ASNT
Level III
Study Guide
Ultrasonic Method
by
Matthew J. Golis
The American Society for Nondestructive Testing, Inc.
ASNT
Level III
Study Guide
Ultrasonic
by
Matthew J. Golis
The American Society for Nondestructive Testing, Inc.
thod
The Ultrasonic Testillg Level III Study Guide. prepared by Dr. Matlhew J.
earlier efforts by Robert Baker and Joseph Bush.
Goli~.
is partially based on
Publication and review of this Study Guide was under the direction of the Level III Program
Committee (known as the National Certification Board).
Published by
The American Society for Nondestructive Testing. 1nc.
171 1 Arlingate Lane
Colum bus, OH 4322 8-05 18
(800) 222-2768
© 1992 by The American Society for Nondestructive Testing, Inc. ASNT is nOl responsible for the
authenticity or accuracy of infonnation herein. Published opinions and statements do not necessarily
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endorsement or recommendat ion of ASNT
IRRSP, The NDT Techlliciall and www.asnLorg are trademarks of The American Society for
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AS NT exists to create a safer world by promoting the profession and technologies of nondestructive
testing.
ISBN- 13: 978-0-931403-29-3
ISBN- IO: 0-931403-29-4
Printed in the United States of America.
first printing 02/92
second printing with revisions 04100
third printing with revisions 09/01
fourth printing with revisions 08/06
fifth printing with changes 06/08
Preface
This slUdy guide has been developed to assist persons preparing to take the Ultrasonic Level III
examination offered through ASNT. It is intended to fea ture the major concept s considered central to
the traditional uses of Ultrasonics NDT as it is practiced throughout the USA, and to present
abstracts of several of the Iypical tech nical speciali ties. codes, and standards from whic h
"appli cations" quest ions are sometimes derived. It is not intended lO be a comprehensive coverage of
all possible technical issues that may appear on the Level III test, but rather it is intended to reflec t
the breadth of the possible technology topics wh ich comprise potential questions material. It is vital
that the suppl emental references be carefully reviewed to amplify on the statements in the Guide in
order to place each technical topic into its proper contex l.
The problcms at the end of each sectio n are int ended to be used as feed back regarding the user's
understanding of the concepts discussed in the sections. They require both a general understanding
of many of the topics as well as an abi lity to solve complex interpretation and analysis issues. Mixed
systems of units are used (both Eng lish and metric) because both are found in contemporary codes
and specifications. They sometimes ca ll for interpretat ions of graphs. plots, and related fi gures.
which are an integral pan of the language of the engineering sciences and techno log ies.
Suggestions for improvement to the Guide, its questions, or the related codes and spec ifi cations
should be sent to Ed uca ti onal Materials Supervisor. ASNT, 1711 Arlingate Lane, PO Box 28518,
Columbus. OH 43228-0518. The author acknow ledges the suppo rt given to this project by the
technical reviewers, publications staff at ASNT, and particu larly the Technical Services Department .
who recogni zed the need fo r this document and made the necessary arrangemen ts for gettin g it
comp leted.
iii
Contents
3
4
5
5
6
7
7
8
II
Chapter I - Physical Principles
Wave Characteristics
Reflection
Refraction
Mode Conversion
Critical Angles
Diffraction
Resonance
Attenu ation
Chapter I Review Questions
29
Chapter 2 - Equipment
Basic Instrumentation
Transducers and Coup ling
Spec ial Equipment Features
Chapter 2 Review Questions
35
39
40
41
49
Chapter 3 - Common Practices
Approaches to Testing
Measuring System Performance
Reference Reflectors
Calibration
Chapter 3 Rev iew Questions
17
20
26
55
56
58
58
60
63
64
65
7]
72
7.
76
77
78
81
82
83
84
87
Chapter 4 - Practical Considerations
Signal Interpretation
Causes of Variability
Special Issues
Weld Inspection
Immersion Testing
Production Testing
rn~ service Inspection
Chapter 4 Re view Questions
Chapter 5 - Codes and Standards
Typical Approaches
Summaries of Requirements
ASTM
Excerpts Taken from ASTM A609
ASME
Excerpts Taken from ASME Boiler and Pressure Vessel Code
Military Standards
Excerpts Taken from MIL-STD-2154
Building Codes
Excerpts Taken from a Representative Building Code
Chapter 5 Review Questions
v
93
93
Chapter 6 - Special Topics
Resonance Testing
Flaw Si zin g Techniques
99
103
104
105
Appendix A - A Representati ve Procedure for Ultrasoni c Weld In spection
Fonn A. Ultrasonic Testing Technique Sheet
Form B. Ultrasonic Inspection Results Form
Review Questions for a Representati ve Procedure for Ultrasonic
Weld In spection
109
Appendix B - Li st of Material s, Ve loc ities, and Impedances
111
Appendix C - Answer Key to Chapter Review Questions
113
Appendix D - References
vi
Chapter 1
Physical Principles
Chapter 1
Physical Principles
Sound is the propagation of mechanical
energy (vibrations) through solids, liquids and
gases. The ease w ith whi ch the sound travels,
however, is depe nde nt upon the detailed nature
of the material and the pilch (freque ncy) of the
sound. At ultrasoni c freque ncies (above
20.000 Hertz [H z]) , sound propagates we ll
through most e lastic or ncar-el astic so lid s and
liq uids, partic ularl y those wi th low viscos iti es.
At freq uencies above 100 kil ohertz (kH z), sound
energy can be fo rmed into beams, s imi lar to that
of ligh t, and thus can be scanned throughout a
mate rial, 1I0t unl ike that of a flas hl ight used in a
darkened room. Such sound beams follow many
of the physical rules of optics and thus can be
reflected , refracted, di ffracted and absorbed
(when nonel aslic materials are in volved). At
ex tremely high freque ncies (above
100 mcgahcrll. rMH zl), the sound waves are
severely attenuated and propagati on is lim ited to
Sh0l1 trave l di sta nces. The comillo n wave modes
and their characteri stics are summari zed in
Table 1.1.
Wave Characteristics
The propagat ion o f ultrasonic waves depends
on the mechani cal characteri stics of densi ty and
elasti city, the degree to which the material
support ing the waves is hOlllogeneous and
isotropic, and the d iffracti on pheno mena found
wi th continuous (or quas i-continuous) waves.
Contin uous waves are described by thei r
wavelength . i.e., the di stance the wave advances
in each repeated cycle. T-h.i.£...wave length is
proportional to the veloc ity at which the wave is
Table 1.1. Common Wave Mode Characteristics
Mode
Notable Characti'risti cs
Velochy
Aite-rnate Names
l.ongitudinHI
Bulk wave in all media
In·line motion
Pressure Wave
Dilatational (Straight Be-am)
Trun~wrsc
Bulk wa\e in solids
Polarized. e,g. Sv. SH
Transverse motion
Shenr
Torsional (Angle Beam)
Surface (GUided)
Boundary wave in solids
Polarized vertically
Elliptical motion
Polarized horizontally
Rayleigh Wa\e
PI;Jte (Guided)
( ... )
F(f. T. rn)
Twin-boundary wave· solids
F(f.T.m)
Symmetrical
Hourglass motion
Asymmetrical
Flexing motion
Common colloquial tenns
Signifies approximate relationship for common Illllterials
Depends on Frequency. Thic kness. lind Material
3
Lamb Wave
advanc ing and is inversely proportional to its
frequency of oscillation. Wavelength may be
thought of as the distance from one point to the
nex t identical point along the repetitive
waveform. Wavelength is described
mathematically by Equation I- I.
Tabl e 1.2 it is seen that. in steel. a longitudinal
wave travels at 5.9 km/ s. while a shear wave
travels at 3.2 km/s. In aluminu m. the longitudinal
wave velocity is 6.3 km/s while the shear ve locit y
is 3. 1 kmls. The wavelengths of sound for each of
these material s are calculated using Equation I- I
for each applicable test frequenc y used. For
exampl e, a 5 MHz L-wave in water has a
wave length equal to 1483/5( I 0)6 m or 0.298 mill .
Wavelength = Ve loci ty
Frequency
(Eq. I-I )
When sound waves are confined within
boundaries, such as alo ng a free surface or
between the surfaces of sheet material s, the
waves take on a very different behavior, being
controlled by rhe confining boundary condition s.
These types of waves arc cull ed gu ided waves,
i. e., they are gu ided along the respec tive surfaces,
and exhibit veloc ities that are dependent upon
elastic moduli , density, thickness, s urface
conditions, and relative wavelength interac tio ns
with the surfaces. For Rayleigh waves, the useful
depth of penetration is restricted to about one
wave length below the surface. The wave motion
is that of a retrograde ellipse. Wave modes such
as those found w ith Lamb waves have a ve locity
o f propagation depende nt upon the operating
frequency, sample thickness and clasti c moduli .
They are di spersive (ve loci ty changes with
frequency) in that pulses transmitted in these
modes tend to become stretched or dispersed as
they propagate in these modes and/or material s
whi ch ex hibit frequen cy-depe ndent velocities.
The velocity at which bulk waves travel is
determined by the material' s elastic moduli and
density. The expressions for longitudinal and
tra nsverse waves are g iven in Equations 1-2 and
1-3. respectively.
,
V=
p(1+ ~ )(1- 2~ )
(Eq . 1-2)
(Eq. 1-3)
where
VL is the longitudinal bu lk wave velocity,
VT is the transvcrse (shear) wave velocity,
G is the shear modulu s,
E is Young's modulus of e lastici ty
~
is the Poi sson ratio, and
p is the material densi ty .
Reflection
Typical values of bulk wave velocities in
common malerials are given in Table 1.2. A
more complete list is given in Appendix A. From
Ultrasonic waves, when they encounter a
di screte change in materials, as at the boundary of
two dissimi lar materials, are usual ly partially
reflected. If the incident waves are perpend icular
10 the material interface, the refl ected waves are
redirected back toward the source from which
they came. The degree to which the sound energy
is reflected is dependent upon the difference in
acoust ic properties, i.e., acoustic impedances,
between the adjacent materi als.
Table 1.2. Acoustic Velocities, Densities and
Acoustic Impedances of Common
Materials
Muterilll
V
( m /s)
V
(m/s)
Z
[JIil!./c m J )
Steel
5900
3230
45.0
7.63
Aluminum
6320
3130
17.0
2.70
Plexiglass
2730
t430
3.2
1.17
Water
1483
-
1.5
1.00
Quartz
5800
2200
15.2
2.62
Acoustic impedance (Eq uat ion 1-4) is the
product of a wave's veloci ty of propagation and
the density of the material through which the
wave IS passlOg.
Z= P X V
(Eq. 1-4)
4
where
Z is the acou stic impedance,
p is the density, and
V is the applicable wave velocity.
transmitted wave may be ( I) refracted (bent),
depending on the relative acou stic velocities of
the respective media, and/or (2) partially
con verted to a mode of propagation different
from that of the incident wave. Figure 1.1 a
shows normal reflection and partial transmission ,
while Figure 1.1 b shows oblique reflection and
the partition of waves into reflected and
transmitted wave modes.
Table 1.2 lists the acoustic impedances of
several common materials.
The degree to which a perpendicular wave is
reflected from an acoustic interface is gi ven by
the energy rcflcction cocfficient. The ratio of thc
reflected acoustic energy to that which is
incident upon the interface is given by
Equation 1-5.
Referring to Figure 1.1 b, Snell's Law may be
stated as:
. " (V,)sma
.
sm..., =
~
(Eq. 1-6)
For example. at a water-plexiglass interface,
the refracted shear wave angle is related to the
incident angle by
(Eq. 1-5)
where
R is the Coefficient of Energy Reflection
for normal incidence
sin ~ ~ (I43011483)sin IX ~ (O.964)sin a.
Z
is the respective material acoustic
impedances with
ZI = incident wave material ,
Z~ = transmitted wave material , and
T is- Lhe Coefficient of Energy
Transmission.
Note: T+R = l
For an incident an gle of 30 degrees ,
sin ~ ~ 0.964 x 0.5 and ~ ~ 28.8 degrees
Mode Conversion
It should be noted that the acoustic velocities
(VI and V2) used in Equation 1-6 must conform
to the modes of wave propagation which exist
for each given case. For example, a wave in
water (which supports only longitudinal waves)
incident on a steel plate at an angle other than
90 degrees can generate longitudinal, shear, as
well as heavily damped surface or other wave
modes, depending on the incident angle and test
part geometry. The wave may be totally reflected
if the incident angle is sufficiently large. In any
case, the waves generated in the steel will be
refracted in accordance with Snell' s Law,
whether they are longitudinal or shear waves.
In the case of water-to-steeJ, approximately
88 percent of the incident longitudinal wave
energy is reflected back into the water, leaving
12 percent to be transmitted into the stee!. ! These
percentages are arrived at using Equation 1-5
with Z ,\ ~ 45 and Z '" ~ 1.5. Thus, R ~(45 - 1.5)'1
(45 + 1.5)' ~ (43.5/46.5)' ~ 0.875 , or 88 percent
and T ~ I - R ~ I - 0.88 ~ 0.12, or 12 percent.
Refraction
Whcn a sound wave cncounters an interface
at an angle other than perpendicular (oblique
incidence), reflections occur at angles equal to
thc incidcnt angle (as measured from the normal
or perpendicular axis). If the sound energy is
partially transmitted beyond the interface, the
Figure 1.2 shows the distribution of
transmitted wave energies as a function of
incident angle for a water-aluminum interface.
For example, an L-wave with an incidence angle
of 8 degrees in water results in (1) a transmitted
shear wave in the aluminum with 5 percenl of
the incident beam energy, (2) a transmitted
'When Equation 1-5 is e~ pressed for pressure waves rather than
the energy contained in the waves. the te rms in parentheses are
not squared.
5
Figure 1.1. Incident, reflected, transmitted, and refracted waves at a
liquid-solid interface
a.
--
b.
I
R
z,
v
Norma l
Incidence
v,
T
Oblique
Incidence
L-wave with 25 percent and (3) a renected
L-wavc with 70 percent of the incident beam
energy. It is evident from the figu re that fo r low
incidence ang les (less than the first cri tical ang le
of 14 degrees), more than one mode may be
generated in the alum inum. Note that the sum of
the reflected longitudinal wave energy and the
transm itted ene rgy or energies is equal to unity
at all angles. The relati ve energy amplitudes
partitioned into the different modes are
dependent upon several variab les. including each
material' s acoustic impedance. each wave mode
veloc ity (in both the inciden t and refracted
materials), the incident angle. and the
tran smitted wave mode(s) refracted angJe(s).
Critical Angles
The critical angle for the interface of two
medi a with dissimil ar acollstic wave velocities is
the incident angie at which the re fracted angle
equals 90 degrees (in accordance wi th Snell 's
law) and can only occur if the wave mode
vel oci ty in the second medium is greater than the
wave ve locity in the inc idcnt medi um. It may
also be defined as the incidcnt angle beyond
which a specific mode can not occur in the
second medium. in the case of a water-to-steel
interface. there are two critical angles derived
from Sne ll' s law. The fi rst occurs at an incident
angle of 14.5 degrees for the longi tudinal wave.
The second occ urs at 27.5 deg rees for the shear
wave. Equation 1-7 can be used to calculate the
critical incident angle for any material
combinati on.
Figure 1.2. Reflection and transmission
coefficients versus incident
angle for water/aluminum
interface
..
c
'0
IE
•.•
8
0.8
0.1
~
-
~~
\.z..
~,
M
0.3
1i:i
0.2
.'
f..- .. .... ........ \
........
..
Transmuted ...... .
LongilUdinal .- .....
Wave
I
_ _ _
--....'
(Eq. 1·7)
For example. the fin.t critical ang le for a
water-alum inum interface is calculated using the
criti cal angle equation a<.,
Transmitted
Shear Wave
,
I
::i "'0l-..=
-::.-'=
-'c..::L"'.:u~!:--!:-~\---f;--!;.81216202421)23640
Incidence Angle (degrees)
a Cril
6
= sin- I (J.f83 / 63::!0) = 13.6 degrees
Diffraction
sin$ = 1.2!:
D
Plane waves advanci ng through
homogeneous and isotropic e lastic media tend to
travel in straight ray paths unless a change in
med ia properties is encountered. A flat (much
w ider th an the incident beam) interface of
differing acoustic properties redirects the
incident plane wave in the form of a specu\arly
(mirrorlike) refl ected or refracted plane wave as
(Eq. 1-8)
D'
N= -
4A
(Eq. 1-9)
where
$ is the beam divergence half angle,
A is the wavelength in the media,
discussed above. The assumption in th is case is
that the interface is large in comparison to the
incident beam's d imensions and thus docs not
encou nter any "edges."
D is the diameter of the aperture
(transducer),
N is the length of the Near F ield (Fresnel
Zone).
On the ot her hand, when a wave encounte rs a
po in t renec lor (small in comparison to a
wave length), the reflected wave is reradiated as a
spherical wave front. Th us, when a plane wave
encou nte rs the edges of reflective interfaces.
such as ncat" thc tip of a fat igue crack, specular
reflections occur along the "flat" surfaces of the
crack and cy li ndrical wave lets are launched from
the edges. S ince the waves are coheren t, i.e., the
same frequency (wavelength) and in phase, the ir
red irecti on into the path of subsequent advancing
p lane waves results in incident and reflected
(scattered) waves interfe ri ng, i.e., forming
regions of reinforcement (constructive
in te rference) and cancellat ion (destructive
interference).
Note: The mu ltipl ier of 1.2 in Equation [·8 is
fo r the theoret ical null. 1.08 is used for 20 dB
down poi nt (10 percent of peak), 0.88 is used for
10 dB down po int (32 percent of peak) and 0.7
for 6 dB down po int (50 percent of peak).
For example, a 20 mm diameter, L-wave
transducer, radiating into steel and operating at a
frequency of 2 MHz. will have a near field gi ven
by
3
N=
T hi s "in terfering" behavior is characteristic
of contin uous waves (or pulses from "ringing"
ultrasonic transducers) and, when applied to
edges and aperrures serving as sources of sound
beams, is known as wave diffrac tion. It is the
fu ndamen tal bas is for concepts such as
transducer beam spread (direct ivity). near field,
wavelength-limited flaw detection sensitivity,
and assists in the sizing of discontinui ties using
dual transducer (crack-tip diffraction)
techniq ues. Figure 1.3 shows examples of plane
waves bei ng changed into spherical or
cylindrical waves as a result of diffraction from
poin t reflectors, linear edges and (transducerlike) apertures .
[20{lOr x 2(10)']
4xS.9{lO)
3
=
200
3
- (lOr = 33.9 nun
S.9
and half-beam spread angle given by
. - ,{ 1.2xS.9(1O)3
} 02d egrees
$ = Sill
3
6 = 1.
20(10) x 2(10)
If the J 0 percent peak value was desired
rather than the theoret ical null, the 1.2 would be
changed to 1.08 and 4> would equal 9.2 degrees.
Using the multiplier of 0.7 for the 6 dB down
value, the half angle becomes 6 degrees.
Resonance
Another form of wave interference occurs
when normally incident (at normal incidence)
and reflected plane waves interact (usually
within narrow, parall el in terfaces). The
am plitudes of the superimposed acoustic waw s
are additive when the phase of the doubly
reflected wave matches that of the incoming
Beam spread and the length of the near field
for round sound sources may be calculated using
Equations 1-8 and 1-9.
7
Figure 1.3. Examples of diffraction due to the presence of edges
;f;(~ *:.~
a. Point Refl ector
b. Edge Reflector
c. Square Aperture
d. Round Aperture
incident wave and creates "stand ing" (as
opposed to trave ling) acoustic waves. When
standi ng waves occur, th e item is said to be in
resonance, i.e., resonating. Reso nance occu rs
when the th ickness of the item equals half a
wavelength 2 or its multiples, i.e., when T = V12 F.
Th is phenomenon occurs when piezoe lectric
transducers are el ectrically excilCd at their
characte ri st ic (fund amental resonant) frequency.
It also occu rs when longitudin al waves travel
through thi n sheet materials during im mers ion
testing.
materials (that are generall y homogeneous but
contain even ly distribu ted scutterers, e.g., gas
pores, segregated inclu sions, and grain
boundaries), the waves are parti ally re nected at
each disconti nuity and the energy is said to be
scattered into many different directions. Thus,
the acoustic wave that starts out as a coherent
pl ane wave fro nt becomes parti all y redirected as
it passes through the materi al.
The relati ve impact of the presence of
scatte ring sources depends upon the ir size in
co mparison to the wavelength of the ultrason ic
wave. Scatterers much smaller than a
wavelength are of little consequence. As the
scatterer size approaches that of a wavelength,
scattering within the material becomes
increasingly troublesome. The effects on such
signal attenuat ion can be partially compe nsated
by using longer wavele ngth (lower frequency)
sound sources, usuall y at the cost of decreased
sensi ti vity to discon tinu ities and resolution.
Attenuation
Sound waves dec rease in intensity as they
travel away from their source, due to geometrical
spreading, scatterin g, and absorption. In
fin e-grained, homogeneous, and isotropi c elastic
materials, the strength of the sound fie ld is
affec ted mainly by the nature of the radiat ing
source and its attendant direct ivi ty pauern . Ti ght
patterns (s mall beam angles) travel farther than
widely diverging pattern s.
Some scatters, such as colu mnar grai ns in
stainl ess steels and lami nated composites,
ex hi bit hi ghly anisotropic elastic behavior. In
these cases, the incident wave front becomes
distorted and often appears to change direct ion
(propagate better in certain preferred directi ons)
in response to the maleriar s anisotropy. This
behav ior of some materia ls can totally destroy
the usefulness of the UT approach to materials
evaluation.
When ult rasonic waves pass through
common polycrystall ine elastic engineeri ng
' If a layer between two differing media has an acoustic imped·
ance equal to the geometric mean of the outer two and its
thickness is equal to one-quartcr wavelength. 100 percent of the
incident acoustic energy. at normal incidence. will be transmitted
through the dual interfaces beeause the interfering waves in the
layer combine to serve as an acoustic impedance transformer.
8
Table 1.3 shows some typical va lues of
allenualion for common NDT applications. Be
aware that attenuation is highly dependent upon
operating frequency and thus any stated values
must be used with caution.
Sound waves in some materials are absorbed
by the processes of mechanical hysteresis,
internal friction, or other energy loss
mechanisms. These processes occur in nonelastic
materials such as plastics, rubber, lead, and
nonrigid coupling materials. As the mechanical
wave attempts to propagate through such
materials, parI of its energy is given up in the
fo rm of heat and is not recoverable. Absorption
is usually the reason that testing of soft and
pliable material s is limited to relatively thin
section s.
Because many factors affect the signal s
returned in pulse.echo testing. direct
measurement of material attenuation can be quite
difficult. Detected signals depend heavily upon
operating frequency, boundary conditions, and
waveform geometry (plane or other). as well as
the precise nature of the materials being
evaluated. Materials are highly variable due to
their thermal history, balance of alloying or other
integral constituents (aggregate. fibers, matrix
uniformity, water/void content, to name a few ).
as well as mechanical processing (forging.
rolling, extruding, and the preferential directional
nature of these processes).
Attenuation is measured in terms of the
energy loss ratio per unit length, e.g .. decibels
per in. or decibel s per meter. Values range from
less than 10 dB/m for aluminum to over
100 dB/m or more for some castings, plastics,
and concrete.
Table 1.3. Attenuation Values for Common Materials
Nature of Material
Attenuation*
(dB/m)
Principal
Cause
Normalized Steel
70
Scatter
Aluminum ,
6061-T6511
90
Scatter
Stainless Steel,
110
ScatterlRedirection
380
Absorption
,XX
Plastic (clear acrylic)
*Frequency of2.25 MHz, Longitudinal wave mode
9
Chapter 1 Review Questions
Q.l· J Sound waves continue to lf3vel:
A. until they are reflected by material
su rfaces.
B. gradually di ss ipating by the effects of
beam spread.
C. gradually diss ipating by scattering
and absorption.
D. all of the above.
Q. J -2 Wavelength may be defined as:
A. frequency divided by velocit y.
B. the di stance along a wave train frolll
peak to trough.
C. the di stance from one point to the
next identica l point along a
wavetrain.
D. the di stance along a wavclrain from
an area of high particle motion to one
of low particle motion.
A dissipated.
B. discontinuous.
C. dispersive.
D. degenerat ive.
multi ply ve locity by frequency.
divide velocity by frequency.
divide frequency by velocity.
nOlle of the above.
Q . l -S Plate thickness = 25.4 mm, pulse-echo,
straight beam measured elapsed time =
8 ~ s. What is the most likely material?
A. carbon steel
B. lead
C. titanium
D. alumi num
Q. I-4 The wavelength of a 5 MHz sound wave
in water is: (VL = 1.4S( IO)Scmls)
A. 0.01 in.
B. 0.10 in.
C. 0.296 m.
D. 3.00mm.
Q.I-9 It can be deduced from Table 1.2 that the
densities of:
A water and plexiglass are in the ratio
of 1.16: 1.
Q. I-5 Th ickness resonance occurs when
tran sduce rs and test paris are excited at a
frequency equal to:
(where V = sound veloci ty and
T = item th ickness)
A.
B.
C.
D.
A. materi als with higher densities will
usuall y have higher acoustic
velocities.
B. materials w ith hi gher moduli will
usuall y have higher velocit ies.
C. wave veloc ities rely most ly upon the
ratios of e lastic modu li to materi al
dens ity.
D. VT wi ll always be one-half of VL in
the same material.
Q. I-7 Veloc ity measurements in a material
revealed that the veloc ity decreased as
frequency increased. This material is
called:
Q. I-3 To determine wavelength :
A.
B.
C.
D.
Q. I-6 The equations that show VL and VT be ing
dependent on e lastic propert ies suggest
that:
B. steel and aluminum are in the ratio of
2.8: I.
C. quartz and al uminum are in the rati o
of 1.05: I.
D. all of the above.
2TIV.
T/2V.
VI2T.
2v/T.
Q.l-IO The acoustic energy refl ected at a
plexiglass-quartz interface is equal to:
A.
B.
C.
D.
11
64 percent.
41 percent.
22 percent.
52 percent.
Q.I-II The acoustic energy transmitted through
a plexiglass-water interface is equal to:
Q.I-16 From Figure 1.2 it is evi dent that the sum
of the inc ident wave's part itions
(transmitted and reflec ted) is:
A. 87 percenl.
S. 36 percent
C. 13 percent
D. 64 percent
A. highly irregular at low angles, but
constant above 30 degrees.
B. lower at angles between 16 and 26
degrees.
C. rarel y more than 0.8.
D. al ways equal to unity.
Q.I- 12 The first critical angle at a waterplexiglass interface will be:
A. 16 degrees .
Q.I-17 The principal attenuation modes are:
B. 33 degrees.
C. 22 degrees.
D. none of the above.
A. absorpt ion, scatter, beam spread.
B. beam spread, collimation, scauer.
C. scalier, absorption, foclising.
D. scatter, beam spread, adhesion.
Q.I- 13 The second critical angle at a waterpl ex iglass interface will be:
Q.I-18 Attenuation caused by scatterin g:
A. 22 degrees.
A. increases with increased frequency
B. 33 degrees.
C. 67 degrees.
D. none of the above.
and grain size.
B. decreases with increased frequency
and grain size.
C. increases with higher frequency and
decreases with larger grain size.
D. decreases with hi gher frequency and
decreases with larger grain size.
Q.1-14 The inc ident angle needed in immersion
testing to deve lop a 70-degree shear
wave in pl exiglass usi ng the information
in Table 1.2 equal s:
A. 83 degrees.
B. 77 degrees.
C. 74 degrees.
Q.I-19In very fine-grain, isotropic crystalline
material, the principal loss mechanism at
2 MH z is:
D. 65 degrees.
Q.I-15 Figure 1.2 shows the partition of incident
and tran smitted waves at a
water-aluminum interface. At an
incidence angle of 20 degrees, the
renected wave and tran smitted waves are
respective ly:
A.
B.
C.
D.
60 percent and 40 percent.
40 percent and 60 percent.
113 and 2/3.
80 percent and 20 percent
A.
B.
C.
D.
scatter.
mechanical hysteres is.
beam spread.
absorption.
Q.I-20 T wo plates yield different backwall
renections in pulse-echo testing ( 18 dB)
with their on ly apparent difference being
in the second materi al's void content
The plates arc both 3 in . thick. What is
the effect ive change in acoustic
attenuation between the first and second
plate based on actual metal path
di stance?
A.
B.
C.
D.
12
3 dB/in.
6 dB/in.
18 dBlin.
none of the above
Q.I-21 The equation, sin $::: 0.7 IJD, describes:
A . beam spread ang le at 50 percent
decrease in signal from the centerline
value.
B. one-half the beam spread angle at
50 percent decrease in signal from the
centerl ine value.
C. one-half the beam spread angle at
20 percent decrease in signal from the
centerli ne value.
D. one-half the beam spread angle at
100 percent decrease in signal from
the centerline value.
Q. I-22 The beam spread half-angle in the far
field of a I in. diameter transducer
sending 5 MHz long itudinal waves into a
pJexiglass block is:
A. 0.5 degrees.
B. 1.5 degrees.
C. 3. 1 degrees.
D. 6.2 degrees.
Q. I-23 The near field of a round 1/2 in. diameter
contact L-wave transducer being used on
a steel test part operating at 3 MHz
is:
A. 0.5 in.
B. I in.
c. I em.
D. 2cm.
Q. I-24 The depth of penetration of the sound
beam into a material can be increased by:
A. using a higher frequency.
B. using a longer wavelength.
C. usi ng a smaller transducer.
D. usi ng a lower frequency and a larger
transducer.
13
Chapter 2
Equipment
Chapter 2
Equipment
Basic Instrumentation
The basic electronic in strument used in
pu lsed ul trasoni c test ing contai ns a source o f
voltage spikes (to acti vate the sound source, i.e.,
the pulser) and a di spl ay mechanism that permits
interpretation of rece ived ultrasonic acoustic
impul ses, i. e., the sweep ge nerato r, receiver and
display scanner or cathode ray tube (CRT). A
block di agram of the bas ic uni t is shown in
Figure 2. 1.
Seve ral operati ons are synchroni zed by the
clock (timer) circuitry whic h triggers appropriate
components to initiate actio ns including the
pui ser (that activates the transducer), the sweep
generator (that forces the electron beam within
the cathode ray tube to move hori zontall y across
the screen), and other special circuits as needed
including markers, sweep de lays, gates.
electroni c di stance ampli tude correction (DAC)
unit s, and other support c ircuit s.
Pul se signals fro m the rece iver search unit 3
are ampl ifi ed to a leve l compat ible with the CRT
'The tern} pulse is used in twO contexts in ullrJsonic NDT
systems. The electronic system sends an exciting electri cal
"pulse"to the transducer being used to emil the ultras.onic wave.
This electrical pulse is usually a unidirectional spikc with a fast
rise-t ime. The resulting acoustic "wave packet" emilled by lhe
transducer is the ultrasonic pulse. characterized by a prcdominant
central frequency at the transducer's naturallhickne~s resonance.
Figure 2.1. Block diagram of basic pulse-echo ultrasonic instrument.
Timer
Sweep
Generator
/
CRT
Pulser
Y • ~A
H.
v.
V
Lt
It
17
t-
'--'
Table 2.1. Instrumentation Controls Effects
InSlru ment Control
('ulser
Pulse Length (Damping)
Comments on Signal Respon se
If shon , improves depth resolution;
I f long. improves penetration
Repetition Rate
Receh'cr
Frequcncy Response
If high. brightens images-but may cause wra p·around "ghost" signals
Wide Band- faithful reproduction of signal. higher background noise
Narrow Band- higher sensitivity. smoothed signals. rcquires ma tched (tuned) syste m
If high. improves sensitivity. higher background noise
Gain
Display
Sweep
Material Adjust
Delay
Calibration critical fo r depth information
I)ermits "spreading"of echo pulses for detailed analysis
Rcjcct
Suppresses low-level noise. alters opponent vcnical linearity
Smoothing
Suppresses detailed pulse structure
Output (Al;mll, Record)
Gates
Time Window
(Delay, Width)
Selects portion of display for analysis, gate may diston pulses
Threshold
Sets automatic output sensiti\'ity
I'ol arity
Pcnnits positi ve and negative images, allows triggering on both increasing and
dec reasing pulses
of an ultrason ic test. If desired, a particu lar
port ion of the trace may be Hgated" and the
signal within the gate sent to some external
device, i.e. , an alarm or recording device, which
registers the presence or absence of echo signals
that are being sought.
and appear as ve rtical excursions of the e lectron
beam sweeping across the screen in response to
the sweep generalOf. The rece ived signals are
often processed 10 enhance interprelation
through the lise of filte rs (that lim it spurious
background noise and smooth the appearance of
the pul ses), rectifiers (that change the oscillatory
radio-frequency [RF] signals 10 unidirectional
"video" spikes), and clipping circuits (that reject
low- level background signals). The final signals
are passed on to the ve rti cal denection plates of
the CRT or display unit and produce the
time-delayed echo signals interpreted by the UT
operator, commonl y referred to as an A Scan
(signal ampli tude displayed as a fun ct ion of
lime).
C haracteristics of the initi al pu lse (shape and
fre quency con tent) are carried forward
th roughout the syste m, to the transducer, the test
item, back to the transducer, the receiver, the
gate, and the CRT. In essence, the information
content of the in itial pul se is modified by each of
these items and it is the result of thi s collective
signal processing that appears on the screen.
All of these func tion s are within the control
of the operator and their collec ti ve sett ings
represent the Hsetup" of the instnllnen l. Table 2. 1
li sts the variables under the control of the
operator and the impact they have on the validity
18
The initi al pulse may range from several
hundred to over 1000 V and have a very short
rise· time. In other syste ms, the in itial pulse may
represent a portion of a sinusoidal osc illati on
that is tuned to correspond to the natural
frequ ency of the transducer. The sinu soidal
exc itation is often used where longer duration
pulses are needed to penetrate highly attenuative
materials such as rubber and concrete.
Signals may be di splayed as RF waveforms,
representing a close replica of the acoustic wave
as it was detected by the receiv ing transducer, or
as video waveforms, (half- or fu ll-wave
rectified), used to double the effectivc viewing
range of the screen (bottom to top rather than
centerline to topfbottom), but suppressing the
phase information found only in RF
presentation s.
Signals from the receiv ing transducer
(usua ll y in the millivolt range) are too small to
be directly senilO the display unit. Both linear
and logari thmic amp liriers are used to raise
signal levels needed to drive the display. These
amp lifie rs, located in the receiver sections of the
A Scan units, must be able to produce output
signals that are linearly related to the input
signals and which supply signal process ing
intended to ass ist the operator in interpreting the
disp layed signals.
To enhance the ability to accurately identify
and assess the nature of the received ultrason ic
pulses, particu larly when there exists an
excessive amount of background signals, various
means of signal processing are used. Both tuned
receivers (narrow-band instruments) and low
pass filters are used to se lect ively suppress
portions of the received spectrum of signal
frequencies which do not contain useful
informat ion from the test material.
Am pl ifiers may raise incoming signal s to a
maximum level, fo ll owed by precision
attenuators that decrease the signal strength to
usable levels, i.e. , or capab le of being positioned
on the sc reen face, capable of chang ing
am plification ratios in direct response to the
"Gain" con trol.
Linear system s, such as the ultrasonic
in strument's receiver sect ion (as well as each of
the elements of the overall system), are
characterized by the manner in which they affect
incoming signal s. A common approach is to slart
with the frequency content of the incoming
signa l (from the receiv ing transducer) and to
desc ribe how that spectrum of frequencies is
altered as a result of passing through the system
element.
Di screte attcnuators (which have a
logarithm ic respon sc) arc currently used due 10
their ease of precise construction and simpfe
means for altering signal levels which extend
beyond the vicwing range of the sc reen. Their
extensive use has made "decibel notation" a pan
of the standard terminology used in describ ing
changes in signal levels, e.g., receiver gain and
material atten uation.
Equation 2-1 (ratios to dec ibels) shows the
relationship between the ratio of two pul se
ampli tudes (A 2 and A I) and their equ ivalence
expressed in decibel notat ion (NdIJ
(Eq.2-1 )
Inversion of thi s equation results in the
usefu l expression
A/A I = 1(}"'1'.1O,
where a change of20 dB , i.e., N = 20, makes
ION/2Q = 10 1 = 10
Thus 20 dB is equivalent to a ratio of 10: I.
When both useful target information (which
may be predominantl y contained in a narrow
band of frequencies generated by the sending
transducer) and background noi sc (which may be
distributed randomly over a broad spectrum of
frequencies) are present in the signal emering the
receiver, selective passing of the frequencies of
interest emphasizes the signal s of interest while
suppressing the others which interfere with
interpretation of the CRT display.
When an ultrasonic instrument is desc ribed
as being broadband, that means a very wide
array of frequencies can be processed through
the in strument with a minimum of alteration. i.e ..
the signal observed on the screen is a close, but
ampl ified, representation of the electrical signal
measured at the receiving transducer. Thu s both
useful signal s and background noise are present
and the signal-to-noise ratio (SIN) may not be
19
Figure 2.2. Comparison of time domain and frequency domain representations of typical
signals found in ultrasonic testing
•
time
time
[Input]
[Output]
Hand Ilass]
[ Response
Frequency Domain
Frt(IUcncy H.e.<;ponse
A
A
frequency
frequ ency
very good. The shape and amp litudes of the
signa ls, however, tend to be an accurate
representation of the recei ved response from the
tran sducer.
A probe or search unit may contain one or more
transducers. plus facinglbacki ng materials and
connectors in order to meet a specific UT design
need.
A narrow-banded instrument, on the other
hand , suppresses that portion of the frequen cy
content of the incoming signal that is ou tside
(above or below) the ··pass'· frequency band.
With the high-frequency noi se suppressed, the
gain of the in strument can be increased, leading
to an improved sensitivity. Howeve r, the shape
and re lati ve amplitudes of pulse frequency
co mponents are often altered. Fi gure 2.2
graphi ca ll y shows these effects for a typica l
ultrasonic signal.
A critica l element of eac h searc h unit is the
tran sducer's active material. Com monly used
materia ls ge nerate stress waves when they are
subjected to elec trical stimuli , i.e., piezoelectrics.
These material s arc characteri zed by thei r
conversion factors (electrica l to/from
mechanical), thermal/mechanica l stabili ty, and
other phys ical/chemical features. Table 2.2 li sts
many of the material s used and some of their
salient fea ture s. The cri tica l temperature is the
temperatu re above which the maleri al loses its
piezoe lectric characteri sti c. It may be the
depoling temperature of the ferroelcctrics, the
deco mposition temperature fo r the lithium
sulfate or the Curie temperature for the quartz.
Transducers and Coupling
A transducer. as appli ed to ultrasonic test ing.
: ... the mean,"> by which elec trica l energy is
" med illlo acoust ic energy and back again.
n.:- j.e-... l ...·e. adapted for UT. has been called a
. l. ~c h unit. a crystal. and a transducer. 4
"The 1erm 1rallsduccr i~ generic in lh:u il applies 10 any device
thnt converts one form of cnerg~ into another. e.g .. light bulbs .
electric he:uer\ and ~olar co llector,.
20
Table 2.2. Piezoelectric Material Characteristics
Material
Efficiency
T
R
Irnpedance
TIR
Quartz
X-cut
C ritical
Temp
(0C)
(Z)
15 .2
PZT5
Lead Zirconate
Titanate
10
14.6
8.4
BaTi
Barium Titanate
PMl'"
Lead Metaniobatc
0.21
32
LSI-I
6.9
- 2.0
Displacement
(dJl)
Electrical
Density
Note
(g.ll)
pO
57
2.65
(1 )
576
2.3
33
193-365
374-593
20-25
7.5
(2)
31.2
115-150
125-190
14-21
5.4
(2)
20.5
550
80-85
32-42
6.2
(2)
11.2
75
15-16
156-175
2.06
(3)
Lithium Sulfate
Hydrate
LN
2.8
0.54
1.51
34
6
23
4.64
Lithium Niobatc
PVDF
6.9
1.35
9.3
4.1
165-180
14
140-210
1.76
Poly( vinylidcnc
Fluoride)
Notes:
(1)
Mechanically and chemically stable; X-cut yields longitudinal wave motion while V-cut
yields distortional transverse waves.
(2)
Ferroelectric ceramic requiring poling and s ubject to extensive cross-mode coupling.
(3)
Soluble in water, R estimated at -2.
(4)
Flexible polymer.
(4)
Figure 2.3. Quality factor or "Q" of a transducer
Time Domain
Frequency Domain
Amplitude
1.0
0.7
a.
a.
Frequency
b.
Amplitude
1.0
0.7
b.
Frequency
21
The qual ity factor, or "Q," of tuned ci rcu its,
search un its or indiv idual transducer elements is
a performance measu re of their freq uency
selecti vity. It is the ratio of the search unit 's
fundamen tal (resonance) freque ncy (f) to its
bandwidth (f2 - f l) at the 3 dB down points
(0.707) and shown in Figure 2.3.
The rat io of the acoustic impedance of the
transd ucer and its facing materials governs how
welllhe sound from the transducer can be
coupled into the material and/or the backing
material. From the table of piezoelectric material
characteri stics, it is apparent that none of the
materials is an ideal match for NOT. Thus du al
transducer search units are sometimes made such
that the transmitter and receiver are made of
di fferent transducer material s in order to take
advantage of the ir respecti ve strengths and to
minimize their weaknesses.
As a result of diffraction effects, the sound
beam emitted fro m search units tends to spread with increasing distance away from the sou nd
source. The sound beam ex iting from a
transducer can be separaled into two zones or
areas. The Near (Fresnel) Field and the Far
(Fraunhofer) Field are shown in Figure 2.4 with
the shaded areas represent ing regions of
relatively high pressure.
The near fie ld is the region directly adj acent
to the transducer and characte ri zed as a
collection of symmetrical hi gh and low pressure
reg ions caused by interfering wavefront s
emanating from a continuous, or near continuous,
sound source. Hu ygen's principle treats the
transducer face as a seri es of poi nt sources of
sound , whi ch interfere wi th each other's wavelets
throughout the near field. Each point source emits
spherical wavefronts which start out in phase at
the transducer surface. At observation points
somewhat removed from the plane wave source
(the transducer face), wavefronts from variou s
point sources (separated laterall y from each
other) interfere as a resu lt of the differing
distances the waves had to travel in order to reach
the observation point. Both hi gh and low pressure
zones result, depending on whether the
superimposed aggregate of interfering waves arc
constructive (in phase) or destructi vc
(180 degrees out of phase).
As a special case, the variat ion in beam
pressure as a fu nction of di stance from a circular
transducer face and along its major axis is given
by Eq uation 2-2.
y+ = D 2-I'?(2m+ 1)2. 111=0
± l, ±2, ... i m
//I
4A(2m + 1) '
,
(Eq.2-2)
where
Y+ is the position of maxima along the
central ax is,
D is the diameter of a circular radiator, and
A is the wavelength of sound in the med ium.
Figure 2.4. Conceptual representation of the sound field
emitted by a circular plane~wave piezoelectric
transducer
1+'----N----+i·1
Near
Far
(Fres nel)
(Fralin/lOfer)
22
Since ')...2 is in significant compared to D2 for
most ultrason ic testing frequencies, particularly
in water, at the last maximum, (m = 0),
Equation 2-2 becomes:
y,+
o
resolution but allow less penetration into
com mon engineering materials. A short
time-duration pulse of only a few cycles is
known as a broadband pulse because its
frequency-domain eq ui valent bandw idth is large.
Such pulses exhibit good depth resolution.
,
~
D-
41.
(Eq. 2-3)
Th is point defines the end of the near field
and is the same expression as given in
Equation 1-9.
At distances well removed from the sound
source (the far field), the waves no longer
interfere with each other (since the di ffere nce in
travel path to the center and edge of the source
are much less than a wavelength) and the so und
field is reduced in strength in a monotonic
manner. In the fa r field, the beam is diverging
and has a sphericall y shaped wave front as if
radiating from a point source. The far field sound
field intensi ty decreases due to both the distance
fro m the source and the diffraction-based
direc ti vity (beam shape) factor. Maximum
pressure amplitudes exist along the beam
ce nterline. Figure 2.5 shows a graphi cal
representation of a typical di stance-amplitude
variation for a straight beam transducer.
The penetration, depth resolution, and
sensit ivity of an ultrasonic system are strongly
dependent upon the nature of the pulse emitted
by the transducer. High-freq uency,
short-duration pulses exhibit bener depth
Figure 2.5. Typical straight beam
DAC curve
Near F"icl!.f-!ar Field
i
y;
Metal Travel Distance
-----+
Most search units are constructed with a
backing material bonded to the rear face of the
transducer that provides strength and damping
for the transducer elemen t. This backing material
is usuall y an epoxy, preferentiall y fill ed with
tungsten or so me other hi gh-density powder that
increases the effective density of the epoxy to
somethi ng approaching that of the transducer
element. Thus the tungsten assists in matching
the acoustic impedance of the transducer (which
is usually relatively high) to the backing
material. When the backing is in intimate contact
with the transducer, the pulsc duration is
shortened to a few osc ill atio ns and decreased in
peak signal amplitude. The pulse energy is
therefore partitioned between the item being
tested and the backing material (which removes
the rearward-directed waves and absorbs them in
the eoarse·surfaced epoxy) .
Search unit s corne in many types and styles
depending upon their purpose. Most search units
use an L-wave-generati ng sound source.
"Normal"
or "straight" beam search units, the
,
colloquial names given to longitudinal wave
transducers when used in contact testing , are so
named because the sound beam is directed into
the material in a perpendicular (normal )
direction. These units generate longitudinal
waves in the material and are used for thickness
gaging and flaw detection of laminar-type flaws.
Both contact and immersion search units are
readil y available. To improve near-surface
resolu tion and to decrease noise, standoff
devices and dual crysta l uni ts may be used.
Transverse (shear) waves are introduced into
test material s by inclining the incident L-wave
beyond the first critical angle, yet short of the
second critical angle. In immersion testing. thi s
is done by changi ng the ang le of the search unit
manipulator. In the case of cylindrical products,
shear waves can be generated by offsetting the
transducer from the centerl ine of the pipe or
round bar being inspected. Fi gure 2.6 shows a
23
Figu re 2.6. Introduction of shear waves
through mode conversion
10·
.
-;;;
7-\1
,
Search Unit
Incident Beam
_ 45 Degree
Refracted Beam
~
typical testing configuration for solid round
material s. For the case of a 45-degree refracted
beam, a rule of thumb for the di splacement d is
116 the rod diameter.
In contact testing. the so-called angle-beam
search unit s cause the beam to proceed through
the material in a plane that is normal to the
surface and typically at angles of 45 , 60, and 70
degrees. Transverse waves are introduced by
pre-cut wedges which, when in contact with
metal s, generate shear waves through mode
conversion at the wedge- meta l interface. (Sec
Figu re 2.7).
Hi gh-freq uency (ultrasonic) sound waves
travel poorly in air and not at all in a vacuum. In
order fo r the mec hanical energy generated by a
transducer to be transmilled into the med ium to
be exam ined, a li quid that bridges the gap
between the tran sducer and the test piece is used
to coup le the acoustic wave to the item be ing
tested. T his liqu id is the "couplant" often
mentioned in UT. When immers ion testin o" is
being conducted, the part is immersed in water
which serves as the couplant. When contact
testing is be ing conducted, liquids with varying
viscos iti es are used in order to avoid unnecessary
runoff, particu larly with materia ls with very
rough contact surfaces or when testing overhead
or vertica ll y.
Liquids tran smit longitudinal sound waves
rather well. but because of their lack of any
signifi cant shear moduli (except fo r highly
viscous materials), they do not transmit shear
waves. s Couplants should wet the surfaces of
both the search uni t and the material under test in
order to exclude any air that might become
entrapped in the gap(s) between the transducer
and the test piece. Couplants must be inert to
both the test material and the search unit.
Contact couplants mu st have many desirab le
properties including: wetability (crystal, shoe,
and teSt material s), proper viscosity, low cost,
removability, noncorros ive and nontoxic
properties , low attenuation, and an acoustic
impedance that matches well with the other
materials. In se lect ing the couplant, the operator
must consider all or most of these factors
depending on the surface fini sh, type of material ,
tem penHure, surface orien tatio n, and avail abil ity.
Th e couplant shou ld be spread in a thin , uniform
film between the transducer and the material
under test. Rough surfaces and vertical or
ove rhead surfaces requi re a hi ghe r viscos ity
coup lantthan smooth , horizontal surfaces.
Materi als used in thi s application include vari oll s
grades and viscosities of oi l. g lycerin , paste
couplants using cellul ose gum (which tend to
evaporate leav ing litt le or no res id ue), and
vari ous mi sc ible mix tures of these materi als
using water as a th inn er.
Because stainless stee ls and other high-nickc l
alloys are susceptible to stress- re lated corrosion
crack ing in the prcsence of sulphur and chlorin e,
the use of couplants contai ning even trace
amounts of these material s is prohibi ted. Most
commercial coupl ant manufacturers provide
certificates of conform ance regarding absence of
these c lements, upon request.
In a few hi ghly spec ial ized appli cat ions, dry
couplants, such as a sheet of elastomer, have
been used. Bond ing the tran sducer to the test
item, usuall y in di stributed materials
characteri zatio n studies, is an accepted practice.
High pressure and intermittent co ntact without a
coupling medium, has also been used o n
' Because the acoustic impedance of ai r is so much different than
thai of the commonly used trJnsducers and test materials. its
presc~ce ~flects an obj~t ionable amount of acoustic energy OIl
coupl ~ng tn!crfa.ces. but LS the main reason ullrasonic testing is
effective with aLr-filled cr.acks and similar critical discontinuitics.
24
high-temperature steel ingots.
Although these approaches
have been reported in the
literature, they are not
commonly used in production
appl ications.
Figure 2.7. Contact shear wave transducer design
Angle Beam Wedge
Water is the most widely
used couplant for immersion
testing. It is inexpensive,
plentiful, and relatively inert
to the material s involved. It is
so metimes necessary to add
wetting agents, antirust
additives and antifouling
agents to the water to prevent
corrosion, ensure absence of air bubbles on test
part surfaces, and avoid the growth of bacteria
and algae. Bubbles are removed from both the
transducer face and the material under
exam ination by regular wiping of these surfaces
or by water jet.
In immersion testing, the sou nd beam can be
focused using plano-concave lenses, producing a
higher, more concentrated beam that results in
better lateral (spatial) resolution in the vicinity of
the focal zone. Thi s focusing moves the last peak
of the near field closer to the transducer than that
found with a flm transducer. Lenses may be
formed from epoxy or other plastic materials,
e.g., polystyrene. The focal length is detennined
using Equation 2-4.
(I1-J)
R = F--
(Eq.2-4)
11
where
R is the len s radius of curvature,
F is the focal length in water,
1/
is the ratio of the acoustic L-wave
velocities,
/I = V/V where
1
VI is the longitudinal velocity in epoxy,
V2 is the velocity in water.
For example, to get a focal length of 2.5 in.
using a plexiglass lens and water, the radius of
curvature equation uses a velocity ratio of
n = 1.84 and the equation becomes
R = 2.5 (0.84/1.84) = 1.14 in.
L
s
Focusing has three principal advantages.
First, the energy at the focal point is increased,
which increases the sensitivity or signal
amplitude. Second, sensit ivity to reflectors above
and below the focal point is decreased, which
reduces the ';noise." Third, the lateral resolution
is increased because the focal point is normally
quite small, permitting increased definition of
the size and shape of the reflector.
Focusing is useful in applications such as the
examination of a bondline between two
materials, e.g., a compos ite material bonded to
an aluminum frame. When examined from the
composite side, there are many echoes from
within {he composite which interfere with the
desired interface signal; however, focusing at the
bondline reduces the interference and increases
system sensitivity and resolution at the bond line
depth.
Where a shape other than a si mple round or
square transducer is needed, particularly for
larger-area sound field sources, transducer
elements can be assembled into mosaics and
exc ited either as a si ngle unit or in special timing
sequences. Mosaic assemblies may be linear,
circular, or any combination of these geometries.
With properly timed sequences of exciting
pulses, these units can function as a linear array
(w ith steerable beam angles) or as transducers
with a vari able focus capabi lity. Paint brush
transducers are usually a single element
search-unit with a large length-to-width ratio and
are used to sweep across large segments of
material in a single pass. The sound beam is
25
broad and the lateral resol ution and flaw
sensi tivity is not as good as smaller transducers.
Special Equipment Features
The basic e lectronic pulser/receiver di splay
units arc augmented with spec ial features
intended to ass ist operators in easing the burden
of maintaining a hi gh leve l of alertness during
the often unin teresting process of conduct ing
routine inspections, particularly of regular
shapes during origi nal manufacture, as well as
obtain ing some type of permanent record of the
results of the ins pect ion.
A SCl:m information represents the material
cond ition through whi ch the sound beam is
passing. The fundamental A Scan display,
although hi ghl y informative regarding material
homogeneity, does not yield infonnation
regarding the spatial distribution of ultrasonic
wave reflectors until it is connected with
scanning mechanisms that can suppl y the
physical locat ion of the transducer in
conjunct ion with the reflector data obtained with
the A Scan unit.
When cross-sect iona l information is recorded
lI sing a rectilinear B Scan system, it is the time
of arrival of a pu lse (vertical direction) ploued as
a fun ction of the transducer position (horizontal
di rection) that is di splayed. Circu lar objects are
often displayed using a curvili near coordinate
system whi ch displays time of pulse arrival in
the radial direction (measured from the
transducer) and wi th transducer location
fo llow ing the surface contour of the test objecl.
When pl an views of objects are needed, the
C Scan system is used and is partic ul arl y
effective for flat materials includi ng honeycomb
panels, rolled products, and adhesively bonded
or lami nated composites. The C Scan is
developed usin g a raster scan pattern (X versus
Y) over the test part surface. The presence of
questionable conditi ons is detected by gat ing
signals fallin g withi n the thick ness of the part (or
moni tori ng loss of transmi ss ion) as a function of
location. C Sca nning systems usc either storage
oscilloscopes or other recording devices, coupled
to au tomati c scanning systems which represent a
" plan ," i. e., map. view of the part, similar to the
view produced in radiography. Figure 2.8 shows
examp les of these display options.
Accumulation of data for display in the form
of B or C Scans is extracted lI sing electronic
"gates." Gates are circu its which ex tract time
and amplitude information of selected signals on
the A Scan presentati on and feed these as analog
data to other signal process ing or displ ay circu it s
or devices. The start time and durat ion of the
gate are operator se lectable. CRT representations
of the gate are raised or depressed baseli nes, a
horizont al bar, or two vertica lli ncs. Availab le
Figure 2.8. Comparison of common display modes
/
Front Surface
.....-- Lamination
A Scan
B Scan
LJL....Jf\:...~== Back Surface
Top of Plate
Bottom of Plate
II
C Scan
26
with adjustable thresholds, gates can
be set to record signals whic h either
exceed or drop be low spec ified
threshold seuings.
Details of rece ived signals can be
seen and/or disregarded through use
of the RF di spl ay and the Reject
controls, respect ive ly. The RF display
shown in Figure 2.9 is representative
of the actual ultrasonic stress pul ses
received. In thi s mode, the first
oscill atio n (downward at 17 ~ s)
shows the nature of the pul se
(compress ion or rarefacti on) when
rece ived. Note the in version of the
shapeofth e pulseaI19,2 1, ... ,
microseco nds du e to phase inversion
caused by reflectio n from a "free"
boundary . This phase reversal can be
llsed to disc riminate between " hard"
boundaries (hi gh impedance) and "soft"
boundaries (low impedance such as air).
Figure 2.9. RF display showing phase reversal
upon reflection
I
~
"0 _
=
~
;:.:::
0
Q.~
f-
E~
<
II
II
r
I
-I
16
18
20
22
24
Time
(Microseconds)
The reject control, o n the other hand, tends
to discri minate agai nst low-leve l signals,
th rough use of a threshold , below which no
information is made avail able to the operator.
Earl y vers ions of the reject circuitry tended to
alter the verti cal linearity of UT systems;
however, thi s condition has been corrected in
several of the newer digital fl aw detector
in struments .
27
26
Chapter 2 Review Questions
Q.2- 1 Barium titanate is a piezoelectric
materi al which:
Q.2-5 A 5 MHz, 0.5 in. diameter, flat search unit
in water has a ncar field length of
approximately:
A. occurs naturally.
B. is piezoe lectric al temperatures
A. 7 in.
B. 2 in.
above the critical temperature.
C. has a high acoustic impedance.
D. is highly soluble in water.
Q.2-2 Du ri ng an immersion test, numerous
bubbles are noted in the water attached
to the test item. These bubbles are small
relati ve to the part size. What steps
should the operator take?
c.
D.
3-1/3 in.
5-1/2 in.
Q.2-6 A concave lens on a transducer will result in
the near field in water being:
A. twice as long as with a flat lens.
B. three limes as long as with a fl at lens.
C. the same length as with a flat lens.
D. shol1er than with a fl at lens.
A. Remove the bubbles by blowi ng
them off with an air hose.
B. Ig nore the bubbles because they are
small and wi ll not interfere with the
test.
C. Remove the bubb les, with brush or
other mechan ical means such as
rubbing with the hand while the test
is stopped .
D. Count the bubbles and mark thei r
echoes on the test record.
Q.2-3 A couplant is needed for a test on a hot
steel plate (250 ' F). Whieh of the
follow ing materials can be used?
Q.2-7 A 10 MHz, 0.5 in. d iameter search unit is
placed on steel and acrylic plastic in
succession. The beam spread in these two
materi als is approx imately:
A. 3 and 1.5 degrees, respect ively.
B. 1.5 and 3 degrees, respectively.
C. equal in the (Wo materials.
D. less than the beam spread of a 15 MH z
search un it of the same diameter.
Q.2-8 Focused transducers are useful because the:
A. smaller beam diameter increases the
A. water
B . mercury
c. tractor o il
D. none of the above
Q.2-4 A couplant is needed for a test on
stainless steel welds. Numerous
couplants are availab le. Which should
be chosen and why?
A. a couplant free of ch lorine because
thi s element corrodes stainl ess steel
number of scans required to examine an
object.
B. lateral resol uti on is improved.
C. lateral reso lution is unimportant.
D. focal po int is located beyond the end of
the near field length of a similar,
unfocused transducer.
Q.2-9 In spite of the fact that a long pul se has
bener depth penetration than a short pulse,
the use o f a lo ng pul se is not recommended
because:
B. glycerin because it is no nflammable
A. the long ringing may interfere with
C. oil because it is easily removed
D. water because stainless steel does
not corrode in water
nearby pu lses.
B. the shorter pulse will provide beller
penetration.
C. a long pu lse contains less energy than a
shorter pulse.
D. a long pulse is recommended .
29
Q.2. 10 Backing material on a transducer is used
to:
A. damp the pulse and absorb the sound
from the back of the transducer.
B. decrease the thickness oscillations.
e. increase the radial mode osci ll ations.
D. increase the power of the transmiued
pulse.
Q.2· l l Ang le beam search units are used to:
A. inspect bUll joint welds in thick·wall
steel piping.
B. produce shear waves through mode
conversion.
e. examine material vo lumes
inaccessib le to nonnal beams.
D. all of the above.
Q.2.14In Figure 2.6 and using the conditions of
Q.2-13, what is the offset distance
needed for a 45-degree refracted
longitudinal wave to be generated?
A. 0.395 in.
S. 0.450em
C. 0.505 in.
D. 1.026cm
Q.2-15 It is desired to detect flaws 1/4 in. or less
from the entry surface using angle beam
shear waves. The search unit must be
selected with the choice between a
narrow band and a broadband unit.
Which should be chosen and why?
A. The narrow band unit because it
examines on ly a narrow band of the
material.
B. The broadband unit because the entire
volume is exam ined with a long
pulse.
e. The broadband unit because the near
surface resolution is better.
D. The broadband unit because the
lateral resoluti on is excellent.
Q.2· 12 An angle beam transducer produces a
45-degree shear wave in steel. What is
the approximate inciden t angle? (velocity
in steel = 0.125 in.lms, veloc ity in plastic
: 0.105 in.!m,)
A. 54.9 degrees
B. 19 degrees
C. 36.4 degrees
D. 45 degrees
Q.2-13 In Figure 2.6, the aluminum rod being
examined is 6 in. in diameter. What is the
offset di stance needed for a 45-degree
refracted shear wave to be ge nerated?
[L-wave veloc ity in aluminum =
6.3 ( 10)5 cm/s, T -wave velocity in
aluminum = 3. 1 ( I O)Scmls,
velocity in water = 1.5 (lO)s cm/s]
A. 0.513 em
B. 1.026 in.
C. 2.052 in.
D. 1.505 em
Q.2-16 In a longitud in al-wave immersion test o f
commercially pure titanium plate
(V, : 6.1 ( 10)' COlis, VT :
3.12 ( 10)5 cm/s). an echo pulse from an
internal defect is observed 6.56 Il s
fo llow ing the front surface echo. How
deep is the renector below the front
surface?
A. 2cm
B. 4cm
e. I em
D. 2in.
Q.2-17 A change in echo amplitude from
20 percent of full screen height (FSH) to
40 percent FSH is a change of:
A.
S.
C.
D.
30
20dS.
6dS.
14dB.
50 percent in signal ampli tude.
Q. 2-18 In Figure 2.10. what is the rate of
attenuation, expressed in dBlin .. of the
5 MHz transducer as observed in the far
field? The horizontal scale is 0.5 in. per
divi sion and the vel'lieal scale is linear.
A. 1.00 dB/in.
B. 2.22 dB/in.
C. 2.55 dB/in.
D. 3.25 dBlin.
Q. 2-l9 In Figure 2.10. what is the rate of
attenuation of the 2.25 MHz transducer
using the condition s of Q.2-18?
A. 2.0 dB/in .
B. 3.5 dB/in .
C. 4.0 dB/in.
D. 8.0 dB/in.
Q.2-22 A change of 16 dB o n the attenuator
corresponds to an amplitude rat io o f:
A. 6.3: I.
B. 5.2: I.
C. 7.4: I.
D. 9.5: I.
Q.2-23 When checked again st a previous
calibration level. a search unit which is
classified as highly damped is
considerably more sensit ive. A check of
the RF waveform shows that the unit
rings for at least three times the nu mber
of cycles previous ly achieved. What
condi tion mi ght explain this phenomena?
A. The search unit has been dropped and
the facing material has been cracked.
B. The backing material has separated
from the crystal , thu s decreasi ng the
mechanica l damping.
C. The housing has separated from the
transducer and thinks it is a bell.
D. The coax connector is fill ed with
water.
Q.2-20 What lens radiu s of curvature is needed
in order to havc a 2 cm diameter, 5 MH z
tran sducer focus in watcr at a distance of
4 em from the lens face? [V1/10 =
1.49 ( 10)' CIll/S, V,,", = 2.67 ( 10)' CIll/S I
A. 1.77 em
B. 3.50cm
C. 3. 17 in.
D. 2.23 in.
Q.2-24 The sound beam emanating from a
continuous wave sound source has two
zones. These are called the:
0.2-21 Two signa lS were compared in amplitude
to each other. The second was found to
be 14 dB less than the first. This change
cou ld have represented a change of:
A. Fresnel and Fraunhofer zones.
B. Fresnel and near fie ld s.
e. Frau nh ofer and far fields.
D. focused and unfocused zones.
A 70 percent FSH to 14 percen t FSH.
B. 100 percent FSH to
50 percent FSH.
e. 20 percent FS H to
100 percent FS H.
D. 100 percent FS H to
25 percent FS H.
.•,
"0-e
Figure 2.10. Distance-amplitude response of two 3/4 in.
diameter search units
5 MHz
3
".:•• 2
d
-' 1
c
0
'~"• 0
2.25 MHz
Metal Travel Dista n ce
31
Chapter 3
Common Practices
Chapter 3
Common Practices
Approaches to Testing
Most ultrasonic in spection is done using the
pul se· echo technique wherein an acoustic puise,
reneeted from a loca l change in acoustic
impedance, is detected by the original sending
sound source. Rece ived signal s indicate the
presence of di scontinuities (i nternal or external)
and their di stances from the pulse-echo
transducer, which are directly proportionailO the
time of echo-pul se arri val. For this situation.
access to only onc side o f the test item is needed ,
which is a tremendous advantage over
throu gh-transmi ssion in man y applications. For
maximum detection reliability, the sound wave
~ hould encounter a rc n cctor at normal incidence
to its major surface.
If the receivi ng transducer is separated from
the se nding transducer, the configuration is
called a pitch-catch. The int.erpretation o f
discont inuity locati on is determined us ing
triangulation techniques. When the rcceive r is
positioned alo ng the propagatio n axis and across
from the transmitter, the technique is call ed the
through -tran smi ss ion approach to ultrasoni c
testing. Figure 3. 1 shows these three modes of
pul se-echo testing with Iypica l inspection
appl ications.
[n the through-transmission techn.ique. the
sound beam travels through the test item and is
rece ived on the side oppos ite from the
transmitter. Two transducers. a transmitter and a
rece iver, are necessary. The time represented on
the screen is indi cat ive of a single traverse
through the material , wi th coupling and
ali gnment bein g critica l to the technique's
success ful application.
[n some two-transducer pitch-catch
techniques, both transducers are located on the
same side of the materi al. The time between
pulses corresponds to a sin gle tra verse of the
Figure 3.1. Pulse-echo inspection configurations
Pitch-catch
Pulse-echo
l1a
!.&
~ (WeldRoot)
(Plate)
Through-transmission
Delta
R
r---T
(Honeycomb)
(Weld Porosity)
R
35
sound fro m the transm itter to the reflector and
then to the receiver. One approach uses a
"tandem" pitch-catch arrangement, usuall y for
the centra l region of thi ck materials. In this
technique, the transmitter sends an angle beam to
the midwall area of the materi al (often a double
V we ld root) and deflections from vert ical pl anar
surfaces are rece ived by one or more transducers
located behind the transminer. Another
pitch-catch tech niq ue, fou nd in immersion
testing, uses a focused receiver and a
broad-beam transm itter, arranged in the shape of
a triangle (delta technique). This technique rel ies
on reradiated sound waves (mode conve rsion of
shear energy to long itudinal energy) from
internal reflectors, with background noise
reduction through use of the focused receiver.
When sound is introduced into the materi al at
an angle to the surface, angle beam testing is
being done. When thi s angle is red uced to
odegrees, it is called "straight" or "normal"
beam exami nation and is used extensively on
plate or other flat materi al. Laminations in plate
are readily detected and sized with the srraight
beam technique. Although it is poss ible to
transmi t shear waves "st raight " into materi als,
longitudinal waves are by far the most common
wave mode used in these appli cations.
Sou nd bea ms can be refracted at the
interfaces of two diss im ilar med ia. The angles
can range fro m just greater than 0 degrees to
90 degrees (correspo nding to thei r li mit ing
critical incident angle conditi on) if the second
medium has the hi gher acoustic wave veloci ty.
Shear wave angle beams are usua ll y greater than
20 degrees (in order to avoid the presence of
more than one mode being present withi n the
material at the same time) and less than
80 degrees (in order to avoid the spurious
generation of surface waves).
Angle beams (both shear and longitudinal)
arc often used in the exami nation of welds since
cri tica l flaws such as cracks, lack of fu sion,
inadequate penetration. and slag have
dimensions in the throughwa ll direction. Angle
beams are used because they can achieve
c1ose-to-normal incide nce for these reflectors
with gene rall y vertical surfaces. Other types of
structures and configurations are exami ned using
angle beams, partic ul arly where access by
straight beams is unsati sfactory, e.g., irregul arl y
shaped forg ings, castings, and assemblies.
Surface (Rayleigh) waves are not as common
as the long itudinal and shear waves , but are used
to great advantage in a li mited number of
applications that requi re an abi li ty of the wave to
follow the contours of irregul arly shaped
surfaces such as jet engine blades and vanes.
Ray leigh waves extend from the surface to a
depth of about one wavelength into the material
and thus are onl y sensitive to surface or very
ncar-surface fl aws . They are very sensit ive to
surface condi tions including the presence of
res idual coupling compound s as well as fi nger
dampi ng. Ray leigh waves are usually generated
by mode conversion using angle beam search
un its des igned to produce shear waves j ust
beyond the second critical angle.
Two major modes of coupling ultrasound
into test parts are used in UT: contact and
immersion. The manuaJ contact technique is the
most common fo r large items whi ch are diffic ult
to handle. e.g., plate materi als, structures, and
pressure vessels. Both straigh t and angle beams
are used. Coupl ing for the manual contact
technique requires a medium wi th a hi gher
viscosity than that of water and less than that of
heavy greases. In mechanized (automated)
test ing, the coupl ant is often waler that is made
to now between the transducer and the test pi ece.
During manua l tests. the operator provides the
couplant repetiti vely during the examination.
Manual contact testi ng is very versatile si nce
search units are easily exchanged as the needs
arise, and a high degree of flex ibi li ty ex ists for
angul at ion and changes in directi ons of
inspection. Test items of many different
confi gurations can be examined with little
difficulty. One of the prime advantages of
contact testing is its portability. UT instrument s
of briefcase size and weighing less than 20 Ibs
are readily avai labl e. With this type of
instrumen t and contact tec hniques, UT is
performed almost anywhere the inspector can go.
Ski ll ed operators can make evaluations on the
spot and with a high degree of re li abi lity.
Immersion testi ng uses a column of liquid as
an intermediate med ium for conducti ng sound
36
"'a\'es 10 and from test parts, Immersion testi ng
can be performed with the test item immersed in
\\ater (or some other appropriate liquid) or
throug h use of vari ous devices (bubblers and
squi l1ers) that mainlain a continuo us watcr path
betwee n the Iransducer(s) and the test item. Most
examinations are conducted using automatic
scanning systems. The immersion technique has
many ad vantages . Many sizes, shapes and styles
of searc h units are availab le including flat ,
foc used, round, rectangular. paintbrush, and
arrays , Automated examin ation is easi ly
accom modate. Surface fin ish is less troubleso me
si nce transducer wear doe s not take place.
Various size and shape objects may be tested.
Scann ing can be faster and more thorough than
manual scanning. Recordin g o f pos ition and fl aw
data is straight forward . Data prec ision is hi gher
si nce hi gher freq uency (and more fragile)
transdu cers can be used.
Di sad vantages include long setup time,
maintenance of coupling liquids. preset scan!
artic ul ation plans reduce usc of spontaneous
posi tionin g, high signal loss al test part-water
in te rface, hi ghly critical positi oning/angulation
problems. and system align ment in gene ral.
Of all the adv:,ulI ages, perhaps the most
important is thc ability to use different search unit
sizes and shapes in an automat ic inspection mode.
Beam focus ing is commonly used to improve
spat ial resolution and increase sensitivity;
however, scan times increase dramatically.
Automated testing has man y advantages,
incl uding increased sca nning speed. reduced
operator dependence. and adaptability to imag ing
and signal processi ng equi pment.
Immersion tank s may be long and narrow (for
pipe and tubing in spection) or short and deep (for
bulky forgi ngs), In general, tanks are equ ipped
with a mean s for filling. drain ing, and fi lteri ng the
water. The tank may contain test item
manipulators (for spinning pipe and rotating
samples) and a scanning bridge system (for
translat ing search units along rectilinear and/or
polar coord inates). Tan k capacities range from
one or two cubic feet to a few thousand cubi e feet.
Most tanks are equ ipped wit h one or more
scanning bridgcs whi ch trave l on tracks the length
of the tank and are under the control of the
operator or an automatic test sy ste m. The bridge
across the tank contains rails on which the search
Figure 3.2. Typical immersion ultrasonic scanning system
37
unit manipulator rides. Other equipment carried
on the bridge may incl ude the ultrasoni c
instrument, a C Scan or other recorder, and
signal processing equipment needed to ex tract
information from the ultrasonic signals.
Figure 3.2 shows an example of a typical tank
configuration used for inspect ion of smaller
items.
of water at the test pi ece. The search unit,
located inside and coaxially with the nozzle,
emits a sound beam axially through the stream.
Figure 3.3 shows a conceptual draw ing of an
ultrasonic water jet (sq uirter).
If the nozzle is designed properl y and the
water flo w parameters are set correct ly, there are
no bubbl es at the interface of the water and the
test piece and sound can be transmitted into the
piece. The sound beam impinging on a test part
is restricted in cross-secti onal size by the stream
of water which acts as a wavegu ide and
collimator. Both the squi rter and the bubbler
(water co lumn) can be used wi th pulse-echo or
lhrough· transmi ss ion techniques and can take
advantage of beam foc using. If the free slream of
the squ irter is long, the deflection due to gmv ity
may have to be considered in the scanning plan.
In scanning flat test objects with a
longitudinal beam, the search unit manipulator
traverses the test item in a raster· like pattern
(tra verse-i ndex·traverse-index· ...· ... ). The
recorder, "enabled" using the gating circuits,
records the data in sy nchroni sm with the position
of the search uni t manipulator.
There are several types of manipulators used
for handling test parts. These manipulators shi ft
or rotate the test item under the bridge in such a
manner that the search unit may scan the
requ ired speci men surface. Rotational axes may
be hori zontal, vertical , or other desired angles.
Manipulator mot ion may be under the control of
the operator or the automatic system. Control
centers may be programmed to perform very
basic scan patterns or, in the case of some
computer·based systems, very complex
operations. Most scans are preprogrammed and
thus are not changed readily .
It is often desirable to keep a test item
relat ively dry wh ile performing ultrasonic
examinations. One way of doing thi s and yet
maintain many of the advantages of immersion
testing is to use wheel transducers. The wheels
used for UT testing are sim ilar to automOli ve
tires in that they are largely hollow and there is a
fl ex ibl e "tread" in contact with the test item. In
the UT wheel, the search unit is mounted on a
gimbal manipulator inside the tire and the tire is
filled with a liqu id - usually water. The search
unit is aimed through the tread (a thin
elastomeric me mbrane such as polyurethane).
The gimbal mounting permits the incident sound
It is imperative that the search unit be in the
des ired posi tion at all times so that the sound
beam is in terrogating the intended test area. Thi s
is accompli shed by a positioner attached to the
end of the search tube used to "point" the search
unit in the desired direct ion. Thus the search unit
has several degrees of positi onal freedom (X, Y,
Z, 8, $).
Figure 3.3. Diagram of a water jet for
ultrasonic tests
It is not always feasible to immerse a test
object in a tank for UT testing. Limits are
imposed by the size and shape of the test object
as well as by the capaci ty of the tank . To
circumvent these problems, scan ning systems are
often provided with squirters or water columns.
While differing sli ghtl y in design, each of these
serves the same purpose - to establish a column
of water between the search unit and the test
item through wh ich the sound beam will pass.
Squirters employ a nozzle which squirts a stream
38
To Ultrasonic instrument
1
(
•
•
Transducer
Water Couplant
•
beam to be orien ted so that it produces either
shear or longitudinal waves (or other modes) in
the test part as if immers ion testing were taking
place.
Because the tire is flexible and conforms to
the surface, littl e external cou pl ant is needed. At
times, howe ver, a sma ll spray of water or alcohol
is introduced just ahead of the wheel to exclude
the possibili ty of small amounts of air becom ing
trapped at the wheel' S contact surface. Th is thin
layer of liquid evaporates rapidly without
damage to the test item. Although wheels are
somewhat limited as to the shapes of materia ls
they can ex amine, th ey are useful on large,
reasonably nat surfaces. More than one whee l
can be used at the same time , e.g., tandem
configurati ons are poss ible. They are useful in
hi gh temperature app lications (where the liquid
is continuously coo led) and sets of transducers
can be placed wi th in a sing le wheel. A major
problem is the elim inat ion of internal echoes
from structural members within the liquid
chamber. These echo problems are usually
eliminated by careful design incorporating the
empirical placement of baffles and absorbers.
Tn both manu al and automatic scanning , the
pattern of scanning is important. If too many
scan traverses are made the part will be
overtested, with time and money be ing lost. On
the other hand, if the coverage of the scans is
insuflic ienL, sections of the part wi ll not be
examined and defec ts may be missed. Therefore,
time dedicated to developi ng a scanning plan is
seldom wasted. In developing the plan, whi ch
lays out the patterns of search unit manipu lation,
it is necessary to cons ider appUcable codes,
smndards, and specifi cations as we ll as making
an engineering evaluation of the potenti al
locations, orientations. sizes, and types of flaws
expected in the part. After these criteri a have
been deve loped, sound beam modes, angles,
beam spread, and attenuation must all be
considered to ensure that all of the material is
interrogated in the desired direction(s). Thi s
in formation is used to establish scan lengths.
di rect ion, overlap. index increments, and
electronic gate seuings.
Measuring System
Performance
UT calibrat ion is the practi ce of adj usting the
ga in , sweep, and range, and of assessing the
impact that other parameters of the instrument
and the test confi guration may have on the
re li able interpretation of ultrasonic signal
echoes. Gain seuings are normally established by
adj usting the vertical height of an echo signal, as
seen on the CRT, to a predetermined leve l. The
level may be required by spec ification and based
on echo respon ses from specific standard
rc nectors in material similar 10 that which will
be tested. Sweep di stance of the CRT is
estab li shed in terms of eq ui va lent "sound path."
where the sound path is the di stance in the
material to be tested from the sound entry point
to the reflector.
It is important to establ ish these parameters.
Gain is establi shed so that comparisons of the
reference level can be Illade to an echo of
interest in order to dec ide whether the echo is of
any consequence and. if so, then to aid in the
determination of the size of the reflector.1i Sweep
distance is establi shed so that the location of the
re Oector can be detenn ined.
Hori zontal lineari ty is a measure of the
uniformity of the sweep speed of the instrument.
The in strument must be wi thin the linear
dynami c ranges of the sweep ampl ifiers and
assoc iated c ircuitry in order for e lectron beam
position to be directly pro portional to the time
elapsed fro m the start of the sweep. It may be
checked using multiple back·echoes from a flat
plate of a conve nient thickness, i.e., I in. With
the sweep set to display mult iple back-echoes.
the spacing between pul ses should be equal. The
instrument should be recali brated if the sweep
linearity is not wi thin the specified tolerance.
Yerticallinearity impli es thallhe height of the
pulse displayed on the A Scan is directly
proportional to the acoustic pul se rece ived by the
transducer. For example, if the ec ho increases b)
~It
is important to recognize that the use of amplitude to ~ize a
reflector is subject to large. uncontrolled errors and must b<
approached with caution.
39
50 percen t, the indicated ampl.itude on the CRT
should also change by 50 percent. Thi s variable
may be checked by establi sh ing an echo signal
on the screen , changing the vertical amplifier
gain in set increments, and measuring the
correspo nding changes in A Scan response. An
alternate check uses a pair of echoes with
amplitudes in the ratio of 2: I . Changes in gain
should not affect the 2: 1 ratio, regardless of the
amplifier" s senings.
It is of note that when electronic DAC units
are used in an ultrasonic system, the vertical
amplifier's displayed output is purposefully
made to be nonlinear. The nature of the
nonlinearity is adj usted to compensate for the
estimated (or measured) variat ion in the test
material/inspect ion system's aggregate decay in
signal strength as a funct ion of di stance (time)
from the sending transducer.
Reference Reflectors
There arc severa l reflector types commonly
used as a basis for establi sh ing syste m
performance and sensit ivity. Included among
them are spheres and flat-bollom holes (FBH),
notches, side-drilled holes (SDH), and other
spec ial purpose or designs. Table 3.1
summari zes these reflectors and their advantages
and limitat ions.
Figure 3.4. Spherical reflector measuring
sound field
3
,
,
"1
Focal Point
v"'·'----- Focused Search Unit
omn idirectional sound wave response. The
effecti ve refl ectance from a sphere is much
sma ller than that received from a nat reflector of
the same diameter due to it s sphcricaJ directivity
pattern. Most of the reflected energy does not
return to the search unit. Spheres of any material
can be used; however, steel ball bearings are the
norm si nce these are reasonably priced,
extremely precise as to size and surface finis h,
and available in many sizes.
Flat renectors are used as cal ibration
standards in both immersion and contact testing.
They are usually flat-bottom drilled holes of the
des ired diameters and depthS. All flat renectors
have the inherent weakness that they requi re
Spherical reflectors are used most oflen in
immersion testi ng for assessing transducer sound careful sound beam-renector axis al ignment.
Deviation s of little more than a few degrees will
fields as shown in Figure 3.4. Spheres provide
lead to sign ificant ly reduced echoes and become
excellen t repeatability because of their
unacceptable for
calibration. However,
Table 3.1. Reference Reflectors Used in Ultrasonic Testing
for flaws of crosssec tion less than the
Type
Characteristics
Uses
beam width and wi th
a perpendicular
Solid Sphere
Omnidirectional
Transducer sound field
ali gnment, the signal
assessment
amplitude is
Simulates ncar-surface cracks
Notches
Flat, corner
proponional to the
area of the refl ector
Flat-Bottom Hole (FBH) Disc reflector
Reference gain
as shown in Figure
3.5. Generally, if a
Side-Drilled Hole (SOH)
Cylindrical symmetry Distance DAC calibration
flaw echo am plitude
is equal to the
Special
Custom reflectivity
Simulate natural flaw conditions
amplitude of the
40
longitudinal waves and a mult itude of
shear wave angles. It is essential that the
hole surface be smooth, thus reami ng to
the final diameter is often the fi nal step
in preparing such holes.
Figure 3.5. Area-amplitude relationship for
FBHs
100
~
90
>?
80
-
~
.c
OIl
"<)
:t
..
#8
70
1/
60
6
SO
jo'"
40
"= 30
20
ii5
10
4
•
os V
Point of
"1/
.#2
0;:)10
20
S~.~d~r~iz~ti,on,
30
4 0 ; :. ) 0 6 0 7 0
Area Units
calibration re nector, it is assumed that the naw
is at least as large as the calibration reflector.
Used in sets with differing di stances
from the surface and different diameters,
side-drilled holes are freq uent ly used for
developing dista nce-ampl itude
correction curves and for setting overall
sensiti vity of shear wave test in g
schemes. After the sweep cii stance is set.
signal s from each reflector are
80
maximi zed (by maneuvering the search
unit) and the resu lts are recorded on the
screen using erasab le markers or stored
in a di gital fo rmat. The peak signals from each
renector are then connected by a smooth line and
it is thi s line that is called the di stance-amplitude
correction (DAC) curve.
Notches are frequentl y used to assess the
detectabilit.y of surface-breaking flaws such as
cracks, as well as for instrument calibration.
NOiches of several shapes arc used and can
eit her be of a rectangular or " Vee" cross section.
Notches may be made wi th milling cutters (end
mills), circular saws, or straight saw s. End-mill
(or EDM) notches may be made with highl y
variable length and depth dimensions. Circular
saw cut s are limited in length and depth by the
saw diameter and the configuration of the
device hold ing the saw. Even though it is
somewhat more difficult to achi eve a desired
length to depth ratio with the ci rcular saw, these
notches are used frequently because of their
resemblance to fatigue cracks, e.g., shape and
surface finish. Notches may be produced
perpencii cular to the surface or at other angles as
dictated by the test configuration. On piping,
they may be located on the inside diameter and!
or the olltside diameter and aligned e ither in the
longitudin al or transverse directions.
Calibration
The setting of basic in strument con trols is
ex pedited by the use of several standard sets of
blocks containing precision reflectors arranged to
feature a specific characteri st ic of the in spection
systems. For example, area-amplitude blocks
contain flat-bottom holes of differing diameters,
all at the same di stance from the sound entry
surface. The block material is normally sim ilar to
that of the tcst material. In the distance and area
amplitude blocks, a hole is placed in a separate
cylinder, 2 in. in di ameter. Other blocks, intended
for the same purpose of establi shing the
correlation of signal amplitude with the area of
the reflector, may contain a number of hol es in
the same block, usually a plate. Hole sizes
increase in sixty-fourths of an inch and are
designated by that value. For exampl e, a III 6 in.
(4/64 in. ) hol e is a #4 hole. Area ampli tude
blocks are used to establish the area/amplitude
response curve and the sensitivity of the UT
system. Maximum signals are obtained from each
of the holes of interest and the signal amplitude is
recorded. These values may be compared to
ec hoes from the same metal path and reflector
sizes estimated for the test item. Figure 3.6 shows
a cross-sectional diagram of a block composed of
Side-drilled holes are placed in calibration
blocks so that the axi s of the hole is parallel to
the entry surface. The sound beam impinges on
the hole, normal to its major axis. Such a
reflector provides very repeatable calibrati ons,
may be placed at any desired di stance from (he
entry surface and may be used for both
41
di stance. Distance-amplitude
blocks are useful in setting
instrument sensitivity (gain) and
if present the electronic distanceamplitude correction circuits.
Figure 3.7 shows a composite set
of DAC and area-amplitude
calibration curves taken from a
block containing three different
hole sizes (I mm, 2 mm and
3.25 mm), measured al distances
ranging from 2.5 mm to 32 mm.
Figure 3.6. Schematic diagram of FBH calibration
block
Entry Surrace
~
r
----+-:]43iln40~.~.li\O\~~
Mat.dal Alloy
",;;;::,j::::::::?~<~l~l
Hole Size x 1164 in.)
(Diameter
Metal Distance
(1.5 in.)
There are numerous blocks
corrunerciaJly avai lable that are
Plug
used in calibrati ng UT
L~~~~~~~~~~~~~--':':':::~~~~~
. ~~~_
instruments, both for sweep
4340 steel, w ith a FBH size of 5/64 in. (#5 hole) distance (sound path) and for sensitivity (gain) as
and a travel distance of 1.5 in.
well as depth resolution. Included in thi s group
are the ~IW (International Institute of Welding),
DSC (distance and sensitivity calibration), DC
Distance-amplitude blocks differ from
(di~tanc.e calibration block), SC (sensitivity
area-amplitude blocks in that a sin oole diameter•
cahbratlOn block), and the A WS RC (Resolution
0al-bOl.tom hole is placed at incrementally
Calibration Block).
mcreasmg depths from very near the entry
surface to a desired maximum depth. Sets of
Other special blocks are often required in
blocks are avajlable in different materials and
response to specification and Code requirements
with diameters ranging from Number 1 to
based on the construction of the blocks, using
Number 16 and larger. Distance-amplitude
materials of the same nature as those to be
blocks arc used to establish the distance/
inspected.
Included are the ASME weld
amplitude response characteri stic of the UT
inspection blocks such as the SDH for angle
system in the test material; the measured
beam calibration , curved blocks for pipin g!
response includes the effects of attenuation due
nozzles simulation, and nozzle dropouts (c ircular
to beam spread and scattering and/or absorption.
blanks cut from vesse l plates) for custom nuclear
With this curve establi shed, the operator can
in-service inspection applications. Finally,
compensate for the effects of attenuation with
Flat Bottom
Test Hole
Figure 3.7. Combined distance and area-amplitude response.
0
-"
c
•
,.
"
l.~
-
LEGEND
E
X
•
....
E '.0o.,
.5
,
o.
• '6
'(.,'\.'\,\>'
'0
'0'0 '0'0 'q
'q
'~~!:'~~~
~
'0
.~
I:.f.
-;..
"9
Distance from Block Face to Hole
millimeters (inches)
42
~
-;..
.~
2 mm hole
3.25 mm hole
1 mm hole
attempts are ongoing to develop schemes for
making reflectors which directl y behave as
racks and to ge nerate actual cracks.
panicu larly in tergranular stress corrosion
crac ks. Table 3.2 summari zes many of these
blocks and their intended uses.
One o f the best known calibration blocks is
the IIW b loc k shown in Fi gure 3.8. Thi s block
I:> used primarily for measuring the refracted
ang le of ang le beam search units, setting thc
meta l path , and establi shin g the sensitivity for
\~e ld in specti on. To measure the refracted
angle. the sOLind beam ex it point is determined
on the 4 in. radiu s. The angle is then determined
by max imi zin g the signal from the large
side-drilled hole and reading the ex it-poin t
posi tion o n the engraved scalc.
Various rcflectors are provided in modified
IIW blocks to provide the capability to set the
sweep distance. These incl ude grooves and
notches at various locations wh ich yield cchoes
at prec isely known di stances. The block may
al,o be uscd for sctting di stances for normal
b tra ight bcam) search units usi ng the I in.
th ickness of the block. Di stance resolution may
also be c hecked o n the notches adjacent to the
4 in. radiu s surface. Because different
manufacturers provide variations in the
confi guration of the block, other specific uses
may be dev ised.
The di stance ca libration (DC) block is
spec ifica ll y designed for selling up the sweep
di stance for both no rlllal and ang le beam testing
fo r e ither lo ngitudinal, shear, or s urface waves.
For straight beam ca li bration, the search unit is
placed on the I in. or 112 in . thi ck portion and
the sweep di stance adjusted. For angle beam
ca libration. the search unit is placed o n the flat
surface at the center of the cy lindri cal surfaces.
Bea m direction is ill a plane normal to the
cy lindcr axis. When the beam is dirccted in such
a manner, cchoes shou ld occur at 1, 2, or 3 in .
intervals. With a surface wave search unit at the
centerline. a surface wave may be calibrated for
di stance by observin g the echoes from the I and
2 in. radii and adj usting the control s
according ly.
A min iat ure multipurpose block is shown in
Fig ure 3.9. The block is I in. thick and has a
1/ 16 in. d iameter side-drilled hole for sensiti vity
seuings and ang le determinations. For strai ght
beam calibration , the bloc k provides back
re nect ion and
Table 3.2. Ca libration Rlock Usage
multipliers of I in.
For angle beams, the
search
unit is placed
Chllrllclcril'tic
Block Designation
on
the
tlat
surface
ij
II\\,
DSC
AS!\1E
DC
AWS
SC
A
(SDH)
( RC)
with the beam
directed toward
Sweep R:lI1 ge
X/O
XlO
XlO
XlO
0
0
either of thc curved
surfaces. If toward
Sel1~itivjty
XlO
X/O
XlO
X
0
0
the I in. radius,
echoes will be
Ex it Poi11t
X
X
X
received at I in .. 4
Exit Angle
X
X
X
in., and 7 in.
intervals. If toward
DAC
XlO
0
the 2 in. rad ius, the
intervals w ill be
X
Depth
0
2
0
2 in. , 5 in., and 8 in.
Resotution
Refracted angles are
Curvature
X'
measured by
Compensation
locating the exit
Legend:
point using either of
X - Shear Wave
the curved surface s.
0- Longitudinal Wave
The response from
I - SCI of Curved Blocks Used
the side-drilled hole
2 - Nea r Surface Only
is maximized and
43
Figure 3.8. IIW block for transducer and system calibration
a.
\?; 91
IT
LlI 01
a.
W ' 50'40'
vVV
b.
IUr""
10'
)
10' ' ''
... //:~
<.
d.
b.
~ 91
O /w
",
...
'fl
I
/ 80'
19 IC{
<.
High Resolution
I
~
Main Pulse
,.
I
I 2 J
L.ow Resolution
L--A
I
'"
Main Pulse
)
d.
r
the angle read from the engraved scales. Single
po int (zone) sensitiv ity can be estab li shed by
max imi zing the signal from the SOH.
or
An example of a special block designed to
compensate for convex surface effects is shown
in Figu re 3. 11. Included are the geometrical
fea tures with tolerances needed in the
constnlction of typical calibration blocks.
Distance-amplitude correction curves can be
developed for any number of test part
thicknesses using the SO H block shown in
Figure 3. 10. By placing thc angle beam
transducer on surfaces which change the sound
path distance, a series of peaked re spon ses can
be recorded and pl oued on the CRT screen in the
form of a OAC over the range of distances of
interest to inspect ion.
A more suitable, but ex pensive, approach to
the testing of complex parts involves the use of
sac rificial samples into which are placed wave
reflectors such as FBHs, SO Hs, and notches.
(See Figure 3. 12.)
44
Figure 3.9. Miniature angle beam calib ration block
1)-1
L
6.25mm
(0.25 in.)
1'-1
P-2
I"f ----"
:!
'
r-t---- ,u,
f
,-
-t
25mm
:.,••
( I in.)
-.L
,
P_I
" ·2
R·2
R·'
o
60°
" . ~
o
" , "
'.'
f igure 3.10. Calibration block for DAC development using angle beams
2 in. long to 1/4 in. diameter Oat end:
mill notches 2% T deep
•
/
t.
t
,,--_2_;_"'_7 ' -_ +_ _ _ _ _ _ _ _,::;:::/
3 in. [Note (1)J
/.
TI4
+
"
I
")' ) - - - - - ,
,
'
. .
"
----<;."0", ,','
#Of-- Clad LNote (4)J
.. //
.....'
-
n2 JT~4~~~~:t~~~~~~;;;;~·~·'~·~~
1-1/2 in. Minimum _ l
Through Clad
T hickness 2% T
Deep into the
Base Metal
6 in. [Note (I)]
hOles rLj~ Tl2 (Note ( 1)1
Drilled and reamed
3 in. Deep [NOIe (1)1
45
Figure 3.11. Convex surface reference block
G
I'
·1
Grain Flow
®
mm m
"
Lm mm ::11~1
:: ::
®
c ®
0
1
A
c
~ m ~ I~I~~L
E E
.~
~
:::
:::
:::
'0
~
~
~
~ ~
~
~
N
N
R
E
E
~
N
:: ::
±O.Q2S mm (0.001 in.)
LEGEND
'
~3
@
90 degrees ±30 minutes typical
Tolerance: ±0.025 in.
Tolerance: ±O.Ol in.
100 RHR maximum to p sur face
Figure 3.]2. Use of reflectors in sacrificial (simulated) test parts
Search Unit
Rotor Spider
Test Surface
,
" ' ,
" " ,' , ,
" ' ,
" ',
"" ' ' ,' ,,
"
" ' ,,
,,~
,,
""
""
Reference Notch 0.75 mm (0.03 in.) Deep
o
o
o
46
Refere nce bloc ks based upon imbedded
DalUra l refl ecto rs such as cracks by diffu sio n
bonding. altho ugh use ful for the purposes of
~ta bli s hin g a base line for self- teaching adapti ve
learn ing nctworks and relatcd tec hno logies. are
\ery d iffic ult to dupl icate and suffer from an
mability of developing an exac t corre lat ion with
natu rall y occurring fl aws. Of co ncern is the
inabili ty to dupli cate test sa mpl es on a
widespread productio n basis; once dcstructi ve
correlations are carried out, remaking the same
config urat ion is questio nable. Even when such
reflectors ca n be duplicated to so me exte nt, the
nat ura l vari ability of fl aws found in nature sti ll
tends to make thi s approach 10 reference
... [andard s hi ghl y questi onable. In all cases, the
block materials used fo r ca li bration purposes
must be sim ilar to the test mate rials to which the
techniq ues wi ll be appli ed. The conce pt of
trans fer functio ns has bee n used with limited
... ueccss in most criti cal calibrati on settings.
47
Chapter 3 Review Questions
Q .3-5 A reflector signal was found to be 6 dB
less than that from the cali bration
reflector at the same sound path. The
calibration reflector was a No . 8 FBH.
W hat can be sa id about the unknown
refl ector?
Q.3- 1 Calibration is the term lI sed to:
A. describe the means to measure the
diameter of a shaft.
B. set up the lest item for examination in
accordance with ru les estab li shed by
the NIST (forme rly the NBS).
C. describe the means to establish the
work in g characteristics of a search
unit.
D. describe the process of estab li shing
the gain level and the sweep distance
of the UT in strument.
A. It is 4/64 in. diameter.
B. It is 8/64 in . diameter.
C. It is probably 8/64 in. diameter or
larger.
D. It is an unknown size.
Q.3-6 In Fig ure 3.7, the response froml hc
3.25 mm FB H at a depth of25 mm, is
above that detected fro m the I mm FBH
by:
Q.3-2 An area-amp li tude block has the
designation 4340-4-0500. T hi s indicates
that it is:
A. an alumin um block with a #3 hole at
a depth of 5 in.
B. a steel block with a 1/16 in. ho le at a
depth of 5 in .
C. a steel block w ith a #5 hole at a depth
of 4 ill.
D. a Titanium block with a #4 hole at a
depth of 5 in.
A. 24.0 dB.
B. 18.2 dB.
C. 12.0 dB.
O. 10.8 dB.
Q.3-7 The half-angle beam spread o f the
reflected wave front fro m a #8 FBH in an
aluminum "A" block bei ng immersion
tested using a 25 MHz transdu cer is:
Q.3-3 T he term "sweep distance" is used to
describe:
[VL = 1.5 (Water); VL , = 6.3; VT _A1 = 3. 1:
... all times ( 10)5 em/s .
f,
A. how fas t the sound is able pass
through the materi al.
B. the equ ivalent sound beam path
d isplayed on the CRT in terms of unit
distances in the test material.
C. the ve locity with which the search
unit is moved across the materiaL
D. how electrical energy passes from the
transducer to materi al being tested.
A.
B.
C.
O.
Q.3-4 A calibrated CRT screen is necessary for:
1.30 degrees.
5.47 degrees.
22.77 degrees.
48.50 degrees.
Q.3-8 A DAC Curve is to be establi shed using
the SD Hs in the block as shown in
Figure 3.10. Three points have been
establi shed: 118,2/8, and 3/8 nodes from
1/4, 1/2,314 T SO Hs. What would be the
next point?
A. measurement of signa l amplitudes to
determine distance to the reflectors.
B. measurement of electric curren ts
generated by the piezoelectric crystal.
C. measurement of d istances from the
beginn ing to the end of the scan path.
D. measurement of d istance along the
sound path to establ ish thickness or
refl ector location.
A.
B.
C.
O.
49
4/8
5/8
6/8
8/8
node
node
node
node
Q.3-9 Which of the follow ing is an advantage
of side-drill ed hole reflectors for
calibration?
A. They can be placed at essentially any
distance from the entry surface.
S. T he surface of [he ho le is rough,
providing a strong, specular
rell ection.
C. The hole depth is li mited to 3 times
the d iameter.
D. The hole diameter can be used
d irectly and easily to measure the size
of an unknown reflector.
Q.3-10 When measuring the angle on an ang le
beam search unit using an nw block, two
signa ls are noted. The first measures at
an angle of 49 degrees and the second
peaks at an angle that is est imated to be
25 degrees. Plastic longitudinal velocity
= 2.76 mm/ ms; steel shear velocity =
3.23 nun/ms; longitudina l ve loc ity =
5.85 mm/ ms. Identify the signals.
Q.3-12 A search unit wi th a foca l length in water
of 4 in. is used. A steel plate, 8 in. thick,
velocity = 0.230 in./ms, is placed at a
water path of 2 in. from the search unit.
At what depth is the foca l po int in the
steel?
A. 1.0in.
B. 2.0 in.
0.5 in.
e.
D. 0.8 in.
Q. 3- 13 During an examination, an indication of
25 perce nt FS H is detected and
max imized. For better analysis the gain is
increased by 12 dB and the indication
increases to 88 percent FS H. What va lue
shou ld have been reac hed and what is the
apparent problem?
A. 50 percent FS H and the screen is
nonlinear
B. 75 percent FS H and there is no
problem
C. 100 percent FSH and the sweep speed
is nonlinear
D. 100 percent FS H and the sc reen is
nonlinear
A. First is shear, second is longitudinal.
S. First is longitud inal, second is
surrace.
C. First is longitud inal , second is Love
wave.
D. First is longitudinal, second is shear.
Q. 3- 14 The difference between
through-tran smi ss ion and pitch-catch
techniques is:
Q.3- l l When usin g a focused, straight beam
search unit for lamination scanning in an
immersion test of a steel plate, a change
in water path of 0.2 in. wi ll result in the
focal point moving in the steel a di stance
of:
A. that the tran sducers in
through-transmission face cach other,
while in pitch-catch the transducers
are often side-by-side in the same
housing.
S. that the transducers in
through-transmiss ion are
side-by-side, while in pitch-catch the
transducers are fac ing each other.
C. that the transducers in
through-transmission are always
angle beam.
D. that in through-transm iss ion the depth
o r the flaw is easily determined.
A. 0.2 in.
B. 0.2 m Ol.
e.
0.05 in.
D. 0.8 in.
so
Q.3· 15 In the tandem tec hn ique a signal is
received frolll the test matcrial. The
reflector Illay be located:
Q.3- 19 While pe rformi ng a straight-beam ,
immers ion test , an ind ication is noted
lying midwall . W hat immed iate act ion
should the operator take?
A. near the front surface.
S. at the back surface.
C. somew here near midwa ll.
D. by any of the above, depe nding o n
the material thi ckness. the refracted
ang le. the distance betwee n scarch
uni ts, and the d istance between
transducer and the reflec tor.
Q.3·16 In a tandem 70·degree pilch-catch shear
wave arrangement , the plate bein g
in spected is 2 in . thick and the regio n of
interest is midway betwee n top and
bottom surfaces. How far behind the
transmi tter shoul d the rece iving
transducer be located?
A. 0.68 in.
B. 1.88 in.
C. 4.00 in .
D. 5.50 in .
A . Report it to hi s/her supervisor.
S. Chec k to e nsure that the search unit
to part di sta nce is correct.
C. Rcplace the component wi thin
anothcr iden tical one to see if the
same ind icat ion ex ists in the second
unit
D. Check 10 ensure the refracted angle is
45 degrees.
Q.3-20 The refl ected pul se reaching the
im mersio n transduce r from the back
surface of a 4.5 in . al umi num plate
standing in a tan k of water is cqual to
_ _ o f the energy pulsc which was
transmitted fro m the transducer.
(Z" = 17. Z"20 = 1.5)
A. 6.22 percent
B. 70.2 percent
C. 50.7 percen l
D. 14.7 percent
Q.3 -1 7 Angle beam search un its are frequently
used in we ld testing. One reason for th is
IS that the angle beam:
Q.3-2 1 A test on a thick part will be performed
using a foc used search un it with a
0.50 in. long foca l zone as determined by
the 3 dB down poi nts. To ensure
complete coverage at uniform se.nsitivity,
the operator shoul d take which of th e
following acti ons?
A. is more se nsitive to slag and poros ity.
B. is more sensitive 10 inadeq uate
penetration an d cracks.
C. does not attenuat e as it traverses the
material.
D . provides mu lt iple back-surface
echoes for thi ckness testing.
A. Set the foc al ZO Il C mid way in the pari
and proceed w ith the examination.
B. Set the foca l spot at the front surface
such that the di vergent beam will
attain max imum coverage.
C. Set the focal zone al the back surface
because th at is the most critical area.
D. Perform multi ple examinations with
the metal pat h dec reased by no more
than 0 .5 in . pe r examinatio n.
Q.J. 18 An automated examination o f a large
cy linder is to be performed usi ng a
focused search unit (focal poi nt =
0.050 in . di ame ter, foc al lcngth = 2 in ..
and crystal d iamete r = 0.500 in.) . To
ensure 10 percent overl ap between scans.
of the follow ing. what increment shou ld
be used?
A. 0 .005 in .
B. 0.495 in .
C. 0.040 in .
D. 0.0495 in.
51
Q.3-22 A pair of squirters each with a 9 in. water
stream are used in the examination of a
large panel in the through-transmission
mode. The search units are arranged in a
horizontal position. It is desi red to locate
discont inuities within 0.0 10 in. of their
true posi tion. The ana lyst should take
which of the following actions?
A. Assume that the coordinates given by
the scanning system are correct and
use those values for the coord inates.
B. Determine the curve of the Waler
stream due to the influence of grav ity
and adjust the coordinate va lues to
compensate for the deflection.
C. Overlay the test record on the part
and mark the reflector locations.
D. Precisely meas ure from the index
point on the panel to the indicated
location and mark the part.
Q.3-23 In prepari ng a scanning plan (the set of
d irections describing the performance of
an ultrasonic examinat io n), which of the
follow ing parameters should be
considered, as a minimum ?
A. sound beam diameter, refracted
angle, beam direction. gate settings,
starting point for the first scan ,
number of scans
B sound beam diameter, refracted
angle, operator' s name, gate settings,
starting point , number of scan s
C. sound beam diameter, refracted
angle, beam direction , expected
flaw s, instrument serial number
D. sound beam far field length, refracted
ang le, beam direction, gate seuings.
starting point. number of scans
Q.3-25 A major problem in the use of search unit
wheels is:
A. insufficient traction lead ing to
skidding and bad wrecks.
B. eli mination o f troublesome in terna l
echoes.
C. installing adequate brakes.
D. selecting a rigid tire material
Q.3-26 A scanning plan is a:
A. document which out lines the various
steps in preparing a procedure.
B. document whi ch defines the most
effic ient way to ana lyze the data.
C. documen t whi ch gives the detailed
steps entailed in examini ng the test
item.
D. document which gives the compl ete
hi story of previous examinations.
Q.3-27 In contact testjng. the back surface sig nal
fro m a 2 in. plate was set at full screen
height Pass ing ove r a coarse grai ncd
area, the back surface signal dropped to
10 percent of the full scale signal. What
wou ld be your estimate of the change in
attenuation in this local area based on
actual metal path dista nce?
A.
B.
C.
D.
na'
pla'e o r Pol YSlyrene
Q.3.24 A 3 in. 'hi ck
during im me rsion test ing exhibi ts an
echo fro m the back surface of the plate
that is
of that received from the
front surface . ( Both sides immersed in
water,ZPoI =2 .7,ZIl1O
. = 1.5 .)
,
A.
B.
C.
D.
8.4 percent
84.00 percent
8.16 percent
6.88 percent
52
20 dB/ in.
10 dB/ in .
5 dB/in.
10 percent/in.
Chapter 4
Practical Considerations
Chapter 4
Practical Considerations
Many issues of a practical nature ari se during
both routi ne and speciaJi zed ultrasonic
inspecti on activities. Issues o f concern include
interpretation o f echo signals (as viewed on the
A Scan), equipme nt adjustme nt to exped ite
interpretati o ns, and set-up conditions for
producti on inspections.
S ignal ampli tudes arc generally relia bl e for
the reseu ing of instrumentatio n, based upon
controlled calibration bl oc ks and the ir rderence
refl ectors. But the ampli tude of the pul ses
received fro m naturall y occ urring refl ectors has a
high level of variability depending on the
refl ector's orientation and morphology, neither of
which are known in most circum stances.
Signal Interpretation
Corre lations of signal ampl itudes wi th
specifi c re fl ectors are generall y recogni zed as a
valid means of establi shin g the level of sensiti vity
of an ultrasonic system. Thu s fl at-bottom ho les,
with cross-sections smaller than the sound beams
incident upon them and ori ented at normal
incidence, do ex hibit sig nal responses that are
proportional to the area of the re fl ector. But
correlati on with naturally occurring
di scontinui ties of irregular shape and orie ntation
has proven to be less th an accurate, largely due to
an inability to sati sfy the no rmal incidence
requ irement and to the fact that the reflect ing
surfaces are rarely fl at and smooth . Where natu ral
di scontinuiti es ex hibit these conditions, as w ith
s mall lami nations in plate material s, the area
relatio nShi p has validity. Although the degree of
signal-fl aw correlation at a single transducer
location is less than desired , observing changes in
signal response as the transducer is moved along,
across, over, and around a suspect area can
suggest if the reflector is round or flat (linear),
rough or smooth, parallel or vertical, and fill ed
with materials which have a higher or lower
density than that of the surrounding material.
Table 4. 1 li sts the techniques used in making
these determination s.
The interpretation of ultrason ic pul ses
received fro m test pan renect ive surfaces can be
very complex. depending upon the geometry of
the test piece and the wave mode/scan a pproach
hc in g used. The most reli able measure avail able
from an A Scan system is the li me of arri va l of
acoll stic pul ses , due to its lack o f ambiguity
when testing fine-grained . homogeneous
materi als. tn contact testing o f materials w ith
known and constant sound wave velocities, the
time of arri va l is directly proport ional to the
di stance between the contact surface and the
refl ector. The precise time of arri val is usuall y
determin ed by whe n the pul se initially de parts
from the scree n baseline. Systems using
threshold devices to trigger del ay time monitors
can be in error, de pending upon the slope of the
pul ses ri se time and the leve l to which the
threshold device is set.
The s ignal peak is less reliabl e for thi s time
meas ureme nt because pul ses may spread
follow in g passage through di spersive media.
Estimating lhe actual time the e nvelope of the
RF signal reac hes a max imum is also a
somewhat uncert ain approach. De pending upon
which portio n of the pul se is used for trave l time
measureme nt s, the estim ates of thi ckness and
di stance to refl ecti ve surfaces can vary by one or
more wavelengths.
Finger damping is a technique where by a
moiste ned fi nger, pl aced o n the surface o f a test
piece at a location where sound waves are
present, w ill affect the wave pro pagation and will
oft en be detecta bl e as sli ght changes in signal
55
Table 4.1. Signal Interpretation Schemes
ChBracte ristic
Ac tion
A Scan Response
Orientiltion (Front Surface)
Rotate. Approach
Maximize signal
Vertical
Tr:lIIslate, Across
"Walking signal"
Flatness
Rot:lIe
Unidirect ional
Spherical
Rotate
Omnidirectional
Thickness
Both (many) sides
Thin if one side predominates
Graphical plot
Length (large)
Tr:lIIslate in major direction
Drop-off at ends
Depth/width (large)
Translate in minor direction
Drop·off at edges
Graphical plot
Tip diffrac tion
Surface Texture
Smooth
Rough
Crisp, fast rise
Jagged. wide pulse
MullirefleclOf
Multi·echoes
Contents
RF phase reversal
ampl itudes on the CRT. Thi s technique is very
effect ive in separat ing collect ions of signals,
part icularl y when some of them are caused by
spurious reflections from corners, weld crowns,
or other surfaces which are readily accessible to
the inspector.
Causes of Variability
There are many instrument variab les whi ch
can have a signifi cant bearing on the outcome of
a test and the interpretat ion of data. Horizontal
sweep extent and accuracy affect estimates of
time du ration from initial pul se to significant
echoes. These are used as measures of thickness
("'straight beam" testing) and slant dislance
("angle beam" testing) and should ex tend over
the entire range of interest
Although amplitude is not a reliable indicator
of a natural discontin ui ty's actual size, due to
variations in shape, aspect angles, tran smiss ion
properties of base material s, and othcr factors, it
is often indi cat ive of the relative size of many
common renectors and is vita l for being able to
establish an instrument 's sellings with respect to
a calibration reflector or for reestab li shing
settings from one inspection to the nex t.
Ideall y, an ultrason ic system should be
capable of detecting reneclOrs throughout the
region from the sound entry surface th roughout
the test item's en tire vo lume. However, the
length of the incidel1l sound pu lse (due in part to
transducer element ringing) rcpresents a distance
within which echoes, particu larly weak ones,
cannot be di stingui shed from the reflection
caused by the entry surface itse lf. If short
duration pulses are used, i.e. , if high- frequency,
we ll -damped transducers are used, the near
surface resolution is significant ly improved over
system s using long duration pulses.
In contact testing, the ability to detect
reflectors just under th e near surface is furthe r
aggravated by the "dead zone" that ex ists
immed iately after the in itial electrica l pu lse. The
dead zone is caused by an inabil ity of saturated
electrical components to respond linearl y to
incoming signals as a result of their having been
overdriven by the in itia l pulse. The " near-surface
resolution"/dead zone problem can be solved by
56
determines, to a high degree, the characteristics
of the sound beam including shape. ncar-field
length, focal point (if appropriate), and refracted
angle. The transducer (with its mounting and
backing members) also determines the pul se
shape, frequency, and lengt h in conjunction wit h
the electrical exc iting pu lse and the instrument
load imposed on the crystal.
testi ng parts from oppos ite surfaces rather than
from onl y one side.
Some codes and speci fi cat ions have reject
cri teria based on the size of the flaw. W here two
re flecto rs ex ist in approximately the same plane
and are in close proxim ity to eac h other, it is
importan t to be ab le to differentiate one from the
ot her. Systems with ve ry narrow beams are
capab le of sat isfyi ng thi s requirement and are
said to have good lateral resolution. Lateral
resol ution is principall y a funct ion of the search
unit's beam width. Thi s factor is very important
in imaging systems where clear delineation of
s mall and indi vidual fl aws is desired.
Because of these factors, it is important that
the proper search unit be chosen, and each search
unit characleri stic be checked against the desired
va lues on the UT in strument to be used in the
examination . Manufacturers often provide
cert ifi cates with the measured values deemed
important by the manufacturer. These include,
but arc not limited to, photographs of the RF
waveform , the frequency spectrum con tent , and
a di stance/amp li tude characteri stic curve
measured on a test b lock. Usuall y a value for the
damping factor is calcu laled. Since this factor is
not defined the same uni ve rsally, it may be
desirable to determine the definitions used in the
calcu lation. For exam pl e, definitions may be
based on the number of cycles or half cycles
meeting a certa in parameter, e.g., the number of
negative half cycles in a pul se greater than the
amplitude of the first negative cycle. Each of
these definitions serves the same purpose in
Sensitivity is a measure of the abili ty to
detect small reflectors. Systems w ith high level s
of amplification (hi gh gain) are usually systems
wi th a high sens itivi ty. However, when the
ultrasoni c system is considered in its entirety.
seve ral factors can alter the sensi ti vity that might
be expected for a g iven co mbination of
instru ment, transducer, test material, or
discontinuity of interest. The important factors
affect ing sensil ivi ty arc li sted in Table 4.2.
The search unit is the most important
component in the UT system. Thi s device
Tahle 4.2. System Factors Affecting Detection Sensitivity
Fllctor
Gain
Transducer
Comment
Conversion efficiency
Field concentrators
Coupling Coef - d}} . Sl}
Lenses, beam pattcrn
Amplifier
Electronic amplification
High linear gain . l-ligh sensitivity
Pulse Length
Masks nearby reflectors
Depth resolution, bener penetration
Wavelength
Reflectance. directivity
Smaller L - beller sensitivity,
resolution. higher noise (poly mtls)
Signal processing
Gain x:::bandwidth = constant
Smoothing, IiIlering, reject reduce
sensitivity
Nois(' sources
Random
Electrical (outside, inside)
Lights, welders. cranes plus circuit
cross-talk, instability
Transducer construction
Material surface
Material homogeneity. isotropy,
and geometry
Cross-coupling, damping
Coupling
Uncertainty of velocity. scatter
Geometrical reference surfaces
Coherent
57
different ways, i.e., to describe the pulse length
and shape.
Test item surface condition is an important
variable, especially when performing con tact
tests. A rough surface affec ts the exa mination in
man y ways, including causin g d ifficu lty in
mov ing the search uni t across the part; causing
local variations in the entry angle resulting in
scattering the beam; causing reverberations of
the sound in the pockets o n the surface, resulting
in a wide front surface echo wi th a resulting
increase in the dead zone; using excess coupl ant
and making coupling difficult ; possi bly caus ing
po rtions of the examinatio n volume to be
mi ssed; and causing rapid wear of contact search
units.
In some cases, it may be necessary to sand or
grind the scanning surface prior to the
examinat ion in order to accompli sh the test.
Rough sand castings, some forgi ngs, and welded
surfaces typically require rework prior to the UT
test.
Extreme ly smooth surfaces may be d ifficult
to test using the contact tec hnique because the
cou p Ian! may not wet the surface. This can lead
to air be ing trapped betwee n the search unit and
the part. Thi s pheno menon is readi ly observed
when using transparent angle beam wedges.
Part confi guration (geo metry) plays an
important ro le in definin g each examination 's
operational parameters and practices. Geometry
and access often decide the choice between
contact and immersion tesling; however, there
are no rules which relate the compl exi ty of shape
to making the choicc. Technique selection is
governed by many things such as equipment
avai lability, part criticality, confi gurat ion ,
operator experience, and knowledge; a number
of highl y symmetrica l parts, e.g., plates , pipe,
cones, spheres, and cy linders, lend themselves to
both immers ion and contact auto mated testing.
Irreg ularl y shaped pans are onen beyond the
capability of conventional au to mated scanning
systems and are better left to manual
exam inations. With the advent of computeri zed
scanners with learning modes. the operator leads
the system through o ne examination and the
com puter then automaticall y repeats the
exa min atio n.
The presence of irrelevant signals from
geometric features is a major in spection
consideration. The most common of these is the
back surface echoes from pl ate material (where
mul ti ple echoes are freq uently present).
Fortunate ly, these are easily recognized. In other
cases, however, irrelevant echoes such as from
the root of a weld, may not be easily
differentiated from actual fl aw indications. In
these cases, careful analys is is required
incorporati ng consideration of beam spread and
mode conversion as well as the normal issues of
transit time. Changes in beam direct ion and
ve loc ity due to materi al conditions must be
fa ctored into these analyses . Refl ec tions from
internal stmcturaJ features must also be
recogni zed and considered.
Special Issues
The largest application of UT is for fl aw
detection. It is used in rece ivi ng inspection of
raw materi als, for in-process in spection of items
under construction, and fo r in-service
inspect ions (as part of ongoing maintenance
programs). Although most appli cations involve
metallic materials, UT is also found in the
inspection of plastics, composi tes, concrete,
lumber products, and affili ated spec ialty
materi als.
Weld Inspection
Ultraso nics is a primary method of weld
in spection, part icularl y when major construct ion
projects are involved. Welds, including their heat
affected zones, are exam ined because the
probability of fa ilure is hi gher in these areas than
in most base materials. Although weld metal is
normall y stronger than the base metal, stress
ri sers may occur due to we ld conto ur,
processing, or the presence of defects. The we ld
process itself creates residu al stresses whi ch,
when added to applied stresses, may cause
crac king due (0 fatigue or stress corrosion .
Exam ination of butt welds in materials from
about 1/4 to 15 in. thi ck are normally performed
using an angle-beam, shear wave tec hnique
because the sound can be ori ented at near-normal
incidence to the critical fl aws, i.e., cracki ng,
inadequate penetration, and fu sion. The bodies
of the welds can be inspected wi tholl t removing
58
Figure 4.1. Angle beam geometry used in weld inspection
--I
II
I I
T
I·
-I
Skip Distance = 2T tan ~
the weld crown. When part geometry allows, the
exam should be conducted from each side of the
weld. Refracted angles are chosen according to
the fusion line angle, material thickness. or other
expected defect orientations.
Figure 4.1 shows the basic geometry used for
defining the angles and paths followed by sound
beams when doing shear wave (angle beam)
testing. As shown, the sound, introduced at an
angle which complements the geometry being
examined, follows a sou nd path that often
reflects from the opposite surface, particularly
for platelike product form s. The V -shaped path
permits inspection looking "down" into the weld
in the first leg of the Vee while the second leg is
the region used to look "up" into the weld. By
scanning the transducer toward and away from
the weld, the sound can be made to interrogate
the entire volume from two or more sets of
angles.
Analysis of signals observed on the A Scan
display requires converting the information
found along the sound path (along the Vee path)
into positional data related to the base material
and weld centerline. This is done using
conventional trigonometry to sol ve for
eq uivalent surface distances, e.g., ski p distance,
or depths below or above the base material
surface. For example, for the I in. plate shown in
the figure and using a 70-degree angle, the ski p
distance (distance from tran sducer exit point to
location at which center of sound beam reaches
the top surface after reflection) is given by
2T tan ~ = 2 tan 70° = 5.5 in.
For thi s same case, the sou nd path is given by
2T leos
~
= 2/eos 700 = 5.85 in.
Common problems found during weld
examination involve rough surfaces (including
weld spatter), irregular part geometry (including
hidden cond itions such as counter-bores in
piping systems), and physical inaccessibility
(due to in sulation and being embedded in
reinforcing structures). During production and
under some in-service inspections, examinations
may be done at elevated temperatures which can
aJter the effective soun d velocity of the material,
transducer performance (particularly refracted
angles or critical temperature limits), and
operator's performance. All of these factors must
be addressed and considered in the procedure.
Where irregular inner surface conditions exist,
interpretation of reflector signals is often very
difficult. For example, the presence of a baCking
bar (placed at the root of the weld in order to
ensure adequate penetration and fusion) tends to
entrap the incident sound waves which
reverberate around the bar and eventually exit
along the same path by which they entered the
backing strip. Thus, strong echo signals are
returned to the sendi ng transducer at an apparent
depth of sl ightly more than the thickness of the
base material. The interpretation might be that a
large defect exists just beyond the root area of
the weld on the opposite side of the weld.
Another troublesome welding configuration
is introduced by the prese nce of a counter-bore
"ledge," machined or ground into the inner
radius of a pair of fitted pipes, so placed in order
59
Figure 4.2. Reference standard for weld inspection using notches
,--I'
11)'_~<
&
I
:"
cO
"
/I
~I
""
h-
t
t
4xMinirnum
I' t 'I
LI'_~-./'..Jl1.-!,~:,=-'-'<1'-----"1
4x Minimum
12
II
LEGEND
, '
c'
3 ;----3,-- ' 5
L
------fO
,.-,
- --
-,. --'- -('
'-
l. Angled notch
2. Undercut notch length per welding specification
3. Separation two times transducCl" width or 2 in.
maximum
4. Crack, LF and LP notch length two times
transducer width or 2 in. maximum
5. Hole size maximum allowable
6. Hole size minimum allowable
7. Notch depth tIlO maximum
8. Hole depth t / 2 maximum
8
'- --
,:.6
'- --
that the ir initi al fit-up (gap and ali gnmen t) is
generally uniform. Such a geometry can give rise
to strong geometrical refl ector signals in the
immediate vicinity of the weld root, an area well
known for the initi ation of stress corros ion
cracks in stain less steel piping systems. If the
angles of inspect ion and cou nter-bore arc such
penetration is permitted, ultrasoni c testing is
usually not recommended. In ot her cases, such as
stai nless steel pip ing, ultrasonic inspect ion may
be success ful in the base materia l (a wrought
product) but not in the we ld zone (a cast
product).
that the refl ected wave is below the fi rst cri tical
angle, interna l mode conversion can take place
with a longitudinal wave travel ing in a direction
other than that of the reflec ted shear wave.
Immersion Testing
Figure 4.2 shows the use of notches
introduced in to a separate sample of the welded
structural steel to serve as a mock-up for the
weld inspector to accurately locate where on the
CRT echo signals can be expected to appear.
Welds such as fillet welds and d iss imilar
metal we lds may requi re the app licat ion of
d iffere nllechniq ues in order to exa mine all
port ions of these welds and the ir heat-affected
zones. Due to the geometry of many fi ll et welds,
particu larly those in whic h incomplete
The immersion method of coupling
ultrasound to test parts permits a wide variety of
test conditions to be used without the need for
custom-des igned transducer assem blies, and with
consistent coupling characteri stics, aJlow ing for
imaging of test parts with regular shapes, i.e.,
plate, rod, cy linder, pipe, and simple forg ings,
and assemblies such as honeycomb panels.
The flexibility of immers ion testing is both a
blessing and a bane in that it permits the use of a
single SCI of test equipment (transducers, mostly)
to be lIsed for a large variety of inspect io n
protocols (i nspection angles, modified beam
paHerns, regulated scanning patterns, and hi gh
sensitivity transducers), bu t it involves relative ly
60
expensive systems and signi ficant ly extends the
setup time fo r each inspection.
Align ment of sound beams to test part
surfaces is expedit ed by the use of the multipl e
reflecti ons wh ich occ ur as a result of sound
be ing reflected from the water-test part interface
back to the transduce r face, and re-reflected back
and forth between the transducer and the test
part . By monitoring these mult iple
reverberat ions while angu lating the transducer
man ipulator, the presence of the largest array of
mult iples ensures that the sound beam is aligned
perpendicular to the test part's fro nt surface and
th us the sound beam is normal to the surface. In
immersion testing, because of the large
difference between the ve locities of sound in
water and metalli c part s, thi s ali gnment is cri tical
because sli ghtl y off-axis beams are refracted by
a leverage fac tor of approx imately 4: I.
Figure 4.3 shows the presence of water multi ples
as well as the multiple echoes developed withi n
the flat steel pl ate.
The gain used in im mersion testing is rather
high, due to the large amoun t of sound energy
lost at lhe water-test part interfaces which are
often very different in acoust ic im pedance.
When the transducer is rela.tive ly close to an
item with parallel surfaces, the CRT often
displays an array of multi ple reverberations from
within the item, as well as from the water
mu lti ples. In thi s case, the water mu ltiples are
read il y identified by displaci ng the transducer
along its longitudinal axis toward the test item.
As the transducer moves, the water mult ipl es
wi ll tend to gather closer together as the
transducer approaches the test part, tending to
"walk th rough" the test part multiples, and
eventually piling up at the first interface signa l.
Immersion testing is used in the pu lse-ec ho
mode as well as through-transmission. A
variation on the through-transmission approach
uses a fixe d beam reflector placed beyond the
test panel and adj usted so that its echo can be
detected by the sending transducer in the
pulse-echo manner. Thi s de layed refl ector-pl ate
signal is indicati ve of the strength of the sound
beam after passi ng through the panel two times.
A weak refl ector-pl ate signal (if properly
aligned) usuall y signi fies a material with a high
level of attenuati on due to ils composition, or the
presence of highly attenuating voids or scallerers
which may not result in a discrete back scattered
echo of their own.
Angle beam, shear wave testing is often
achieved by rotat ing (sw iveling or angulatin g)
the transducer with respect 10 the sound entry
surface. For cylindrical items, it can also be done
by offsetting the transd ucer to the point where
the curvalUre of the test part yields a refracted
shear wave as shown in Figure 4.4. The
Figure 4.3. Multiple echoes found in immersion testing
Initial Pulse
Inter face Echo
Second
Interface
Echo
Backwall
Echoes
2
Tr ansducer
Multiple
Echoes
]
3
Water Standoff
~S'-te-e-:-I~rI-i--='
61
Figure 4.4. Shear waves induced in tubular materials
E
Water
"l.
E
E
d
_ _ _ Tra nsducer
focused Longitudinal
Source Beam
-+-+- + --=--+-+-
R
LEGEND
4t
:: Angle of incident sound beam
o
VLW
VSM
VLM
d
BW
sin 41
= Angle of refracted sound beam
= Longitudinal velocity in water
'" Shear velocity in metal
= Longitudinal velocity in metal
= distance of transducer centerline offset
from normal to cylinder outside diameter
:: Beam width
= (VLWN11) sin a
curvature of the test surface results in the
refraction of the sound beam in a manner that
tends to spread the sound with the water-i tem
interface func tioning as a cylindrical lens,
di verging the beam. Areas with concave
surfaces. such as inner radiused forgings, are
sometimes difficult to in spect because they focus
the sound beam into a narrow region, maki ng
compl ete, uniform coverage quite difficult.
It is poss ible to compen sate for some of these
contoured surfaces through the use of speciall y
designed transducers or the introductio n of
contour-correct ing lenses applied to fl at
transducers. Fi gure 4.5 shows the effect of
contour correction on the A Scan d isplay
obtai ned wi th and without correction being used.
By matching the curvature of the sound beam to
the curvature of the tube, a set of well spaced
multiple reverberation s from within the tube wall
is clearly ev ident.
When using transducers equipped with
focu sing lenses for the purpose of increasi ng
flaw sensi tivity or lateral resolution, the
in troduction of flat surfaces associated with test
parts al so di storts the beam pattern, tending to
foreshorten the foc al length due to the refraction
of the wavefro nts enteri ng the higher velocity
metalli c parts. The foc al di stance is usually
reduced in length equi va lent to one-fourth of
what it would have been in the water without the
presence of the metallic test part. The facto r of
one-fourth ari ses from the ratio of the
longitudinal wave acoustic veloc ities within the
water and metallic, respecti vely. Figure 4.6
conceptually demonstrates this effect.
The automation of immers ion inspections
relies on the use of special circuits (gates) that
send control signals to recorders, alarms,
transporters, and marking devices in response to
the presence (or absence) of special ultrasonic
echo response pul ses. By using time delay
circuit s, initi ated by e ither the ini tial exc itation
pu lse of the pul ser/rece iver units or by
reflectio ns from the front surface of the test part,
the time of arrival of ultrasoni c echoes with
respect to benchmark echoes (rece ived from
fron t surfaces, back surfaces or other strategic
62
Figure 4.5. Contour correction through focused transducers
o
I
I
o
Flat Transducer
,, ,, ,
"
-t-t-+
Contoured Transducer
Thbing
refl ecting surfaces) indicates when
discontinuities are present within the test part.
The use o f fron t surface gating is a very
effecti ve way of having the gate follow a
s li ghtl y curving surface, relievi ng the need for
identi cal tracking of mechan ical posilioncrs and
rig id test part surfaces. The re li abl e tri ggering
of recorders and alarm systems relieves the
operator of continual moni toring and perm its
other acti vities to take place while immers ion
testing is progressing.
Problems found in automatic immersion
testing incl ude the continual maintenance of the
condition o f the water (corrosion inhibitors,
an li-foulants, wetting agents) and the
outgassing of test parts during testing. The
outgassi ng is most troublesome due to the
formation of bubbles on the surfaces of
materials upon their introductio n in the water
tanks. Although wiping them off removes much
of the problem, the bubbl es tend to continue
forming even after being submerged for
relative ly long periods of time. Upon test part
remova l, care must be taken to thoroughly dry
and protect the items since they will be prone to
suffer corrosive attack. As w ith any heavy-duty
mechani cal pos itio ning system, wear and
backlash in drive trains tend to introduce a
mechanical hysteresis which can affect the
results ex pected from C Scan recorders and other
image generating devices.
Production Testing
Immersion testing is the preferred approach
to automated testing due to the abse nce of
contact coupling problems, min imum
deteri oration of performance due to use, and
ability to use hi gh frequency systems withom
concern for fragile transducer fracture.
As with many industrial processes, UT
testing is reali zing the benefits of computer
integration in test applications and the
interpretation of resul ts. This phenomenon has
opened many previously inaccessible areas of
testing. Computer integration is providing
examin ation of complex shapes, real-time
analysis o f data with accept/reject decisions,
different data di spl ays, signal analysis and
pattern recognitio n, a hi gh degree of operator
independence, and hi gh speed calibration .
Computer integratio n is an ex pen sive and
time-consuming activi ty requ iring cons iderable
engi neering and development effort.
63
Figure 4.6. Second lens effect of metallic
test parts when using foc used
transducers
Focused
Transducer
=
f::;".... ......
Lens _
Beam
Beam Refracted with
,...,W
.,..;;;t;;;.:,.,....."'tt,f-G
.:......_a_t_"...,Convergence
Metal '
·
r
N~ ew P!,lIlt 0
Focus In Metal
A' .'/.
':',
:
:'
I
:
•:
,
"
'
.•..
./
.y
..
Divergence
Bel'ond Focus
Lrocal Distance
if in Water
product rather than on the product itself, and is
used extensively in the nuclear power and
petrochemical industry. This serv ice is often
performed under poor working conditions,
requiring highly qualified personnel and
appropriate teChniques.
Field test ing is a conglomerate of
applications and lechniques used in a variety of
industries for a variety of reasons. Numerous
testing laboratories provide field testing services
and can provide quick response with qualified
personne l. Ultrasonic fi eld testing is used on
pipe li nes, building construction, maintenance,
and fa ilure analysis. Field testing techn iques are
many and varied, and change from day to day,
depending upon the particular job at hand; hence
the requirement for qualified personnel.
Field techn iques include straight (normal)
beam, angle beam, and surface waves. In
construction, these are used to detect fabrication
defects in maintenance; service induced defects
and corros ion are the usual culprits. Most of this
work is manual because the appl icat ions are so
varied and job site inspect ion is requ ired.
Compuler integration into imaging processes
offers advanced data analysis capab ilities
because of its ab ili ty to visualize the size, shape ,
and locat ion of re nectors. Images can be rotated
and otherw ise man ipu lated to maxi mi ze the
information available to the analyst. Through
color or gray scale coding, amplitude and depth
information can be integrated into the di splays to
enhance the quali tati ve interpretation of the data.
Quantitative information is also available, but as
in the case of virtually all nondestructive
inspection methods, it is corre lated to material
performance on ly through infere nce and not
throu gh direct measurement. The prime
advantage to the analyst is the simultaneous
display of large amounts of both signal response
and positiona l data.
In -service Inspection
In- service inspection and maintenance naw
detect ion are used pri marily to locate
service- induced naws such as fatigue and other
load-induced cracks. In-service inspect ion is
performed on equipment used to produce the
64
Chapter 4 Review Questions
QA-4 An immersion, pulse-echo test is
QA-I In a through-transmission, immersion
examination of an adhesively bonded lap
joint, the signal is noted to decrease in
amplitude in a small area of less than
II I 6th in. diameter as recorded on a
C Scan. What condition might cause this
indication?
performed on a thin adhesively bonded
joint between a composite material and
an aluminum substrate. The sound beam
enters the joint normaJly and from the
composite side. The amp litude gate is set
on the interface between the co mposite
and the aluminum. If the joint is
unbonded, the sig nal shou ld:
A. a bubble on the surface of the joint or
an unbanded spot in the joint
B. the joint is tightly bonded in this area
C. there is nothing that cou ld cause this
conditi on - it is an anomaly
D. the adhesive has melted in this area
causing an increase in sou nd
transmissivity
A. decrease, because water has a lower
velocity than the aluminum.
8. decrease, because water in the
un bond will conduct sound better
than air.
C. increase, because air in the un bonded
area will reflect more sound energy
than the aluminum.
D. increase, because the compos ite will
resonate.
QA-2 Advantages of computer controlled
ultrasoni c testing include:
A. lower capital equipment costs.
B. high dependence of the test results on
QA-5 Three major sources of noise which
the capability of the operator.
C. real -time analysis of test results.
D. no need for instrument calibration
even though such action is required
by the specification.
interfere with the signal s on the CRT are:
A. front surface roughness, hydraulic
motors, and enlarged grain structure.
B. back surface rough ness, electric
motors, and decreased grain structure.
C. depth, size and location of defect.
D. front surface roughness, arc welding
operations, and enlarged grain
structure.
Q.4-3 During the test of a fiberglass-epoxy
composite, numerous echoes are recorded
in the pulse-echo mode. What action
should be taken?
A. The part shou ld be rejected because
all echoes are from flaws.
B. The part should be rejected because
the supervisor was not there to give
advice.
C. The part should be accepted because
all composites will have numerous
echoes.
D. The procedure should be consulted to
determine the analysis technique and
the acceptJrejecn::riteria.
QA-6 A single Vee, bun weld in a 3 in. plate is
being exam ined using a 60-degree shear
wave. An indicati on on the CRT appears
at a sound path distance of 9 in. At the
same time the exit point of the transducer
is 7.8 in. from the centerline of the weld.
This suggests the reflector could be:
A. a crack in the near side HAZ.
B. lack of fusion at the weldlbase
material interface.
C. a slag inclusion in the cenler of the
weld.
D. an undercut condition on the far side
of (he weld.
65
QA-7 Under the conditions above, but with the
ind ication at a 6 in. sound path distance
and with the exit point 5.2 in. from the
weld centerline, another strong indication
is received indicating a probable reflector
in the
the we ld.
Figure 4.7.
A. root area of
B. crow n area of
C. midsect ion of
D. base metal adjacent to
QA-I I Under the above condition s, an L-wave is
internally mode converted at an angle
wi th the sin b given by:
QA-8 Under the conditi ons above, but with the
indication at a sound path di stance of
9 in. and with the exit point 8.1 in. fro m
the weld centerline, the refl ector lies in a
plane that is
fro m the
center of the weld.
A.
B.
C.
D.
A. 0. 1 in. (on the far side)
sin ~ = (V/Vs) sin (i ncident angle).
sin 13 = (V/Vs) sin 45 degrees.
sin p = (VJV,) sin 90 degrees.
sin ~ = 4 si n (i nc ident angle).
QA- 12 A pipe being exami ned automatically
using immersion techniques (with mode
conversion to a 45-degree shear wave at
the pipe wall-water interface) is
experienci ng a wobbling displacement
(transverse to the pipe ax is) of
± IO percent of its nominal offset value.
The corresponding change in inspection
angle would be:
B. 0.3 in. (on the near side)
C. 0.3 in. (on the far side)
D. 0.5 in. (on the near side)
QA-9 Under the conditi ons above, the reflec tor
is at a depth of
(measured
from the transducer side).
A. 1.5 in.
B. 1.0 in.
C. 2.0 in.
A. +l l ,- 14percen t.
B. + 13, - 12 perce nt.
C. + 10, - 10 percen t.
D. + 14, -10 percent.
D. 2.25 in.
QA- IO In a th ick-walled piping weld inspection ,
the counter-bore on the 10 refl ects the
incident 45-degree shear wave so that it
strikes the top surface (outer diameter) at
normal incidence. In order for thi s to
happen, the taper on the counterbore
must be: (See Figure 4.7.)
Q.4-1 3 During production testing, a rod is
passing under a transducer in a stuffing
box (immersion testing). What is the
expression that relates pu lse repetition
rates (of the UT instrument, i.e., PRR)
wi th the longitudin al speed of travel (Vp)
of the test part, given a transducer of
width D?
A. 30 degrees.
B. 45 degrees.
C. I 1.25 degrees.
D. 22.5 degrees.
A . D= VplPRR
B. PRR = D xVI'
C. VI' = DIPRR
D. none of the above
66
Q.4- 14 An inspection specification ca ll s for three
hits of an echo in order fo r the flaw to be
considered valid and for the alarm to
sound. The maximum axial speed of test
part movement is therefore
for
a I in. d iameter tran sducer (assume no
beam spread) and a PRR of 600 pu lses
per second (PPS ).
A. 1800 in .!s
B. 600 in .!s
C. 300 in.!s
D. 200 in .ls
Q.4- 15 A 1.5 in. butt weld is to be exam ined
from both sides using a 70-degree shear
wave. The scan program ca ll s for be ing
able to inspect 3 legs (1.5 Vee paths).
Weld access fo r completing thi s pattern
wi ll requ ire ±
plus the
physical dimen sions of the tran sducer
assembly.
Q.4-17 A 0 degree ax ial test is bei ng performed
o n a stee l railroad ax le 8 ft long and 6 in.
in diameter. A strong but un steady signal
is seen near the center of the CRT screen.
A similar signal is seen from the Olher
end of the axle. The follow ing condi tions
are given:
Screen Distance: 10 ft ( 12 in.ldiv.),
Damping: Min imum , Gain: 85 dB ,
Pul se Repetit ion Rate: 2000 pu lses per
second ,
Frequency: 2 MHz, Range: 50 in. ,
Reject: Off, Filter: Off,
Sweep Speed: As Req ui red,
Sweep Delay: As Required
What action should the operator take?
A. Record the indication and notify
supervisor.
B. Change Ihe PRR 10 1000 pu lses per
second and observe the effect.
C. Compare the signal to the reference
standard and reject the ax le if the
reference level is exceeded.
D. Determine if the signal respond s to
finger damping by touching the
opposite end.
A. 4.50 in.
B. 8.24 in.
C. 12.36 in .
D. 24.73 in .
QA-16 The sou nd path sweep setting on the LO
Division CRT for the above case should
bc:
A. 1.35 in.ldiv.
B. 1.00 in.!div.
C. 1.25 in .ldiv.
D. 0.50 in .!di v.
Q.4-1 8A 10 ft long turbi ne shaft is to be
inspected from one end wi th 0 degree,
longitudinal wave for radial ,
circumferential fatigue cracks in an area
between 90 and 110 in. from the
inspection end. The available instrument
screen can di splay a maximum of 80 in.
How should the operator proceed?
A. Give up .
B. Sct up 20 in. sc reen and delay the
start to 90 in .
C. Sct up an 80 in. screen and delay the
start to 30 in.
D. Assume there arc no cracks and turn
in a report.
67
Chapter 5
Codes and Standards
Chapter 5
Codes and Standards
Every ultrasoni c examination should be
governed by one or more procedures that are
structured to compl y wi th the rules and criteri a
of applicabl e codes, standards, and/or
speci fi cations. S impl e maintenance tasks such as
thickness measurement for corTOsion detectio n
may not be governed by any regulatio n, but a
spec iri c procedure should still be fo llowed in
order to ensure the gathering of valid and
accurate data.
Typical Approaches
Ultrasonic examinations in a criti cal or
well- regulated indu stry are often covered by
multiple doc umen ts. For example, the nuclear
power generation industry uses proced ures
written in accordance with the American Society
of Mechanical Engineers (ASME) Code. The
Code, in rurn, is supported by publi shed
applicab le American Society of Testing and
Matcrials (ASTM) Standards. Somet imes these
are aug mented by company, customer, or
Nuclear Regulatory Commission (NRC)
Regulatory Guides, i. e., supplemental detai led
speci fi cat ions. In order to mcctthc intent of
these documents as well as their obvious stated
requirements, the Level In must be able to
understand t.he point of view that led to the
statements within the document s and be able to
ensure an employer that ultrasonic inspection
activities, documented in straightforward
procedures, are in compliance with the entire
spectnlm of applicable codes and standards.
TIlC manner in which requirements are stated
in codes and standards varies from document to
document. Some, such as the ASTM standards,
tend [0 emphasize the manner by which
inspection activities are to be conducted, but
leaves the issue of acceptance criteria to be
decided between buyer and service organization.
In thi s way, the actual procedures to be followed
are left up to the senio r technical personnel who
mu st agree upo n an appropriate set of acceptance
criteria and related operatio nal iss ues.
In the ASME Code, o ne sect ion of the Code
(Sect ion V) serves the same purpose as the
ASTM standards and even uses some of them as
the technical basis for ultrasonic acti vities.
Because the Code addresses several levels of
component crit icality, however, acceptance
criteria, requiremen ts fo r perso nnel certificat ion,
and definit ion of what will be in spected are
reserved for other sections, namely the
product-speci fi c referenc ing sect ions. For
example, Sections 11J (for new Nucl ear
construction), VIII (for new Pressure Vessels
construction) and XI (for Nuclear In-service
in spection) defin e the acceptance criteria and
personnel certification iss ues completely
separate from Section V, Nondestructive
Examination. In order to adequately address the
ultrasoni c in spection requirements in this case,
all applicable sections o f the Code, including {he
supplemental Code Cases that clarify spec ific
issues, must be considered when operating
procedures are being prepared to meet thi s
well -known code.
In the above cases, a fai r amount of latitude
is g iven the user of the codes and standards in
regard to the detaiJ s of assessing whether an ite m
is acceptable or not. The American Welding
Society (AWS) Structu ral Welding Code (used
in building, bridge, and o il rig inspection) is far
more prescriptive in the manner by which
transducers shall be selected , in which region s of
specific welds they are to be used, what
compensation for attenuation and beam spread
are to be used in analyzing in spectio n results,
and how welds shaH be laid ou t and marked.
71
Table 5.1. Typical Code and Standard Requirements
Issue
Approac h es
Examples
Transduce r selection
Ranges (size and angle)
Prescribed angles
Angles for each case
... transducers betwt!en 40 & 80 degrees
... transducers of 45, 60, 70 degrees
.. .45° in mid-section, 70° near surface
Scan t echniques
General coverage
Intervals
Overlap
Scanning levels
Rates
... scan in two orthogonal direction
... use 9-inch centers for grid
... overlap each pass by 10% of active area
... scan sensitivity to be 6 db above ref
... maximum scan rate of6 inches per sec.
Calibration
Instrument
Transducers
... vertical, horjzontallinearity
... beam location (IHV), depth resolution,
response from SDH, F8H, notch
... set DAC at 80% FSH, electronic 1;I:lIiIl8$
... recalibrate at start, sh ift, changes
Distance correction schedule
Special proble ms
Component curvature
Transfer
Use fig X.f to correct for curved items
Use dual tronsduL-ers to :.-et transfer
Reporting
Formats/forms
Analysis
Authorizations
Form xyz to be used in recording data
Classification ofre/Zector found by ..
All reports signed by Levell! & III
Accep tun ce criteria
General types
Dimensions
Collections
Reject all crocks and lack of fusion
Reje<:t slag over 3 / 4 in 2" plate
Reject pore spacing of 3 within 2"
Personne l cer tification
Per undefined procedure
Per SNT-TC-IA
Per MIL-STD-41O
or 250-1500
Supplier to have certification program
Written practice to SN7'-7'C-IA, 1988
Procedure per ....
Records of e xamination
List of documentation
Retention period
Final documentation shall include ... .
Supplier to retain records for 5 years
In a sim il ar vei n, many military standards,
because of their hi ghl y restricted appl ications
to certain component s and con fi gurati ons, tend
to establish more structured approaches to
specific confi gurations of test parts and require
inspection personnel to use these customized
approaches in conduct ing ultrason ic
inspections.
Table 5.1 li sts several of the typical items
included in codes and standards which need to
be addressed as clements of the manner in
which ultrasonic in spect ion procedures are to
be carried out. For example, an ult rasonic
procedure, as ciled in some requirements must
address the fo ll owing items: (I ) instrument
(selection, operating ranges), (2) calibration
standard (tie- in to test material s), (3) search
H
unit type, size, frequency (wave geomcLry),
(4) screen settings (metal path), (5) area to be
scanned (coverage inten sity), (6) scanning
techn iqlle (manual/coupl inglautomat ic),
(7) indicat ions to be recorded (minimum
sensit iv ity) , (8) data record fo rmat (form s to be
fo llowed), (9) accept/reject criteria (bas is or
specification reference), and ( 10) person nel
quali fication s (cert ifications). The degree to
which these and other item s are controlled is
usuall y dependent upon the cri ticali ty of the
appl ication.
Summaries of Requirements
Excerpts of contem porary specifications,
taken from both commercial and military
72
pract ice, are displayed on the fo ll owing pages in
order to gain an overview of thei r typical
conten ts and to be used as source materi als for
questi ons li sted at the end of thi s section. They
are not complete in their coverage and should
not be considered a surrogate for the original
issues of these documents.
73
ASTM
(American Society for Testing and Materials)
ASTM standard s are largely structured to
defi ne the basic operations which are to be done
in conductin g nondestructive inspections in an
orderly and technically sound manner and often
wi th regard to specific materials. However,
because they are intended to be used in many
different si tuati ons, the details of operational
practices are often left to supplemental
contract uaJ agreements between buyer and seller
of the inspect ion services. Thu s, some of the
requiremen ts of these standards tend to serve as
recommendat ions for specific actions or
candidates for requirements; if not, alternates are
agreed to by the buying and selling part icipants.
O n the following page is an excerpt from
ASTM A 609, "Standard Specification for
Longitudinal Beam Ultrasonic lnspection of
Carbon and Low-all oy Steel Castings." It has
defined a syste m of reference blocks using
nat-bottom holes, whi ch can be used as the
basis for developing distance-amplitude
corrections and establishing a reference
sensiti vity for straight beam in spection systems
to be used on cast steel components. It further
defines conditions under which inspections are
to take place (material conditions, scan rates,
DAC [ARL] development, reporting
requiremen ts), but it does not give specific
information regarding recalibration intervals,
quality levels, or personnel certificatio n. These
are, in large part, left up to the buyer to incl ude
as supplemental requi rements.
7S
(Excerpts Taken from ASTM A 609*)
Standard Specijicationjor Longitudinal Beam Ultrasonic Inspection
oj Carbon and Low-Alloy Steel Castings
1.
Scope
reflection from block and casting in same
thickness, conditions.
7 .4 ...Attenuator only control that can be changed
during inspection. Signals may be increased for
visibility but retumed to base level for signal
evaluation. Calibration rechecked periodically
using transfer block as basic reflector.
7.5 ... Regions having parallel walls and exhibiting loss
of back reflection shall be rechecked and treated
as questionable until the cause(s) is resolved
using other techniques.
1.1 This specification covers the standards and
procedures for the pulse-echo ultrasonic
inspection of heat-treated carbon and low-alloy
sleel casting by the longitudinal·beam technique.
2.
Basis of Purchase
2.1 When this specification is to be applied to an
inquiry. contract, or order, the purchaser shall
fumish the following information:
2.1.1 Quality levels for the entire casting or
portions thereof.
2.1.2 Sections of castings requiring inspection,
8.
and
2.1 .3 Any additional requirements to the
provisions of this specificaUon.
3.
Equipment
3.1 Electronic Apparatus:
.. .Pulse-echo, 1-5 MHz, linear ± 5% for 75% of
screen height.
9.
4.
Acceptance Standards
9.1 ... Criteria for individual castings should be based
on a realistic appraisal of service requ irements
and the quality that can normally be obtained in
production of the particular type of casting.
9.2 Acceptance quality levels shall be established
between purchaser and manufacturer on the basis
of one or more of the following criteria.
9.2. 1 No indication equal to or greater than that
specified in one 01 the quality levels listed
in Table XI, or
9.2.2 No questionable areas trom paragraph 7 .5,
unless proven acceptable by other means.
9.3 Other means may be used to establish the validity
of a rejection based on ultrasonic inspection.
3.2 Transducers:
3.3
Data Reporting
8.1 ... Total number, location, amplitude and area of all
indications equal 10 or greater than 100 percent
ARL, questionable areas (7.5), testing parameters
and sketch showing uninspected areas and
location and sizes of reportable indications.
... L-wave, 1-1 1/8 dia, 1 in. square; prefer 1 MHz
beyond 2 in. depth.
Reference Blocks:
... FBH, # 16, DAC - 1-10 in ., cast materials that
have a metallurgical structure similar to the
castings being inspected. Other blocks may be
used provided they are proven to be acoustically
equivalent to the cast steel. The hole bottom shall
be cleaned and plugged. Each block identified.
Block specifications: 32 ons, flaVparaliello within
0 .00 1 in., hole diameter 1/4 ± 0.002 in.,
perpendicular within 30 min.
Table Xl Rejection Level
Personnel Requirements
4.1 The seller shall be responsible for assigning
qualified personneL .. , a qualification record shall
be available upon request.
5.
6.
7.
Casting Conditions
5. t Heat treat before UT.
5.2 Surfaces shall be free of interference.
Test Conditions
6.1 Each pass of transducer to overlap.
6.2 Rate less than 6 in i s.
across the CRT.
7.2 ... Mar1<. the FBH indication height for each of the
applicable blocks on the CRT screen. Draw line
through indication mar1<.s. Set peak at 314 screen
height. This is the amplitude reference line (ARl).
7.3 ... Use transfer mechanism to compensate for
surface roughness differences. Use back wall
Arca
Level
inch2
1
2
3
0.8
4
5
6
7
Procedure
7.1 Adjust sweep to put back wall at least halfway
Quality
1.5
3
5
8
12
16
Notes:
Table XI applies to signals above the 100% ARL line.
1.
2.
The areas refer to casting surface area over which
a continuous indication exceeding ARL exists.
Beam spread and curvature must be considered
where long distances and curved castings are
involved.
*Ex tracted. with pcnnission. rrom t he Annual Book or ASTM Standards, copyright American Society ror
Testing and Materials, 19 16 Race Street. Philadelphia. PA 19 103.
76
ASME
(American Society of Mechanical Engineers)
ASME has structured its nondestructive
testing requirements as part of the Boiler and
Pressure Vessel Code. This comprehensive set
of rules defines the allowable design practices,
materials, construction practices, examination
approaches, and documentation needed to ensure
consistent construction of new boilers, pressure
vessels, and ancillary components including
piping systems, containment systems, and
support systems. The Code is subdi vided into
section s devoted to specific classes of
components (pressure vessels, boilers, piping)
and supporting technologies (welding,
nondestructive examination, materials). Thus
items "constructed in accordance with the Code"
often must satisfy a multillide of requirements.
The following pages include brief excerpts from
Section V, "Nondestructive Examination," as
well as very brief examples of how the
referencing sections of the Boiler and Pressure
Vessel Code are used for the introduction of
specific requirements. An example of ultrasonic
testing of ferritic cast materials was chosen to
compare the ASTM spec ification and the
modified set of requirements of Sections III
and V.
The important area of weld inspection is
included to highlight the use of special purpose
calibration blocks (as opposed to commercially
available standard cal ibration blocks, i.e. , the
IIW block) and to describe methods of verifying
instrument linearity and accommodating test part
curvatures.
77
(Excerpts Taken from ASME Boiler
and Pressure Vessel Code*)
Section V (Nondestructive Examination)
Article 5 - Ultrasonic Examination Methods fo r Materials and Fabrication
T·510 SCOPE
This Article describes or references requirements which
are 10 be used in selecting and developing ultrasonic
examination procedures for welds, parts, components,
materials and thickness determinations. This Article
contains all of the basic technical and methodological
requirements for ultrasonic examination. When examination to any part of this Article is a requirements of a
referencing Code Section, the referencing Code Section
shall be consulted for specific requirements for the followIng.
Personnel Qualification/Certifications
Procedure Requirements andlor Techniques
Examination System Characteristics
Retention and Control of Calibration Blocks
Acceptance Standards for Evaluation
Extent and Retention of Records
Report Requirements
Extent of Examination andlor Volume to be Scanned
S-Wave - per Figure plus other holes, notches for
reference.
Method - Straight Beam per SA-609 exclusive of
paragraph 7.3 (transfer method).
- Angle Beam 80% peak, SOH OAC curve from
bk>ck
T-541.4.3 Examination.
per SA-609 plus ..
(a) A supplementary angle beam examination shall be
performed on castings or areas of castings where a back
reflection cannot be maintained during the straight beam
examination, or where the angle between the front and
back surfaces of the castings exceeds 15 deg.
(b) The requirements for extent of examination and
acceptance criteria shall be as required by the referencing
Code Section.
T-S22 Written Procedure Requirements
Ultrasonic examination shall be performed in accordance with a written procedure. Each procedure shall
Include at least the following information, as applicable.
(a) , (b), (0), .. . (I), (m) , (n), (0)
NB·2574 Ultrasonic Examination of Ferrltlc
Steel Castings
Ultrasonic examination shall be performed in
accordance with T-54 1.4 of Article 5 of Section V.
T-S23.1 Examination Coverage
10% overlap of piezoelectric element
Rate SS inls unless calibrated elsewise
NB-2574_1 Acceptance Stds,
(a) The Quality Levels 01 SA-609 shall apply per
(1) Levell , T<2 in .
(2) Level 3, 2!>T:S4 in.
(3) Level 4, T>4 in.
(b) Supplemental Requirements
(1) Length vs. Level
Levell, 1.5 in.
Level 2, 2.0 in.
Level 3, 3.0 in.
Level 4, 3.0 in.
(2) Q Levell applies to first inch of any volume
of material.
(3) Measured change in depth up to lesser of
one-half wall or 1 in .
(4) Two or more indications in the same plane,
separation<longest dimenSion, within (b)( l ).
(5) Two or more indications greater than next
higher Q-Ievel permits.
T·S30 EQUIPMENT AND SUPPLIES
Frequency' (1·5 MHz)
Screen Linearity - ± 5 % in 20-80% range
Control Linearity - ± 20% amplitude ratio
Check Calib. at beginning, end, personnel change,
suspected malfunction
Linearity methodology prescribed .
T-540 APPLICATIONS
T· 541 Materi al Product Fo rms
Plate , Forgings-Bars, Tubular Products
T -541 .4 Castings. When ultrasonic examination of ferritic
castings is required by the referencing Code Section, all
sections, regardless of thickness, shall examined in
accordance with SA-609; supplemented by T-Sl0, T-S20,
as well as T-541.4.1 , T-541.4.2 and T-S41.4.3
T-S41 .4.1 Equipment Transducer: 1-11/8dia, I in2t
MHz, others allowed if sensitivity o.k.
T-541.4.2 Calibration
Blocks - same material specification, grade, product
form, heat treatment, and thickness ± 25%. Surface
representative.
l-Wave - per SA-609
Excerpts from Section /If (Nuclear Construction), a
sample of a referencing Gode section.
* Extracted, with pennission, from the ASME Boiler and Pressure Vessel
of Mechanical Engineers, 345 E.'lst 47th Sucet, New York , NY 100 17.
78
Code,
co pyright American Socicty
T-541.5 Bolting Material
T-580 EVALUATION
With DAC, any reflector wh ich causes an indication in
excess of 20% of OAC to be investigated to criteria of
referencing Code.
T-542 Welds
Requirements for UT of full penetration welds in
wrought and cast materials including detection, location,
and evaluation of reflectors within the weld, heat affected
zone , and adjacent material. Covers ferritic products and
pipe. Austenitic and high nickel alloy welds covered in
T-542.8.5
T·590 REPORTS AND RECORDS
A report shall be made indicating welds examined ,
locations of recorded reflectors with operator 10. Records
of calibrations (instrument, system, cal block ID) shall also
be included.
T-542.2 Calibration
Basic Calibration Block
Material - Same product form and material specification
or equivalent P-Number grouping. P-Nos. 1, 3, 4, and 5
are considered equivalent for UT. Test with Straight
Beam .
Clad - Same welding procedure as the production part.
Surface representative.
Heat Treatment - At least minimum tempering treatment
of material spec for the type and grade and postweld HT
of at least 2 hr.
Geometry - see Figure 5.2
Curvature - >20 in. dia, considered flat
- <20 in. dia, see Figure 5.1
System Calibration
Angle Beam (Ref: Article 4, Appendix B)
(a) sweep range - 10% or 5% full sweep
(b) distance-amplitude correction - 20"lol2dB
(c) position
(d) echo from surface notch
UW-53 TECHNIQUE FOR ULTRASONIC
EXAMINATION OF WELDED JOINTS
Ultrasonic examination of welded jOints when
required or permitted by other paragraphs of this
Division shall be performed in accordance w ith
Appendix 12...
Appendix 12 ULTRASONIC EXAMINATION OF
WELDED JOINTS
12-1 SCOPE
This Appendix describes methods which shall
be employed when UT of welds is specified in this
Division . Article 5 of Section V shall be applied
for detailed requirements. A certified w ritten
procedure is required.
Straight Beam (Ref: Article 4, Appendix C)
(a) sweep range - 10% or 5% full sweep
(b) distance-amplitude correction - 20°/o/2dB
12-2 PERSONNEL QUALIFICATION SNT-TC-1A
Frequency
(a) change of system component
(b) before, end of examination (series), each 4 hrs, and
at personnel change .
12-3 ACCEPTANCE-REJECTION STANDARDS
All indications over 20% DAC shall be investi·
gated to determine shape, identity, and location .
Rejection criteria:
(a) interpretations of crack, lack of fu sion or
incomplete penetration, regardless of
length.
(b) liner type reflectors exceeding the reference level and the length exceeds
(1) 1/4 in . for T <3/4 in.
(2) T/3 in . for 3/4:SrS2 1/4 in.
(3) 3/4 in. for T>2 1/4 in.
If the weld joins two members having different
thicknesses at the weld, T is the thinner of these
two thicknesses.
T-542.6 Welds in Cast Ferritic Products...
Nominal frequency is 2.25 MHz, unless material
requires the use of other frequencies. Angle selected as
appropriate for configuration. DAC not required in first onehalf vee path in material less than 1 in. thick.
T-542. 7 Examination of Welds
Base Metal - Free of surface irregularities.
- Scan with L-wave for laminations at 2X
sensitivity.
Longitudinal Reflectors - Manipulate, rotate, perpendicular to weld axis at 2X sensitivity over reference level.
Transverse Reflectors - Manipulate along weld at 2X
from both directions.
r-542.7.2.5 Evaluation
An indication in excess of 20% OAC shall be investigated
to the extent that it can be evaluated in terms of the
acceptance standards of the referencing Code Section.
T-542.8.5 Austenitic and High Nickel Alloy Welds
Ultrasonic examination is more difficult than in territic
materials due to variations in acoustic properties of
austenitic and high nickel alloy welds, even those in alloys
of the same composition, product form, and heat treatment.
It may, therefore, be necessary to modify andlor supplement the provisions of th is Article in accordance with T110(c) when examining such welds .
12-4 REPORT OF EXAMINATION
Retain report for 5 years . Include re qu ired
entries from Section V plus a record of repaired
areas and a record of all reflections from uncor·
rected areas having responses that exceed 50%
of the reference level including location, response
level , dimensions, depth below surface and
classification .
(Excerpts from Section VIII (Pressure Vessels)
79
Figure 5.1. Basic calibration block
2 in. long to 1/4 in. diameter nat end;
millllotches 2% T deep
,/
•
,',
t
,,-_2_;n_'_7''--_ +________,,::;::?
t
3 in. [Note (l)J
,,;/
/.
Through Clad
Thickness 2% T
Deep into the
Base Metal
I
)-----p'''f-- Clad [Note (4)]
T/4
,'/
,','
','
6 in. [Note (I)]
1- 1/2 in. Minimum
_I
Drilled and reamed hOles r-Tj:'" Tl2 fNote (\)]
3 in. Deep [Note (I) I
8a<i<
W,14
Tbk ~ .....
(tl
C.tib .... _
"~
810<11. TbKli.naS!D
Dj;upclrr (:s.... ( J l(
lin .... '
JJI6 ...
1/4;n.
5116 ;ft_
:Win
0. .. 2 'ft. _ah ~ ,n.
0. ... 4 ift. lhrouall 6 in.
0. ... 6 ,n. ''''''''all 8 (n.
0.,<.8 ,n. ,tItousJI10 in.
Ove. to in. throusJI t2;".
0.", t2 in. throusJI t4;".
Over t4 in.
'in.'"
7;" ... ,
'Ii.... '
II;".... '
7/16 "'_
)] in. 01"
(Nooc(211
IN"" (1)J
In ift
Noles:
(\) Minimum Dimensions.
(2) For euch increase in thickness of2 in. or fraction thereof. the hole diameter shall increase 1/ 16 in.
(3) The tolerances for the hoic diameters shall be ± 1I)2 in.; tolerances on notch depth shall be +iO and -20%; tolerance or hole location through
the thickness shall be ± IIS; perpendicular tolerance on notch reflccting surface shall be ±2 deg.
(4) Clad shall OOt be inc luded in T.
T-593 Examination Records
(a), (b), (c), ... (k), (I), (m) lists information 10 be included
such as procedures, equipment, personnel, and map of
indications.
Figure 5.2, Ratio limits for curved
surfaces
Appendi x I - Screen Height Linearity
Get dual signal on screen with amplitude ratio of 2:1,
with the larger set at 80% FSH. Adjust gain to successively set the larger indication from 100% to 20%, in 10%
increments (2dB steps) and read smaller indication at each
selling. Reading must be 50% of the larger, within 5%
FSH.
=
,2
"il
=
Appendi x II - Amplitude Controt Linearity
Get single signal on screen and change gain sellings in
accordance with table. The indication must fall within the
specified limits. Sellings and readings are to be estimated
to the nearest 1% of full screen.
~""'1----"i D .)
----. -- 8
Origina l Limits
Setting
Change in Gain
Control
Indication
(%FSH )
(dB)
(%FSH)
1-;-:-;--;4''7;7,.,._",,,,,_,,
- ,,,--:1-f-:-,-=", 4.8
2.9
1.7
u
80%
80%
40%
20%
·6 dB
-12 dB
+6 dB
+12dB
~
.~
32·48%
16·24%
64-96%
64-90%
'"
80
0
__~--~-~-------~,~--~ l
5
10
15
20
E xamination Surface Diameter, In.
Military Standards
Military standards tend to use hi ghl y spec ific
instructions as part of their req uirements,
incl uding the design and use of ca li bration
blocks, methods of system performance analysis,
and other operating instructions. Included below
are excerpts from MIL-STD-2154 which is
intended to standardize the process for applying
ultrasonic inspection in the evalu ation of
wrought metals and their products greater than
0.25 in. thick. It is applicable to the in spection
of forgings, rolled billets or plate, extruded or
rolled bars, extruded or rolled shapes, and parts
made from them. It does not address
no n-metals, welds, casti ngs or sandwich
structures.
It addresses both immersion (type J) and
contact (type II) methods of inspection of
wrought aluminum (7075-T6, 2024), magnesium
(ZK60A), titanium (Ti-6A I-4V annealed) and
low alloy steel products (4130, 4330, 4340),
using five classes of acceptance.
81
(Excerpts Taken from MIL-STD-2154)
!nspeclion, Ullrason ic, Wrollghl Metals,
Processfor
1.
SCOPE
Water path ± 1/4 in. of standardization,
maximize water-metal interface signal, develop DAC if
needed, angle transducer 23 0 ± 4 to get S-wave from
45-70 degrees in aluminum, steel and Ti. Set primary
reference response a180% FSH. Set scan index at
between 50 and 80% of the half-amplitude response
distance from reference standard. Establish for each
transducer used. Establish transfer factor using
4 points from differenllocalions based on back surface
reflections or notches, but only if the response is more
or less than the comparable Signal from the reference
standard, allowable range between 60 and
160 percenl Of ± 4 dB.
Detection of flaws in wrought metals having cross
section thickness equal to 0.25 In. or greater.
4.
GENERAL REQUIREMENTS
Orders shall specify type of inspection and quality
class in drawings including identification of directions of
maximum stresses.
Personnel shall be Level II or better, Mll-STD-410.
Levell Special permitted per 410.
Detailed procedure to be prepared for each part and
type of inspection. It shall cover all of the specific
information required to set-up and perform the test, i.e. , (a) ,
(b), (e). " (0), (p), (q) ,
5.
DETAIL REQUIREMENTS
5.1 Malerials.
Couplants
- Immersion (Type I), free of visible air bubbles,
use preapproved additives i.e. inhibitors, wetting
Acceptance Criteria
Discootinuities are evaluated with gain sel for 80%
FSH on a test block with hole diameter aquallo the
smallest acceptable for the applicable class and wilh a
melal Iravel distance aqualto the reflector depth within
- ±10%.
agents
- Contact (Type II) , viscosity and surtace
wetling sufficient to maintain good energy
transmission.
Standard Test Block Materials - listed alloys
or from the same alloy as the part, free from spurious
indications. To be tested to class AA using Immersion,
L-wave.
5.2 Equipment.
Frequency: 2 .25 - 10 MHz, Ref: ASTM E317
Gain : ± 5% FSH over full range
Alarm: Front surtace synchronization
Transducers
- L-wave, 3/8 - 3/4 in. dia.
- S-wave, 1/4 - 1 in. dia. or length
Manipulators
- Angular adjustment - ± 1 degree
- Linear accuracy - ± 0 .1 in.
5.3 Reference standards.
Flat surface - #2,3,5,8 FBH per E-127
Curved surtace - R < 4 in., special block
Angle Beam - IIW, for transducer exit/angle
SDH block, rectangular beam hollow
cylinder block, pipes
Verification - drawings/radiographs, comparison
amplitude plots, linearity plots, surface finish,
maleriat certs.
5.4 Inspection procedures.
Scan parallel to grain flow up to speeds that
found reflectors in base materials and at
reference amplitude, angulale to maximize,
check high stress regions
Near surface resolution limit for 2: 1 SIN
- 1/8 in. for 1 in. range thru
t /2 in. for 15 in . range
failure = test from both sides
Immersion -
Acceptance Criteria Matrix
Quality
a...
AAA
AA
A
B
C
Single
( U -n1l)
(II FBII) ·
"
""
""..
.
"" -----
Multiple
LlMlir
(ind ,)
10% lli
118
In
,
,
I
I
---NfA----------·
" 'Y'wo or more less than I ,n. apart .
For L-wave inspections, loss of back reflection
exceeding 50 percent shall be cause for rejection unless
due to non-parallelism or surface roughness.
Linear discontinuity length is measured using the 50%
drop method .
5.5 Quality assurance provisions.
System performance to be checked prior to, at 2 hour
intervals during continuous testing , at instrument setting
changes or modules, and after testing. DAC setups are to
be checked daily for the thickness range 01 material being
inspected.
Data records shall be kept on file in accordance with
contractlorder. Location and general shape (size) 01
rejectable indications are to be recorded. Indications in
excess of acceptance criteria are permitted if they will be
subsequently removed by machining. A C Scan shall be
made that shows the location and size (by discontinuity
grade) with respect to the material being scanned.
82
Building Codes
Nondestructive testing requirements are
ofte n melded into the detailed requirements
associated with the construction of welded
structures stressed with static loads (buildings),
dynamic loads (bridges), or tubular structures.
Different sets of acceptance criteria are used
based on the intended purpose of the structure.
The base metals involved are mostly carbon and
low alloy steels, commonl y found in the
fabrication of steel structures.
severity class is determined by the degree to
which the flaw indication exceeds the reference
level, as modified by sound path attenuation , and
the weld thickness and search unit an gle. The
classes and reject criteria are as following:
Class A (large) - All are rejectable
Class B (medium) - Reject if longer than
3/4 in.
C lass C (small) - Reject if longer than 2 in.
C lass D (minor) - All are acceptab le
The wording and approaches included on the
next pages use typi cal criteria based upon static
loads. Included are those for scanning levels
(which change with sound path) and bases for
rejection depending upon flaw class. The flaw
The presence of more than one class in close
proximity are addressed in special notes, as are
the trealment of primary tensi le stress weld s and
eleclroslag welds.
83
(Excerpts Taken from a
Representative Building Code)
1. INSPECTION
Personnel Qualification
Personnel pertorming nondestructive testing other than
visual shall be qualified in accordance with the current
edition of the American Society for Nondestructive Testing
Recommended Practice No. SNT-TC-1A. Only individuals
qualified for NDT Levell and working under the NOT
Level II or individuals qualified for NOT Level II may
perform nondestructive testing.
Extent of Testing
Information furnished to the bidders shall clearly identify
the extent of nondestructive testing (types, categories, or
location) of welds to be tested.
ULTRASONIC TESTING OF GROOVE WELDS
General
The procedures and standards described below are to
be used in the ultrasonic lesting of groove welds and heataffected zones between the thicknesses of 5/16 in.
(B.O mm) and 8 in. (203 mm) inclusive, when such testing
is required. These procedures and standards are not to be
used for testing tube-to-tube connections.
Variation in lesting procedure, equipment, and acceptance standards may be used upon agreement with the
Engineer.
Transducers
L-wave, 1/2 S Area ~ 1 in2
2-2.5 MHz
resolve #3-hole
S-wave, (518-1) x (518-13/16)
ralio:l .2: 1
angle: ± 2 degrees (70, 60, 45)
clearance: 1 in.
Reference Standards
IIW Block + portables
Resolution Block
Qualification Frequency
Horiz lin - 40 hrs.
Gain· two months
Probe Noise - 40 hrs.
Shoes & Angles - 8 hrs.
6.18 Calibration for Testing
Sensitivity/Sweep
Prior to test at location
30 Minute inlervals
Changes in personnel , equipment or electrical
disturbances
Zero Reference Level
Gain setting @ 80% FSH from 0.06 in. SOH
Testing Procedures
Positional Layout X, Y
Surface condition clear
Lamination check- L-wave
Ali bult joint welds shall be tested from each side of the
weld axis .. ., It is intended that, as a minimum. ali welds be
tested by passing sound through the entire volume of the
weld and the heat-affected zone in two crossing directions,
wherever practicaL
Ultrasonic Equipment
1-6 MHz, Pulse-Echo
Horizontal linearity- 2%
Stability - ±1 dB for 15% voltage change
Gain - 60 dB, ±1 dB
Ta ble B-l Ultrasonic Acceptance-Rej ection Criteria (St atic)
Weld Thickness· in in. (mm ) and Search Unit Angle
Discontinuity
Severity
Class
Class A
Class B
Class C
Class D
5116(8)
thru
>31'
thru
314(19}
1-112(38)
70·
700
700
.5&
lower
.2&
lower
-2&
lower
••
.3
-1
0
.7
.,
>1·1/2 thru 2·112(64 )
.1
.2
6fY'
.1 &
lower
.2
.3
.,
>2-112 thru 4(100 )
>4 thru 8(200)
".
700
6fY'
".
70·
60·
".
.3&
lower
-5&
lower
-2&
lower
0&
lower
-7 &
lower
-4 &
lower
-1 &
lower
.,
-,-3
-1
0
.1
.2
-
.5
-5
-3
-2
0
.1
.
••
.7
-2 <0
.2
.1
.2
.3
.5
.4
-'<0
.2
-1<0
.2
.2
.3
. 8&
+5 &
.3&
•• &
.8&
.3&
.3&
.5&
.3&
.3&
., &
"P
"P
"P
"P
"P
"P
"P
"P
"P
"P
"P
84
Evaluation - Set signal from indication at 80% FSH.
Difference between "Indication Lever setting and ~Zero
Reference Level" setting is measure of severity. For sound
paths over 1 in., attenuation compensation (2 dB/in. over
1 in.) is used.
"Indication Rating" =
Indication Level - Zero Reference Level - Attenuation
Each weld discontinuity shall be accepted or rejected on
the basis of its indication rating and its length.
Notes:
1. Where possible, all examinations shall be made in Leg I
unless otherwise specified. Examinations in Leg II or III
shall be made only to satisfy provisions of this table or
when necessary 10 lesl weld areas made inaccessible by
an unground weld surface, or interference with other
portions of the weldmen!.
2. Whenever indications occur at the weld metallbase
metal interface, they shall be further evaluated with 45 , 60,
or 70 degree transducers, whichever sound path is nearest
10 being perpendicular to the suspected fusion surface.
3. B is the malerial surface opposite to the surface from
which the initial scanning is done.
4. Al ternative angles permitted if flush Ref. 6.19.5 .2.
Table B-2 Scanning Levels
Sound pa th** in inc h es (mm)
Abo ve Ze r o Refer e n ce,
dB
th rough 2-1/2 (64mm)
>2-1/2 through 5 (64-127 mm)
>5 th rough 10 (127-254 mm )
>10 through 15 (254-381 mm)
14
19
29
39
" This column refers to sound path dista nce; NOT mate ri a l t hi ck ness
Table B-3 Procedure Lege nd
Material
Thickness
(inches)
Top
Quarter
Middle
H a lf
B ottom
Quarter
Procedure
Numbe r
5/16 to 1-3/4
70"
1-3/4 to 2-1/2
2-112 t o 3-112
3-112 to 4-1/2
4-112 to 5
5 to 6-L'2
6-112 to 7
60"
70"
70"
70"
70"
70"
70"
70"
# 1
# 4
45"
6O"B
6O"B
45"B
45°B
# 5
# 7
#10
#11
#13
60"
60"
60"
45"
45"
70"
45"
A
B
85
Chapter 5 Review Questions
Q.5~
I A governing specifi cation calls for shear
wave, angle beam examination of the
component. What angle should be used?
A. 45 degrees when inspecting a thi ck,
45 -degree preparation weldmcnt.
B. 60 degrees when inspecting a I in.
thi ck weldment.
Q.5-4 A set of curves of amplitude versus area
were developed for examination o f a
steel forging. A refl ector was found
which was determined to be larger in
ex tent than the sound beam diameter.
Which criterion, of those given below,
shou ld be used to size the refl ector?
C. Both A and B.
A. Directly compare the amplitudes and
select the size giving the same
amplitude.
S. Multiply the reflector amplitude by
1.36 and select the equi valent size
from the curves.
C. Move the search unit in orthogona l
directions until the amplitude drops to
SO percent of maximum to establi sh
the boundaries of the refl ector.
D. Multipl y the sound beam diameter by
1.36 to yield the refl ector size.
D. The angle(s) permitted by procedure
qualifi cation.
Q.5-2 Accept/reject criteria may be specified in
a code, spec ification , or the procedure.
Upon what should these accept/reject
levels be based?
A. accept/reject criteri a should be based
upon the experience of the operator
B. upon the item's end use and the
criti cal flaw size
C. minimum size that can be detected
D. upon the largest size that can be
detected
Q.5-3 What is the critical fl aw size in a forging
to be used in an aircraft landing gear?
A.
B.
C.
D.
0.200 in. long
2 mm long by 3 mm wide
a flaw that will grow during serv ice
a flaw whi ch may cause failure
during service
87
The Following Questions Apply to
Q.5-5
Q. 5-6
Q.5-7
Q.5-8
Q.5-9
ASTMA 609
Reference standards are to be constructed Q.5-1 0 The work order has designated the
fro m materials that:
inspectio n to be done lO a quality level of
"4" throughout a disk-shaped casting,
12 in. in diameter and 4 in. thick. Which
A. come from the same heat as the test
of
the observed di scontinuities are
parIs.
rejectable?
E. represe nt the alloy and heat treatment
of each part.
C. have been L-wave tested to ensure
A. signal 50 percent above ARL, 2 in .
freedom from major flaws.
long by 2 in. wide
D. have a si mil ar metallurgical structure.
B. signal 20 percent above ARL, 2.6 in.
in diameter
Personnel conducting UT shall be
C. signal 100 percent ARL, 1.5 in . wide
certifi ed in accordance with:
by 3 in. long
D. signaJ 90 percent ARL, area of
6.2 in .2
A. SNT·TC· JA
B. the manufacturer's written practice
(procedure),
Q.5-1 1 The instrument reca libration schedul e
C. the buyer's wril.len practice
caUs for the system to be checked (during
(procedu re).
test ing):
D. nothing, they do not have to be
certified.
A. prior to, every 4 hours, at personne l
changes and at testing end.
Reference bl ocks are to be made using
8. every 8 hours per union contract.
FBHs:
C. if system performance suggests
proble ms are present, e.g. , the battery
li ght starts to fl ash.
A. ranging in s ize fro m 3/64 - 8/64 in.
B. of a single size equal 10 1/4 in.
D . period ica ll y, using the transfer block
as a basic reflector.
C. al depth s covering the range from
1-8 in.
D. nonc o f the above.
Q.5- 12 A region wi th loss of back reflection
(below 50 percent) has been found; the
nex t step is to:
Scanning practices ca ll for transducer
position s lO:
A. inspect the region using another
means such as radiography .
A. be fro lll two orthogonal direction s.
B. overlap each other by 10 percent.
8. inspect the reg ion using angle beams
fro m two directions.
C. change at rates at least equallO
6 in.ls.
C. recheck to e nsure operati onal errors
were not at fault.
D. none of the above.
D. li st as "questionable area" in final
report.
The ARL is to be set o n the sc reen such
that:
A. the peak signal amplitude eq uals
3/4 FSH.
B. surface effects are refl ected as a
rev ised ARL.
C. the backwall echo is in the middle
third of the sweep.
D. scanning can be done at 6 dB over
re ference level.
88
The Following Questions Apply to
ASME Section V, Article 5
Q.5- 13 Reference standard s (calibration blocks)
are to be constructed from materials that:
A. came from the same heal as the test
paIls.
B. have a si milar metallurgical structures
as the lest part s.
e. are the same materi al specificat io n,
grade, and heat treatment as parts.
D. are of the same thick ness as the test
Q.5-17 A 3.5 in. thick casting, intended for a
nuclear appli cation , is being inspected to
T-54 1.4. The quality level is to be
ass igned:
A. in cooperation with the buyer as per
Par. 2 of SA 609.
(Note: SA 609 is identical to ASTM A
609.)
B. as leve l 3, s ince the thi ckness is
parts.
between 2 and 4 in.
C. as levell , for near surfaces and
leve l 3 for middle 1.5 in.
D. fo ll owing a forma l NRC review for
approval.
Q.5-14 Person nel co nducting UT shall be
certified in accordance with:
A. SNT· TC·JA .
B. the referencing Code section.
C. the vendor's written practice.
D. the Code of Ethics for ASME.
Q.5-18 For a 3.5 in. nuclear grade casting, which
of the following indications is (arc)
considered rejectable?
Q.5- 15 The cali bration blocks for L-wave testing
of casti ngs shall use SDHs as show n in :
A.
B.
C.
D.
A. 120% ARL, Depth = 0.75 in. ,
Area = 1.3 in .2, Length:;:; 1.0 in.
B. 110% ARL, Depth = 1.25 in.,
Area = 1.8 in. 2 , Length = 2.75 in.
C. >100 % ARL, Depth = 2.0 in. ,
Area = 3.1 in. 2, Length = 2.0 in.
D. all of the above
II W block.
Figure 5.1.
SA·609.
none of the above.
Q.5 - 16 Scanning practices call for transducer
positions to:
Q.5-19 Compensation for differences betwee n
calibration blocks and cast lest part s is:
A. be from two orthogonal directions.
B. overlap each other by 10 percent.
C. never scan at rales in excess of
6 in.ls.
D. none of the above.
A. made by adjusting the reference ga in
in accordance with backwall
reflections.
B. made by adju sting the reference gain
us ing pairs of matched transducers.
C. not all owed.
D. not addressed.
Q.5-20 Several sc reen height linearity checks
y ielded the half amplitude results li sted
below for initial settings of 100, 80, 60,
40, and 20 percent FSH. Which set of
readings (%FS H) is considered Ollt of
ca libration ?
A. 54,42,27, 19,9
B. 50,34,26,20, II
C. 48,3 7,32,21, 10
D. 45,44,33, 18,9
89
T he Following Q uestions Apply to
the Representative Bui/ding Code
Q.5-2 1 A check of transducer perform ance using
the IfW block indi cated the follow ing
angles were being used. Wh ich se( s) is
Q.5-23 How long would the ind icatio n have to
be in o rder to be considered rejected for
the above q uestion?
not in compli ance wi th the requirements
A. longer than 2 in.
B. longer than 3/4 in.
C. any length
D. it would be acceptable regardless of
of the Representat ive Building Code?
A.
B.
C.
D.
68,72,44,62
46, 69,63, 59
45,7 1,59,62
43,62,72, 68
length
Q.5-24 The transducer in the above problem was
bei ng used in accordance wi th Procedure
Number:
Q.5-22 T he signal from a weld discontinu ity, set
at 80 percent FS H, results in the gai n
being set at SO dB. The reference
re nector req ui red a gain setti ng of onl y
44 dB . The travel path was less than 1 in.
The materi al thickness is 2.6 in. and a
45-dcgree angle beam transducer was
used. What is the flaw severity class?
A. #4.
B. #5.
C. #7.
D. all of the above.
A. A
B B
C. C
D. D
90
Chapter 6
Special Topics
Chapter 6
Special Topics
This section di scusses a few items which
represent technologies which are not in the
mainstream of UT but are of imporlance in that
they represent former app li cat ion areas of
interest and/or emergi ng issues which will
become part of the way UT is performed in the
future.
Resonance Testing
The resonance technique is, perhaps, the
oldest acoust ic/ultrasoni c nondestructive testing
technique other than the visual method. Metal
structu res, especia ll y casti ngs and forg ings, wi ll
audi bly ring when struck a sharp blow. An
experie nced listener could often tell by the
ringing tone whether the part was flawed or not.
A structure sLlch as a bell when severely fla wed
sounds wrong to most anyone, experienced or
not; however, the accuracy of this technique left
much to be desired. W ith the advent of
equipment capable of operati ng at ultrasoni c
freq uencies, resonance was one of the first
techn iques used for thickness measurement ;
al though some flaw detection, such as for
lamin ations, was also performed. When a
pi ezoelectric crystal is exc ited wi th a voltage
vary ing at the resonant frequency, the
mechani cal energy produced is great ly
increased. Th is frequency is achieved when the
wavelength in the material is twice the
thi ckness or a multiple thereof.
In general use, a transducer is exc ited by a
time-varying frequency designed to sweep the
crystal through the fundamental and several
harmonic freq uencies. W hen a resonant
cond ition is ac hieved, it is sensed as an
increased loading on the transducer by the
electronics and di splayed on the readout de vice.
Since the diffe rence between harmonic
freque ncies is equal to the fundamenta l
frequency, it does not matter whi ch harmoni cs
are excited.
Resonance testi ng was commonly used,
especially in the basic materia l ind ustries such as
the steel producers, as a qual ity control measure
for both thickness and lam inar defects. Improved
e lectronic ci rcuits have been used to create
pu lse-echo devices whi ch are more accurate and
easier to use and interpret. As a result, resonance
testing is no longer in common use except for
some primary materials characteri zations.
Flaw Sizing Techniques
Flaw detect ion w ith ultrasonics is at an
advanced state o f the art. S ignifi cant flaw s in
most str uctu res can be detected . When a UT
indication is identified as a flaw, normally some
estimate of its size is required. Below is a list of
variables which affect these measurements. This
li st inc ludes, but is not li mited to, fl aw type, flaw
shape, location, multiple fl aws in same location,
geometric reflectors in same location, grain s ize
and orien tation, fl aw orient ation, part
confi guration, search unit characteristics, and
sound beam characteristics. Each of these
variables can affect the measurement to a degree
whic h is not the same from flaw to flaw.
In general, there are two flaw size categories
which are usually treated differently, those wi lh
flaws larger than the beam diameter and those
smaller than the beam diameter. As a result of
these factors, no one technique provides accurate
flaw sizing on all flaws; however, numerous
techniques have been dev ised fo r flaw sizing.
Most of these are based on some considerat ion
of signal amplitude.
93
Flaws can generally be described by three
dimensions, length, width, and height , where the
length and height are in a plane normal to the
direction of max imum stress and the width is in
the direction of the stress. In most situations li ttle
emphasis is placed on the determination of width
since it has lillie effect on the stress pattern.
Length is measured normal to the stress and
parallel to the test item surface, whil e height is
measured normal 10 both the stress and the
surface. Of these two, length can ordinari ly be
measured successfull y with the desired accuracy.
Height, on the other hand , is much more difficult
to measure.
For lami nar-type flaws, the length and width
refer to the dimensions in a plane paralle l to the
entry surface. Orientations of these dimensions is
a mailer of procedure or choice.
Small fl aws may be class ifi ed into two
categories, fl aws smaller than the wavelength
and fla ws larger than the wavelength. A c ircu lar
disk fl aw much small er than the wave length will
reflect a spherical wave wi th pressure
proportional to the third power of the flaw
diameter and inverse ly proportional to the
wavelength . Very small flaws re fl ect very li ttle
e nergy and are difficult to detect.
Flaws larger than the wavelength and less
than the beam diameter reflect sound
proportionally monotoni ca ll y with flaw size.
That is, as the flaws get larger, the amplitude
increases, although not in a li near fashion. Two
approaches commonl y used include
area-amp litude blocks and the Krautkramer DGS
(d istance-gain -size) diagram. tn the first,
specimens are prepared with di fferen t size
reflectors. The amp li tude from the fl aw is
compared directly wit h the amp litude from a
known re flector. When a match is ach ieved, the
flaw is ass igned the reflector size.
In the DGS diagram, a series of curves with
fl aw size as the parameter are plotted on an
amp Iitude- versus-sou nd-path -diagram.
Backsurface echo amplitude is plotted on the
same diagram. Flaw ampli tudes are then used to
ass ign a flaw size where the equi valent flaw size
is a circular disk.
Large fl aws arc measured by scan ning or by
time-d ifference measurements, and, of course,
these may be combi ned. In lamin ar flaw
measurement, the search unit is moved back and
forth until the ampl itude of the fl aw Signal drops
to a predetermined level. Us ing this technique,
the fl aw perimeter can be determj ned. Thi s
tech nique is usually quite satisfactory.
Thi s method is not the same for ang le beam
measure ments whic h are usuall y used in weld
examination. Measurement of the through wall
dimen sion (height) is much more diffi cult.
Several techniques have been developed in
relationship to thick-wall weld examination and
a few of these will be discussed.
One of the most common techniques is the so
call ed "dB drop" techni que. In this technique,
the maximum amplitude signal is located and the
sound path and location recorded . The search
un it is then moved toward the reflector until the
signal drops by a prese lected amount, usually
6 dB. At thi s point , the sound path and location
are recorded. Thi s step is repeated with
movement away froIll the reflector. Plots of the
data using the known refracted angle provide a
measure of the heigh t of the reflector.
A si mil ar but slightly differe nt techn ique is
the leadi ng-lagging ray approach. In thi s, the
search un it is maneuvered across a side-drilled
hol e reflector in a cal ibration block as in the dB
drop technique on a reflector. These data arc
used to establi sh the leading and laggi ng beam
edge angles. In the examinat ion, the locat ions of
the search unit are establi shed as in the dB drop
techniq ue bUl the plots are made on the basis of
the pre-established beam edge angles.
In the dynamic time of flight techn ique, a
focused, longitudinal wave, angle beam search
unit mounted on a mechanical scanner passes the
search unit across a crack. The sound path
reflection from the crack is recorded with the
search unit position. The distance to the tip of
the crack is determined by triangulat ion and the
minimum sound path. Thi s techniq ue shows
promise of good accu racy in some applications.
Several techniques rel y on the detection of
diffracted waves e manat ing from the lips of a
94
crack. These very low ampli tude waves, if
detected and iden tifi ed, can be used to measure
the fl aw height. In the satellite pulse techn ique
the screen is calibrated in through wa ll di mension
rather than in metal path to the reflector. The
distance from the tip-diffracted pu lse (satellite)
to the comer echo is a direct measurement of the
flaw height. This tec hnique has been
successfully applied to measure intergranular
stress corrosion cracks in the nuclear e lectric
power indu stry.
Original exam in ation with lip-diffraction
used through-transmi ssion techniques. This
technique is still used in selected application s. In
this techn ique, angle beam search units are
placed on each side of a crack on the entry
surface. These are manipulated until the peak is
maximized and the crac k tip is then located by
triangulation .
95
Appendices
Appendix A
A Representative Procedure for Ultrasonic Weld Inspection
1.0 SCOPE:
5.1.2 Using the selected angles and material
thickness(es) , calculate the expected beam
path and range of straight beam coverage
required.
5. 1.3 Using Table C of Scan Levels shown in
Section 9.0, identify the scan levels to be
used for each segment of the weld.
5. 1.4 Using Reference Table D, identify the
indicating rating levels which correspond 10
Classes I through IV and enter them on
Form A.
5.1.5 Enter any other special requirements for a
specific configuration or job in the
comments section 01 Form A.
1.1 This procedure is to be used for detecting,
locating and evaluating indications within the weld
and heal affected zone of carbon steel and low
alloy welds using the contact inspection
technique.
2.0 PERSONNEL:
2.1 Personnel performing this examination shall be
qualified in accordance with PO-I which is in
accordance with the guidelines 01 SNT· TC·1A
(1988). Only Levell! or 111 personnel shall
evaluate and report lesl results.
3.0 REFERENCE :
3.1 NE· l "Nondestructive Testing Equipmenr,
Rev. O.
5.2 Prepare all applicable surfaces for UT inspection:
5.2.1 Clean con tact surfaces of weld spatter, dirt,
rust, grease and any roughness that will
interfere with the free movement of the
search unit or would prevent the
transmission ot ultrasonic vibrations.
5.2.2 Smooth weld surfaces adequately to
prevent interference with the interpretation
of the examination . Weld surfaces shall
merge smoothly into the surfaces of the
adjacent base metal.
4.0 EQUIPMENT:
4.1 Pulse-echo Instruments and Transducers shall be
selected only from the equipment inventory which
has been qualified and calibrated to meet the
requirements of NE·l , -Nondestructive Testing
Equipment.4.2 The calibration block to be used for production
inspection shall be Ihe DSC (Distance/Sensitivity)
block.
5.3 Verify all equipment qualification and system
calibration checks prior to testing:
5.3. 1 Verify that all equipment to be used has
been qualified in accordance with NE-l and
the schedule requirements of Table A.
4.3 Couplants may include cellulose gum (mixed with
water) or glycerine.
5.0 PROCEDURE :
5.1 Review each test item's inspection requirements
to be aware of contract stipulations for each weld
joint configuratioo prior to conducting production
weld inspection. Select an established Technique
Sheet for the weld joint configuration or create a
new one that identities the inspection parameters
of transducer angles, applicable segments of the
weld(s) to be examined, maximum beam path and
companion longitudinal wave scan region, scan
levels, and acceptance criteria in accordance with
Form A, shown in Section 10.0 of this procedure.
I! a new Technique Sheet is prepared by other
than the Level III individual, the Technique Sheet
shall be reviewed and approved by the Level III
prior to use during production inspections.
5. 1.1 Using Relerence Table B shown in
Section 9.0 ot this procedure, identify the
transducer angle(s) required to totally
inspect the material Ihickness(es) and joint
design(s) being considered .
5.4 Conduct and Maintain System Calibration Checks:
5.4. 1 Conduct the inspection system calibration
in accordance with NE-l , being sure that
the reject control is turned off and remains
off throughout the inspection process.
5.4.2 Calibrate the inspection "system~
(instrument, cable and transducer) before
first use and
a. Every 60 min.,
b. At the completion of each examination or
series of similar examinations,
c. When examination personnel change,
and
d. When ele<:trical Circuitry is disturbed in
any way, e.g ., changes in transducer,
battery, ele<:trical outlet, co-axial cable or
power outage.
5.4.3 Straight Beam Calibration
a. Using a location on the base metal free
of any indications, set sweep range to
99
Table A. Schedule of Equipment Qualification
Check
Transducers·
Angle
Before First Use
Resolution
Dimensions
Approach Distribution
Index Point
Sound Path Angle
Internal Refle<:tion
After 4 hours of use
Index Point
Sound Path Angle
Instrument
Horizontal linearity
Vertical Linearity
Horizontal Linearity
Vertical Linearity
• Straight Beam T ransducer s are to be checked for resolution
before first. use.
After 80 hours use
Internal Reflection
Form B and columns X. Y, Depth,
Length , and Comment.
d. Satisfactory base metal tests results are
to be indicated for each weld by placing
a check mark in the column identified
"L-wave" in Form B.
clearly display both the first and second
back surface reflections.
b. Set the pulse reflected from the first back
surtace to a height of 80% FSH.
5.4.4 Angle Beam Calibration
a. Using the DSC block, adjust the
instrumenllo represent the actual sound
path distance using either the 5 in. or
10 in. range on the CAT screen.
b. Using the DSC block, adjust the
maximum attainable signallrom the
0.06 in. SDH to 50% of FSH and record
the "Reference Level" reading of the gain
control, on Form B, "Ultrasonic
Inspection Results."
6.0 WELD AND HAZ EXAMINATION USING ANGLE
Base Material Examination:
5.5.1 Using a calibrated 2.25 MHz longitudinal
transducer over the area identified in the
Technique Sheet, scan the base malerial
through which angle beam testing will take
place using a 20% overlapping pattern and
at a speed not to exceed 6 in. per second.
This initial base material examination is for
the purpose of assuring a predictable
environment for the angle beam testing that
is to follow and is not to be used as an
acceptancelrejection examination.
5.5.2 If any area of the inspected base metal
exhibits total loss of back reflection or any
indication equal to or greater than the
original back-reflection height, its size,
location and depth shall be reported on the
Form B, shown in Section 10.0
a. Size is to be determined using the 50%
amplitude loss (6 dB) method for
discontinuities larger than the transducer.
b. Size is to be determined using the
transducer edge approach method for
discontinuities smaller than the
transducer.
c. Unsatisfactory regions are to be
identified using the shaded areas in
100
BEAM TRANSDUC ERS :
6 .1 Using the 2.25 MHz angle beam transducer
identified in the technique sheet and operating at
a scanning level about the 0.06 in. SOH reference
level in accordance with the technique sheet, scan
the entire volume of the weld and HAl (a) using a
30% overlapping pattern. (b) while continuously
rotating the transducer a few degrees alternately
to each side and (c) at a speed not to exceed 6 in.
per second. Enter all applicable information onto
"Ultrasonic Inspection Results," Form B, as each
item in the form is identified. For butt welds,
repeat the scan from the opposite side of the
weld.
6.1.1 Repeat 6.1 for all requ ired examination
angles as identified in the technique sheet.
6.1.2 If pari of the weld is inaccessible for
examination due to base material laminar
con tent or restrictive geometric conditions,
full weld coverage shall be attained using
one or more of the following alternatives.
a. Grind the weld surtace{s) flush and scan
on the weld surtace.
b. Scan from other accessible surlaces.
c. Use other search unit angles such as
45°, 60 Q , or 70° .
6.2 Evaluation of Discontinuities
6.2.1 When an indication of a discontinuity
appears on the screen, use the gain control
(or attenuator) to adjust the maximum
attainable indication to 50% of the CRT's
FSH . Record the gain control reading (dB)
on Form B, "Ultrasonic Inspection Results"
shown in Section 10.0, in the "Indication
Level" column.
6.2.2 Estimate the effect of sound attenuation by
subtracting 2 in. from the sound path
distance to the indication and multiply the
remainder by 3 (i.e., triple the remainder).
Record this value (dB) in the "Indication
Factor" column of Form B.
6.2.3 Determine the "Indicating Rating~ by
subtracting the sum of the ~ Indicat ion
Lever and the "Indication Factor" from the
"Reference Level" setting and record the
result in the "Indicating Rating" column of
Form B.
6.2.4 Evaluate the length of each discontinuity by
measuring the distance between the center
line of the transducer's 50% drop locations.
6.2.5 Classify (I , II, III, IV) each discontinuity in
accordance with the criteria listed in the
Technique Sheet and establish its accepU
reject status based on each indication's
class, length, and sepa ration from nearby
surfaces and adjacent indications.
6.2.6 For each weld that is inspected. the results
of that inspection shall be recorded using
Form B, however only the weld 10. L-wave
check, acceptance status and comments (if
any) need be noted for those welds free of
any measurable ultrasonic indications.
7.0 DOCUMENTATION:
7.1 Record the detailed test results of all inspections
on Form S, ~Ultrasonic Inspection Results," as
shown in the attachments.
7.2 Mark locations of unacceptable indications directly
over the discontinuity and note the depth and
class of each discontinuity on nearby base metal.
8.0 REPAIRS:
8.1 After weld repairs have been made, re-examine
repaired areas in accordance wi th this procedure
and enter results on the interlaced lines of
Form B.
9.0 REFERENCE TABLES: (See Tables B, C, and D)
10.0ATTACHMENTS AND SAMPLE FORMS: (See
Forms A and B)
Table B. Testing Angle Selection
Material Thickness
(inches)
0.30 - 1.50
>1.50-1.75
>1.75-2.50
>2.50-3.50
>3.50-4.50
>4.50-5.00
>5.00-6.50
>6.50-7.00
Angles of Inspection
Top
Middle
Bottom
70
70
60
45
60
60
45
45
70
70
70
70
70
60
70
45
70
70
70
70
60
60
45
45
General Notes:
1. The "Top" of the weld extends one-quarter through the
thickness of the base material and is the region closest
to the surface from which the angle-beam scanning
takes place. The "Bottom" of the weld is the
quarter· thickness region opposite from the scan surface.
The "Middle" zone is the central region of the weld and
is equal to one-half of the thickness of the base
material.
2. Inspections should be made in first Jeg of beam path.
3. Legs II and In can be used when access is limited.
4. All fusion-line indications shall be further evaluated
with transducers which exhibit beam paths nearest to
being perpendicular to the suspected fusion surface.
101
Table C. Ultrasonic Scanning Levels
Sound Path (in.)
Above Zero Reference dB
thru 2·1/2
>2·1/2 to 5
>5 to 10
>10 to 15
12
19
29
39
Table D. Ultrasonic Acce pt-Reject Criteria
Weld
Thickness
(inc h es)
Class
r'
Angle
[!
III
IV"
0.30·0.75
+5
+6
+7
+8
70"
>0.75·1.50
+2
+3
+4
+5
70"
>1.50·2.50
+1
-2
+2 & +3
·1 & 0
+4 & +5
+1 & +2
+6
+3
60"
70"
>2.50·4.00
0
-2
-5
+1 &+2
·1 & 0
-4 &·3
+3 &+ 4
+1 & +2
·2 to +2
+5
+3
+3
45"
60"
70"
>4.00·8.00
-1
-4
-7
0&+1
·3 &·2
·6 &·5
+2 & +3
· 1 to +2
·4 to +2
+4
+3
+3
45"
60"
70"
• and below
•• and above
General Notes:
1. Class II and III indications shall be separated by at least 2L, L being the
length of the longer naw.
2. Class II and III indications shall not begin at. a distance less t han 2L
from weld ends carryi ng primary tensi le stress, L being the indication
length.
3. Weld thickness shall be defined as the nominal thickness of the thinner
of the two parts being joined.
4. Rejectable are all Class I indications, Class II indications in excess of
0.60 in. , and Class III indications over 1.25 in . All Class IV indications
are considered acceptable.
102
Form A. Ultrasonic Testing Technique Sheet
REF NUM BER: _T,-,S"-W,,,- _ __
DAT E: _ _ _ _ _ _ __
APPROVED: _ _ _ _ _ __
Applicable
Leve l III
)oi nl(s)
Th ickness: _ _ _ _ _ _ _ _ _ _ __
Transducer Angles:
TO P: _ _ _ _ __
MID: _ _ _ _ __
BOT : _ _ _ __
L-wave Range: _ _ _ _ _ _ _ _ _ __
Scan Leve l: _ _ _ _ _ _ _ _ _ _ __
Rating/Class/Reject Criteria:
_ _ db /I / All
Sketch of Inspection Scheme
_ _ db / II / L>O.60 in.
_ _ db / III / L> 1.25 in. (M)
_ _ db / IV / Accepl
COMMMENTS: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
Prepared By: _ _ _ _ _ _ _ _ _ __
Level
FORM: UT-TSI ,8/89
103
II
III
~
il
ANGLF;
LINE
RH I
WELD
dO SOI!/SU fAIII
n~ ~' 1.
L-WAVE
(Its )
I.EG I
INDICATION
ill
NO.
LEVEL
PATH
Location
STATUS
COM.MENT
SOUND
NO.
~
I E'G II
FACTOR
HATING
CLASS
LENGTH
ACCIREJ
X
Y
DEPT
H
I
~
'o"
:0
~.
"
~
'g
"o
~
~.
2
:0
~
....<:
...
E-
3
li
~
,
5
6
il
Review Questions for a Representative Procedure for
Ultrasonic Weld Inspection
Q-A 1 With scanning being done from the top
surface of a 1-1/4 ill. thick weldment, the
scanning level for inspection of the rOOt
area would be, with respect to the
reference level:
Q-A4 One of two C lass II indications in a
0.75 in. weld that is carrying primary
tensile stress is 0.45 in . from the end of
the weld and 0.15 in. long. The other is
0.25 in. long and they are within 0.35 in .
of each other. The statu s of the weld
should be identified as:
A. 12dB.
B. 14dB.
C. 19dB.
D. 29dB.
A. acceptable, based on proximity to the
next nearest indication.
S. acceptable, based on
indication-Iength-to-weld-thickness
ratio.
e. rejectable, based on proximity to the
end of the weld.
D. rejectable, based on proximity to the
next nearest indication.
Q-A2 The reference level recorded using the
DSC block for the above case was 32 dB.
A n indicati on detected near the root of
the weld was 34 dB when corrected for
attenuation. Thus the indication is to be
designated as being:
A.
B.
C.
D.
Class
Class
Class
C lass
I.
II.
III.
IV.
Q-A5 A Class III indication found at a fusion
interface in a weld that is in a region
which is carrying a primary tensi le st ress
is I in . from the end of the 0.75 in . thick
weld and within 0.5 in. of another
Class II indkation that has been
determined to be 0.2 in. long. The
Class III indication has been determined
to be 0.5 in. long. The status of the weld
should be identified as:
Q-A3 The weld joint being inspected has a
backing bar near the 114 in. foot with a
45-degree groove angle and unground
weld crown. Having found an indication
at a depth equal 10 112 the thickness of
the base material and in the vicinity of
the interface between the base metal and
the weld metal, further investigations
should be conducted using:
A. an L-wave transducer to ensure the
base material is free of laminations or
any other sou nd reflecting conditions.
B. the same angle beam transducer that
detected the indication , only scanning
from the opposite side of the weld.
e. a 45-degree angle beam transducer
and a beam path within the first leg of
the Vee path.
D. a 45-degree angle beam transducer
and a beam path within the second
leg of the Vee path.
105
A. acceptable, based on proximity to the
next nearest indication.
S. acceptable, based on the indication
being at a fusion interface but less
than 1.25 in.
e. rejectable, based on proximity to the
next nearest indication.
D. rejectable, based on proximity to the
end of the weld.
Q-A6 An indication in the top quarter of a 3 in.
thick weld has been exam ined using three
di fferent angle beam transducers (45, 60,
and 70 degree), each of wh ich has
res ulted in a rating equal 10 0 dB. The
indication should be identified as:
Q-A9 Inspections conducted in accordance with
the procedure are based on contact
testing using
as a couplant.
A. water bubblers and similar
water-based scanning dev ices
B. water and cellulose gum mixtures
adjusted for surface conditions
C. industrial grade o il s and greases
adj usted for surface conditions
D. commercial mixtures of proprietary
fluids designed to reduce residues
prone to cause corrosion in carbon
steel
A. Class I.
B. Class II.
C. Class III.
D. Class IV.
Q-A 7 The procedure calls for compensating fo r
attenuation effects through the use of
correction factors which, upon
examination, appear to be based upon:
Q-A 10 When usi ng a 70-degree transducer to
examine the root area of a single Vee
wel d, the scannin g level must be
increased by 7 dB over the thin materi als
scanning level (12 dB) for base metals
with thicknesses between:
A. an effective near fi eld that does not
exceed 2 in.
B. an e ffecti ve beam spread and/or
scatter that is at a rate of 3 dB per in.
beyond the near field.
C. both A and B.
A. 0.50 and 1.00 in.
B. 0.75 and 1.53 in.
C. 0.85 and 1.7 1 in.
D. 0.95 and 2.25 in.
D. the changes in ultrasonic wave energy
scatter caused by changes in
allowable operating freq uencies.
Q-A8 A transition butt weld is to be exami ned
in accordance with the procedure . The
weld is to be a smooth transition from a
3.75 in. thick base material to a 3.25 in.
thick material. The proced ure calls for
the weld to be examined usi ng:
A. a 70-degree transducer from both
sides.
B. a 45-degree transducer from both
sides ..
C. a 60-degree transducer from both
sides.
D. a ll of the above.
Q-A II The scannin g level for use with a
60-degree transducer is set for 29 dB
above the reference level established
during the system calibration. Thi s
scanning level is thus applicab le to
materi al thic knesses in the range fro m:
A. 2.50-5 .00 in.
B. 5.00-10.00 in.
C. 3.54-7.08 in.
D. 4.00-8.00 in.
Q-A 12 1n preparing for the angle beam
inspection, a longitud ina l wave scan of
Lhe base metal is conducted throughout a
region extending at least
to
either sidc of the weld center li ne when a
1 in. welded plate is to be inspected.
A. I in.
B. 1.7 1 in.
C. 2.25 in.
D. 2.75 in.
106
Q-A 17 If part of the weld is inaccess ible for
examination due to base materi al lamin ar
content or restrictive geometric
cond itions, the best alternative and
permitted approach to testing a weld is
to:
Q-A 13 Sound path angle and index (exit) point
need to be checked:
A every 4 hours of use.
B. every 60 minutes.
C. when examinati on personnel chan ge.
D. at the comp let ion of each series of
similar exam inatio ns.
scan the we ld using search unit
ang les other than that initi all y
selected , such as 55 or 65 degrees.
B. exam ine the weld fro m other
accessible surfaces using the
magnetic particl e method and using
the yoke or prod techniques.
C. grind the weld surface(s) nu sh and
scan on the weld surface using the
long itud inal wave technique.
D. none of the above.
A
Q-A 14 Longitudinal wave testing conducted for
the purpose o f sc reening base materials
prior to ang le beam testing for we ld
di scontinui ties, requires an overl ap scan
pattern of at least:
A. 10 percent.
B. 15percent.
C. 20 pe rce nt.
D. none of the above.
Q-A 15 Lami nar types of di scontinui ties are to be
recorded on Form B (the "U ltrason ic
In spectio n Results" sheet) provided they
exhibit a pul se height equal to or greater
than :
A. 50 percent
B. 75 pe rcent
C. 80 perce nt
D. 90 percent
FS H.
FSH.
FSH.
FSH.
Q-A 16 Angle beam testing conducted for the
purpose of detecting di scontinuities
within welds and thei r adjacent
heat-affected zones requires an o verl ap
scan pattern of at least:
Q-A 18 An indication is fo und at a sou nd path
distance of 5.6 in. T hu s the effect of
sound attenuatio n to be entered into
Fonn B is estimated to be:
A. 8dB.
B. 9 dB.
c. 10dB.
D. II dB.
Q-A 19 A series of welds are examined and
found to be free of any objectionable
indications. Thu s:
Form B need not be fill ed out in its
entirety.
B. the statu s of each we ld needs to be
marked as acceptable.
C. the indicatio n of sati sfactory L-wave
inspection needs to be marked wi th a
check mark .
D. all of the above.
A
A. 10 percent.
B. 15 percent.
C. 20 percent.
D. 30 percent.
107
Q-A20 A series o f welds are examined and
found 10 con tain several unacceplable
indications. Thus:
Q-A22 An indicat ion in a 3 in. weldmen t yields
an indication level of + I dB fo r the
45-degree tran sducer and -2 dB for the
70-degree transducer. The indication
shou ld be identified as:
A. each unacceptable weld needs to be
marked with a check mark at the end
of each weld loaded in tension.
S. each unacceptable ind ication location
needs to be marked direct ly over the
d iscontinuity.
C. location and depth/class of each
discontinuity need to be marked
directly over the discontinuity and
nearby on the base material ,
respectively.
D. Form S , completed in compliance
with the procedure, is the full
documentation required for each
indication.
A. Class 1.
B. Class II.
e. Class 1Il.
D. Class IV.
Q-A23 An indication in the middle of a 5 in.
weldment has been identified Class 111
with a 6 dB down length of 1.1 in. This
indication, in accordance with the
procedure, is:
A. considered acceptable.
B. considered rejectable.
C. 1O be considered for furthe r
exanunalion by other NDT means.
D. none of the above.
Q-A21 In reviewing a completed Form S , it is
found that two complete sets of
discontinuity data are recorded for a
rcnector found at the same locat ion and
depth in the same weld. The second set of
data is recorded on the line directly
below the first set of data. Both sets
indicate an unacceptabl e condition. It is
evidentlhat:
Q-A24 An indication 1.75 in. long and in the
vicinity of the base-metal to weld-metal
fu sion line of a 5 in. weldment has been
tentati vely identified as Class IV us ing a
si ngle angle beam transducer. This
indication , in accordance wi th the
procedure, is:
A. a repair has been completed and the
repair has been judged to be
unacceptable.
B. the inspector mi sread the data taken
during the ins pect ion.
C . a repair is in process and the data will
be changed pending the inspection of
the repaired region.
D. none of the above.
108
A. considered acceptable since all
Class IV indications are considered
acceptable.
B. considered rejectable si nce it exceeds
the 1.25 in. lim it for fu s ion type
flaws.
C. to be considered for fu rlher
exami nation by transducers with
angles closest to being perpendicu lar
to the fusion line.
D. to be subjected to X-ray examination
in order to obta in a second
"techn ical" opin ion.
AppendixB
Answer Key to Chapter Review Questions
Chapter I
I.D
2. C
3. B
4.A
5. C
6. C
7. C
S. D
9. B
10. B
II. A
12. B
13. D
14. B
15. A
16. D
17. A
IS. A
19.C
20. A
21. B
22. B
23. D
24. D
Chapter 2
I. C
2. C
3. D
4. A
5. D
6. D
7. A
S. B
9. A
10. A
II. D
12.C
13. B
14.C
15.C
16.A
17. B
IS. B
19. B
20. A
2 1. A
22. A
23. B
24. A
Chapter 3
I.D
2. B
3. B
4. D
5. D
6. D
7. B
S. B
9. A
10. D
II. C
12.C
13. D
14.A
15. D
16. D
17. B
18. C
19. B
20. A
2 1. D
22. B
23. A
24. B
25. B
26. C
27. C
Chapter 4
I.A
2. C
3.D
4. C
S. D
6. C
7. A
S. B
9. A
10. D
II. A
12. B
13. A
14. D
15. C
16. A
17. B
IS. B
Chapter 5
I.D
2. B
3. D
4.C
S. D
6. D
7. B
S. D
9. A
10. B
II. D
12. C
13. C
14. B
15. D
16. B
17. C
18. both A andC
19. C
20. none or the
above
21.
22.
23.
24.
109
B
C
A
B
Appendix A
A I. C
A2. A
A3. D
A4. D
AS.C
A6.A
A7. C
AS. D
A9. B
AIO.C
All. A
A12. D
AI3. A
A I4.C
AIS. C
A16. D
A17. D
AIS. D
A19. D
A20. C
A21. A
A22. B
A23. A
A24. C
Appendix C
References
4. Krautkramer, J. and H. Krautkramer.
Ultrasonic Testin g of Materials, 4th ed.
New York: Springer-Verlag, Inc., 1990.
I. Bray, D.E. and R.K. Stanley.
Nondestructive Evaluatioll: A Tool ill
Design, Ma nufacturing and Service. Boca
Raton: CRC Press , 1997.
5. McMaster, R. c.. editor. Nondestructive
Testing Handbook, VoL I-II. New York:
The Ronald Press Co., 1959.
2. Metals Handbook, ninth ed ition,
Volume 17, "Nondestructive Evaluation
and Quality Control." Metals Park, Ohio:
ASM International, 1989.
6. Birks, Albert S. and Robert E. Green ,
tcchnicaJ edi tors; Pau l Mcintire, editor.
Nondestructive Testing Han dbook, second
edition ,Vo lu me 7: Ultrasonic Testing.
Col umbus, Ohio: The American SocielY
ror Nondestructive Testing, inc., 1991.
3. Silk, M.G. Ultrasonic Transducersfor
Nondestructive Testillg. Bristol , Eng land:
Adam Hilger Ltd., 1984.
111
The American Society for
Nondestructive Testing, Inc.
1711 Arlingate Lane
PO Box 28518
Columbus,OH 43228-0518
Catalog No. 2261