001-Introduction to Phased Array

7/25/2019 001-Introduction to Phased Array

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Basic Principles of Ultrasonic

Phased Array

Prepared by:

Applications Department

February 20111

Outline

Conventionnal Ultrasonic Testing

Phased Array Ultrasonic Testing

Imaging and views

Calibrations

Basics of TOFD

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Goal and Motivation

Train the attendees to better understand the veo

and UT Studio software

Provide trainees with a good understanding of

Phased Array UT

Provide trainees with hands-on experience

Provide trainees with a good understanding of the

competition and market place

Overview of PA applications

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Conventional Ultrasonic TestingBasic Concepts

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Conventional ultrasound has been commercially available

for about 50 years. The technology has almost remained

unchanged for that period of time.

Single crystal (or two)

Single beam for inspection

Single pulser/receiver (spike or square)

Single angle using a mountable wedge for refraction

A-scan signal representation, B-scan on some units

Aperture and frequency define the acoustic field


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Conventional Ultrasonic Testing

Basic Concepts

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Sound waves are mechanical vibrations propagating intothe piece under test. Waves are generated by exciting a

piezoelectric transducer. When a change (boundery) in

the medium occurs, waves are reflected back to the

transducer and converted into an electric signal

displayed as an A-scan.

Amplitude

Time or sound path

Conventional Ultrasonic TestingSound Field Characteristics

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The resulting ultrasonic beam is composed of three main

components.

Near Field

Far Field DOF

DepthofField

Near Field: Unstable sound field.

Far Field: Gradual decay of sound

field energy.

Focal spot, also known as DOF

region. Region with the highestenergy.

Source Image: http://en.wikipedia.org/wiki/Ultrasonic_sensor


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Conventional Ultrasonic Testing

Sound Field Characteristics

The characteristics of the sound field are mainly drivenby the probe aperture and frequency.

Increasing Aperture

Increase near field lenght

Narrow beam width

Shorten DOF

Increasing Frequency

Increase near field lenght

Narrow beam width

Increase resolution

Shorten DOF

Conventional Ultrasonic TestingFocusing

By focussing a sound beam, it is possible to achieve a

higher sensitivity (energy concentration) and resolution

(smaller beam width). Focussing can be achieved by

using curved radiator or more commonly by using curved

lens.

Focusing Rules

A plane radiator can only be focused to a distance

shorter than its near-field length.

When focusing, the near-field is compressed into the

space between the radiator and the new focus.


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Phased Array Ultrasonic Testing

Basic Concepts

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For Phased Array, the physics remains exactly the samethan with conventional UT. The main differences come

from the fact that the crystal is splitted into multiple

ones and each of these crystals are driven by a pulser-

receiver circuitry.

Phased Array Ultrasonic TestingBasic Concepts and Advantages

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With PA we have the ability to control the beam. It gives

the ability to steer and focus the beam. This is achieve

by controlling the electronic delay applied to each

crystal. This is the equivalent of using a focusing lens in

conventional UT.

Main Advantages

No safety issue

Full waveform recording

Automated reporting

Covers all angles of conventional UT and more

Combines various techniques (UT, TOFD, PA)

Higher Probability of Detection (POD)c


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Phased Array Ultrasonic TestingBeam Steering

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Delays

Beam steering is the ability of controlling the angle atwhich beams are fired.

Maximum Beam Steering Angles

As a rule of thumb, beam steering is limited to 20

each side of the natural refraction angle.

The steering angles limits can be defined as the

maximum and minimum refracted angles in the test

piece that can achieve a 6 dB drop between two

adjacent side drilled holes.

6 dB

Phased Array Ultrasonic TestingBeam Steering


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Phased Array Ultrasonic TestingBeam Focusing

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Delays

Beam focusing is the ability of concentrate the beam to asize smaller than the aperture.

Phased Array Ultrasonic TestingBeam Focusing

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Maximum Focal Distance

It is very important to remember that focusing is only

effective within the near-field length.

Focusing beyond the near field is equivalent to work

with the natural focus point.

The aperture is of key importance when focusing.

10 elmts 16 elmts 32 elmts


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Phased Array Ultrasonic TestingBeam FocusingPhotoelastic visualization

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Phased Array Ultrasonic TestingBeamforming

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One Particular Beam = One Focal Law


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Phased Array Ultrasonic TestingSectorial Scan

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The Sectorial scan or S-scan:

A different focal law per angle.

Give the ability to cover a whole weld volume

without any probe movement.

Useful for inspection of complex geometries.

Can be used as a screening tool with no focusing or

as a sizing tool using its various focusing patterns.

Phased Array Ultrasonic TestingType of ScanSectorial Scan

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Phased Array Ultrasonic TestingSectorial ScanSecond skip inspection

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Example of weld examination in second skip.

Phased Array Ultrasonic TestingSectorial ScanFocalisation Patterns

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Three focalisation patterns are

available on the veo unit.

1. Constant Path

For generic focusing or

fusion face.

2. Constant Depth

For corrosion/erosion/lamination detection.

3. Constant Offset

For crack detection in pins,

detection of indication in

weld center.


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Phased Array Ultrasonic TestingSectorial ScanConstant Path Focusing

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Phased Array Ultrasonic TestingSectorial ScanConstant Depth Focusing

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Phased Array Ultrasonic TestingSectorial ScanConstant Offset Focusing

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Phased Array Ultrasonic TestingLinear Scan

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The Linear scan or L-scan, also called E-scan:

The same focal law is sweep along the array.

Ability to perform a fast rastering without any probe

movement.

Useful for inspection of weld bevel/fusion face and

corrosion mapping.

Precise resolution along the array axis


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Phased Array Ultrasonic TestingType of ScanLinear Scan

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Delays

Phased Array Ultrasonic TestingLinear ScanExample of Corrosion


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Phased Array Ultrasonic TestingLinear ScanDelamination in Composite

Phased Array Ultrasonic TestingSectorial Scan vs Linear Scan

S-scan

The whole array

aperture is used to

generate each beam

One different focal law

per angle.

Varying angle

3 focalisation patterns

L-scan

A subset of theaperture is used, calledactive aperture.

The same focal law ismultiplexed across agroup of activeelements

Constant angle

Only one focalisationpattern

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Imaging and Views

Color Encoding

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An A-scan waveform represents the reflections from onesound beam position in the test piece. Imaging

capability is provided for the rectified A-scan signal by

color encoding the amplitude.

Imaging and ViewsProjected viewsExtraction Box

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In addition to the S-scan and L-scan views, the veo has

the capability of displaying projected views. These views

are generated by the extraction box.

Extraction

box


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Imaging and Views

Projected viewsTop View

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The top view is a 2D projection seen from a plan view.Scan Axis

IndexAxis

Index Axis

DepthAxis

Imaging and ViewsProjected viewsEnd View

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The End-view is a 2D projection seen from the back of

the probe for all angles within the extraction box.Scan Axis

DepthAxis

D

epthAxis

Index Axis


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Imaging and Views

B-Scan View

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The B-scan view is a 2D projection seen from the back ofthe probe at one angle.

Scan Axis

SoundPath

Axis

DepthAxis

Calibrating the Scan

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The Calibrate tab allows access to

calibration wizard. In stop mode,

you can clear existing calibrations,

while in play mode you can

create/modify them.

The items in this menu are sorted

in the order the calibrations

should be performed. If you are

using a multi-scan setup, each

scan must be calibrated

independently.

Calibrate

Stop Mode

Play Mode


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Calibrating the Scan

The table below is a summary of the wizards available along with the

scan type they apply to.

Calibrate

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Calibrating the ScanVelocity Wizard

The first wizard to start with

is the velocity wizard. The

velocity wizard shall be used

when the velocity is

unknown. Otherwise, the

velocity can be entered

manually in the Part tab.

Scan Selection

For multi-scan setup, the

first step is to chose the scan

that needs to be calibrated.

Calibrate

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Reflectors Selection

Select the type of reflectors

used to calibrate the

velocity.

Tip:

Ideally, choose a block with

reflectors that do not

require probe movement or

a minimal probe movement.

Calibrate

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Reflectors Position

According to the selected

reflectors, set the distance

at which they should be

found.

Tip:

Chose reflectors that have a

separation distance long

enough to obtain accurate

results.

Calibrate

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Scan Settings

Make sure that the RangePath is long enough todetect both reflectors.

Typically, the middle angle ischosen to calibrate thevelocity.

Calibrate

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Reflector 1

Make sure that the peak is

within the gate and then

maximize the reflector.

The gate is automaticallypositioned by the software,

but some adjustments are

sometimes required.

Calibrate

Tips:

The gate can be set from the menu or by pressing and then use

click wheel to move it freely. The worst case is to use 2 SDH and add

couplant in between 2 reflectors. 40


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Reflector 2

Make sure that the peak is

within the gate and then

maximize the reflector.

Tip:

Properly maximizing the

indication is crucial to get an

accurate result.

Calibrate

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Validate Result

The last step of the velocity

calibration wizard is to

validate the calculated

velocity.

If the calculated velocity

doesnt correspond to the

expected value, go back to

Reflector 1 step.

Calibrate

Tips:

When the velocity is known, it can be entered in the

Part tab.42


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Calibrating the ScanWedge Delay Wiz.

The Wedge Delay wizard

aims to compensate for the

sound path variation in the

wedge. The calibration

ensures that indications are

displayed at the right depth.

Wedge delay calibration is

performed using only one

reflector.

Calibrate

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Calibrating the ScanSensitivity Wizard

The Sensitivity Wizard aims

to compensate for the

sound attenuation due to

the wedge and the angle

variation in the S-scan. The

calibration ensure a uniform

amplitude response for eachfocal law for a given

reflector.

Sensitivity calibration is

performed using only one

reflector.

Calibrate

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Calibrating the ScanTCG Wizard

The TCG wizard aims to

equalize the amplitude level

of a given reflector size

along the sound path.

TCG equalizes the A-scan %

FSH of a reflector as well as

its representation in S-scan

or L-scan.

Calibrate

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Basics of TOFD

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TOFD stands for Time Of Flight Diffraction. It was

originally developed as a sizing technique for the nuclear

industry in the 70s. The technique is now well

recognized by the industry and many codes and

standards are available.

The combination of Phased-Array and TOFD is becoming

a very popular and efficient inspection technique.


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Basics of TOFD

Advantages

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Cover a wide area

Fast encoding speed

Accurate sizing capability in height

Permanent data recording

Detection and sizing almost orientation

independent

Basics of TOFDLimitations

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Blind areas

Near Surface: The width of the lateral

wave can be a limitation on thin

components.

Back wall: The large signal reflected from

the back wall can hide indications.


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Basics of TOFD

How does it work?

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FLAW

Diffracted

waves

Diffracted

waves

Incident

wave

Reflected

wave

TOFD is based on signal diffraction.

Basics of TOFDHow does it work?

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TX RX

Lateral wave

LW

Upper tip Lower tip

Back-wall reflection

BW


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Basics of TOFD

The Lateral Wave

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The Lateral Wave travels at the compression velocity

speed.

Always arrives first.

On curves surfaces, will travel straight across the metal.

Not a true surface wave, but a bulk wave generated at

the edge of the wide beam generated by the send

transducer.

Becomes weaker with increased PCS.

Basics of TOFDColor Encoding

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Imaging capability is provided for the non-rectified A-

scan signal by color encoding the amplitude.

White+

Black-

Time


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Basics of TOFD

TOFD View

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The TOFD view is a B-scan parallel or particular to thebeam axis.

Scan AxisBeam Axis

Basics of TOFDTypes of TOFD Scan

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Two types of TOFD scan are possible.

Non-parallel

Movement of probes at right angles to direction of the

beam.

Parallel

Movement of probes in same direction as the beam.


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Basics of TOFD

Typical TOFD ScansNear Surface Crack

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The crack blocks the Lateral Wave

And the lower tip appears on the A-scan

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1

2

Basics of TOFDTypical TOFD ScansIncomplete Root Pen.

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Note the two signals from the top & bottom

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3

4

1 2 3 4


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Basics of TOFD

Typical TOFD ScansLack of Root Pen.

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Note the inverted phase between LW and defect

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2

3

1

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Basics of TOFD

Typical TOFD ScansLack of Fusion onthe Side Wall

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Note the two signals from the top & bottom

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2

3

4

1

2

3

4


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Basics of TOFD

Typical TOFD ScansPorosity

Porosity may image in many forms whether individual or

cluster

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3

1

2

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Basics of TOFDTypical TOFD ScansTransverse Crack

In the LW we can observe the wide beam effect onthe crack

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2

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4

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2

3

1

2

3


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Basics of TOFD

Typical TOFD ScansConcave Root

Distortion of back-wall echo

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2

3

1

2

3

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Basics of TOFDTypical TOFD ScansLOF - Interpass

1

2

3

Documents

001-Introduction to Phased Array