the quantitative assessment of touch point corrosion wall ... · basics of guided wave testing...

The quantitative assessment of touch point corrosion wall loss at contact supports

David Alleyne

7MENDT, Bahrain

14 September 2015

1

2Guided Ultrasonics Ltd. - 29/09/2015

Presentation Outline

Biography

Basics of Guided Wave Testing (GWT)

Generations of Guided Wave Testing Technologies

From screening to quantitative measurements

Examples of Touch point corrosion

Developing application specific techniques


Biography Summary of GUL

Guided Ultrasonics Limited: Primary function development, design and manufacture of GWT equipment (Wavemaker® systems).

Guided Ultrasonics Ltd. was set up in 1998 to commercialize guided

wave inspection systems.

World experts in Guided wave testing of plates and pipe from Imperial

College of Science, Technology and Medicine (London, UK). Patent

holder for GWT methods in pipes, plates.

Over 200 man years experience in the guided wave field within GUL,

including outstanding academic contributions supported by field and

application specific knowledge and experience.

Driver for the development of GWT standards, qualification and

certification.

Motivation

Supports are areas of increased risk and are inaccessible to direct assessment.

© Guided Ultrasonics Ltd. 2014

Requirement for both fast screening due to the huge number and quantitative evaluation.

Basics of GW Testing

The pipe walls form a guide for ultrasonic waves,

which directs them down the length of the pipe

Propagation of ultrasonic waves (kHz range) guided by pipe wall along the pipe, excited by a transducer array.

Transducer

Structure

Region of structure inspected

Transducer

Structure

Region of structure inspected

Conventional

Guided waves

© Guided Ultrasonics Ltd. 2014

6

1st Generation – Lamb waves

Longitudinal mode (LRUT) 1986 – 1996 Researcher, Academic staff (GW

technology patented while at Imperial College)

Dispersion curves - Disperse software developed

Finite element modelling methods developed

Single mode and single direction

Laboratory expertise on plates, bars and pipe

Data processing methods, 2D-FFT

Transduction and electronics developed

Guided Ultrasonics Ltd. - 29/09/2015

7

2nd & 3rd Generation – Guided Waves

Torsional & Flexural modes

1999 – Present

Pipe testing system

Battery powered portable GWT system

Generalised PZT based transduction

Development of training schemes

Development of GWT (site expertise)


8

On-board calibration channel and self checking

HD rings and modules for different corrosion types

Axial and circumferential configuration and GWT strategies

Wide frequency range for optimum selection

Improved SNR and O/P power boost


4th Generation Application Specific

9

GWT Result



From screening to quantitative measurements

In order to make quantitative measurements it is necessary to calibrate the guided wave response.

Several methods of calibration have been historically been used in GWT Assumed weld reflection Measured weld parameters Absolute calibration

In addition to this it is necessary to be able to convert from reflection coefficient to change in cross-sectional area.

11

Guided Waves Calibration

DAC curves are used to estimate the CSC of other indications

-18dB

-20.0 -10.0 0.0 10.0 20.012

9

6

3

12

Clo

ck

-20.0 -10.0 0.0 10.0 20.00.0

0.5

1.0

1.5

2.0

Distance (m)

Am

p (

Lin

ear)

W3

S2

S1

F1

U1

W4

S3

B1

S4

U2

Distance (m)

Am

plit

ude

(a

rb.)

Standard reflection amplitude of a weld can corresponds to approximately 10 – 25% CSC

Weld DAC 20 – 25%

Call DAC


12


One method: Measure dimensions

Wavemaker® software calculates weld reflection

In general very good approximation


13


Still errors in calibration if

Weld defective in a way that reflection amplitude influenced

Variation in the measured dimensions even in a single weld

Also not satifactory if

There are no welds in the test range

The weld dimensions cannot be measured


New calibration method

14


-18dB

-20.0 -10.0 0.0 10.0 20.012

9

6

3

12

Clo

ck

-20.0 -10.0 0.0 10.0 20.00.0

0.5

1.0

1.5

2.0

Distance (m)

Am

p (

Lin

ear)

W3

S2

S1

F1

U1

W4

S3

B1

S4

U2

Distance (m)

Am

plit

ude

(a

rb.)


Advantages

Direct measurement of reflection coefficients

Works also with other features (not just welds), even if defective

Accurate weld DAC then allows accurate prediction of cross-sectional area change of anyother signal

Difficulties

Not always possible to generate reverberation signals– Due to high attenuation

– Lack of suitable test location

15



16

Contact corrosion types at touch points The cross-sectional change of the corrosion (shape and depth) is

important for detectability and quantification


17

GWT work instructions

GWT Procedures and work instructions using knowledge of specific application and corrosion type that is the major threat

– Equipment and certification requirements

– SNR and access restrictions

– Accuracy and range

– Limitations

– Confidence

Calibration is critical


18

Example 1


-16dB

-20 0 20 40 6012

9

6

3

12

Clo

ck

-20 0 20 40 600.0

0.2

0.4

0.6

0.8

1.0

1.2

Distance (ft)

Am

p (

Lin

ear)

F

weld

ed p

late

Weld

Weld

Cat 1

Corr

osi

on

Support

Weld

Cat 3

Support-F1

Call DAC 4%

Touch point corrosion

patch with pitting

19

Example 3


-18dB

-10.0 0.0 10.0 20.012

9

6

3

12

Clo

ck

-10.0 0.0 10.0 20.00.0

0.5

1.0

1.5

Distance (ft)

Am

p (

Lin

ear)

-F1

+F1

+F2

20

Example 4


Touch point corrosion

patch. GWT used for

detection and

classification of the

corrosion.

-18dB

-8.0 -6.0 -4.0 -2.0 0.012

9

6

3

12

Clo

ck

-8.0 -6.0 -4.0 -2.0 0.00.0

0.5

1.0

1.5

2.0

Distance (m)

Am

p (

Lin

ear)

Conta

ct support-F1

6 o’clock

position

Developments

Monitoring

using repeated measurement from same location

Alternative transduction

Guided wave tomography


22

GWT can monitor supports


5.0 10.0 15.0 20.0

1

0.5

0.25

0.1

0.05

0.025

G3-5

1#1583 (

34dB

)

5.0 10.0 15.0 20.0

1

0.5

0.25

0.1

0.05

0.025

Distance (m)

G3-9

6#5453 (

34dB

)

weld

conta

ct s

upport

weld

weld

+F1

conta

ct s

upport

weld

Call DAC 1%

Call DAC 1%

CollectionOct 2007

CollectionDec 2011

Corrosion growth at support area over 4 year period

GWT transduction options


+

+ +

+ +

Pulse echo

Pitch catch

Direct transmission

Aim

Produce map of depths of corrosion

Critical parameter is maximum depth

GW tomography

Concept of tomography

GW tomography


GW tomography

Transducer arrays placed either side of defect


0.0 0.2 0.4 0.6

0.000000

0.000005

0.000010

0.000015

0.000020

Time (ms)

Am

p (

mV

)

Pulse Echo Traces (25 kHz 3 cycle Hanning Toneburst)

0.0 0.2 0.4 0.6

0.000000

0.000005

0.000010

0.000015

0.000020

Time (ms)

Am

p (

mV

)

Pulse Echo Traces (25 kHz 3 cycle Hanning Toneburst)

GW tomography

Results from defect free case Results from defect case

Development of this as an inspection technique is in the processing of this type of data to produce defect maps

Two Main Tomography Techniques:

Time of Flight Tomography (TFT)

Diffraction Tomography (DT)

Ray Approximation d >> λ

d ~ λ

GW tomography

As reduced size and cost of computing power has enabled site implementation of GWT, tomographic techniques have required similar improvements to become practical.

29

GWT enables rapid screening of many supports

Improved calibration allows better

estimation/measurement of wall loss at supports

Requires detailed procedures and training

Continuing research for quantitative measurements

of touch point corrosion using GW tomograghy.

Conclusions


30

Questions


Thank you

the quantitative assessment of touch point corrosion wall ... · basics of guided wave testing...

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