AN OVERVIEW OF

NON-DESTRUCTIVE TESTING METHODS

R.S.RAJPUROHIT,SO/F,QA
ISNT-L-III-RT,MT,ET & LT
ISNT-L-II- PT,VT&UT,BARC-RT-L-II
 Non-Destructive Testing (NDT)- Definition

Non-Destructive Testing are used to represent techniques that

are based on the application of physical principles employed
for the purpose of determining the characteristics of materials
and for detecting and assessing the in-homogeneities and
harmful defects without impairing the usefulness of such
materials.
 Introduction to Non-Destructive Testing (NDT)
NDT not only improves the quality, it also brings down the cost of
production by eliminating the defective components right at the
beginning of manufacturing stage. NDT instills confidence in the
manufacturer for meeting the customers’ satisfaction.
 Classification of NDT Methods
Non-
Destructive
Testing

Surface &
Surface Volumetric Performance
Sub-surface
Examination Examination Test
Examination

Magnetic Radiographic Acoustic

Visual
Particle Testing Emission

Liquid Ultrasonic
Penetrant Eddy Current Leak Testing
Testing
 NDT TECHNIQUE
Conventional :
 VT (VISUAL TESTING).
 PT (Penetrant Testing).
 MT (Magnetic Particle Testing).
 ET (Eddy Current Testing).
 RT (Radiography Testing).
 UT (Ultrasonic Testing).
 LT (Leak Testing).

Non Conventional :
 NRT (Neutron Radiography Testing).
 AET (Acoustic Emission Testing).
 Thermography.
 Vibration Analysis.
 Advanced NDT Methods/Techniques
• (1) Optical Holography
• (2) Acoustic Holography
• (3) Real Time Radiography (RTR), Fluoroscopy
• (4) Flash Radiography
• (5) Radiometry
• (6) Digital and Computed Radiography
• (7) Tomography
• (8) Phased Array UT
• (9) Time of Flight Diffraction Technique (TOFD)
• (10) Synthetic Focus Aperture Technique (SAFT)
 CLASSIFICATION

• Surface Methods: NDT methods which are suitable

for the examination of surface only.
– Visual Testing
– Liquid Penetrant Testing
• Subsurface Methods: Suitable for detecting surface
as well as sub-surface discontinuities.
– Magnetic Particle Testing
– Eddy Current Testing
• Volumetric Methods: Suitable for the examination
of whole volume of the object.
– Ultrasonic Testing
– Radiography Testing
 CRITERIA FOR SELECTION
OF NDT METHOD(S)
• Type of flaw to be detected (surface/sub-surface, planar/volumetric)
• Type of material (conducting/non-conducting, casting/wrought)
• Geometry of component to be examined (shape & thickness)
• Accessibility (flaw on inside/outside surface, access to one/both surfaces)
• Sensitivity (fatigue/SCC, lamination/porosity)
• Cost
VISUAL TESTING
Visual Testing or visual inspection is probably the most widely used and oldest
test method among all the non-destructive tests.
It is simple, easy to apply, quickly carried out and usually low in cost
 
Basic Principle
The basic procedure used in visual NDT involves illumination of test specimen with
light, usually in visible region. The specimen is then examined with eye or by light
sensitive devices. The equipment required for visual inspection is extremely simple,
but adequate illumination is absolutely essential. The surface of the specimen
should be thoroughly cleaned before being inspected.
OPTICAL AIDS USED FOR VISUAL INSPECTIOIN: -
Eye
Most valuable NDT tool is human eye. For visual inspection adequate lighting i.e.
800-1000 lux is of prime importance. The period of time during which a human
inspector is permitted to work should be limited to max. 2 hrs at a time
Visual inspection by an experienced inspector can reveal :-

• General condition of component

• Presence or absence of oxide film or corrosive product
• Presence of cracks, its orientation etc.
• Surface porosity, weld beads etc.
• Sharp notches, misalignment etc.
• Result of visual examination may be great assistance to other
NDT tests.
Borescope
As the name implies, a Borescope is an instrument designed to inspect inside a
narrow tube. Borescope consists of precision built in illumination system,
having a complex arrangement of prisms and lenses through which light is
passed to the observer with maximum efficiency. With increase in length of
borescope the image becomes less bright because of loss of light. Borescopes
are available in various models from 2.5 to 19mm dia & a few meters (2-3 m) in
length.
 
Flexible fiber- optic Borescope (Flexi scope / Fiberscope)
 
Flexiscope permits manipulation of the instrument at the corners and through
passages with several directional changes. Generally it is available in 3 to
12.5mm dia and 600 to 3650mm length
Telescope
It is used to examine the object with magnified images of the surfaces which are
otherwise inaccessible . It consists of essentially 2 lenses called objective & eye
piece.
 

Videos cope
Records images & seen on monitor
 

APPLICATION
• Misalignment of parts in the equipment
• Corrosion, erosion, cracks, fractures etc.
• Defects in the new / repaired weldments such as gross surface cracks, lack of
penetration, tear cracks, excess reinforcement, porosity etc.
• Minute discontinuities with the help of optical aids.
• Inspection of plant system / component for any leakage, abnormal operation etc.
 Bore-scopes
Inspection of bores

Rigid Flexible
Bore-scope Bore-scopes
Bores not having
Inspection of straight passage way
straight bores

Video-scopes
Fibre-scopes Electronic image
Optical image transfer
transfer
15
 Flexible Borescopes

• Flexible bore-scopes are used primarily in applications

that do not have a straight passageway to the point of
observation.
• The two types of flexible bore-scopes are,
– flexible fiberscopes (optical image transfer)
– Video-scopes with a CCD image sensor at the distal tip
(electronic image transfer).
 Fibrescope
Fibrescope
 INTRODUCTION

LIQUID PENETRANT TESTING

 Liquid Penetrant Testing (PT)
• PT is used to detect imperfections which are essentially open to the surface.
• In this method, a liquid penetrant is applied to the surface of a product for a certain
pre-determined time known as dwell time, during which the penetrant seeps through
any surface opening defect by capillary action.
• After the dwell time, the excess penetrant is removed from the surface. The surface is
then dried and developer is applied to it. The penetrant which remains in the
discontinuity is absorbed by the developer(Blotting action) to indicate the presence as
well as the location, size and nature of discontinuity.
• Developer normally white in colour offers a very good contrasting background for
penetrant which is either red (visible) or yellow-green (fluorescent) in colour.
• As a special case, Ultraviolet (UV) light is required for the inspection of fluorescent
penetrant.
 PT- PROCEDURE
Clean the surface
Surface
Cleaning Remove Contaminants that block the flaw opening

Penetrant drawn inside the

Penetrant flaw by capillary action
Application

Removal of Penetrant on surface is

Excess Penetrant removed after ‘Dwell Time’

Application Developer draws out penetrant

of Developer within the flaw by blotting
action

Evaluation Linear (L>3W) or Rounded Indication 6

 PT- ADVANTAGE
• This method is best adopted to inspect all types of cracks, porosity,
laminations, lack of bond and leak across the wall if exposed to the
surface.
• This is one of the cheapest and simplest NDT methods which
require less skill.
• Because of its portability, it can be easily adopted to the field
application.
 Welding Cracks
Table 3: Photographs of Defect Samples
Welded sample W-2 (Visible Dye)

Weld face before PT

Weld face after first time PT

Weld face after second time PT

Fluorescent Dye Indication
 Sample with grinding cracks (Fluorescent Dye)

Face ‘A’ before PT Face ‘B’ before PT

Face ‘A’ after PT

 INTRODUCTION

MAGNETIC PARTICLE TESTING

 Principal

Magnetic particle testing is a very useful method for detection of surface & sub-surface crack in ferrous
material components. In this method, when the part being inspected is first magnetized, there is flow of
magnetic lines of force on the portion under test. At this stage magnetic powder is sprayed on the surface.
If there is any discontinuity or flaw in the surface or just below it, the flow of magnetic lines is interrupted
& intermediate poles are induced at either side of discontinuity. These interpoles attract the sprinkled
magnetic powder. This forms an exact image of the flaw. The image is more sharp if the flaw is closer to
the surface. One thing to be kept in mind during magnetic particle testing is that the discontinuities
parallel to the line of magnetic force will not show any indication.
 Leakage Flux

• At surface breaking crack in a bar magnet, north and south poles are created. The magnetic field
spreads out when it encounters the small air gap created by the crack because the air cannot support
as much magnetic field per unit volume as the magnet can.
• When the field spreads out, it appears to leaking out of the material and, thus, it is called a flux
leakage.

MPT
 Formation of an Indication
If iron particles are sprinkled on a cracked magnet, the particles
will be attracted at
(a) At the poles at the ends of the magnet and
(b) At the poles at the edges of the crack.
This cluster of particles is much
easier to see than the actual crack.

MPT
 Transverse and longitudinal defect

• Defect oriented perpendicular to the magnetic

field creates the largest disruption of the magnetic
field within the part and the greatest flux leakage at
the surface of the part.

If the magnetic field is

parallel to the defect,
the field will see little
disruption and no/less
flux leakage field will
be produced.
MPT
 TEST METHOD & TECHNIQUE
A. As per method of Magnetization
 Longitudinal Magnetization :
 Coil Technique.
 Yoke Technique.
 Circular Magnetization :
 Head Shot.
 Prod Technique.
 Central Conductor (Indirect Induction).
B. As per sequence of Operation
 Continuous method.
 Residual method.
C. As per Examination Medium
 Dry method.
 Wet method.
 Defect orientation & direction of
current
• The best detection of defects occurs when the lines
of magnetic force are established at right angles to
the longest dimension of the defect.

MPT
 Longitudinal Magnetic Field

A longitudinal magnetic field

has magnetic lines of force that
run parallel to the long axis of
the part.
Longitudinal magnetization of a
component can be accomplished
using the longitudinal field set
up by a coil or solenoid. It can
also be accomplished using
permanent or electromagnets.
MPT
 Circular or Transverse Magnetic
Field

A circular magnetic field has

magnetic lines of force that run
circumferentially around the
perimeter of a part.
A circular magnetic field is
induced in an article by either
passing current through the
component or by passing
current through a conductor
surrounded by the component.

MPT
Producing a Longitudinal Magnetic Field Using
a Coil- Indirect Method

A longitudinal magnetic field is Coil on Wet Horizontal Inspection Unit

usually established by placing
the part near the inside or a
coil’s annulus. This produces
magnetic lines of force that are
parallel to the long axis of the
test part.

Portable Coil
 Coils

Preformed coil Cable wrapped into a coil

MPT
Circular Magnetic Fields
Circular magnetic fields are produced by
passing current through the part (direct
method) or by placing the part in a strong
circular magnet field (indirect method).
A headshot on a wet horizontal test unit
and the use of prods are several common
methods of injecting current in a part to
produce a circular magnetic field (direct).
Placing parts on a central conductors
carrying high current is another way to
produce the field (indirect).
 Yoke and prod techniques
Yoke is an electromagnet which creates Prods are a current carrying electrodes
longitudinal field between legs. (+ & -) which create circular field.

Yoke technique for plate examination. Prod technique for testing butt weld.
Both Yoke and Prod can be manipulated to change the direction of field
relative to orientation of the flaw for its detectability.
 Magnetic particles
• The magnetic particles can be applied in powder form or as liquid suspension
known as ‘magnetic ink’. Like PT it has two variants- visible and fluorescent
magnetic powder/ink, later being inspected under UV light.
 Large Bolt with
Service Induced Crack

Fluorescent, Wet Particle Method

Throat and Toe Cracks in
Partially Ground Weld

Visible, Dry Powder Method

Advantages:
 It is the best method and most reliable method available for finding surface and sub- surface
cracks, especially very fine and shallow ones.
 It is rapid and simple to operate.
 The indications are produced directly on the surface of the part.
 Operators can learn the method easily, without lengthy or highly technical training.
 There is little or no limitation due to size or shape of the part being tested.
 It will detect cracks filled with foreign material.
 Surface preparation is not as rigid as in the case penetrant testing.
 It will work well through the coatings of part.
 It is relatively low in operational costs.
 
Limitation:
 It does not work on non-ferromagnetic materials.
 As the magnetic flux lines should be almost perpendicular to the discontinuities, many times
more than one magnetic field has to applied to the part.
 Sometimes, parts have to be demagnetized after testing.
 Post cleaning, to remove remnants of the magnetic particles clinging to the surface, may
sometimes be required after testing and demagnetizing.
 Sometimes, the geometry of the part is a limitation i.e. how to apply the magnetizing force to
produce a field in a proper direction in the matter.
 Normally, there is no permanent record of the test.
EDDY CURRENT TESTING
 Principle

• It involves the use of a varying magnetic field produced by a

test coil to induce small, circulating currents called eddy
currents into electrically conductive materials. Any factor
existing in the material under test, that affects the eddy
currents can be detected.
 Generation of Eddy Currents
In order to generate eddy currents for an inspection a “probe” is used. Inside the
probe is a length of electrical conductor which is formed into a coil.
 Generation of Eddy Currents (cont.)
Alternating current is allowed to flow in the coil at a frequency chosen by the
technician for the type of test involved.
 Generation of Eddy Currents (cont.)
A dynamic expanding and collapsing magnetic field forms in and around the coil as
the alternating current flows through the coil.
 Generation of Eddy Currents (cont.)
When an electrically conductive material is placed in the
coil’s dynamic magnetic field electromagnetic, induction will
occur and eddy currents will be induced in the material.
 Generation of Eddy Currents
Eddy currents are induced electrical currents that flow in a circular path. They get
their name from “eddies” that are formed when a liquid or gas flows in a circular
path around obstacles when conditions are right.

Test Probe

Eddy Currents
 Generation of Eddy Currents (cont.)
Eddy currents flowing in the material will generate their own “secondary” magnetic
field which will oppose the coil’s “primary” magnetic field.
 Generation of Eddy Currents (cont.)
This entire electromagnetic induction process to produce
eddy currents may occur from several hundred to several
million times each second depending upon inspection
frequency.
Any thing that affects the strength
AC Test Probe of the eddy currents will affect the
(coil) impedance of the coil, and thus be
detectable by the test circuits.
Primary Mag. Field

Conductor
Secondary Mag. Field
(Test piece)

Eddy Current
 Impedance (Z)
Definitions:
Resistance - The opposition of current flow (mainly to DC),
resulting in a change of electrical energy into heat or another
form of energy.
Inductive Reactance (XL) - Resistance to AC current flow
resulting from electromagnetic induction in the coil.
Impedance (Z) - The combined opposition to current flow
resulting from inductive reactance and resistance.

Impedance (Z) in an eddy current coil is

the total opposition to the current flow. R Test
In a coil, Z is made up of resistance (R) ~ XL
Coil
and inductive reactance (XL).
 Detection
• The flow of eddy currents in the material causes a
fluctuating magnetic field (secondary) of its own. This
magnetic field is always in opposition to the coil’s magnetic
field (primary) thus strength of the coil is lessened.
• This change in the magnetic field causes change in the
impedance of a coil which in turn, causes a change in the
current flowing through the coil.
• Information about the strength of the eddy currents within
the specimen is determined by monitoring changes in
voltage and/or current that occur in the coil.
• Any thing that affects the eddy currents will affect the
impedance of the coil, and thus be detectable by the test
circuits.
 Crack Detection
Cracks cause a disruption in the circular flow patterns of the
eddy currents and weaken their strength. This change in
strength at the crack location can be detected.

MagneticField
Magnetic Field
FromTest
From TestCoil
Coil

MagneticField
Magnetic Field
From
From
EddyCurrents
Eddy Currents

Crack
Crack
EddyCurrents
Eddy Currents
 Depth of Penetration
Eddy currents are strongest at the surface of the
material and decrease in strength below the surface.
The depth that the eddy currents are only 37% as strong
as they are on the surface is known as the standard
depth of penetration or skin depth. This depth changes
with probe frequency, material conductivity and
permeability.

Standard Depth
of
Depth

Penetration

Depth
(Skin Depth)

1/e or 37 %
of surface density
Eddy Current Density Eddy Current Density
High Frequency Low Frequency
High Conductivity Low Conductivity
High Permeability Low Permeability
 Materials’ property
Three fundamental properties of materials that affect
the eddy currents are
• A) The conductivity of the material (property)
– B) The amount of solid material in the vicinity of the test
coil i.e. dimensions of the material.
• C) The permeability of the material (Permeability
creates problem in testing Ferro-magnetic material.)
 Materials’ property

A) Factors affecting conductivity (and to some extent

permeability) are
• (a) Alloy Composition
• (b) Hardness
• (c) Temperature & Residual Stresses
• (d) Conducting Coatings
B) Dimensional factors are
(1) The dimensions and shape of the material.
(2) The presence of discontinuities in the material.
 Applications
• Detection of discontinuities,
• Material Identification
• Sorting materials,
• Measurement of conductive and nonconductive
coating thickness,
• Measurement of material thickness
• Measurement of hardness
• Measurement of residual stress
• Determination of heat damage
• Heat treatment monitoring
 Eddy Current Testing
Advantages
• Sensitive to small cracks and other defects
• Detects surface and near surface defects
• Inspection gives immediate results
• Equipment is very portable
• Method can be used for much more than flaw detection
• Minimum part preparation is required
• Test probe does not need to contact the part
• Inspects complex shapes and sizes of conductive materials
 Eddy Current Testing
Advantages
• High inspection speeds possible ( ~ 5 m/s)
• Eddy current test can readily detect very shallow and tight
surface fatigue cracks and stress corrosion cracks (~ 5
microns width and 50 microns depth)
• High temperature and on-line testing is possible, even in shop
floors.
• Non-contact / remote / inaccessible testing is possible
(Couplant is not required, like in ultrasonic).
• Recording and analysis of inspection data is possible.
 Eddy Current Testing
Limitations
• Only conductive materials can be inspected
• Surface must be accessible to the probe
• Skill and training required is more extensive than other techniques
• Surface finish and and roughness may interfere
• Reference calibration standards needed for setup
• Depth of penetration is limited
• Flaws such as de-laminations that lie parallel to the probe coil winding
and probe scan direction are undetectable
 Eddy Current Testing
Limitations

• Maximum inspectable thickness is ~ 6 mm (12 mm possible

by tuning frequency, probes, instrumentation etc.)
• Inspection of ferromagnetic materials is difficult using
conventional eddy current tests (Saturation ECT and Remote
field ECT  are possible for tubes).
ULTRASONIC TESTING
 Basic Principle of Ultrasonic Testing

• Ultrasonic Testing (UT) is a NDT method which uses high frequency

(>20kHz) sound energy to conduct examinations and make
measurements. The sound energy is introduced inside the material
using piezoelectric transducer which converts sound energy into
electrical energy and vice versa. Sound propagates through the
materials in the form of waves. When there is a discontinuity (such as
a crack) in the wave path, part of the energy will be reflected back
from the flaw surface to the transducer (pulse echo).

Typical Frequency Range: 1 – 10 MHz

Frequency : Sensitivity & Resolution , Attenuation

 Basic Principle of Ultrasonic Testing

Probe
Sound travel path
Flaw

Couplant Work piece

Reflection of Sound from a Flaw
 Basic Principle of Ultrasonic Testing

amplifier

screen
IP horizontal
BE sweep

clock

pulser
probe

work piece
Couplant
Block diagram: Ultrasonic Instrument
 Test Techniques

• Ultrasonic inspection techniques are commonly divided into

three primary classifications.
– Pulse-echo and Through Transmission
(Relates to whether reflected or transmitted energy is used)
– Normal Beam and Angle Beam
(Relates to the angle that the sound energy enters the test article)
– Contact and Immersion
(Relates to the method of coupling the transducer to the test article)
 Ultrasonic Testing Technique

Ultrasonic beam is made to fall normal to the flaw for

good detectability

Normal Beam Angle Beam

Pulse-Echo Through-
Transmission
 Basic Principle of Ultrasonic Testing

• Signal travel time can be directly related to the distance traveled by sound
wave in side the material. From the signal, information about the reflector
location, size, orientation and other features can be gained.

IP

probe BE

Couplant F

25
50 0 2 4 6 8 10
plate
Back Wall
IP = Initial pulse, F = Flaw Echo
BE = Backwall echo
 Basic Principle of Ultrasonic Testing

probe IP-Initial Pulse

BE-Backwall echo
Couplant

25 F-Flaw
50
plate
0 2 4 6 8 10
thickness = 50 mm Back Wall
X axis scale, 1 div = 10 mm
 Flaw Detection in Welds
• One of the most widely used
methods of inspecting weldments
is ultrasonic inspection.
• Full penetration groove welds lend
themselves readily to angle beam
shear wave examination.
 Applications of Ultrasonic Examination
 Defect Detection in material
 Thickness Measurement
 Bond Testing
 Online monitoring of material for acceptance
 Corrosion Mapping
 Pre-Service Inspection (PSI), In-Service Inspection (ISI) and
Life Extension of Components
 Stress analysis by velocity measurement
 Advantages of Ultrasonic Examination
 Single side accessibility is enough.
 Very good for planner defect.
 Depth positioning is possible.
 Sizing is accurate.
 Discontinuity of different orientation can be easily identified.
 Good & High sensitivity of defect detection – Immersion Technique.
 Used for In-Service Inspection (ISI) and life predication of components.
 Limitations of Ultrasonic Examination
 Specimen shape - Odd & irregular shape difficult to examine.
 Specimen, Metallurgy - Coarse grain difficult to examine.
 Data & single acquisition may not be possible in the conventional
analog / digital equipment.
 Technical Knowledge is required for interpretation
RADIOGRAPHY TESTING
 Principle of Radiography

The film darkness (density) will vary

with the amount of radiation reaching
the film through the test object.
X-ray film

= less exposure

= more exposure
Top view of developed film
 Principle of Radiography
Fractional Change
in thickness=Δt/t
Contrast,
Here
I0 C=I2-I1=ΔI
I2>I1
Contrast,
t Δt C=ΔI∞ Δt/t
X-ray film
I1 I2

I1 = less exposure
I2 = more exposure
Top view of developed film
 Electromagnetic Radiation
The radiation used in Radiography testing is a higher energy
(shorter wavelength) version of the electromagnetic waves that we
see every day. Visible light is in the same family as x-rays and
gamma rays.
 Sources of radiation
• Both X-ray and Gamma rays can be utilized for RT. X-rays and
gamma rays differ only in their source of origin. 
• X-rays are produced by an x-ray generator and gamma radiation is
the product of radioactive atoms.  They are both part of the
electromagnetic spectrum.
• They are waveforms, as are light rays, microwaves, and radio
waves. X-rays and gamma rays cannot been seen, felt, or heard.
• They possess no charge and no mass and, therefore, are not
influenced by electrical and magnetic fields and will generally
travel in straight lines. However, they can be diffracted (bent) in a
manner similar to light.
 Radiation Sources
Two of the most commonly used sources of radiation in
industrial radiography are x-ray generators and gamma ray
sources. Industrial radiography is often subdivided into “X-
ray Radiography” or “Gamma Radiography”, depending on
the source of radiation used.
 Radioisotopes
• The unstable isotopes which undergo radioactive decay
are known as radioisotopes or simply radionuclides.
• Radioisotopes continuously gets transformed into new
element along with emission of particulate radiations.
Quite often, this is followed by the emission of gamma
radiation.
For example, 192 Ir 77 , 60 Co 27
 X-rays
• X-rays are just like any other kind of
electromagnetic radiation. They can be produced
in parcels of energy called photons, just like
light. There are two different atomic processes
that can produce X-ray photons.
• One is called Bremsstrahlung and is a German
term meaning "braking radiation."
• The other is called K-shell emission. Both can
occur in the heavy atoms of tungsten. Tungsten
is often the material chosen for the target or
anode of the x-ray tube.
 ISOTOPE Camera
A device called a “camera” is used to store, transport and
expose the pigtail containing the radioactive material. The
camera contains shielding material which reduces the
exposure to radiographer during use.
 X-ray GENERATION
• The cathode contains a small filament
much the same as in a light bulb. High Electrical Potential

• Current is passed through the Anode Cathode

filament which heats it. The heat Electrons

causes electrons to be stripped off. + -

• The high voltage causes these “free”

electrons to be pulled toward a target X-ray Generator
Creates Radiation
material (usually made of tungsten)
located in the anode.
• The electrons impact against the
target. This impact causes an energy
exchange which causes x-rays to be Radiation
created. Penetrates
the Sample

Exposure Recording Device

 Imaging Modalities
Several different imaging methods are available to
display the final image in industrial radiography:
• Film Radiography
• Real Time Radiography (RTR) or Fluoroscopy
• Digital Radiography (DR) and Computed Radiography (CR)
• Computed Tomography (CT)
 Film Radiography
• Film must be protected from visible light. Light, just like x-rays
and gamma rays, can expose film. Film is loaded in a “light proof”
cassette in a darkroom.
• This cassette is then placed on the specimen opposite the source of
radiation. Film is often placed between screens to intensify
radiation.
 RT - TECHNIQUES

1 SWSI 3 DWDI
CIRC. SEAM OF PIPES CIRC. SEAM OF PIPES

2 DWSI
CIRC. SEAM OF PIPES

FILM FILM

4 PANORAMIC 5 DIRECTIONAL
CIRC. SEAM OF PIPES
FILM
LONG SEAM

FILM FILM
 Image Quality Indicator (IQI)
• One of the methods of monitoring the quality of a radiograph is through
the use of image quality indicators (IQIs).
• IQIs, which are also referred to as penetrameters, provide a means of
visually informing the film interpreter of the contrast and definition
(sensitivity) of the radiograph.
• The IQI indicates that a specified amount of change in material
thickness will be detectable in the radiograph, and that the radiograph
has a certain level of definition so that the density changes are not lost
due to un-sharpness.
 Image Quality Indicator (IQI)
• Image quality indicators take many shapes and forms due to
the various codes or standards that invoke their use.
Generally, two IQI styles are prevalent: the hole-type and the
wire type IQI. IQIs comes in a variety of material types. So
that one with radiation absorption characteristics similar to
the material being radiographed can be used.
 Image Quality (cont.)

• Quality typically being determined based

on the smallest hole or wire diameter that
is reproduced on the image.
 Porosity
• Porosity is the result of gas entrapment in the solidifying metal.
Porosity can take many shapes on a radiograph but often appears as
dark round or irregular spots or specks appearing singularly, in
clusters, or in rows. Sometimes, porosity is elongated and may
appear to have a tail. This is the result of gas attempting to escape
while the metal is still in a liquid state and is called wormhole
porosity. All porosity is a void in the material and it will have a
higher radiographic density than the surrounding area.
 Cluster porosity
• Cluster porosity is caused when flux coated electrodes are contaminated
with moisture. The moisture turns into a gas when heated and becomes
trapped in the weld during the welding process. Cluster porosity appear just
like regular porosity in the radiograph but the indications will be grouped
close together.
 Slag inclusions
• Slag inclusions are nonmetallic solid material entrapped in weld metal or
between weld and base metal. In a radiograph, dark, jagged asymmetrical
shapes within the weld or along the weld joint areas are indicative of slag
inclusions.
 Lack of penetration (LOP)
• Incomplete penetration (IP) or lack of penetration (LOP) occurs
when the weld metal fails to penetrate the joint. It is one of the most
objectionable weld discontinuities. Lack of penetration allows a natural
stress riser from which a crack may propagate. The appearance on a
radiograph is a dark area with well-defined, straight edges that follows
the land or root face down the center of the weldments.
 Lack of fusion/ Incomplete fusion
• Incomplete fusion is a condition where the weld filler metal
does not properly fuse with the base metal. Appearance on
radiograph: usually appears as a dark line or lines oriented in
the direction of the weld seam along the weld preparation or
joining area.
 Cracks
• Cracks can be detected in a radiograph only when they are propagating in a
direction that produces a change in thickness that is parallel to the x-ray
beam. Cracks will appear as jagged and often very faint irregular lines.
Cracks can sometimes appear as "tails" on inclusions or porosity.
 Tungsten inclusions
• Tungsten is a brittle and inherently dense material used in the electrode in
tungsten inert gas welding. If improper welding procedures are used,
tungsten may be entrapped in the weld. Radiographically, tungsten is more
dense than aluminum or steel, therefore it shows up as a lighter area with a
distinct outline on the radiograph.
Radiographic Images
 Radiation Safety

There are three means of protection to reduce exposure to radiation:

LEAK TESTING
Identifying the Leaky Component,
Pin Pointing the Leak and
Quantifying the Leak
Detection of Visible Leakage of Solid and Liquid

Leakages of solid and liquid, kept in a

container open to atmosphere do not pose
much problem as they are identifiable and
the only matter of concern is to find out
someEffect
innovative
of leak
methods to stop them.
Quantity of leak

Loss of liquid Volume or mass per unit time

 Detection of Gas Leakage
Gross leak of gas can be detected by
 Traditional immersion technique if part is
small in volume; example- detection of
puncture in a bicycle tube.
 Sniffer technique (modern) if part can not
be immersed in a liquid- gas is sniffed and
sent to analyzer.
Immersion or
Leakage of gas
sniffer technique
 Gaseous Leak Rate
• For gaseous medium the unit of leak-rate is
expressed in terms of
Pressure x Volume
Time
• standard cubic centimeters per second
(std.cc/s)
• Pascal cubic meters per second (Pa.m3/s).
• mbar liter per second (mbar.l/s)
 Types of Leak
Leaks can be classified based on their size and nature.

Gross leak – up to 10-5 std. c.c. / sec

Fine leak – less than 10-5 std. c.c. / sec
 Leak Testing Methods
• Three common types of leak tests are
1. Bubble emission leak test,
2. Pressure change leak test and
3. Tracer gas leak test.
• Other leak test methods which can not be grouped in these
three categories are ultrasonic leak test and liquid penetrant
leak test.
Bubble Emission Technique
 Immersion leak test
An internally pressurized test subject is immersed in a
test medium, normally water. The subject stays in the
test medium for a period of time and is then examined
for bubbles coming out through a leak.
Internal pressure can be created either by
(i) Compressed air supply
(ii) Heating the object
(iii) Cooling the object in LN2 and then immersing
it in water or alcohol.
Immersion Leak Test or Air Glycol Leak Test
• Item is immersed in a an ethylene glycol bath and
pressure above the liquid is reduced to 125 mm of Hg
(1.6x 10-1 kPa absolute).
• Because of high internal pressure and low outside
pressure (differential pressure), atmospheric air
inside comes out through leak as a stream of bubble.
• Ethylene glycol is used as immersion liquid because it
possesses a low surface tension, a low vapour
pressure and is easily washed of from the test item
with water.
Film solution leak test or Soap Bubble Test

Example: To check the leak in valve of LPG

cylinder soap solution is used.
Vacuum box technique
Pressure (Volume) change leak test
• The presence of leakage is detected by loss of
pressure or vacuum (pressure/vacuum decay).
• The leakage rate Q is equal to the measured
pressure change ΔP, multiplied by the test system
internal volume V, and divided by the time t
required for the change in system pressure to occur,
as shown by the equation Q= V(ΔP/t).
• When air flow rate ΔV/t is known for maintaining
the constant pressure P the equation for leak rate is
Q= P (ΔV/t).
Pressure decay test setup, simplified
Helium Mass Spectrometer Leak Detector

• Air sample consisting

of Helium gas, from the
test object is analyzed
and measured in a
mass spectrometer
tube working at a
vacuum of the order of
10-4 torr.
 Helium Mass Spectrometer Leak Detector

There are three modes of leak-detection with a helium leak

detector:
– Pressure Test/Sniffer Mode/Detector Probe
– Vacuum Test/Tracer Probe
– Pressure -Vacuum Test
Pressure Test or Sniffer Mode or Detector Probe Leak Location
Detector-probe leak measurement technique
Sniffer Test- Global Leak
Vacuum Mode-Tracer probe leak location technique
 Pressure – Vacuum Mode
This is a combination of above two tests. The job
is filled with helium at around atmospheric
pressure and is placed in a chamber, which is
evacuated and connected to HLD. Any helium
from the job first leaks out in the outer vacuum
chamber and then enters the HLD where it is
detected by the spectrometer.
There is practically
no dilution of helium
and is the most
sensitive technique.
 Pressure – Vacuum Mode
• In another variation of Pressure Vacuum
Mode the job is evacuated and connected
to HLD and it is kept in chamber filled with
helium at pressure above atmosphere.
• Helium in the chamber enters the job
through leak and then enters the HLD
where it is detected by the spectrometer.
 Major NDT Methods- A Comprehensive Overview

Method Principles Application Advantages Limitations

Visual testing (VT) Uses reflected or transmitted Many application in many Can be inexpensive and simple Only surface conditions can be
light from test object that is industries ranging from raw with minimal training evaluated. Effective source of
imaged with the human eye or material to finished products required. Broad scope of uses illumination required. Access
other light-sensing device. and in-service inspection. and benefits. necessary.

Penetrant testing (PT) A liquid containing visible or Virtually any solid Relatively easy and materials Discontinuities open to the
fluorescent dye is applied to nonabsorbent material having are inexpensive. Extremely surface only. Surface condition
surface and enters uncoated surfaces that are not sensitive, very versatile. must be relatively smooth and
discontinuities by capillary contaminated. Minimal training. free of contaminants.
action.
Magnetic particle Test part is magnetized and All ferromagnetic materials, Relatively easy to use. Only surface and a few
testing (MT) fine ferromagnetic particles for surface and slightly Equipment / material usually subsurface discontinuities can
applied to surface, aligning at subsurface discontinuities; inexpensive. Highly sensitive be detected. Ferromagnetic
discontinuity. large and small parts. and fast compared to PT . materials only.

Radiographic testing Radiographic film is exposed Most materials, shapes, and Provides a permanent record Limited thickness based on
(RT) when radiation passes through structures. Examples include and high sensitivity. Most material density. Orientation of
the test object. Discontinuities welds, castings, composites, widely used and accepted planar discontinuities is critical.
affect exposure . etc., as manufactured or in- volumetric examination. Radiation hazard.
service.
 Major NDT Methods- A Comprehensive Overview
Method Principles Application Advantages Limitations
Ultrasonic testing High-frequency sound pulses Most materials can be Provides precise, high- No permanent record
(UT) from a transducer propagate examined if sound sensitivity results quickly. (usually). Material
through the test material, transmission and surface Thickness information, depth, attenuation, surface finish, and
reflecting at interfaces. finish are good and shape is and type of flaw can be contour. Requires couplant .
not complex. obtained from one side of the
component.
Eddy current testing Localized electrical fields are Virtually all conductive Quick, versatile, sensitive; Variables must be understood
(ET) induced into a conductive test materials can be examined for can be non-contacting; easily and controlled. Shallow depth
specimen by electromagnetic flaws, metallurgical adaptable to automation and of penetration, lift-off effects
induction . conditions, thinning, and in-situ examinations. and surface condition.
conductivity .
Thermal infrared Temperature variations at the Most materials and Extremely sensitive to slight Not effective for detection of
testing () test surface are measured / component where temperature changes in small flaws in thick parts. Surface
detected using thermal temperature changes are parts or large areas. Provides only is evaluated. Evaluation
sensors / detectors related to part conditions / permanent record . requires high skill level.
instruments / cameras . thermal conductivity .
Acoustic emission As discontinuities propagate, Welds, pressure vessels, Large areas can be monitored Sensors must contact test
testing (AE) energy is released and travels rotating equipment, some to detect deteriorating surface. Multiple sensors
as stress waves through composites and other conditions. Can possibly required for flaw location.
material. These are detected structures subject to stress or predict failure. Signal interpretation required.
by means of sensors . loading.
 Comparison of Destructive & Non Destructive Tests.
Destructive Testing is generally mechanical test of material where certain specific characteristics
of material can be evaluated quantitatively. The information obtained is quite precise. The
specimen being tested get damaged & unlikely be used further. Destructive tests provide useful
information related to material design consideration. Following properties can be determined :

• Ultimate tensile strength

• Yield Point
• Ductility
• Elongation Characteristics
• Fatigue life
• Corrosion Resistance
• Toughness
• Hardness
• Impact Resistance
UTM can measure – UTS, YS & ø elongation
Destructive tests (DT) Non-destructive tests (NDT)
Advantages Limitations
Measurements are direct and reliable. Measurements are indirect and hence reliability is to be
verified.
Usually quantitative measurements. Usually qualitative measurements.
Measurements can also be done quantitatively.
(Tomography)
Correlation between test measurements and material Skilled judgment and experience are required to interpret
properties is direct. indications.
Limitations Advantages
Tests are not made on the objects directly. Hence correlation Tests are made directly on the object. 100% testing on
between the sample specimen used and object needs to be actual components is possible.
proved.
A single test may measure only one or a few of the Many NDT methods can be applied on the same part and
properties. hence many or all properties of interest can be measured.
In-service testing is not possible. In-service testing possible.
Measurements of properties over a cumulative period of time Repeated checks over a period of time are possible.
cannot readily be possible.
Preparation of the test specimen is costly. Very little preparation is sufficient.
Time requirements are generally high. Most test methods are rapid.
 Importance of Basic Metallurgy for
NDT Professionals
• No engineering structure is free from flaws. Flaw tolerance
depends on metallurgical characteristics

• Flaw characteristics (Location, Size, Shape, Orientation &

Nature depends on nature of Material Processing

• Knowing Flaw Characteristics helps in

- Selection of appropriate NDT method
- Selection of test parameters
- Interpretation of Relevant / False indications
 Engineering Materials

I Metals & Alloys

II Ceramic & Glasses
III Polymers
IV Composites
V Semiconductors

Structural Materials : I to IV

Electronic Materials : V
 Crystal Structure

• Body Centered Cubic (BCC): Fe, Cr

• Face Centered Cubic (FCC): Cu, Ni, AISI 304 SS

• Hexagonal Close Pack (HCP): Zr, Ti

FCC Metals and Alloys

- Most tolerant to flaws
- Easy to deform plastically
- Do not undergo Ductile-to-Brittle transition
 Lattice Defects

• Point Defects: Vacancies & Interstitials

• Line Defects: Dislocation

• Surface Defects: Grain Boundaries

• Volume Defects: Voids

Defects in Materials

Origin & Nature

 Interruption in Normal Physical Structure
- Keyways, Grooves, Holes present by design
Discontinuity

Discontinuity with undesirable

Flaw connotation
Defect - Slag, Porosity, Lamination

Flaw which makes component unfit for service

- Cracks, Lack of Fusion in Weld
 Classification of Engineering Products
Based on Manufacturing Route

I Castings
Melting - Pouring into Mould Cavity - Solidification

II Powder Metallurgy Products

Powder Preparation - Pressing into Mould Cavity -
Sintering

III Wrought Products

Cast ingot - Mechanical Working - Machining -
Welding - Heat Treatment
 Defects in Materials
Origin & Characteristics
I Inherent Discontinuities
* Melting, Casting & Solidification
II Processing Discontinuities
* Mechanical Working (Hot/Cold)
- Forging, Rolling, Extrusion, Forming
* Welding
* Heat Treatment
III Service Discontinuities
* Fatigue, SCC, Creep
Discontinuities are not necessarily Defects
 Defects in Casting, Forging, Rolling & Heat Treatment

Casting
* Gas Defects – Blow Holes, Porosities
* Shrinkage Cavity – Piping
* Non-Metallic Inclusion – Exogenous, Indigenous
* Chemical Inhomogeneities – Segregation
* Contraction Defects – Hot Tears, Cold Cracks
* Shaping Faults – Misrun, Cold Shuts

Forging Rolling
* Central Burst * Laminations
* Laps * Stringer
* Hydrogen Flakes * Seams
* Improper Flow Lines

Heat Treatment
* Quench Cracks
* Undesirable Phase
* Coarse Grain Size
 Cracks in Weldments
* Cold Cracking
- Hydrogen Absorption
* Hot Cracking
- Segregation at Grain Boundaries
- Low melting point Eutectics
* Intermediate Temperature Cracking
- Stress Relief Cracking or Reheat Cracking
- Precipitation within Grains
- Localization of Creep Strain at GBs
* Lamellar Tearing
- Laminations Opening under Thermal Stress
Welding Defects Weld Cracking

Operator Defects Crack Type

Lack of Fusion Hydrogen

Lack of Penetration Solidification

Slag Entrapment Liquation

Porosity Reheat

Undercut Lamellar Tear

 Important Flaw Characteristics for
Fitness-For-Service Assessment
Location • Surface or Sub-surface

Size • Length/ Area/ Though-thickness dimension

Orientation • Flaw orientation w.r.t. Principal Stress

Shape • Smooth or Irregular or Sharp

Proximity • Proximity of a flaw to other flaw(s)

Nature • Planar Flaws severe than Volumetric

A good NDT should have high reliability for harmful flaws

and provide maximum information on above flaw characteristics
 Important Flaw Characteristics for
Fitness-For-Service Assessment

Location Surface Flaw

Sub-surface Flaw

• Surface flaw more severe as compared to sub-surface flaw because of

higher stress intensity associated with it
• Code provides guidelines on classification of flaw in to surface or sub-
surface, if it lies just below the surface of the component
 Important Flaw Characteristics for
Fitness-For-Service Assessment

Size KIC = σ . (π. a) 1/2

Surface Flaw
a
2a
Sub-surface Flaw

• Flaw size should never exceed the critical flaw size decided by the
operating stress & fracture toughness, with adequate safety margin
• It refers to through wall dimension & length for crack like defects and area
for laminations
• Most important flaw characteristics and also most difficult to predict
accurately by conventional NDT methods
 Important Flaw Characteristics for
Fitness-For-Service Assessment

Orientation Hoop Stress = PD / 2.T

Axial Stress = PD / 4.T

• Flaw perpendicular to maximum tensile stress more severe than the

one oriented parallel to it
• For internally pressurized pipe, axial flaw more severe than
circumferential flaw
 Important Flaw Characteristics for
Fitness-For-Service Assessment

Shape

• Flaws with sharp tip like crack more severe than flaws with smooth

surface like porosity

• Small root radius leads to higher stress intensity

 Important Flaw Characteristics for
Fitness-For-Service Assessment

Proximity

• If two flaws are very close, they influence the stress intensity
associated with each other
• Two flaws shall be separated by the length of the longest flaws, or
else they shall be considered together as a singe flaw including
the sound region in between
 Important Flaw Characteristics for
Fitness-For-Service Assessment

Nature

• Weld Flaw
- Operator: Porosity, lack of fusion, slag inclusion, undercut
- Metallurgical origin: Cold crack, Hot crack, laminar tearing
• Planar or Volumetric Flaw
• Planar flaw more severe than volumetric flaw
Thank You