT

• Flaw sizing in pipelines & piping• Temperatures up to 450°C (842°F)

– Current capability up to 250°C (482°F) continuous

• In-service monitoring of storage tank bottoms• Measurement and reduction of internal fouling & deposits• Wireless online monitoring using permanently installed

sensors• Ship/FPSO hull testing + anti-fouling• Marinised systems for subsea pipelines & mooring

chains– ROV deployed– Diver deployed


In-service Monitoring of Tank Floors

• In-service non-intrusive testing oftank floors using guided wave UT

• Joint industry project (JIP) for field validation started May 2013

• Currently up to 30m diameter tanks• No need to clean tank floor

Multiplexer

Tank LRUT System

Communications

Transducers and arrays

Electronics


Guided wave transducer clamp for 10” riser

ROV approaching risers

Transducer clamp attached to ROV

Subsea Guided Wave Deployment by ROV


Guided wave propagation around chains

FPSO Mooring chains

A-scan pattern recognition techniques Chain climbing

robot

Guided wave transducer collar

Inspection of mooring chains with climbing robot deployed guided waves

Mooring Chain Inspection


Guided Wave Screening of Mooring Chains

Initial development work


Summary

• GWT is a non-intrusive screening tool and can be applied to unpiggable pipelines in-service

• GWT is widely accepted as a pipeline NDT technique• Conventional GWT

– Indication of pipe condition and prioritise piping for quantitative NDT

– Follow-up NDT required to quantify (size) indications• Advanced GWT:

– Maximum depth and length of metal loss for use in FFS assessments within certain limits

• Future development:– Enhanced sizing procedure– Validation on in-service pipelines

• In-service condition monitoring of critical areas using permanently installed sensors


Contact Details

EUR ING Sean Fewell CEng MWeldI

Principal Engineer

TWI Ltd

Granta Park, Great Abington, Cambridge CB21 6AL

United Kingdom

Email: [email protected]

Mobile: +44 7585 969268

D/L: +44 1223 899059

Web: www.twi.co.uk

Web: www.plantintegrity.com

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Sesión técnica, sala KM 19, Advances in detection and characterisation of metal loss in pipelines...

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