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Introduction

Ultrasonic Testing (UT)  Sound is a mechanical vibration.

Level II  Sound waves are the vibration of particles in solids, liquids

or gases:

Audible Range: 16Hz - 20KHz

Introduction Introduction

For centuries, objects were tested by hitting them with a

 Ultrasonic is the study and application of sound waves
mallet and listening for a tonal quality difference.
having frequencies above the audible range of the
The natural resonance of an object gave evidence that
human ear.
the struck object was free from imperfections.
 Is a branch of acoustics.
 Begins at 20 000 cycles
per second (20 kHz).
 Uses higher frequencies
for testing materials.

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Introduction Advantage of Ultrasonic Testing

Ultrasonic Testing measures the time for high frequency (0.5MHz-50MHz) pulses of
ultrasound to travel through the inspection material.
Measurement is superior to other
Both surface & Sub-surface defects can be inspected methods
If a discontinuity is present, the ultrasound reflects back to the probe in a time other than
that appropriate to good material. Sensitive to cracks at various orientations Portability

Castings Forgings Able to penetrate thick sections Instantaneous results

Applications
Measures depth and through-wall Extent Single-sided access is sufficient
Welds Composites

Limitations of Ultrasonic Testing Principles of Ultrasonic Inspection

 No permanent record (unless automated) Ultrasonic waves are introduced into a material
where they travel in a straight line and at a
constant speed until they encounter a reflector.
 Skill and training is more extensive than with some other methods.

 Requires coupling medium

At reflector interfaces, some of the wave energy
is reflected and some is transmitted.
 Materials that are rough, irregular in shape, very small, exceptionally thin
or not homogeneous are difficult to inspect.
The amount of reflected or transmitted energy
 Cast iron and other coarse grained materials are difficult to inspect can be detected and provides information about
the size of the reflector.
 Linear defects oriented parallel to the sound beam may go undetected.
The travel time of the sound can be measured
 Reference standards are required for calibration and this provides information on the distance that
the sound has traveled.

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Principles of Ultrasonic Inspection Principles of Ultrasonic Inspection

The distance the sound traveled can be displayed on the Flaw Detector
Sound is transmitted in the material to be tested
The screen can be calibrated to give accurate readings of the distance

The sound reflected back to the probe is Signal from the backwall
displayed on the Flaw Detector

Bottom / Backwall

Principles of Ultrasonic Inspection Principles of Ultrasonic Inspection

The presence of a defect in the material shows up on the screen of the
flaw detector with less distance than the bottom of the materials

The BWE signal

0 10 20 30 40 50 60
Defect signal

60 mm

Defect

The depth of the defect can be read with reference

to the marker on the screen

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Basic Principles of Sound Basic Principles of Sound

Sound is produced by a vibrating body and travels in the form of wave
Examples of oscillation
Travel through materials by vibrating the particles that make up material
Ball on a spring Pendulum Rotating Earth
When a medium is compressed in one direction, it expands in another
direction
Ultrasound are the sound waves with frequency too high to be heard by human

Basic Principles of Sound Basic Principles of Sound

Oscillation
Pulse
The ball starts to oscillate as soon as it is pushed

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Basic Principles of Sound Basic Principles of Sound

Atomic Structures Wave Propagation

Gas Liquid Solid Understanding wave propagation:

• Low density • Medium density • High density Ball = atom Spring = elastic bonding force
• Weak bonding forces • Medium bonding • Strong bonding forces
forces • Crystallographic
structure

Basic Principles of Sound Basic Principles of Sound

One full Time

oscillation T

From the duration of one oscillation T,

the frequency f (number of oscillations
per second) is calculated:

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Basic Principles of Sound Basic Principles of Sound

Frequency Range Hz Description Example

0 – 20 Infrasound Earth quake

16 – 20,000 Audible Sound Speech, Music

>20,000 Ultrasound Bat, Quartz Crystal

Basic Principles of Sound Basic Principles of Sound

T During one oscillation T the wave

front propagates by the distance :

Distance travelled

V = Speed
T = Time Period
λ = Wave Length
(Distance Travelled)

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Basic Principles of Sound Basic Principles of Sound

Velocity of sound in particular material is constant

Elastic
Modulus
Constant Velocity

Materials
Density Frequency
Velocity of
Changing Wavelength
Sound

5 M Hz

STEEL
WATER AIR

Basic Principles of Sound Sensitivity

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Sensitivity Resolution
 Resolution is the ability of an equipment / combination probe
to distinguish between two echoes from reflectors that are
close together.
 To have good resolution a probe must present two signals on
a CRT screen from two separate reflectors.
 If it has poor resolution the echoes from the two reflectors
appear as one signal on the screen.

Resolution Signal Amplitude

 Maximum displacement of the molecules from their
equilibrium position.
 The energy of an ultrasonic wave is in turn expressed as the
square of the amplitude.
 The relative amplitude of ultrasonic signals is expressed
using the decibel, a logarithmic unit of comparison.

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Signal Amplitude Practice Problem

 Using the formula, we can discover that:

 6dB difference means that one signal is 2 times bigger than another.

 10dB difference means that one signal is 3 times bigger than another.
1 M Hz 5 M Hz 10 M Hz 25 M Hz

 12dB difference means that one signal is 4 times bigger than another. LONGEST  = v/f SMALLEST

20dB difference means that one signal is 10 times bigger than another. F  F 
Which probe has the smallest wavelength?
Which probe has the longest wavelength?

Practice Problem Practice Problem

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Practice Problem Practice Problem

Practice Problem Modes of Sound Wave

There are four different modes of sound wave generation
that are used in ultrasonic testing:
Longitudinal Waves (Compression Waves)
Shear Waves (Transverse Waves)
14 db = 5X
Rayleigh Waves (Surface waves)
Lamb Waves (Plate Waves)
So H2= 5X20% = 100 %

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Modes of Sound Wave Modes of Sound Wave

Longitudinal Mode Longitudinal Mode
Longitudinal waves, or compression waves, cause the
particles of the matter to vibrate back and forth in the Direction of propagation
Direction of oscillation
same direction (Parallel) as the motion of the sound
wave.

Modes of Sound Wave Modes of Sound Wave

Shear Mode
Longitudinal Mode
Shear waves, also known as transverse waves, cause
the particles to vibrate back and forth in a direction that
is at right angles (Perpendicular) to the motion of the
wave.

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Modes of Sound Wave Modes of Sound Wave

Shear Mode Shear Mode

Direction of propagation
Direction of Oscillation

Modes of Sound Wave Modes of Sound Wave

Velocity: Rayleigh (Surface Wave) Mode
Rayleigh waves travel along the free boundary
(surface) of a solid. These are also referred to as
surface waves.

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Modes of Sound Wave Modes of Sound Wave

Rayleigh (Surface Wave) Mode Rayleigh (Surface Wave) Mode

Same material

Modes of Sound Wave Modes of Sound Wave

Lamb (Plate Wave) Mode Lamb (Plate Wave) Mode
 Lamb or plate waves propagate in thin plate materials
when the plate thickness is about the same as the
wavelength.
 Lamb or plate waves travel at velocities which vary with
the material, plate thickness and frequency.
 Particle motion is elliptical, as with surface waves.
 Produced by manipulation of surface waves and others.
 Lamb or plate waves are also combinations of
longitudinal and shear waves.

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Modes of Sound Wave Generation Of Ultrasound

Lamb (Plate Wave) Mode Generated in Transducer
Piezoelectric material
(crystal) in the transducer
produce piezo-electric
effect.

The transducer is capable of

Symmetrical Asymmetrical both transmitting and
receiving sound energy.

Generation Of Ultrasound Generation Of Ultrasound

Piezo - Electric Effect: Piezo - Electric Effect:
 Direct Effect: Conversion of mechanical energy
(sound) into electrical energy.
 Indirect Effect: Conversion of electrical energy into
mechanical energy or sound.
 The first people to observe the piezo-electric effect were
the Curie brothers who observed it in quartz crystals.

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Generation Of Ultrasound Generation Of Ultrasound

Piezo - Electric Effect (Indirect): Piezo - Electric Effect (Indirect):

The crystal gets thicker, due

to a distortion of the crystal
Piezoelectrical
Crystal (Quartz)
+ +
Battery

Generation Of Ultrasound Generation Of Ultrasound

Piezo - Electric Effect (Indirect): Piezo - Electric Effect (Indirect):

Sound wave with

frequency f
The effect inverses with
polarity change

AC
+

An alternating voltage generates crystal

oscillations at the frequency f

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Generation Of Ultrasound Reception of Ultrasonic Waves

Piezo - Electric Effect (Indirect): Piezo - Electric Effect
Effect:(Direct):
 A sound wave hitting a piezoelectric crystal, induces
crystal vibration which then causes electrical voltages at
the crystal surfaces.

Short pulse Electrical energy Piezoelectrical crystal Ultrasonic wave

( < 1 µs )

A short voltage pulse generates an

oscillation at the crystal‘s resonant
frequency f0

Piezo-Electric Crystal Practice Problem

Frequency & Thickness:

 By varying the thickness of crystals and subjecting them

to a voltage, they could be made to vibrate at different
frequencies.
 Frequency depends on the thickness of the piezo-electric
crystal, according to a formula:

Thinner the crystal,

Higher the frequency

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Piezo-Electric Crystal Piezo-Electric Crystal

Piezo - Electric Material: Piezo - Electric Material:

Following are the crystal material used in ultrasonic transducers.

Natural Crystal Polarized Ceramic Crystal

Quartz or Silicon Oxide (SiO3) Barium Titanate (BaTiO3)

Lithium Sulphate (LiSO4) Lead Metaniobate (PbNbO6)

--------------------------- Lead Zirconate Titanate (PbZrO3, PbTiO3)

In accordance with ASNT Level III Study Guide

Piezo-Electric Natural Crystal Piezo-Electric Natural Crystal

Quartz or Silicon Oxide (SiO3): Quartz or Silicon Oxide (SiO3):
Compressional or shear waves can be produced according to the
way quartz crystals are cut.
An X cut crystal is cut in a direction that is perpendicular to X-
axis and parallel to Y-axis.
An Y cut crystal is cut in a direction that is perpendicular to Y-
axis and parallel to X-axis.
An X cut crystal produces a compressional wave.

A Y cut crystal produces a shear wave.

Quartz is not much used now.

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Piezo-Electric Natural Crystal Piezo-Electric Natural Crystal

Quartz or Silicon Oxide (SiO3): Lithium Sulphate (LiSO4):
Advantages:
Curie Temperature: 5760C Crystals grow as a solution of lithium sulphate is evaporated.
 Resistant to wear.
 Insoluble in water. Advantages:
 Resistant to ageing (Mechanically and chemically stable).
 The most efficient receiver of ultrasound.
 Easy to cut to give the required frequencies.
 Has very low electrical impedance.
Disadvantages:  Lithium sulphate operates well at low voltages.
 It needs a lot of electrical energy to produce a small amount  Does not age.
of ultrasound. It is inefficient generator of ultrasonic energy.  Has very good resolution.
 Quartz crystals are susceptible to mode conversion.  Crystals are easily damped to give short pulse lengths.
 A high voltage is needed to give low frequency sound.

Superseded by other Piezoelectric Materials.

Piezo-Electric Natural Crystal Piezo-Electric Polarized Crystal

Lithium Sulphate (LiSO4): Barium Titanate (BaTiO3):
Disadvantages: Crystals are made by baking barium titanate at 1250oC and then
cooling it in a 2 kilovolt per millimeter electrical field.
 Dissolve in water.
Advantages:
 Very fragile (Break easily).
 Decompose at temperatures 75-130oC.  An efficient generator of sound.
 Only needs a low voltage.
 Good sensitivity.

Disadvantages:
Unsuitable for
Industrial use
 Its curie point, at which the crystal depolarize is about only
115-150oC, so heating ruins it.
 It deteriorates over a period of time.

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Piezo-Electric Polarized Crystal Piezo-Electric Polarized Crystal

Lead Metaniobate (PbNbO6): Lead Zirconate Titanate (PZT):
Crystals are made in a similar way to Barium Titanate. Crystals are made in a similar way to Barium Titanate.

Advantages: Advantages:

 An efficient generator of sound.  An efficient generator of sound.

 Its curie point is about 193-350oC. Best all-round crystal
 Heavy internal damping, gives out very narrow pulses of for industrial testing.
ultrasound, which gives good resolution.  Easily damped & good resolution.
 Its curie point is about 550oC.  Does not dissolve in water.
Used in most
Disadvantages:  Tough and resistant to ageing. probes.
 Much less sensitive than Lead Zirconate Titanate (PZT). Disadvantages:
 No major disadvantages.

Practice Problem Coupling: Piezo-Electric Crystals

 Probes using piezo-electric crystals require mechanical

1. Which crystal is most efficient transmitter of ultrasonic
coupling between themselves and the material under
energy? (Lead Zirconate Titanate - PZT) inspection.
 Coupling is achieved between the transducer and material:
2. Which crystal is most efficient receptor of ultrasonic
 By immersing them in a fluid tank (Usually water).
energy? (Lithium Sulphate)  Directly using a thin fluid layer (<λ/4).
 Couplant is primarly used to exclude the air between probe
3. Which crystal is soluble in water? (Lithium Sulphate)
and test part.
4. What is the maximum curie point of Lead Zirconate  For shear waves, fluid should have a significant viscosity.
Titanate? (350 0C)  The acoustic impedance of the couplant layer should also
some how match with probe and the material being tested.

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Coupling: Piezo-Electric Crystals Coupling: Piezo-Electric Crystals

For the selection of a suitable couplant, the following points Couplant Types:
should be taken into consideration:  Water:

 Surface finish of the test specimen.  Suitable on a relatively smooth surface.

 Temperature of the test specimen.  A wetting & corrosion agent should be added.
 Possibility of chemical reaction between the test specimen  Promote surface corrosion on carbon steel.
and the couplant.  Sometimes appropriate to add glycerine to increase viscosity;
 Cleaning requirements (some couplant are difficult to however, glycerine tends to induce corrosion in aluminum.
remove).  Heavy oil or Grease

 Should be used on hot or vertical surfaces or on rough

surfaces where irregularities need to be filled.
 Only non-corrosive nature type material can be used.

Coupling: Piezo-Electric Crystals Electromagnetic Acoustic Transducers

(EMATs)
Couplant Types:
 When a coil is placed near the surface of an electrically
 Wallpaper Paste
conducting object and alternating current is applied, eddy
 Especially useful on rough surfaces when good coupling is currents will be induced in a near-surface region of the object.
needed to minimize background noise and yield an adequate  Generate ultrasonic waves due to the interaction between a
signal-to-noise ratio. static magnetic field of a magnet and the high frequency
 More difficult to remove. magnetic field generated by a coil.
 The eddy currents produced in the material due to the coil
Couplant used in contact inspection should be creates a lorentz force causing the atomic lattice of the
applied as a uniform, thin coating to obtain uniform material to oscillate producing an ultrasonic wave.
and consistent inspection results.  Used for the detection of flaws & determination of material
properties (e.g. velocity or attenuation measurement).

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Electromagnetic Acoustic Transducers Electromagnetic Acoustic Transducers

(EMATs) (EMATs)
 Can operate without contact at elevated temperatures and in
remote locations.
 Do not require the couplant.
 Inefficient ultrasound generator.
 Require strong magnetic fields and large currents to produce
ultrasound.
 Often produce weaker ultrasound than that produced by piezo-
electric transducers.
 Rare-earth materials such as samarium-cobalt and
neodymium-iron-boron are often used to produce sufficiently
strong magnetic fields, which may also be generated by pulsed
electromagnets.

Pulse Length and Damping Pulse Length and Damping

Pulse Length:
 Length or width of several vibrations or wavelengths.

 Leading and trailing edges of a pulse measured at a defined

level below the peak amplitude.
 Pulse length (or width) is also sometimes called wave train
length.
Damping:
 Shorten the pulse length (or width) and to absorb the rareward
ultrasonic waves.
How to Achieve?
Backing Material: A slug of tungsten loaded
Araldite is placed behind the crystal.

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Pulse Length and Damping Pulse Length and Damping

Short Pulse
Long Pulse
Normal Pulse

Pulse Length and Damping Sound Beam

Two distinct zones are always present within the sonic

Resolution & Damping beam:
Pulse Length
Sensitivity & Penetration  Near Field or Fresnel Zone

 Far Field or Fraunhofer Zone

Sensitivity & Penetration
Pulse Length
Resolution & Damping

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Sound Beam Sound Beam

Crystal Focus Angle of divergence

Accoustical axis

6

D0

Near Field Far Field

Near Field (Zone) Near Field (Zone)

Sound produces from many points along the surface of the
 Zone between the crystal and the point where the sound field
crystal which interfere with each other.
even out.
 Zone reveal irregular patterns of localized high (maxima) and
low intensities (minima).
 Exist upto last maxima (called 1N or N).
 Uneven sound field intensity in this zone.
 Inside the near zone, signals from reflector bear no accurate
relation to the size of the reflector, specially small reflectors.

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Near Field (Zone) Far Field (Zone)

 Zone where sound field behavior becomes more uniform.
 Sound pulses follow the inverse square law in the far zone
 Intensity reduces exponentially with distance.
Natural Focal Point  Sound beam spreads out as a circular wave front.

Diameter
Frequency Near zone
Velocity

Far Field (Zone): Beam Spread Far Field (Zone): Beam Spread
I=0%

I=10%
Half Beam Spread Angle
I=50%

I= maximum (100%)

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Far Field (Zone): Beam Spread Practice Problem

Where is the N?
N
Diameter

Frequency
Beam Spread

Velocity

Practice Problem Practice Problem

1 2 3 4

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Practice Problem Practice Problem

3- What is the half beam spread of a10mm, 5 MHZ 4- For a 2 MHz shear wave probe of crystal diameter 14mm,
compression wave probe in steel? the theoretical half angle of divergence to 20db of the beam
when used on steel is approximately?

Attenuation Absorption
 Resulting from transformation of ultrasonic energy into other
Decrease of sound intensity (pressure) when a wave types of energy (e.g. thermal).
travels through a material arising from:  Occurs as the sound pulse hits the molecules of the test
 Absorption (Material) material and makes them vibrate.
 The energy lost in vibrating the molecules turns to heat.
 Scattering (Material)
 The rate of absorption varies from one material to another and
even from one type of steel to another.
 Beam Spread (Far Field)
 It is high in soft materials (e.g. Perspex, nylon & lead) and is
low in aluminum.

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Scattering Scattering
 Randomly reflected energy caused by grain structure and/or
by small discontinuities in the beam path.
 The larger the grain size (course grain structure), the more
scatter occurs.
Cast Product
 When grain size ≈ λ/10, Scattering is high. Scattering
(Cast Iron/Brass)
 Grass/Hash/Noise exist on CRT due to course grain structure.

Wrought Product
Wavelength Scattering Scattering
(Refined steel)

Frequency Penetration

Attenuation: Beam Spread Attenuation: Beam Spread

Large Reflector: Area bigger than beam width
Small Reflector: Area smaller than beam width

Law of Large Reflector: I α 1/d (Inverse Law)

Law of Small Reflector: I α 1/d2 (Inverse Square Law)

Where:
I = Intensity of sound
beam.
d= Distance.

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Attenuation: Beam Spread Attenuation: Miscellaneous Source

Reflection inside the probe.

Scattering from a rough surface.

Non-metallic inclusions or laminations in test material.

Reflection from the surface of the test piece.

Internal mode conversion.

Attenuation Measurement Attenuation Measurement

Material Attenuation Cofficient
dB = 20 log (H1/H2) = ΔH - (1) - Without changing the setting
α = ΔHS/2T (dB/m) – For Near Field (ΔH=ΔHS) – (2)
α = ΔHS/2T=(ΔH-ΔHBS)/2T (dB/m) – For Far Field - (3)

For d ≥ 3N: ΔHBS = 6 dB

α = (ΔH-ΔHBS)/2T = (ΔH-6)/2T (dB/m) - (4)
α = Attenuation Cofficient
ΔH=ΔHS+HBS
ΔH=HB1-HB2
ΔHS = ΔH-HBS

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Attenuation Measurement Practice Problem

Plate thickness= 30 mm Probe Frequency= 4 MHZ
Material Attenuation Cofficient
Probe Diameter = 10mm ΔH=10dB (b/w 2nd & 4th BWE)
To calculate the effective material attenuation coefficient per Velocity= 5880 m/s 1st BWE at 30mm.
unit distance. Follow the following procedure: α=?
 Place a compression probe on a piece of the test material,
 obtain a BWE (HB1) outside the distance of 3N and turn the
N 17mm 3N= 3x17= 51 mm
backwall echo to FSH. Note the dB Value.
 Obtain a next BWE (HB2) at double distance of (HB1) and
increase the signal height to FSH. Note dB difference (ΔH) & 2nd BWE is at 60 mm, outside the 3N and distance (T) between
2nd & 4th BWE is 60mm. So using the equation no.4
distance between the echoes.
 From equation no.4, attenuation coffiencient can be calculated. α = (ΔH-ΔHBS)/2T = (ΔH-6)/2T = 33dB/m

Practice Problem Acoustic Impedance

Plate thickness= 30 mm Probe Frequency= 4 MHZ  The resistance offered to the propagation of an ultrasonic wave
Probe Diameter = 10mm Velocity= 5880 m/s by material is known as the acoustic impedance (Z).
Signal Hight =64 % at 2nd & 20% at 4th BWE.
1st BWE at 30mm. α=? Where: V = Acoustic Velocity. ρ= Density.

From Eq#1 ΔH=10dB

 Defines the interface behavior or coupling mismatch
(Reflection and Transmission coefficient).
N 17mm 3N= 3x17= 51 mm
 Higher the acoustic impedance (Z), the better the transmission
through that material.
2nd BWE is at 60 mm, outside the 3N and distance (T) between  Air is a very poor carrier of ultrasound (low Z value).
2nd & 4th BWE is 60mm. So using the quation no.4
 Steel is a good carrier of ultrasound (high Z value).
α = (ΔH-ΔHBS)/2T = (ΔH-6)/2T = 33dB/m

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Acoustic Impedance Reflection & Transmission Coefficient

At Normal Incidence

Medium 1

Interface
Medium 2

Reflection & Transmission Coefficient Practice Problem

At Normal Incidence Calculate the amount of energy reflected and transmitted at a

water-steel interface. Steel (Z2) = 46.7 x 106 kg/m2s. Water (Z1)
= 1.48 x 106 kg/m2s.

R=

T=1-R
R= So,
T= 1-0.88=.12x100= 12%
R=

R=

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Reflection & Transmission Coefficient Snell Law & Mode Conversion

Reflection

Snell Law & Mode Conversion Snell Law & Mode Conversion

Refraction Snell Law

When sound waves pass obliquely (not at 90o) between materials Snell’s law states that the ratio between sound velocity in two
having different acoustic velocities, the direction of sound materials is the same as the ratio between the sine of the incident
propagation is changed on passing through the interface and the and refracted angles (measured for the vertical angle).
sound wave is said to have been refracted.

Is that
Refraction?

NO

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Snell Law & Mode Conversion Snell Law & Mode Conversion

Mode Conversion
Critical Angle
When sound waves pass obliquely (not at 90o) between materials
having different acoustic velocities, one mode of wave energy There are two critical angles:
can be transformed into another mode on passing through the
interface and the sound wave is said to have been mode First Critical Angle:
converted. The incident angle at which a refracted compression wave in the
Is that test material is generated at 900.
Mode
Second Critical Angle:
conversion?
The incident angle at which a refracted shear wave is generated
in the material at 900.

NO

Snell Law & Mode Conversion Snell Law & Mode Conversion

First Critical Angle Second Critical Angle

V1= 2730 (Perspex) V1= 2730 (Perspex)

V2= 5960 (Steel) V2= 3240 (Steel)

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Snell Law & Mode Conversion Snell Law & Mode Conversion

Define the wave

modes areas?

Perspex- Steel Interface

Practice Problem Transducers / Probes / Search Units

Transducer

Contact Immersion

Compression
Normal Angle Beam
(Compression) (Shear) (Shear by
But answer is not correct: Angulation)
Use Vs= 3250 Correct Answer R= 17.80

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Transducers / Probes / Search Units Compression Probe

Immersion Type Contact Type

Generate compressional or longitudinal waves in test material.

Angle Beam Type Some times called Normal Probes or Straight Beam Probes.

Single
Crystal

Angle Beam Probe Angle Beam Probe

In angle probes, a piezo-electric crystal mounted on a Perspex

wedge at an angle calculated to generate a shear (transverse) Why Perspex as Wedge?
wave in the test material.
 Compression velocity in perspex (2730m/s) is less than the
shear velocity (3250m/sec) in steel. So refracted angle is
greater than incident angle (Snell Law).
 Perspex is very absorptive and attenuates unwanted echoes
from the compressional wave as it hits the perspex test
material interface.
Perspex wedge
Angle probes sometimes used to
A compression generate a surface wave.
probe is on an
Standard angles: 450, 600 & 700. angle cut wedge.

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Practice Problem Single Crystal Probe

Calculate the cut angle in perspex wedge to have the 450 shear  Transmits and receives ultrasound with one crystal:
beam refracted angle in steel?

Vp=2730 m/s
VS= 3250 m/s
R=450

Answer I= 36.40

Single Crystal Probe Single Crystal Probe

 Signal appears on the screen at the beginning of the time base, Length of the initial pulse is the dead zone.
Signal from near surface reflector will be
named as initial pulse, transmission signal, crystal strike or merged in initial pulse & will be undetectable.
main bang.

IP IP
Initial Pulse
B
BWE
F F
Flaw Echo

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Twin Crystal Probes Twin Crystal Probes

 Twin crystal probe contain separate

transmitter and receiver crystals, also
named as dual, TR or SE crystal probe.
 If crystal is not at angle, pulse will be
reflected straight back into the
transmitting crystal.
 Delay lines reduce the dead zone.
 Double crystal probes can be focused.
 Can measure thin plate.
 Can detect near surface flaws.
 Has good near surface resolution.

Twin Crystal Probes Immersion Probes

Disadvantages  Used in immersion technique where test part and probe are
 Good contact is difficult with curved surfaces. immersed in water.
 Difficult to size small defects accurately as the width of a  Squirter or bubbler system are variation of immersion test:
double crystal probe is usually greater than that of a single  Have impedance matching layer that helps to get more sound
crystal probe. energy into the water and in turn, into the component being
 The amplitude of a signal decreases if a reflector is situated inspected.
away from the focal distance.  Available in a flat, cylindrically or spherically focused lens.
 Cross talk.  A focused transducer can improve sensitivity and axial
resolution by concentrating the sound energy to a smaller area.
Therefore
 These are high frequency probes.
Single and twin crystal probes are complementary to
each other

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Immersion Probes Focused Immersion Probes

SQUIRTER UNFOCUSED UNFOCUSED

Modified Immersion Probes Delay Line Probes

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Delay Line Probes Phased Array

 Introduce a time delay between the generation of the sound
wave and the arrival of any reflected waves.
 Allows the crystal to complete its transmission function before
it begins to receive returning signals.
 Used with a contact transducer for good near surface
resolution.
 Use to gauge the precise thickness of thin materials and
delamination checks in composite materials.
 Provide the insulation from heat, so used for high temperature
applications.

Test Techniques Pulse Echo Technique

Pulse Echo Use single probe to transmit and receive ultrasound.

Through Transmission IP

BE
Tandem Scanning

Contact Scanning
F

Gap Scanning
delamination 0 2 4 6 8 10
Immersion Testing plate

IP = Initial pulse
F = Flaw
BE = Backwall echo

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Pulse Echo Technique Pulse Echo Technique

Advantages:
 Widely used technique.
 Access is required from one surface only.
Normal Probe  Detect type, size and exact location of the indication within
the item being tested.
Disadvantages:
 Depend on defect orientation.
 Maximum signal will be recieved when defect is normal to the
path of the sound beam.
Angle Beam Probe

Through Transmission Technique Through Transmission Technique

Transmitter probe on one side and receiver probe is on opposite
side, precisely facing each other.

Flaw Signal

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Through Transmission Technique Tandem Scanning

Advantages: It involves the use of two or more angle probes of the same angle
of incidence and facing the same surface with one probe acting as
 Less attenuation of sound energy.
the transmitter and the other(s) as receivers
 No probe ringing.
Used mainly to locate defects lying perpendicular to the surface.
 No dead zone on the screen.
 Orientation of a defect does not matter.
Disadvantages:
 Defect location and type cannot be determined.
 Component surfaces must be parallel.
 Vertical defects do not show.
 Process must be automated.
 Must be access to both sides of the component.

Tandem Scanning Contact Scanning

 Scanning with ultrasonic probe(s) in direct contact with the
object under examination (with or without couplant).
 Normal a thin film of couplant between the probe and the test
surface serves to both transmit ultrasound and to lubricate the
surface and reduce wear on the probe face.
 Ideally the acoustic impedance of the couplant should be
between that of the probe (Perspex) and the material under
test.

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Gap Scanning Immersion Testing

 Gap scanning is a technique in which the probe is not in direct  Three basic techniques used in immersion testing:
contact with the surface of the specimen but is coupled to it  Immersion technique,
through a column of liquid, not more than a few wavelengths  Bubbler & Squirter technique
thick.
 Wheel transducer technique.

 Used in automatic ultrasonic testing.

 Uniform couplant conditions are obtained.
 Longitudinal and transverse waves can be generated with the
same probe simply by changing the incident beam angle.
 Frequently uses high frequency probes (10-50MHz) and
focused probes for automated inspections and is suited to the
inspection of complex components.

Immersion Testing Immersion Testing

1 2  In immersion technique both the probe and the test specimen

surface = are immersed in water.
sound water delay  Ultrasonic beam is directed through water into the test
entry
specimen, using either a normal beam technique for generating
backwall flaw longitudinal waves (fig.a) or an angle beam technique for
generating transverse waves (fig.b) .
IP 1 IP 2
IE IE

BE BE
F

0 2 4 6 8 10 0 2 4 6 8 10

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 4/2/2021

Immersion Testing Immersion Testing

 When the normal beam technique is being used, the water path  In the bubbler or squirter technique, the ultrasonic beam is
distance must always be longer than the distance S. directed through a water column into he test specimen .
 Usually used with an automated system for high speed
scanning of plate, sheet, strip, cylindrical forms and other
regularly shaped forms.

 When the specimen is steel, the water path distance must be

longer than 1/4 steel thickness otherwise the 1st backwall echo
overlaps the 2nd surface echo and defects near the backwall
may not be seen.

Immersion Testing Practice Problem

 In the wheel transducer technique, the ultrasonic beam is Direct contact, Direct contact, Delay Lines
projected through a water-filled tire into the test specimen. single element probe dual element probe

 The probe, mounted on the wheel axle, is held in a fixed

position while the wheel and tire rotate freely.

Through transmission Immersion testing

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Presentation Presentation
A-Scan B-Scan C-Scan
 The flaw detector or UT set sends ultrasound energy into test
materials and some of this returns to the set to be presented as
information on a CRT screen.
 Following are the scan display:
• A Scan Display
• B Scan Display
• C Scan Display
• D Scan Display

Presentation Presentation
A Scan Display: B Scan Display:
 Amplitude of signals displayed as a function of time or  Gives an end or cross-sectional view of the component being
distance. examined with the position of the probe displayed on one axis
and the distance from the surface to the signal on the other.
 Used in immersion testing with an automated scanning device.

Typically used in applications

such as corrosion monitoring
and lamination detection in
metals as well as composites

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Presentation Presentation
C Scan Display: D Scan Display:
 C scan gives a plan view of a defect.  The D scan gives a side view of the defect seen from a
 Used as an automated process to map out laminations in plate. viewpoint normal to the B scan.
 Gives the area of a defect, so it is good for plotting the extent  It is usually automated and shows the length & depth of the
of laminations in sheets. defect.

Ultrasonic Flaw Detector Cathode Ray Tube

Principles:  Measures very small periods of time.
 Displays electrical pulses on a screen in a linear time/distance
relationship.
 The longer the distance on the screen time base, the longer the
time that has been elapsed / measured.

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Cathode Ray Tube Cathode Ray Tube

 Heater H heats the cathod C.  The X plates control horizontal movement and the Y plates
 Negatively charged cathod C emits the electron by process control vertical movement. By altering the potential of the X
called thermionic emission. and Y plates, the dot can be moved on the screen.
 Above process can be performed by a filament.
 Potential difference created by applying the voltage across the +
cathod (nagative) and anode (positive). Uv
-
 The resultant electron beam is focused by the focusing
cylinder F to make it appear on the fluorescent screen S as a + -
spot. Uh
 As the electrons travel toward the CRT screen S, they pass two
pairs of deflecting plates X and Y.
 A voltage applied to the X plates would deflect the electron
beam horizontally while a voltage applied to the Y-plates 0 2 4 6 8 10 0 2 4 6 8 10
would deflect the beam vertically.

Pulse Generation Pulse Generation

 A timer which gives out a number of electrical pulses every  Simultaneously the pulse transmitter sends an electric voltage
second, also called the pulse repetition rate or pulse (usually 100-1000V) through the coaxial cable to the piezo-
repetitions frequency (PRF). electric crystal in the probe.
 Must not be confused with probe frequency.  The crystal vibrates, transmitting the pulse of sound into the
 The PRF on most sets is about 1000 pulses/sec (PPS), though test material.
this can be varied on most sets from 50 PPS for thick  At the end of each pulse the electron beam spot on the CRT
specimens to 1250 PPS for thinner specimens. screen flies back to the left-hand side of the screen to await
 The pulse generator sends the pulse to the time base generator the next pulse.
on the CRT and to the pulse transmitter.  Only one pulse must be in the test material at one time
 The time base generator sends the electron beam spot moving otherwise confusing echoes will result.
uniformly across the CRT screen by putting a charge into the  For this reason the PRF is lowered when thicker specimens
X plates in the tube. are examined.

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Range Control (Time Base) Delay Control (Time Base)

 Varies the speed of the electron beam across the screen.  The delay control makes the time base generator wait before
 It is divided into coarse range which allows large changes in sending the spot moving across the screen.
range, say 10 to 100 to 500mm, and the fine range which  Twin crystal and angle probes have Perspex blocks or wedges
allows small adjustments in distances between these. between the crystal and the test material.
 For thick specimens the spot travels slowly.  Delay control used to move the spot sideways off the display,
 For thin specimens its speed is increased. so the passage time/distance of the ultrasound through the
Perspex in the probe does not appear on the screen.
 Adjusting the speed of the spot in relation to the time taken
for the sound pulse to enter the test specimen and to be  If you only want to look at the bottom 25mm of a 200mm
reflected back to the probe is called setting a time base. specimen, you can adjust the delay so that the spot begins to
travel across the screen at 175mm.
 If the speed of the spot across the screen is not even, as a
result of equipment failure, we say the time base is not linear.
 Flaw detectors should be checked frequently to assess time
base linearity.

Calibrated Gain/Attenuator Control

Range & Delay Control
(Receiver)
 Sound pulse sent into the test material is reflected back at the
proper angle, returns to the probe and hits the receiver crystal.
 The crystal sends AC current (.001-1V) back to the receiver.
Receiver Components:
 Amplifier (Narrow Band and Broad Band)

 Rectifier

 Attenuator

 Amplifier amplifies the signal and filters out irrelevant

signals.
 Rectifier rectify the signal before going to the CRT (Convert
the RF (radio frequency) signal to video spike)

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Calibrated Gain/Attenuator Control

Practice Problem
(Receiver)
Attenuator (Calibrated Gain /Attenuator Control):
 A variable resistance which controls the current passed on to
the CRT.
 Connected to the Y-Plate.

 Controls the amplitude of a signal by controlling the current.

 Comparing the height of one signal with the height of Amplified (RF)
Received from Probe
another.
 Two information's retrieved :

a) Position of a reflector below the probe.

b) Comparative amount of energy reflected from that

reflector to be compared with reference reflector.

Rectified (Video Spike)

Reject/Suppression Control Calibration & Sensitivity

 Used to reduce the noise level, normally named as hash or V1 Block:

grass.
 Grass/Hash/Noise caused by high attenuation material
(course grain size, specially casted products).
 Alter the vertical linearity of the equipment, so must NOT be
used if readings related to the decibel are made.

Should be in off
position in accordance
with ASME V.

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Calibration & Sensitivity Calibration & Sensitivity

V1 Block: V2 Block:
This block is generally used for:
 Time base (Range) calibration for both NP & AP.

 Determination of probe index & probe angle.

 Time base linearity.

 Screen height linearity.

 Amplitude control linearity.

 Resolving power & penetrative power.

 Pulse length & dead zone check.

 The setting of sensitivity.

Particularly suitable for short near field lengths and the time base
calibration of small diameter normal and angle probes.

Calibration & Sensitivity Calibration & Sensitivity

Angle Probes Angle Probes
Initial Checks & Calibration Probe Index (Exit Point):
 Probe Index  The point at which the center of the beam leaves the probe
 Probe Angle and enters the test material is called the probe index or exit
 Range calibration with V1 Block. point.
 Range calibration with V2 Block.  Marked on each side of the probe and checked regularly.
 Surface wears of probe Can be change the probe index and
probe angle.
 Stand-off measurements are taken from the probe index and
are used to check the probe angle.
 Master reference point or datum.

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Calibration & Sensitivity Calibration & Sensitivity

Angle Probes Angle Probes
Probe Index (Exit Point):
 To find the probe index place the probe on a V1 block and
obtain an echo from the 100mm radius and establish at more
than 50% FSH (Normally 80% FSH) using the gain control.
 Maximize the echo by moving the probe backwards and
forwards.
 Mark a line on each side of the probe directly above the slots
which indicate the center of the 100mm radius.
 This is the probe index, where the axis of the beam leaves the
perspex shoe.

Calibration & Sensitivity Calibration & Sensitivity

Angle Probes Angle Probes
Probe Angle: Probe Angle:
 Place the 450 or 600 probe onto V1 block approximately
adjacent to where the appropriate angle is inscribed, and
directed toward the plastic insert hole (50mm).
 Obtain a signal on the screen from the plastic insert and
maximize it.
 Find the position where the probe index coincides with the
angle indicated on the side of the V1 block and this will be
the probe angle.
 Above procedure can be repeated for a 700 probe but
reflecting the energy from the plastic insert radius is
unreliable, use of the 1.5mm hole is suggested as a target.

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Calibration & Sensitivity Calibration & Sensitivity

Share Waves Share Waves
Range Calibration With V1 Block (200mm FSW): Range Calibration With V1 Block (200mm FSW):
 Place the probe on the V1 block and obtain BWE from the
100mm radius.
 Establish this signal to more than 50%FSH (Normally 80%)
1st BWE
using the gain control.
 Maximize the echo by moving the probe backwards and
forwards. 2nd BWE
 Establish a 2nd BWE at 200mm range using range control.
 Adjust the 1st BWE from 100mm at 5 (half-scale) and the one
from 200mm at 10 (full scale), using the delay and range
controls. The time base is calibrated for 200mm.
 Longer ranges can be catered for in multiples of 100mm.

Calibration & Sensitivity Calibration & Sensitivity

Share Waves Share Waves
Range Calibration With V2 Block (100mm FSW): Range Calibration With V2 Block (100mm FSW):
 Place the probe on the block and point it at the 25mm arc.
 Adjust the delay and range controls until two echo's on the
screen represents 25mm and 100mm.
 Maximize the signals by sliding the probe forward and
backward.
 Adjust range and delay until the first echo comes at 2.5 and
second echo comes at 10 across the screen.
 The time base now represents 100mm range.
 Can be verified by pointing the probe at the 50mm arc. If
calibrated correctly, the maximized signal will come up
exactly at 5.

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Calibration & Sensitivity Calibration & Sensitivity

Share Waves Share Waves
Range Calibration With V2 Block (200mm FSW): Range Calibration With V2 Block (200mm FSW):
 Place the probe on the block and point it at the 50mm arc.
 Adjust the delay and range controls until three echo's on the
screen represents 50mm, 125 mm and 200mm.
 Maximize the signals by sliding the probe forward and
backward.
 Adjust range and delay until the first echo comes at 2.5 and
second at 6.25 and third at 10 across the screen.
 The time base now represents 200mm range.

Calibration & Sensitivity Calibration & Sensitivity

Share Waves Share Waves
Range Calibration With V2 Block (250mm FSW): Range Calibration With V2 Block (250mm FSW):
 Place the probe on the block and point it at the 25mm arc.
 Adjust the delay and range controls until four echo's on the
screen represents 25mm, 100 mm, 175mm and 250mm.
 Maximize the signals by sliding the probe forward and
backward.
 Adjust range and delay until the first echo comes at 1 and
second at 4, third at 7 and fourth at 10 across the screen.
 The time base now represents 250mm range.
 Check on the 100mm arc of V1 block, first echo should be at
4 and second at 8 across the screen.

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Flaw Location Flaw Location

By Trigonometery: By Trigonometery:
 Angle of the probe and beam path (metal path or range) of  Skip distance and beam path length to be calculated as follow.
indication should be known.
Full Skip Distance = 2TxTanθ Full Beam Path Length = 2T /Cosθ
 Stand off also named as surface distance. Half Skip Distance = TxTanθ Half Beam Path Length = T /Cosθ

450 Probe-Range ≈ 1.5 x Depth

600 Probe-Range = 2 x Depth
700 Probe-Range ≈ 3 x Depth

Flaw Location Flaw Location

By Trigonometery: By Flaw Location Slide: Surface Distance
 Depth in next consecutive legs can be calculated as follow.
Depth = Range x Cosθ --- For 1st leg.
Depth = 2t-Range x Cosθ --- For 2nd leg.
Depth = Range x Cosθ-2t --- For 3rd leg.
Depth = 4t-Range x Cosθ --- For 4th leg.
Depth = Range x Cosθ-4t --- For 5th leg.

Flaw Depth Flaw Depth

Beam Path/Metal
θ Path

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Flaw Location Flaw Location

By Flaw Location Slide: By Flaw Location Slide:
 Draw a cross section of the weld on the transparent outer  Move the datum line on the plastic envelope to the stand-off
envelope of the slide. distance.
 Draw a mirror image of the weld cross section immediately  Look along the center of the beam plot until you come to the
under it if inspection is performed in 2nd leg. range shown on the screen.
 Use the printed datum line on the plastic envelope as the  Make a mark on the envelope; this will represent the flaw
center of the weld. location.
 Maximise the echo from a flaw and measure the stand-off
distance from the weld center line to probe exit point on
parent metal.
 Note the range (metal path) of the flaw from the UFD screen.

Flaw Sizing
6dB Drop Method:

Flaw Sizing

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Flaw Sizing Flaw Sizing

6dB Drop Method: 20dB Drop Method:
 Used for sizing of reflectors which are equal to or greater
than beam width.
 If the probe is moved until the signal amplitude from a
reflector drops to half its original screen height, then the
sound beam will be half on and half off the reflector.
 So by moving the probe until the signal from the end of a
large reflector halves in height, we can thus estimate that the
edge of the reflector is at the center of the probe.
 This method is called the 6dB drop sizing method because the
amplitude of the signal drops by half which corresponds to
6dB when the probe is moved to the edge of a large reflector.

Flaw Sizing Flaw Sizing

20dB Drop Method: 20dB Drop Method:
 This method utilizes, the edge of the ultrasonic beam where  Mark the position of the probe index on the surface of the test
the intensity falls to 10% (i.e. 20 dB) of the intensity at the specimen at this position;
central axis of the beam for the determination of flaw size.  Now move the probe in the opposite direction through the
Procedure: maximized echo position until the echo amplitude again falls
 Position the probe to get a maximum flaw echo amplitude. to 10 % of its original height;
 Adjust the echo amplitude to some convenient scale on the  mark the position of the probe index on the surface at this
CRT screen using the gain control of the flaw detector; position;
 Move the probe first across the flaw in one direction until the  Measure the distance between the two markings;
echo amplitude falls to 10% of its original height (i.e. by 20  Determine the beam width at the flaw depth from the beam
dB). profile diagram or from the equation below.

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 4/2/2021

Flaw Sizing Flaw Sizing

20dB Drop Method: Normal Beam Profile (-20db):
Beam Width = D + 2(d-N) tanθ  Get the maximum signal from hole at the depth of 13mm on
IOW block using normal probe by moving the probe across it.
Where;
 Turn the signal to FSH using gain.
d = Defect depth
N = Near field length
 Mark the position of the middle of the probe on the side of
the block.
D = Probe diameter
100% FSH
 Subtract the beam width from the distance measured between
two markings. this will thus give the dimension of the flaw.
 This method give more accurate sizing but also overestimate
the size of the flaw.

Flaw Sizing Flaw Sizing

Normal Beam Profile (-20db): Normal Beam Profile (-20db):
 Move the probe to one side of the hole until the signal drops  Move the probe to other side of the hole until the signal drops
to 10%FSH (-20dB) and mark the center of the probe on the to 10%FSH (-20dB) and mark the center of the probe on the
side of the block. side of the block.

10%FSH 10%FSH

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 4/2/2021

Flaw Sizing Flaw Sizing

Normal Beam Profile (-20db): Normal Beam Profile (-20db):
 Move the probe to other side of the hole until the signal drops  Repeat the same procedure for holes at the depth of 25 mm &
to 10%FSH (-20dB) and mark the center of the probe on the 32 mm on IOW block.
side of the block.

10%FSH

 Note down the distance at a depth of 13 mm on a paper.

Flaw Sizing Flaw Sizing

Angle Beam Profile: Angle Beam Profile:
 Use 1.5mm side-drilled holes (SDH) at different depths on
IOW block.
 Use a 20dB beam edge for 450 and 600 probes, but
 Use a 10dB for 700 probes. (Wide beam with 20dB).
 For 450 , use the holes at the depth of 19, 25 and 32mm
 For 600, use the holes at the depth of 13, 19 and 25mm
 Repeat the same procedure as in the normal beam profile, but
beam profile shall be drawn on the slide chart.

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 4/2/2021

Sensitivity Setting
 Setting a sensitivity level is essential to provide reproducible
results from the same inspection carried out by different
operators using different probe set combinations and maybe
Sensitivity Setting working in different locations.

(Pre Reference Level)  The purpose of sensitivity setting is to find a gain level
sufficient to find a flaw.
 Sensitivity depends on the:
• Probe used, in particular its frequency.
• Flaw detector.
• Properties of the test material.
• Ratio of BWE or flaw echo to noise.

Sensitivity Setting Sensitivity Setting

Following calibration blocks and method are used to set the IOW Block
sensitivity setting:  Obtain a signal from 1.5 mm SDH at depth equivalent to the
• IOW Block (SDH) corresponding test thickness.
 Turn the gain control until the signal is at FSH and note the
• Distance Amplitude Blocks (SDH)
gain value (dB Value from UFD).
• Distance Amplitude Blocks (FBH)  Add the transfer correction.
• DGS Method (FBH)  Sensitivity is set now and can be assured that flaws having
• Noise Method the equivalent reflectivity of 1.5mm SDH will appear on the
screen.
Note: Doube the thickness if examination need to be carried at
full skip distance.

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Sensitivity Setting Sensitivity Setting

IOW Block IOW Block
Advantages
 Simple to use.
 Provides a uniform system of reference.
 A fairly large and visible echo is assured from small flaws.
 Side-drilled hole reflectors are independent of angle.
Disadvantages
 Block is heavy and expensive.
 Only refers to 1.5mm side drilled holes.
 Not a reliable method for sizing defects.

Sensitivity Setting Sensitivity Setting

Distance Amplitude Block (SDH): ASME Distance Amplitude Block (SDH):
For NP & AP DAC Construction Procedure:
 Calibrate the time base for the maximum sound path length to
be used.
 Adjust the gain so that the amplitude from the series of
reflectors falls between 20-80% FSH.
 Obtain a signal from the first reflector and maximise it to
80% FSH or as in accordance with reference code.
 Without altering the gain setting, maximize the amplitude of
each reflector in turn and mark the tip of the signal, either on
the screen or on a transparent overlay.
 Record the gain setting used for plotting the DAC curve.

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Sensitivity Setting Sensitivity Setting

Distance Amplitude Block (SDH): Distance Amplitude Block (SDH):
DAC Construction Procedure: Split DAC:

 Split DAC shall be used

when signal hight falls
below 20% FSH from
corresponding reflector.

Sensitivity Setting Sensitivity Setting

Distance Amplitude Block (SDH): Distance Amplitude Block (FBH):
Advantages:  Blocks are drilled with flat bottomed holes to precise
 A quick way of accepting or rejecting discontinuities without diameters and set distances from the top of the block.
too much time consumed in sizing reflectors.  These diameters and distances are stamped on the side of the
 Some idea can be gained of the discontinuities size in relation block.
to reference holes.  When setting sensitivities the specification or technique will
 Uniformity provided by all technicians constructing their specify the block to be used and the amplitude of signal to be
curves from the same test block. obtained from the FBH.
Disadvantages:  Blocks are cut for use with normal probes or angle probes in
 Curves must be constructed for each probe in conjunction different materials.
with each set.  Also known as Alcoa series-B or Hitt blocks.
 Transfer correction must be worked out.

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Sensitivity Setting Sensitivity Setting

Distance Amplitude Block (FBH): Distance Amplitude Block (FBH): Normal Probe
 There are 19 blocks in an Alcoa
series-B set.
 Metal distances:
i. 1/16" (1.59 mm).
ii. 1/8 " (3.17mm) through 1" (25.4 mm) in
1/8" (3.17 mm) increments.
iii. 1-1/4" (31.7 mm) through 5-3/4“ (146
mm) in 1/2" (12.7 mm) increments

A block marked 3-0075 has a 3/64" (1.19

mm) diameter hole and a 3/4" (19.6 mm)
metal distance.

Sensitivity Setting Sensitivity Setting

Distance Amplitude Block (FBH): Distance Gain Sizing (DGS):
Advantages:  Relies on the laws of large and small reflectors in the far zone.
 Easy to use.  Relate the amplitude of a large reflector such as a backwall, to
 Uniformity assured when different technicians use the same various sizes of perfect disc reflectors (flat-bottomed holes) at
blocks. different distances.
 Blocks can be made from different materials.  Provides minimum equivalent reflector size (ERS) size but not
Disadvantages: a exact or actual flaw size. It means flaw size is not at least
smaller than the equivalent reflector size.
 Fairly rigid system for specific applications.
 Use a typical diagram for any normal probe irrespective of its
 Large number of blocks needed for different settings.
size and frequency.
 Transfer correction usually needed.
 Individual DGS diagrams are drawn for each design, size and
 Blocks for angle probes are rarely cut exactly normal to the frequency of angle beam probe.
beam.

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Sensitivity Setting Sensitivity Setting

Distance Gain Sizing (DGS) Method: Distance Gain Sizing (DGS) Method:
Advantages: Disadvantages:
 Can choose a gain level for sizing.  Operators must keep referring to a chart and making
 Tells you the smallest defect you can find at a given range. calculations.
 Provides the basis for an accept/reject system.  Attenuation must be taken into account.
 It gives a rough equivalent to the size of a flaw.  No account is taken of flaw orientation.
 Uniformity between results from different technicians.  Most effective on small defects.
 An equivalence system not a sizing system.
 Flaw surfaces and shapes are not ideal reflectors, therefore
signal amplitudes are not the same as a comparative flat-
bottomed hole.

Sensitivity Setting Practice Problem

Distance Gain Sizing (DGS) Method: (Normal Probe) Plate thickness= 100 mm NP Frequency= 5 MHZ
 The horizontal scale gives the normalized distance (A) in near NP Diameter = 10mm Flaw distance=60 mm
field lengths of the sound beam in the subject material. Velocity= 5950 m/s (Steel) Flaw singal at FSH= 30 dB.
A = d/N --- (Eq. a) ERS (R)=?
 The vertical scale represents the gain values measured in dB. 1. Calculate the near field length: N= 21mm
 To make the diagram independent of the diameter of the probe 2. Calculate the normalized distance (A) for both BWE at
the values of the disc reflector (G) curves are normalized as: 100mm and flaw distance at 60mm.
G = R/Deff --- (Eq. b) 3. A at 100mm is 4.76 ≈5 and A at 60mm is 2.85 ≈3.
Where,
4. Assume from UT set at FSH, BWE gain at 100 mm is 20 dB.
d = Real distance in mm N = Near field length in mm Then as per law of large reflector, BWE gain at 60mm will
R = Real disc reflector diameter in mm (ERS) be 16dB, 4 dB less than at 100 mm. (100/60=1.6 , so 1.6X =
Deff = Effective crystal diameter in mm 4dB).

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Practice Problem
5. Gain difference between the flaw echo and BWE at 60mm is
(30-16=14dB).
6. Look down the scale 14dB at 3N from the BWE which is ≈14+6
equal to 20 dB and found the corresponding curve with 0.3 =20 dB
approximately.
7. Multiply the 0.3 with probe diameter.
8- R= 0.3X10mm = 3mm.

(For NP)
≈0.3

Practice Problem Sensitivity Setting

Second Method: (More Suitable)
1. Note the BWE dB (100mm) value at 5N from DGS diagram
which is 10 dB (G1).
2. From UT set at FSH, Flaw dB value at 60mm is 30dB (G2)
and BWE at 100 is 20 dB (G3).
3. Take Difference: G2-G3 =30-20=10dB (G4).
4. Add: G1+G4= 10+10= 20 dB
5. Intersect the 20 dB value at 3N on DGS diagram.
Corresponding curve value is 0.3mm.
6. R= 0.3x10=3mm (ERS).
(For AP)

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Sensitivity Setting Sensitivity Setting

Noise Method: Noise Method:
 Adjust the maximum range for examining the test material. Advantages
 Place the probe on the material with couplant applied.  Quick and easy.
 Turn up the gain until you have 2mm grass on the screen at the  No reference block is needed.
maximum range.  Any defect larger than the material grains will show up.
 Any discontinuity larger than the grain size will show up on the  No transfer correction needed.
screen. Disadvantages
 No accurate sizing of the defect.
 Discontinuities near the surface of the test material may be
hidden in the grass.

Transfer Correction Transfer Correction

 Allowance for the differences in sound energy transfer between Angle Probe Method:
test material and reference block with same equipment is  Place the two probes opposite each other on the reference
known as Transfer correction. block with one probe transmitting and the other receiving, so
that the sound energy is bounced off the backwall and caught
Normal Probe Method:
by the receiving probe (pitch and catch).
 Place the probe on the reference block and turn the BWE up
 Maximise the signal and adjust the gain until it is at FSH.
to FSH. Note the gain settings.
 Place the two probes on a piece of test material of the same
 Now place the probe on the test material and at a similar
thickness as the reference block and repeat the process.
range bring the BWE to FSH. Again note the gain setting.
 Note the difference between the two gain settings.
 The difference between them is the transfer correction.
 This is the transfer correction needed.

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Signal to Noise Ratio Signal to Noise Ratio

 Measure of detectability of a flaw and the effect of the other • Flaw location with respect to the incident beam.
factors • Inherent noisiness of the metal microstructure.
 Measure of the signal from the defect compares to other • The inherent reflectivity of the flaw which is dependent
background reflections (Noise). on its acoustic impedance, size, shape and orientation.
 A S/N ratio of 3-1 is often required as a minimum. • Cracks and volumetric defects can reflect ultrasonic
 The absolute noise level and the absolute strength of an echo waves quite differently.
from a small defect depends on a number of factors: • Many cracks are invisible from one direction and strong
• Probe size and focal properties. reflectors from another.
• Probe frequency, bandwidth and efficiency. • Multi-faceted flaws will tend to scatter sound away from
• Inspection path and distance (water and/or solid). the transducer.
• Interface (surface curvature and roughness).

Signal to Noise Ratio Signal to Noise Ratio

 General factors to consider with respect to S/N and therefore • The shorter the pulse (often higher frequency), better the
defect detection, are they: detection of the defect.
• Increase with increasing flaw size. • Shorter pulses correspond to broader bandwidth
• Flaw detectability is directly proportional to its area. frequency response.
• Increase with a more focused beam. • Decrease in materials with high density and/or a high
• Flaw detectability is inversely proportional to the
ultrasonic velocity.
transducer beam width. • The S/N is inversely proportional to material density and
• Increase with decreasing pulse width.
acoustic velocity.
• Flaw detectability is inversely proportional to the duration
• Generally increase with frequency.
of the pulse produced by an ultrasonic transducer.

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Ultrasonic Equipment Checks

Following are the equipments charateristic to be checked.

 Time Base (Horizontal) Linearity

 Screen Height or Vertical Linearity

Ultrasonic Equipment Checks  Amplitude Control Linearity (Linearity of Equipment Gain)

 Probe Index & Beam Alignment

 Beam Angle

 Sensitivity and Signal-to-Noise Ratio

 Pulse Duration / Length / Width

 Resolving Power (Resolution)

 Penetration Power

Time Base Linearity Time Base Linearity

 Place the probe on the 25mm thickness of the V1 or V2 block Tolerance:
with any suitable range and adjust the controls to display ten  Unless otherwise specified by the testing standard, a
BWEs. tolerance of ±2% is considered acceptable.
 Adjust the controls so that the first and last BWEs coincide Frequency of checking:
with the scale marks at 1 and 10.  At least once per week or in accordance with reference
 Increase the gain to bring successive backwall echoes to 80% construction code
FSH or in accordance with the procedure.
 The leading edge of each echo should line up with the
appropriate graticule line.
 Record any deviations at approximately half screen height.
 Deviations should be expressed as a percentage of the range
between the first and last echoes displayed (ie 225mm).

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 Screen Height or Vertical Linearity  Screen Height or Vertical Linearity

In Accordance With ASME V (Article 4): In Accordance With ASME V (Article 4):
 Position an angle beam search unit on a calibration block.  Alternate: A straight beam
 Obtain indications from both the 1/2T and 3/4T holes give a search unit may be used on
2:1 ratio of amplitudes between the two indications. any calibration block that
provides amplitude
 Adjust the sensitivity (gain) so that the larger indication is set differences, with sufficient
at 80% of full screen height (FSH). signal separation to prevent
 Without moving the search unit, adjust sensitivity (gain) to overlapping of the two
successively set the larger indication from 100% to 20% of signals.
full screen height, in 10% increments (or 2 dB steps).  Frequency: not to exceed
 Read the smaller indication at each setting. three months. Or in
 The reading shall be 50% of the larger amplitude, within 5% accordance with reference
of FSH. construction code.

 Amplitude Control Linearity  Amplitude Control Linearity

In Accordance With ASME V (Article 4): In Accordance With ASME V (Article 4):
 Position an angle beam probe on a basic calibration block.  Alternate: any other convenient reflector from any calibration
 Obtain indication from the 1/2T side-drilled hole about block may be used with angle or straight beam search units.
midway along the time base.  Frequency: not to exceed three months or in accordance with
 The echo amplitude is set to a 80% FSH and the attenuator reference construction code.
(dB) reading is noted.
 The attenuator setting is then reduced by 6 dB, four or five
times in succession and the decrease in echo amplitude is
noted every time.
 The indication shall fall within the specified limits

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 Sensitivity and Signal to Noise Ratio  Sensitivity and Signal to Noise Ratio

 Provide a simple method which will identify deterioration in  Difference between the first and second measurements (dB)
sensitivity of the probe and flaw detector in combination. gives the S/N ratio.
 Place the probe on the V1 calibration block and adjust its  Frequency: The check shall be carried out once per probe per
position to maximize the signal from the 1.5mm diameter day or in accordance with procedure.
hole.
 Adjust the gain control to set this signal to 20%FSH and note
the dB setting (Sensitivity Value).
 Increase the gain until the overall system noise (electronic
noise and grain structure grass) at the same range as the target
hole reached 20%FSH and note the new dB setting.
 The first gain measurement noted provides a check on the
sensitivity of the probe and flaw detector.

 Pulse Duration / Length/ Width  Pulse Duration / Length/ Width

 Calibrate the time base in millimetres to a range that is to be

used in subsequent testing.
 Maximise the signal from the 1.5mm side-drilled hole (V1
block) for shear wave probes or a BWE for compression
wave probes and set its peak to 100% screen height.
 Measure the width of the signal in millimetres at the 10%
screen height position.
 If desired, the measurement in millimetres can be converted
into microseconds by dividing it by the relevant sound
velocity.
 Frequency: check should be carried out daily or in
accordance with procedure.

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 Resolving Power (Resolution)  Resolving Power (Resolution)

 Ability of an ultrasonic flaw detection system to give separate Method (Using V1 Block):
indication of discontinuities situated close together and
simultaneously within the sound beam.
First Method (Using V1 Block):
 Calibrate the time base to a range of 0-100mm for Normal
Probe .
 A probe is placed on the block and echoes from the three
Poor Resolution Better resolution,
reflectors (85, 91 & 100 mm) are obtained.
 The separation of the echoes from each other indicates the
degree of resolution of the flaw detector for that particular
probe.

 Resolving Power (Resolution)  Resolving Power (Resolution)

Second Method (Using A7 Block):

 Calibrate the time base to a range of 0-100mm for either the
compression or the shear wave probe.
 Place the probe so that the axis of the beam impinges upon
the 2mm step in the A7 calibration block for shear wave
probes, or the 3mm step for compression wave probes.
 Adjust the position of the probe so that the echoes from the
two targets are of the same height and approximately half full
graticule height (50% FSH).
 The steps are said to be resolved when their echoes are
clearly separated at half maximum echo height or lower.
 Frequency: check should be carried out daily or in
accordance with procedure.

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 Penetration Power  Penetration Power

 Used to compare the energy output for a particular set and

probe with its past performance or with similar equipment.
Method (Using V1 Block):
 A normal probe is placed on the plastic insert having a
thickness of 23 mm which is equal to 50 mm of steel.
 Gain for the instrument is set to its maximum.
 The number of multiple echoes and the amplitude of the last
echo are noted and are used to express the maximum
penetrative power of the set and the probe.

 General Procedure
Collection of information prior to the testing of weld:
i. Parent metal specifications.
ii. Weld joint preparation.
Weld Inspection iii. Welding processes.
iv. Parent metal thickness adjacent to the weld.
v. Any special difficulty experienced by the welder during
welding.
vi. Location of any repair welds.
vii. Reference & Acceptance standards requirements.

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 General Procedure  General Procedure

Echo amplitude:
Following stages are involved to determine the exact nature of.
 Compare the amplitude of an indication to DAC level and
i. Echo amplitude. classifying it into one of the four categories shown in the
ii. Directional reflectivity. table below or in accordance with reference code or
procedure.
iii. Echostatic pattern.
iv. Echodynamic pattern.
 S1 indication need not to be evualted. All other indications
are processed for directional reflectivity.
 ASME VIII Div.1 (App#12): Indication which produce a
response greater than 20% of the reference level shall be
investigated to the extent that the operator can determine the
shape, identity, and location of all such imperfections and
evaluate them in terms of the acceptance standards.

 General Procedure  General Procedure

Directional Reflectivity: Echostatic pattern.
 Compare variation in echo amplitude from a discontinuity in  Analyze the shape of a signal.
relation to the angle at which the ultrasonic beam is incident
upon it.
 A spherical indication would show the same echo amplitude
over a wide range of incident angles; 45, 60 and 70o for
instance, and is said to have low directional reflectivity.
 A large smooth planar reflector would show a great variation
in echo amplitude and would therefore be said to have high
directional reflectivity.

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 General Procedure  General Procedure

Echodynamic Pattern. Echodynamic Pattern.
 Analyze behavior of a signal with respect to probe movement
patterns.

Basic Probe Movements

 General Procedure  General Procedure

Echodynamic Pattern. Echodynamic Pattern.

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 General Procedure  General Procedure

Echodynamic Pattern. Echodynamic Pattern.

 General Procedure  General Procedure

Visual Inspection: Establishment of Exact Location and Size of the Weld:
 Make visual examination of weld.
Joint with Ground Flush Weld Reinforcement:
 Surface should be free from weld spatter, rust and smooth
enough for scanning.  By Etching: Etch the weld region to establish the weld width
and then identify the weld center line.
 Note inaccessible areas.

 Look for surface imperfections, lack of fill, undercut and,

 By Normal Probe: The center line of the weld can be
cracks or surface porosity, mismatch and misalignment. determined by marking the center point of a normal probe at
two or three locations on the weld at which a maximum echo
 If surface imperfections exceeding acceptance standard,
is obtained from the weld bead. The line joining these points
should be remedied before carrying out the ultrasonic
is then the center line of the weld.
inspection.

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 General Procedure  General Procedure

Establishment of Exact Location and Size of the Weld: Establishment of Exact Location and Size of the Weld:
Joint with Weld Reinforcement: Joint with Weld Reinforcement:
 By Angle probe: Placing the probe first on one side of the  By Angle probe:
weld and marking the probe index on the specimen where the
echo from the weld bead is a maximum. On the same side of
the weld two or three such points are obtained. Then the
probe is placed on the other side of the weld and the probe
index is again marked at different locations when a maximum
echo from the weld bead is obtained. The center points of
lines joining these marks are then determined. When these
points are joined the center line of the weld is obtained.

 General Procedure  General Procedure

Parent Metal Examination (Normal Probe) Parent Metal Examination (Normal Probe)
 Parent metal should be examined to detect any imperfection
such as laminations, etc., which might interfere with the
subsequent angle beam probe examination of the weld, and
also to assess the thickness of the parent metal.
 The examination should be over a band which is greater than
the full skip distance for the largest angle beam probe
(usually 70° probe) to be used.
 Use either a single crystal or a twin crystal probe, normally
with a 2 to 6 MHz frequency. Higher frequency is preferable.
 The setting of sensitivity for this examination should be in
accordance with the relevant specification or code of practice.

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 General Procedure  General Procedure

Parent Metal Examination (Normal Probe) With Normal Probe & Joint with Ground Flush Weld
Reinforcement:
 Weld body can be examined.

 Bonding at the root can be checked If a backing bar has been

used.
 Root on a double sided weld can be checked.

 Lack of penetration at the root may be detected.

 For a single V weld: lack of inter-run fusion and large pockets

of slag can be revealed.

 General Procedure  General Procedure

Selection of Probe Angle: Selection of Probe:
 Surface Condition: A lower frequency is better on a rough  Internal metallurgical structure: The grain size in the parent
surface from the point of view of coupling efficiency. material can also affect the transmission of sound. When the
 Curved Surface: Small probes do not rock to the same extent grain size, or the size of precipitates or inclusions begins to
as large ones. get greater than 10% of the wavelength it can refract or
 Type of Material: The transmission of sound waves varies
reflect sound, leading to attenuation or noise.
with basic material types, and with the condition of the  Penetration: In a given material, low frequency waves will

material. In weld metal, which is often coarsely crystalline, penetrate further, than high frequency waves.
the sound can be greatly impeded. This is especially true for  Resolution: High frequency probes have superior resolution
austenitic stainless steel, where large crystals reflect some of characteristics, so that small flaws can be found more readily,
the sound back to the receiver, often to the extent that than with low frequency probes.
ultrasonic testing is impractical..

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 General Procedure  General Procedure

Selection of Probe: Selection of Probe:
 Accuracy: In general, high frequency probes provide greater  Probe angle:
accuracy in determining the size of the flaws. • Selected angles shall be able to obtain an echo from all flaws.
 Scanning Speed: Where large flaws are to be covered as in • Orientation of flaw has a significant effect on echo signal
initial detection of flaws; large probes of low frequency, unless the probe angle is favorable for normal reflection., e.g.
provide rapid scanning. lack of fusion on side walls and at the root, and cracks.
 Range Selection: • The probe angles most generally suited to different
• Make the beam path, in relation to frequency, sufficiently thicknesses.
short, to avoid excessive attenuation. • A beam incident on a reflecting surface at 300 will result in
• Subject to considerations of probe angle, nature of defects mode conversion, and in a loss of shear wave energy of up to
and beam spread, the representative ranges may be up to 200 20 dB (90%). Further, a fraction of surface waves is
mm (8 in) for frequencies of 2 to 6 MHz and up to 400 mm generated by 800 probes.
(16 in) for frequencies of 1 to 1.5 MHz.

 Examination of Root  Examination of Root

Scanning Procedure: Scanning Procedure:
 Selection of probe angle in accordance with procedure.  Place the probe index point on the line and put a magnetic
 Calibration of time base on a suitable range. ruler or strip behind it as a guide.
 Determination of the correct probe index and angle using VI  A scan is made by moving the probe slowly from one end of

or V2 block. the specimen to the other, so that the probe index always
 Calculation of 1/2 skip distance (Stand off) and 1/2 beam
coincides with the scan line.
path length (1/2 BPL-Range) for the selected probe.  Areas with echoes from defects are marked on the specimen

 Marking of the scan lines at 1/2 skip distance from the weld
for subsequent examination to establish the nature and size of
center line on both sides of weld. the defects.
 Setting the gain sensitivity for scanning and evaluation.

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 Examination of Root  Examination of Root

Scanning Procedure: Root Flaws:
 Signals from a good root should be small while imperfection
will give a large signal.
 Signals from a fully penetrated root will usually appear just
beyond the range (1/2 BPL) of the root center, call a standard
root /weld bead signal.
 Following are the Root Flaws:
 Lack of Penetration
 Root under cut & Slag inclusion
 Excess Penetration
 Root Concavity
 Root Crack
 Lack of Root fusion
 Misalignment Good Root

 Examination of Root  Examination of Root

Lack of Penetration: Root Under Cut:
 Indication will appear at ½ BPL (range) from both side.  Indication will appear little short of ½ BPL (range) from one

 Good corner reflector. side and little away from other side.
 Large echo amplitude compare to root under cut.  Less echo amplitude compare to lack of penetration.

 No root bead signal.  Root weld bead signal will also appear.

 The echoes will maximize when the probe is moved

backwards from one scanning line.

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 Examination of Root  Examination of Root

Slag Inclusion or Gas Pocket Just Above the Root: Excess Penetration:
 Indication will appear little short of ½ BPL (range) from both  Echo amplitude between 10 and 90%, dependent on depth
side. and probe angle.
 Root weld bead signal will also appear.  Multi-range signal - echo falls rapidly when traversed with

 The echoes will maximize when the probe is moved forward 700 probe and also range increases.
from both scanning line.  Probe Movement - echo falls rapidly when angle probe
traversed forward.
 Measurement - it is not possible to measure depth with angle
probe. Length difficult but usually by 6dB.

 Examination of Root  Examination of Root

Root Concavity: Root Crack:
 Echo sharp and large, with reduced range. Often mode  Usually high amplitude response with fir tree appearance.
conversion with 60° probe.  Probe movement - orbit, echo held over large angle.
 Probe movement - traverse backwards echo falls more rapidly  Lateral, echo held with multi-range signals and variations on
than lack of penetration. time base.
 Measurement - use center of beam and 20dB drop (trailing  Measurement - 6dB for length. Traverse forward with 20dB
edge) for height. Not always possible to measure height. for height.

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 Examination of Root  Examination of Root

Root Crack: Lack of Root Fusion:
 From side 1 a large echo will appear just where the echo from  Similar to corner reflector with large, narrow echo from both
undercut is expected and there will be no accompanying bead sides.
echo.  Probe movement - confirm with 700 probe, when traversed.
 From side 2, however, it is possible to get a bead echo as well  Large movement for 20dB drop. Orbit, echo falls rapidly.
as the defect echo  • Measurement - lateral use 6 or 20dB drop. Traverse use 20
dB or 10dB for 700 probe.

 Examination of Root  Examination of Weld Body

Misalignment: Scanning Procedure:
 Large single echo from one side. No echo from opposite side.  Selection of probe angle in accordance with procedure.
 Probe movement -traverse back echo falls rapidly.  Calibration of time base on a suitable range.

 Measurement - lateral for 6dB drop.  Determination of the correct probe index and angle using VI
or V2 block.
 Calculation of 1/2 & full skip distance and 1/2 BPL & full
beam path length (BPL) for the selected probe.
 Marking the parent metal on both sides of the weld with lines
parallel to the weld center line and at distances of 1/2 skip
and full skip +1/2 cap width.

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 Examination of Weld Body  Examination of Weld Body

Scanning Procedure: Scanning Procedure:
 Setting the sensitivity of the probe/flaw detector system for
the maximum testing range which in this case is the full BPL.
 Scanning the specimen in a zigzag pattern (raster scanning)
between the marked scan limits.
 Each forward scan should be at right angle to the weld center
line, and the pitch of the zigzag should be a half probe width
to ensure full coverage.
 Mark the areas, in which defect echoes occur, for subsequent
location, establishment of nature and sizing of the defects.
 The probe movement may be used to help in establishing the
nature and size of defects.

 Examination of Weld Body  Examination of Weld Body

Selection of Probe Angle: Weld Body Flaws:
 The initial choice of probe angle for the weld body scan Following are the weld body flaws:
depends upon the weld preparation angle.  Lack of fusion
 The angle should be chosen to meet any lack of sidewall
fusion at right angle for maximum response.  Crack
 The angle to meet this fusion face at right angle can be  Gas Pore (Isolated)
calculated from:  Porosity
Probe angle = 900 - θ/2  Linear Inculsion (Slag)

Where, θ = Weld Preparation Angle

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 Examination of Weld Body  Examination of Weld Body

Lack of Fusion: Crack:
 Echo large, single, narrow at time base when sidewall. Poor  Multiple peak reflector usually high amplitude, but dependent
echo from opposite side. Confirm by skip scan. on type of crack and size, echo with fir tree appearance.
 Probe Movement:  Probe Movement:

 Rotate or orbit: echo falls rapidly.  Rotate or orbit: echo falls rapidly but over larger angle

 Lateral or traverse: echo height held. than with fusion defects

 Measurement:  Lateral: signal held with varying height.

 For depth use 20dB.  Measurement:

 For length use 6 or 20dB.  For depth use 20dB.

 For length use 6 or 20dB.

 Examination of Weld Body  Examination of Weld Body

Gas Pore (Isolated): Porosity:
 Spherical even reflector single peak echo, narrow profile,  Multiple echo’s. Low intensity 20% CRT broad at time base
similar to drilled hole or radius of calibration block intensity due to numerous ranges.
approximately 50% CRT.  Probe Movement:
 Probe Movement:  Orbit - echoes held with amplitude variations.
 Rotate: lateral and traverse echo falls rapidly.  Measurement: Indicate area by pin-pointing last maximum
 Orbit: echo height remains. signal from traverse and lateral scans.
 Measurement: Impractical to measure height and length.

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 Examination of Weld Body  Examination of Weld

Linear Inclusion (Slag): Transverse Scan (Transverse Crack):
 Multiple echo may be wide at time base and will be multi-  Weld cap not dressed:
faceted, due to more than a single range. Height will vary  Scan is done parallel to the weld center line alongside the
between 20 and 90%. weld cap with the probe inclined towards the center.
 Probe Movement:  A crack tends to have a ragged edge, it is likely that
 Orbit & Traverse: echo held with varying intensity. some energy will be reflected back to the transmitter.
 Rotational: echo will drop quickly.  A safer technique (Pitch-Catch) is to use a pair of probes,

 Lateral: produce large variations in height. Perhaps with

one transmitting and the other receiving
total loss of signal for short distances less than beam  Weld cap dressed:
width.  A scan along the weld center line and several scans
parallel to and on either side of the weld center line, from
each direction, are done to give a full coverage of the
weld.

 Examination of Weld  Examination of Weld

Transverse Scan (Transverse Crack): Transverse Scan (Transverse Crack):

When weld cap is not dressed When weld cap is dressed

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 Examination of Double V Weld  Examination of Double V Weld

 Similar to examining the single V weld with few variations. Root Examination (Method#02):
Root Examination (Method#01):  Use Tandem technique for double V weld root examination
 Examine the root with a 700 (usually) probe positioned at 1/4
and vertical reflectors inside the material.
skip distance from the weld center line.  For double V welds, the beam is aimed at the center of the
 Run the probe laterally along the weld with sensitivity set in
weld and the probe separation is equal to half skip distance
accordance with procedure at a suitable range; this should for that probe angle.
show any lack of penetration at the root.  Probe separation for depth (d) can be calculated as follows:
 Time base range for an echo from lack of penetration cannot
be predicted precisely.

 Examination of Double V Weld  Examination of Pipes

Weld Body Examination: Longitudinal Scan (Pipe):
 Similar to single V weld examination but scan starts at 1/4  Longitudinal scan (usually circumferential joint) can be made
skip distance from the weld center and goes back to full skip in the same way as butt welds in plates.
plus half weld cap width. Circumferential Scan (Pipe):
 Thickness > 25mm: Scans with 60 and 450 probes from both  Calibration blocks shall be selected in accordance with pipe
sides of the weld using ¼ to ½ skip distance. diameter and reference code requirements (i.e. piping
 Thickness ≤ 25mm: Use a 60 and 700 probe from one side of calibration blocks or etc)
the weld only between 1/4 and full skip + 1/2 weld cap width.  Maximum probe angle (known as limiting angle) shall be
calculated as follow.

Sinθ= ID/OD

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 Examination of Pipes  Code and Standard

 For a given probe angle, the maximum wall thickness of a Review the following codes for understanding.
pipe that allows the center of the beam to reach the bore of
the pipe can be calculated from the following formula:  ASME V Article 4
 ASME VIII Appendix 12
 AWS D1.1 (Part F)

 Thank You

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