Sesión técnica, sala KM 19, Advances in detection and characterisation of metal loss in pipelines using guide wave ultrasonic testing

2nd International Conference and Exhibition on Logistics, Transportation and
Hydrocarbon Distribution
León, Guanajuato, 20-22 November 2013

Advances in Detection and
Characterisation of Metal Loss in
Pipelines Using Guided Wave Testing

Sean Fewell and Peter Mudge
TWI Ltd, Cambridge, UK

Copyright © TWI Ltd 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


Principles of GWT
Conventional UT
Transducer

Localised Inspection

Flange

Conventional UT
Transducer

Metal loss

Weld
Metal loss

Guided wave
transducers

Flange

Pipe
Crosssection

Guided Wave
100% Coverage

Metal loss

Weld
Metal loss

Guided wave
transducers

Longitudinal

Torsional

Flexural


How GWT is Performed


Factors Affecting Performance
Long Range
~200m

Short Range
~20m or less


International Standards
• BS 9690:2011 Parts 1 and 2
Guided 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


Test Data – True Focussing
Polar Plots
Semi-quantitative data using indication of circumferential
extent to estimate severity
Category 3 response

Category 2 response

Category 1 response


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


Test Data – Focussing Example


GWT Capabilities
Current 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

Screen

• Identify high risk lines/segments/areas
• e.g. RBI
• 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

Excavation or
insulation removal

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

Volumetric flaws:
Corrosion, erosion


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
8

Measured flaw depth, mm

7

6

5

4
Part wall flaw
Through wall flaw

3

2

6” Schedule 40 pipe
WT = 0.35” (7.11mm)

1

0
0

1

2

3

4

5

6

7

8

9

10

11

12

Actual flaw depth, mm

TWI Core Research Programme

Assessment of ‘Quasi-real’ Flaws

18° circumference
50% wall thickness

36° circumference
67% wall thickness

Concave profile

Convex profile

15° circumference
83% wall thickness

7.5° circumference
83% wall thickness

Conical profile

Conical 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
50

Predicted throughw all extent, mm

45
40
2" 70kHz
2" 140kHz
6" 27kHz
6" 50kHz
12" 70kHz
24" 70kHz
36" 27kHz
36" 50kHz
36" 70kHz

35
30

Errors caused by
under-estimation of
7.5° flaw

25
20
15
10
5
0
0

1

2

3

4

5

6

7

8

9

10

Actual through wall extent, mm

Range of flaw sizes for a range of pipe diameters

‘Quasi-real’ Flaws – Flaw Depth
20

Depth

Predicted throughw all extent, mm

18
16
14
12
10

24" 70kHz

8
6
Error caused by
over-estimation of
7.5° flaw

4
2
0
0

2

4

6

8

10

12

14

16

18

20

Actual through wall extent, mm

Range of flaw sizes for 24” pipe

Axial Sizing Results - Experimental
18

12” pipe
experimental results

16

Measured axial length, mm

14
12
10
8
6
4
2
0
0

2

4

6

8

10

12

14

16

18

Actual axial length, mm


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 (circumferential
extent) cannot currently
be evaluated. Procedure
enhancements showed that
the limit may be 30
circumferential 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 of
tank 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
Electronics

Tank
LRUT
System

Communications

Multiplexer

Transducers and arrays


Subsea Guided Wave Deployment by ROV
ROV approaching risers

Transducer clamp attached to ROV

Guided wave
transducer clamp
for 10” riser


Mooring Chain Inspection
FPSO Mooring chains

Guided wave
propagation
around
chains

A-scan
pattern
recognition
techniques

Inspection of mooring chains with
climbing robot deployed guided waves

Guided wave
transducer collar

Chain climbing
robot


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: sean.fewell@twi.co.uk
Mobile: +44 7585 969268
D/L: +44 1223 899059
Web: www.twi.co.uk
Web: www.plantintegrity.com


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