TOFD Course 2008 PBE

TIME ‐ OF ‐ FLIGHT DIFFRACTION

COURSE
(Level I and II)

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 TOFD Course 2008 PBE

CONTENTS

PART I ‐ History & theory of TOFD technic

PART II ‐ TOFD Set‐up
PART III ‐ Interpretation
p and analysis
y of TOFD images
g
PART IV ‐ Basics of dimensionning
PART V ‐ Test report

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 TOFD Course 2008 PBE

PART I

HISTORY & THEORY

OF
TOFD TECHNIC

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 TOFD Course 2008 PBE

Historyy of TOFD Technique

q

The most serious types of defects in welds and metal components are planar
cracks since they are the most likely to grow and cause failure of the component
and hence the importance of ultrasonic inspection since ultrasonics is the most
suitable
bl technique
h f determining
for d the
h position and
d sizing such h defects.
d f The
h
importance of developing more accurate sizing techniques than afforded by
conventional pulse‐echo inspections became apparent in the 1960’s, especially in
th nuclear
the l andd chemical
h i l plant
l t industries.
i d ti

For this reason the National NDT Centre at Harwell (then part of the United
Kingdom Atomic Energy Authority ‐ UKAEA) asked Dr Maurice Silk to try and
develop an ultrasonic sizing technique more accurate than the conventional pulse‐
echo method.

In the early 1970’s Dr Silk developed the technique known as Time‐of‐Flight

Diffraction (TOFD).

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 TOFD Course 2008 PBE

Principle of TOFD
Diffraction process
p

When an ultrasonic wave interacts with a long crack‐like flaw it results in the production
of diffracted waves from the crack tips, in addition to any ultrasonic waves reflected
from the surface of the crack. The diffracted waves are much weaker than specularly
reflected waves used for conventional ultrasonic inspection, but they radiate from the
tips in all directions along the same plane as the incident ultrasonic waves as indicated in
figure.

The phenomena of diffraction is nothing new and

occurs with all types of waves, e.g. light and water
waves. It is very well known in light especially
when light is passed through a slit or past an edge
andd contributes
ib to the
h resolving
l i power off
telescopes and other optical instruments. To
explain diffraction when waves pass through a slot

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 Basics of TOFD inspection
TOFD Course 2008 PBE

The TOFD (Time Of Flight Diffraction) is a ultrasonic inspection method. TOFD

method
th d is
i based
b d on imperfections
i f ti character
h t tot emit it diffraction
diff ti echoes
h when
h they
th
interact with ultrasound. In TOFD inspection two probes are used. One probe is
used to send longitudinal ultrasound to the inspected material and one probe is
used to receive this emitted ultrasound. In case this send ultrasound interacts with
imperfection, the tips of the imperfection emitts diffraction echoes. From the
travelling time of these diffraction echoes the depth location of the imperfection
may be calculated.

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 A‐scan TOFD Course 2008 PBE

with no Defect Present

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 A‐scan TOFD Course 2008 PBE

with Defect Present

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 TOFD Course 2008 PBE

Lateral wave
In general a weak lateral wave running between the two probes with the
compression
p velocityy jjust below the surface of the metal is observed first. It obeys
y
Fermat’s principle in that a wave travelling between two points takes the minimum
time. As we shall see later, for a curved surface it will travel straight across the
metal between the two probes. On material with a surface cladding layer the
velocityy of sound in the claddingg mayy be such that the lateral wave travels most of
the way in the material beneath the cladding. The lateral wave is not a true surface
wave but a bulk wave generated at the edge of the beam. The frequency content
of the lateral wave tends to be lower than the waves from the centre of the beam
(the beam spread is frequency related and the lower frequency component has
therefor a wider beam spread). For a true surface wave the amplitude would
decay exponentially with distance from the inspection surface.

The
h lateral
l l wave can be
b very weakk for
f large
l probe
b separations
i and
d may not even
be recognisable.

Because of the basic pitch‐catch probe arrangement the signals from the near
surface region are very compressed in time and these signals may be hidden
beneath the lateral wave.

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 TOFD Course 2008 PBE

Back wall signal

A much larger signal reflected/diffracted from the back wall is observed after the
lateral wave because of the greater distance travelled. If the probe beams are only
directed at the upper part of the metal or there is no suitable back wall there may
be no back wall signal.

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 TOFD Course 2008 PBE

Defect signals

If a planar
l t
type crackk is
i presentt in
i the
th metal
t l in
i the
th overlapping
l i beam
b off the
th two
t
probes diffraction signals from the top and bottom tips are seen between the
lateral wave and the back wall. These signals are generally much weaker than the
backwall signal but stronger than the lateral wave. If the defect has little height
then the signals from the top and bottom may run into each other. Thus the
importance of a minimum number of cycles in the signals in order to improve the
resolution of the signals from the top and bottom of small defects.

Because the diffraction signals are so weak they cannot always be easily seen on a
single A‐scan and it is only by displaying the successive A‐scans from a scan in B‐
scan form
f th t the
that th pattern
tt off the
th diffraction
diff ti signals
i l becomes
b clear.
l Si l
Signal
averaging is very important in these situations because it improves the signal‐to‐
noise ratio.

Again this is why TOFD is very difficult with an analogue flaw detector where only a
single A‐scan display is available.

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 TOFD Course 2008 PBE

Shear or mode converted shear signals

After the compression back wall signal a much large signal generally appears and is
a back wall shear reflected signal and it is often mistaken for the compression back
wall signal. Between these signals other signals are generally observed due to
mode conversion at a defect into shear waves which then takes a longer time for
the signal to arrive at the receiver.

It is often very useful to collect signals in this region since genuine defect signals
are repeated at longer times and near surface defect signals may be clearer since
they are spread out in time more for the shear waves.

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 TOFD Course 2008 PBE

Depth calculation
DEFINITIONS
C ‐ velocity of sound
λ ‐ wavelength of sound
d ‐ depth of reflector below scanning surface
D ‐ thickness of sample being scanned
PCS ‐ probe centre separation
s ‐ half of probe centre separation 2s
t ‐ time of flight of signal from a reflector
2to ‐ time taken for sound to pass through two probe shoes (probe delay)
tl ‐ time of flight of lateral wave
tb ‐ time of flight of back wall signal

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 TOFD Course 2008 PBE

Depth calculation

Depth
h

In practise the depth calculation needs to take into account the extra delay in the
measured time due to the passage of the sound through the probe shoes. This
delay is known as the probe delay2to microseconds. Thus the total transit time
measured, t, is in practice given by :

t = 2(s2 + d2)1/2/c + 2to

and the depth is given by

d = [(c/2)2(t‐2to)2 ‐ s2]1/2

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 Signal time TOFD Course 2008 PBE

The lateral wave signal occurs at a time, tl μs, and is given by

tl = 2s/c + 2to

The back wall at a time, tb μs, and is given by

tb = 2(s2 + D2)1/2/c + 2to

where D thickness of the sample.

By rearranging the two equation the probe delay and velocity can be found if the
PCS = 2s, and the thickness D is known,

c = 2(s2
( + D2)1/2 ) / ‐ 2s
(tb ‐ tl)
and
2to = tb ‐ 2(s2 + D2)1/2
/ /c

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 TOFD Course 2008 PBE

Types
yp of TOFD Scan
There are two types of scan. The initial scan generally used for detection is shown
in Figure
g 1 and is called the non‐parallel
p or longitudinal
g scan because the direction
of scan is at right angles to the direction of the ultrasonic beam. The resultant scan
is known as a D‐scan since it produces a cross section along the weld.

The second type of scan is shown in Figure 2 and is called the transverse or parallel
scan. The direction of scan is parallel to the ultrasonic beam direction. The scan
produced is called a B
B‐scan
scan since it produces a cross section across the weld.

Non‐Parallel or Longitudinal Scan Parallel or Transverse Scan

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 TOFD Course 2008 PBE

Data Visualization
A‐scan

Indication

Lateral wave Back‐wall

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 TOFD Course 2008 PBE

Near Surface Crack

1 2
The crack blocks the Lateral Wave
And the lower tip appears on the A-scan

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 TOFD Course 2008 PBE

Incomplete Root Penetration

1
2

1 2 3 4
Two signals from the top & bottom

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 TOFD Course 2008 PBE

Lack of Root Penetration

1
1

2
3

2
3

1
2 3

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 TOFD Course 2008 PBE

Advantages and Disadvantages of TOFD

Advantages

The two most important differences of TOFD from conventional pulse‐echo are,
‐ the almost independence of angle of the defect for detection of the diffraction
signals
‐ the depth sizing is not dependent on the amplitude of the signals and the
corresponding errors

Thus the main advantages of TOFD are,

a) TOFD has a through wall sizing accuracy of + or ‐ 1 mm and a crack growth

monitoring capability of + or ‐ 0.3 mm
b)) efficient detection of defects of all orientations
c) permanent digital record of the inspection data with cross‐section type views
through the metal.

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 TOFD Course 2008 PBE

Advantages
g and Disadvantages
g of TOFD

Disadvantages
g

The amplitude of the diffraction signals does not depend on the size of the defects
and a simple amplitude threshold cannot be applied for selecting the important
reportable defects, unlike pulse‐echo inspections. TOFD easily detects pores, slag
lines, inclusions etc.

The main disadvantages of TOFD are,

a) no simple amplitude threshold for selecting reportable defects

b) all the TOFD inspection data has to be visually analysed in order to select the
reportable defects
c)) not so suitable for defects near to the inspection
p surface since theyy mayy be hidden
by the lateral wave and the sizing accuracy deteriorates rapidly near to the
inspection surface.

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 TOFD Course 2008 PBE

PART II

TOFD SET‐UP

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 Set up of probes TOFD Course 2008 PBE

The probes shall be set up to ensure adequate coverage and optimum conditions
for the initiation and detection of diffracted signals in the area of interest.
interest

Selection of probes for full coverage of the complete weld thickness (typically pre‐
service
i inspection)
i ti ) should
h ld follow
f ll Table.
T bl

Care should be taken to choose appropriate combinations of parameters.

If set‐up parameters are not in accordance with follow Table, the capability shall
be verified byy the use of reference blocks.

For in‐service inspection the intersection point of the beam centre lines should be
optimised for the specified examination volume.
volume

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 TOFD Course 2008 PBE

Set up
p of p
probes

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 TOFD Course 2008 PBE

Set up of probes

Transmitter Receiver
PCS

2/3T

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 TOFD Course 2008 PBE

Time base settings

1 µS 1 µS

1 2 3

1 : LLateral
t l wave
2 : Back Wall
3 : Shear waves

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 TOFD Course 2008 PBE

Sensitivity settings
For all examination levels the sensitivity shall be set on the test object. The amplitude of
the lateral wave shall be between 40 % and 80 % full screen height (FSH).

In cases where the use of the lateral wave is not appropriate (e.g. surface conditions,
use of steepp beam‐angles),
g ) the sensitivityy shall be set such that the amplitude
p of the
back wall signal is between 18 dB and 30 dB above FSH.

When the use of neither a lateral wave,

wave nor a back wall signal is appropriate,
appropriate sensitivity
should be set such that the material grain noise is between 5 % and 10 % FSH.

80%

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 TOFD Course 2008 PBE

Scan increment setting

The scan increment setting is dependent upon the wall thickness to be examined.
For thickness up to 10 mm the scan increment shall be no more than 0,5 mm.

For thickness between 10 mm and 150 mm the scan increment shall be no more
than 1 mm.

Above 150 mm a scan increment of 2 mm can be used.

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 TOFD Course 2008 PBE

PART III

IInterpretation
t t ti andd analysis
l i
of
TOFD images

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 TOFD Course 2008 PBE

General
Interpretation and analysis of TOFD images is generally performed as follows

• Assessing the quality of the TOFD‐image.

• Identification
d f off relevant
l indications
d and
d discrimination
d off non‐relevant
l indications.
d

• Classification of relevant indications in terms of:

‐ embedded (linear, point‐like).
‐ surface breaking.

• Determination of location (typically position in x‐ and z‐direction) and size (length and
through‐wall extent).

• Evaluation against acceptance criteria.

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 TOFD Course 2008 PBE

Assessingg the q
qualityy of the TOFD‐image
g
Examples of typical scans

Satisfactory TOFD‐image displaying

– undisturbed lateral wave (amplitude between 40 % and 80 % FSH)

– four indications of notches in different depths
– straight backwall reflection
– mode converted signals from notches and backwall

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 TOFD Course 2008 PBE

Assessing the quality of the TOFD

TOFD‐image
image

Gain setting too low Gain setting too high

Amplitude of lateral wave << 40 % FSH Amplitude of lateral wave >> 80 % FSH (saturated)

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 TOFD Course 2008 PBE

Assessing the quality of the TOFD

TOFD‐image
image

Inappropriate time window setting Missing scan lines caused by too high scanning speed
Lateral wave is not present in the time window

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 TOFD Course 2008 PBE

Assessing the quality of the TOFD

TOFD‐image
image

Time base triggering problems Loss of signals due to lack of couplant

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 TOFD Course 2008 PBE

Assessing the quality of the TOFD

TOFD‐image
image

Image influenced by variation of couplant layer thickness

(
(may be
b straightened
i h d by
b software)
f )

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 Classification of relevant indications TOFD Course 2008 PBE

Amplitude,
li d phase,
h location
l i and d pattern off relevant
l indications
i di i may contain
i
Information on the type of discontinuity.

Relevant indications are classified either as indications from surface‐breaking or

embedded discontinuities byy analysing
y g the followingg features :

a) disturbance of the lateral wave.

b) disturbance of the backwall reflection
reflection.
c) indications between lateral wave and backwall reflection.
d) phase of indications between lateral wave and backwall reflection.
e) mode converted signals after the first backwall reflection.

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 TOFD Course 2008 PBE

Indications from surface breaking discontinuities

Surface breaking discontinuities can be classified into 3 categories

1. Scanning surface discontinuity:

This type shows up as an elongated pattern generated by the signal emitted from the lower edge of
the
h discontinuity
d andd a weakening
k or loss
l off the
h lateral
l l wave (not
( always
l observed).
b d) The
h indication
d
from the lower edge can be hidden by the lateral wave, but generally a pattern can be observed in the
mode converted part of the image. For small discontinuities, only a small delay of the lateral wave
may be observed.

2. Opposite surface discontinuity:

This type shows up as an elongated pattern generated by the signal emitted from the upper edge of
the discontinuity and a weakening, loss, or delay of the backwall reflection (not always observed).

3. Through wall discontinuity:

This type shows up as a loss or weakening of both the lateral wave and the backwall reflection
accompanied by diffracted signals from both ends of the discontinuity
discontinuity.

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 TOFD Course 2008 PBE

Indications from embedded discontinuities

E b dd d discontinuities
Embedded di ti iti can be
b classified
l ifi d into
i t 3 categories
t i

1. Point‐like discontinuity:
This type shows up as a single hyperbolic shaped curve which may lie at any depth
depth.

2. Elongated discontinuity with no measurable height:

This type appears as an elongated pattern corresponding to an apparent upper edge signal
signal.

3. Elongated discontinuity with a measurable height:

This type appears as two elongated patterns located at different positions in depth, corresponding to
the lower and upper edges of the discontinuity. The indication of the lower edge is usually in phase
with the lateral wave. The indication of the upper edge is usually in phase with the back wall reflection.
Indications of embedded discontinuities usuallyy do not disturb the lateral wave or the back‐wall reflection.

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 Typical TOFD‐images TOFD Course 2008 PBE

discontinuities in fusion welded joints

Indications of scanning surface notch (disturbance of Elongated indication of an opposite surface breaking
lateral wave) and of opposite di
discontinuity
ti it
surface notch (straight diffracted signal corresponding
to slight disturbance of backwall signal)

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 Typical TOFD‐images TOFD Course 2008 PBE

discontinuities in fusion welded joints

Elongated indication of a far‐surface breaking Indication of through‐wall crack (note the loss of lateral
discontinuity (nearly through‐wall) wave and backwall signal and
also the corresponding diffracted signal patterns left
and right to this region)

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 Typical TOFD‐images TOFD Course 2008 PBE

discontinuities in fusion welded joints

Indications of multiple point‐like

point like discontinuities I di ti off an elongated
Indication l t d di
discontinuity
ti it with
ith measurable
bl height
h i ht

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 Typical TOFD‐images TOFD Course 2008 PBE

geometrical features

I di ti off change
Indication h i wallll thickness
in thi k D bl backwall
Double b k ll reflection
fl ti dued to
t diff
differentt wallll thi
thicknesses
k

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 Typical TOFD‐images TOFD Course 2008 PBE

geometrical features

Image of misalignment in circumferentially welded pipes Indication of corrosion in the root‐area on both sides of
the weld in the heat‐affectedzone

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 TOFD Course 2008 PBE

PART IV

BASICS OF DIMENSIONING

In this section there is explained some general rules for

dimensioning TOFD image indications.

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 TOFD Course 2008 PBE

Height measurement

A principle
i i l ini measuring
i theh height
h i h off the
h indication
i di i is i determined
d i d during
d i the h
calibration of the time scale. The height measurement shall be done from the A‐
scan image.

The measuring the height of the indications must be done with similar principles
as the calibration of the timescale has been made.

Three possibilities for time base calibration and dimensioning are presented.

The rule of phase conversion must be included.

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 Method 1 TOFD Course 2008 PBE

E h corner
Echo
Time base calibration is based on the corner of the first rising echo. On this type of
calibration,, inspector
p must take in count the error p
possibilityy in case of high
g noise.

The first and sixth red lines presents the measuring point of wall thickness. The second
and third red lines presents the measuring point of indication upper tip and lower tip.

In these figures the fist echo is presented as a negative. The firs echo may also appear
as a positive. This alternation must be taken in to account in calibration and in
dimensioning the height.
height

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 Method 2 TOFD Course 2008 PBE

Fi t maximum
First i
Time base calibration is based on the middle point of the first echoes maximum. On this
type of calibration,
calibration inspector must take in count the error possibility in case of echoes
with same level of amplitude.

The first and sixth red lines presents the measuring point of wall thickness. The second
and third red lines presents the measuring point of indication upper tip and lower tip.
I th
In these fi
figures the
th fist
fi t echo
h is
i presented
t d as a negative.
ti TheTh firs
fi echoh may also
l appear
as a positive. This alternation must be taken in to account in calibration and in
dimensioning the height.

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 Method 3 TOFD Course 2008 PBE

M i
Maximum echo
h
Time base calibration is based on the maximum amplitude of the indication. On
this type of calibration,
calibration inspector must take in count the error possibility in case of
phase shift that may increase the amplitude of an echo.

The first and sixth red lines presents the measuring point of wall thickness. The
second and third red lines presents the measuring point of indication upper tip
and lower tip.
tip
In these figures the fist echo is presented as a negative. The firs echo may also
appear as a positive. This alternation must be taken in to account in calibration
and in dimensioning the height.

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 Exemples TOFD Course 2008 PBE

Embedded indication Method 1 Embedded indication Method 2 Embedded indication Method 3

The upper tip position is The upper tip position is measured from The upper tip position is measured from
measured from the corner of the the opposite phase maximum. In this case the opposite phase maximum. In this
first visible echo. The same rule the lateral wave first echo maximum is case the lateral wave maximum is
applies when measuring the negative. The upper position of the positive. The upper position of the
lower tip position. indication is measured from the upper tip indication is measured from the upper
first positive maximum. The lower position tip negative maximum. The lower
of the indication is measured from the first position of the indication is measured
lower tip negative maximum. from the lower tip positive maximum.

The first echo maximum of the lateral wave is

Corner of the first echo of the lateral wave Maximum of the first echo is in the middle
pp tip
in the middle of the white line. The upper p
is the start of the black line.
line The upper tip of the black line.
line The upper tip position is
position is measured from the middle of the
position is measured from the start of the measured from the middle of the white line
white line in the upper tip of the echo. The
white line (corner of the first echo) in the in the upper tip of the echo. The difference
difference of the yellow lines presents the
upper tip of the echo. The difference of the of the yellow lines presents the height of the
upper position of the indication.
yellow lines presents the height of the indication.
indication
indication.

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 TOFD Course 2008 PBE

Length measurement

The
h llengthh measurement shall
h ll b
be made
d ffrom the
h echo
h off the
h upper tip
i or from
f the
h
echo of the lower tip, that presents the maximum measurable dimension of the
indication.

A principle in measuring the length of an indication is that at first the parabolic

shape of an indication is searched.

If this parabolic shape is visible the length is measured from the point where the
reduction of the maximum amplitudep can be noticed,, an alternative method the 6
dB drop method may be applied if possible.

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 Scanning surface discontinuity
Scanning surface discontinuity appears as a disturbance in the lateral wave or a change in the
time scale of the lateral wave. If the disturbance has parabolic ends the dimensioning is done as
shown in the figure 1. The dimension is based on the drop of the amplitude of the echo.
In the case of lack of parabolic ends the length dimensioning is done in most conservative way
(see figure 2).
2) The indication is assumed to begin immediately after a drop or change in the
lateral wave.

Figure 1. Figure 2.
Length measurement from parabolic ends. The Length measurement from the point of the disturbance. The
difference of the yellow lines presents the length of difference of the yellow lines presents the length of the
the indication. indication.

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 Opposite
pp surface discontinuityy
Opposite surface discontinuity appears as a disturbance in the back wall echo, a change in
the time scale of the back wall echo or as an echo veryy close to the back wall echo. If the
disturbance has parabolic ends the dimensioning is done as shown in the figure 3.
In the case of lack of parabolic ends the length dimensioning is done in most conservative
way (see figure 4). The indication is assumed to begin immediately after a drop or change in
the back wall echo. For far surface a special dimensioning method is used. This method is
described in the figure 5.

Figure 3. Figure 4.
Length measurement from parabolic ends. The Length measurement from the point of the
difference of the yellow lines presents the length of disturbance. The difference of the yellow lines
the indication. presents the length of the indication.

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 Opposite
pp surface discontinuityy

Figure 5.
Length measurement of surface open indication. The cursors are set to place where the height of the
indication is 1 / 3 of the total height of the indication. The difference of the yellow lines presents the
length of the indication. This method is valid for both surfaces.

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 TOFD Course 2008 PBE

Through wall discontinuity

In these indications the same rule determined for parabolic shape and echo disturbance is valid.
A through wall discontinuity may not have any echoes inside the material, but may have only
disturbances in the lateral wave and in back wall echo.
In case where no lower tip echo is visible the indication is classified to be without measurable
height.
height

Figure 6. Figure 7.
I di ti is
Indication i embedded
b dd d withith measurable
bl hheight.
i ht Parabolic
P b li Indication is embedded with measurable height. No
pattern is visible in the echo. The length of the indication parabolic pattern is visible in the drawn echo. Length
is measured from the parabolic ends. The difference of measurement is made from the point of the
the yellow lines presents the length of the indication. disturbance. The difference of the yellow lines
presents the length of the indication.

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 TOFD Course 2008 PBE

Embedded point
point‐like
like indication

Measuring
M i theh position
i i off a point
i like
lik indication
i di i is i done
d from
f middle
iddl off the
h highest
hi h echo
h
visible. For an example see figure 8.

Figure 8.
Point like indication. The yellow line presents the position of the echo.

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 TOFD Course 2008 PBE

PART V

Test report

The test report shall include as a minimum the following

information

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 TOFD Course 2008 PBE

Information relating to object under test

a) identification of object under test

b) dimensions including wall thickness

c) material type and product form

d) geometrical configuration

e) location of welded joint(s) examined

f) reference to welding process and heat treatment

g) surface condition and temperature, if outside the range 0 °C to 50 °C

h) stage of manufacture

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 TOFD Course 2008 PBE

Information relating to equipment

a)) manufacturer
f and
d type off TOFD
O equipment
i i l di scanning
including i mechanisms
h i with
ih
identification numbers if required

b) manufacturer, type, frequency, element size and beam angle(s) of probes with
identification numbers if required

c) details of reference block(s) with identification numbers if required

d) type of couplant used.

used

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 TOFD Course 2008 PBE

Information relating to test technique

a)) examination
i i level
l l and
d reference
f to a written
i test iinstruction,
i if required
i d

b) purpose and extent of test

c) details of datum and co‐ordinate systems

d)) details of TOFD set‐ups

p

e) method and values used for range and sensitivity settings

f) details
d il off signal
i l averaging
i and
d scan increment
i setting
i

g) details of offset scans, if required

h) access limitations and deviations from this document, if any

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 TOFD Course 2008 PBE

Information relating to test results

a)) TOFD
O iimages off at least
l those
h llocations
i where
h relevant
l iindications
di i h
have b
been
detected

b) acceptance criteria applied

c) tabulated data recording the classification, location and size of relevant indications
and results ofevaluation

d) date of test

e) names, signatures and certification of personnel

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 TOFD Course 2008 PBE

Bibliography
g p y
• BS 7706
Calibration and setting‐up of the ultrasonic time‐of‐flight‐diffraction (TOFD) technique for the
detection, location and sizing of flaws

• EN 473
Qualification and certification of NDT personnel

• ENV 583‐6
Non‐Destructive testing Ultrasonic examination Part 6 : TOFD technique as a method of
detection and sizing discontinuities

• XP CEN/TS 14751
Technical specification – Welding – used of TOFD for examination of welds

• ASME Code Case 2235‐6

Boiler and pressure vessel code

• TOFDPROOF project
Recommedations for applying TOFD

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