7/28/2019 Introduction to Advanced Ultrasonics

1/24

Phased Array and Time-of-Flight

Diffraction (TOFD)

Introduction to Advanced

Ultrasonic Phased Array

7/28/2019 Introduction to Advanced Ultrasonics

2/24

a linear array (1D) is

basically a long

conventional probe

cut in many small

elements, that can be

individually excited

Design Parameters of Phased-

Array Probes

7/28/2019 Introduction to Advanced Ultrasonics

3/24

Phased-Array probes

Time

Single Trigger

Pulse

Wave front

7/28/2019 Introduction to Advanced Ultrasonics

4/24

Conventional Waveforming

Beam steering using conventional UT probe (Transmit): angled wedge introduces appropriate delays during emission

to generate angle beam

CrystalWedge

Material

Excitationpulse

Wave front

Delay

Location

A B C

A B C

7/28/2019 Introduction to Advanced Ultrasonics

5/24

Conventional Waveforming

Beam steering using conventional UT probe (RECEIVE) : angled wedge introduces delays during reception, so that

only waves in phase.

CrystalWedge

Material

Received signal

Delay

Location

A B C

A B C

S

7/28/2019 Introduction to Advanced Ultrasonics

6/24

Phased-Array Waveforming

Beam steering using phased-array probe : appropriate delays introduced electronically during emission

to generate angle beam

Wave front

Time

Delay

Element

Focallaw

7/28/2019 Introduction to Advanced Ultrasonics

7/24

Beam Focusing

Is the capabi l ity tocon verge the

acoust ic energyintoa small focal spot

Allows forfocus ingat several depths,using a single probe

7/28/2019 Introduction to Advanced Ultrasonics

8/24

Beam Steering

7/28/2019 Introduction to Advanced Ultrasonics

9/24

Beam Steering

Is the capabi l ity tomod ify the refracted

angleof the beamgenerated by thearray probe.

Allows formult ip leang le inspect ions,using a single probe

7/28/2019 Introduction to Advanced Ultrasonics

10/24

Combined Beam Processing

Linear combined with steering and focusing

7/28/2019 Introduction to Advanced Ultrasonics

11/24

7/28/2019 Introduction to Advanced Ultrasonics

12/24

Tandem for Vertical Defects

7/28/2019 Introduction to Advanced Ultrasonics

13/24

TOFD

For Weld Inspection

Description of TOFD technique (Theory)

7/28/2019 Introduction to Advanced Ultrasonics

14/24

FLAW

Diffracted

waves

Diffracted

waves

Incident

wave

Reflected

wave

All directions

Low energy

Independent of

incidence angle

The Diffraction Phenomenon

7/28/2019 Introduction to Advanced Ultrasonics

15/24

2 probes (transmitter, receiver)

Wide beam, longitudinal waves

Symmetric to the weld center

Diffraction signal detection (high

receiver sensitivity)

Basic Setup

7/28/2019 Introduction to Advanced Ultrasonics

16/24

Signals received

Lateral wave, subsurface

Back-wall echo

Mode converted (shear wave) echo

Define top and bottom of part

Note phase change

TOFD Signals

7/28/2019 Introduction to Advanced Ultrasonics

17/24

Transmitter Receiver

Lateral wave

Upper tip

Lower tip

Back-wall reflection

TOFD Signals

7/28/2019 Introduction to Advanced Ultrasonics

18/24

Data Visualization (TOFD)

Lateral

waveBack-wall

A-scan

Indication

7/28/2019 Introduction to Advanced Ultrasonics

19/24

Near Surface Crack

The crack blocks the Lateral Wave

And the lower tip appears on the A-scan

21

1

2

7/28/2019 Introduction to Advanced Ultrasonics

20/24

Lack of Fusion, Interpass

1

2

3

7/28/2019 Introduction to Advanced Ultrasonics

21/24

Lack of Root Penetration

Note the inverted phase between LW and defect

1

2

3

1

23

7/28/2019 Introduction to Advanced Ultrasonics

22/24

Diffracted rather than reflected signals

Longitudinal waves

B-scan type imaging (side view) Accurate sizing capability (height)

Interpretation of defects

Less sensitive to defect orientation

TOFD - Advantages

7/28/2019 Introduction to Advanced Ultrasonics

23/24

Blind area - near surface, backwall ID and OD Geometry (Hi-Lo)

Weak signals

Couplant loss

Flaw classification limitation

Interpretation of defects

Sensitive to grain noise and Coarse

grained materials

TOFD - Limitations

7/28/2019 Introduction to Advanced Ultrasonics

24/24

Typical manual TOFD scanner