NDT REPORTT

NON DESTRUCTIVE TESTING

INTRODUCTION TO NON-DESTRUCTIVE TESTING

Testing

It is defined as to take measures to check the quality, performance or reliability of a material,

especially before putting it into wide-spread use or practice

There are two types of testing:

1. Destructive Testing

It is a method of inspecting or measuring materials with doing harm

Eg: Impact Testing, Hardness Testing

2. Non-Destructive Testing

It is a method of inspecting or measuring materials without doing any harm

Eg: Magnetic Particle Testing, Radiographic Testing

Non-Destructive Testing methods:

i. Visual Testing

ii. Radiographic Testing

iii. Magnetic Particle Testing

iv. Liquid or Dye PenetrantTesting

v. Eddy CurrentTesting

vi. Ultra-sonic Testing

vii. Acoustic EmissionTesting

viii. Infrared or ThermalTesting

ix. LeakTesting

x. Vibration Analysis

xi. Neutron RadiographyTesting

Visual Testing

This is the most common and basic inspection method. This includes:

Fibrescopes, Boroscopes, magnifying glasses and mirrors

Portable video inspection with zoomed lenses for large tanks and vessels, server lines

Alfa Institute of Technology,Udupi Page 1


Robotics crawlers to observe hazardous or tight areas such as air ducts, reactors and

pipe lines

Instruments used for Visual Testing

1. Steel Ruler

2. Indirect Calipers

3. VernierCalipers

4. DialCalipers

5. DigitalCalipers

6. Direct ReadingCalipers

7. Mechanical Gauges

8. Fillet WeldGauges

Non-Destructive Evaluation

It is a method of evaluating materials using different non-destructive techniques

Applications of Non-Destructive Evaluation

To assist in product development

Screening or sorting the incoming materials

To monitor, improve or control manufacturing process

To verify proper processing such as heat treatment

To verify proper assembly

To inspect for in-service damage

Homogeneous materials

Materials without cracks are called Homogeneous materials

Non- Homogeneous materials

Materials with cracks are called Non-Homogeneous materials

Defects and Discontinuities

1. Defect



Defect is a material failure

Types of Defects:

Sensitivity

It is the smallest possible defect in a material

Resolution

It is represented by two or more straight line or cross line defects

2. Discontinuity

It is a local variation in the material due to transportation or atmospheric conditions

Types of Discontinuities

Surface Discontinuity

These are open to the surface of the material

Testings’ used are:

i. Visual Testing

ii. Magnetic Particle Testing

iii. Liquid or Dye PenetrantTesting

Sub-Surface Discontinuity

These are present beneath the surface of the material

Testings’ used are:

i. Ultra-sonic Testing

ii. Radiographic Testing

iii. Magnetic Particle Testing (up to 6mm)

Applications of Non-Destructive Testing

a. Power plant Inspection

b. Wire RopeInspection

c. Storage TankInspection

d. Air craftInspection

e. Pipe-lineInspection

f. RailInspection

g. Bridge Inspection



1.MAGNETIC PARTICLE TESTING

Introduction:

Magnetic particle testing is one of the most widely utilized NDT methods since it is fast and

relatively easy to apply and part surface preparation is not as critical as it is for some other

methods. This method uses magnetic fields and small magnetic particles to detect flaws in

components. The only requirement from an inspectability standpoint is that the component

being inspected must be of ferromagnetic material. Many industries use MPT such as power

generation, automotive, petrochemical and aerospace industries.

Basic principle:

In theory magnetic particle testing is

nothing but combination of two

testing; magnetic flux leakage

testing and visual testing

To explain basic principle in simple

way i.e; when bar magnet is broken

is broken in center of its length ,two

complete bar magnets with magnetic poles end of end piece will result. If the magnet is just

cracked and not broken completely in two, a north and south pole will form at each edge of

the crack as a result of air gap which is formed due to crack,there is a flux leakage which

takes place which is called as flux leakage field

Here if iron particles are sprinkled on the crack , the particles will not only attract towards the

poles at the end of the magnet but also at the poles at the crack

Ferromagnetic material:

These materials have a large positive susceptibility to an external magnetic field. They

exhibit a strong attraction to magnetic field and are able to retain magnetic properties after

the magnetic field has been removed. Some ferromagnetic materials are iron, nickel, cobalt



and their alloys

Fig, 1.2 Ferromagnetic material

Hysteresis loop and Magnetic properties:

Fig, 1.3 Hysteresis loop

A great deal of information can be learned about the magnetic properties of a material

bystudying the hysteresis loop. The loop is generated by measuring the magnetic flux of a

ferromagnetic materialwhile the magnetizing force is changed. A ferromagnetic material

which has never been magnetized or has been properly demagnetized will follow the dashed

line as H is increased. Amongst all the magnetic domains are aligned and an additional

increase in the magnetizing force will produce very little increase in magnetic flux. The

material has reached the point of magnetic saturation. When H is reduced to zero, curve will

from point “a” to point “b”. This is referred to as point of retentivity. As the magnetic force is

reversed the curve moves to point ‘c’ where the flux has been reduced to zero and it is called

as the point of coercivity. As the magnetic force is increased in negative direction, the



material will again become magnetically saturated but in opposite direction, point ‘d’

reducing point H to zero which brings the curve to point ‘e’. It will have a level of residual

magnetism equal to that achieved in other direction. Increasing H back in in the positive

direction which will bring ‘b’ to zero

Basic steps involved in MPT:

1.Pre-cleaning:

Here the material is cleaned by using certain methods such as ;water washing

methods ,solvent methods, vapordegreasing, steam cleaning ,ultrasonic cleaning , sand

blasting , short blasting

2. Check the area to be inspected:

Here the supervisor checks the area which is required to be inspected

3. Selection of current:

Here current which is required for carrying out the procedure is selected , current such as

AC/DC is selected

4. Selection of method:

Method which is most suitable is chosen such as longitudinal magnetization or circular

magnetization

5. Applying the method:

Select and apply one type of magnetization method into the component

6. Iron powder application :

There are two types of method by which we can carry out this process

i. Dry method

ii. Wet method

7. Resultsand interpretation:



There are three types of results

i. False indication

ii. Non relevant indication

iii. Relevant indication

We can find variety of interpretation such as tungsten inclusion ,offset mismatch, internal

undercut, lack of fusion ,lack of penetration ,slag inclusion, cluster porousity , porousityetc.

Some magnetizing equipment :

i. Permanent magnet:

It can be used for magnetic particle testing inspection as the source of magnetism.

Fig, 1.4 Permanent magnet

ii. Electromagnetic yoke:

An electromagnetic yoke is common piece of equipment that is used to establish a

magnetic field. A they can powered with AC from a wall socket or by DC from a

battery pack. This type of magnet generates a very strong magnetic field. Some yokes

can lift weights in excess of 40 pounds



Fig, 1.5 Electromagnetic yoke

iii. Prods:

Prods are handheld electrodes that are pressed against the surface of the component

being inspected to make contact for passing electrical current through the metal. Prods

are typically made from copper and have an insulated handle to help protect the

operator. This is the type of dual prodcommonly used for weld inspections

Magnetic field indicators:

It is used to determine whether the magnetic field is of adequate strength and in the proper

direction is critical when performing magnetic particle testing.

i. Hall-effect meter(Gauss Meter):

As discussed earlier, a gauss meter is commonly used to

measure the tangential field strength on the

surface of the part. By placing the probe next to

the surface, the meter measures the intensity of

the field in the air adjacent to the component

when a magnetic field is applied.

ii. Pie Gage:

The pipe gage is a disk of highly permeable material divided into four, six or eight

sections by non-ferromagnetic material. The divisions serve as artificial defects that

radiate out in different directions from the center. The sections are furnace brazed and



copper plated. The gage is placed on the test piece copper side up and the test piece is

magnetized. After particles are applied and the excess removed, the indications

provide the inspector the orientation of the magnetic field

Fig, 1.6 Pie Gage

iii. Slotted Strips:

It are pieces of highly permeable ferromagnetic material with slots of different widths.

These strips can be used with the wet or dry method. They are placed on the test

object as it is inspected. The indications produced on the strips give the inspector a

general idea of the field strength in a particular area

Advantages and disadvantages:

The primary advantages and disadvantages when compared to other NDT methods are

Advantages:

High sensitivity

Indication are produced directly on the surface of the part and constitute a visual

representation of the flaw

Minimal surface preparation

Portable

Disadvantages:

Only surface and near surface defects can be detected

Only applicable to ferromagnetic materials

Relatively small area can be inspected at a time

Only materials with relatively nonporous surface can be inspected

The inspector must have direct access to the surface being inspected



2.LIQUID PENETRANT TESTING

Introduction

Liquid Penetrant Testing is one of the oldest and simplest Non-Destructive Testing methods.

This method is used to reveal surface discontinuities by bleedout of a coloured or fluorescent

dye from the flaw. It is used in inspection of all non-porous materials

Basic Principle

The Liquid Penetrant Testing works on the principle of Capillary action i.e. rise and fall of

liquid. The settling down of penetrant into the discontinuities is called Capillary fall and

rising of penetrant from the discontinuities by the application of developer is known as

Capillary rise.

Fig.2.1 Principle of LPT

Penetrants

Penetrants are carefully formulated to produce the level of sensitivity desired by the

inspector.

Basic types of Penetrants

Fluorescent Penetrants

Visible Penetrants



Methods used for excess removal of Penetrants

Water washable

Solvent removable

Post-Emulsifiable

Lipophilic

Hydrophilic

Fig. 2.2 Penetrant application and removal process

Application of Penetrants

By spraying

By brushing

By pouring the penetrant on material(when large work material is used

By dipping the material into the penetrant

Developers

The role of the developer is to pull the trapped penetrant material out of defects and spread it

out on the surface of the part so it can be seen by the inspector.

Developers used with Visible penetrants create a white background so there is a great

degree of contrast between the indication and the surrounding background

Developers used with Fluorescent penetrants both reflect and refract the incident UV

light, allowing more of it to interact with the penetrant , causing more efficient



fluorescence. Under UV rays , the defects are visible as green-yellow colour whereas

the developer is visible as black-blue colour.

Basic types of Developers

Dry developers

Water soluble developers

Water suspendable developers

Non-aqueous developer

Fig. 2.3 Developer application and obtaining of indication

Basic steps involved in Liquid Penetrant Testing

1. Pre- Cleaning

It is the most critical step in Liquid Penetrant Testing

All coatings such as paints, varnishes, heavy oxides must be removed to

ensure that defects are open to surface of the part

Processes like machining, sand blasting, steam cleaning can cause metal

smearing. This layer of metal smearing must removed before inspection.

Various methods of cleaning are:

i. Water washing

ii. Solvent or Detergent cleaning

iii. Vapour degreasing

iv. Steam cleaning

v. Ultra-sonic cleaning

vi. Sand blasting



vii. Shot or Abrasive blasting

2. Penetrant application

The penetrant material can be applied in a number of ways, such as spraying,

brushing or immersing the part in a penetrant bath

The penetrant must entirely cover the part of the material to be tested

3. Penetrant Dwell Time

It is defined as the time taken by the penetrant to settle inside the cracks of the

material to be tested

Penetrants require a dwell time of 5-10 minutes

The dwell time depends upon:

i. The contact angle of the penetrant

ii. The capillary pressure at the flaw opening

iii. The specific gravity of the penetrant

4. Excess Penetrant Removal

The penetrant removal procedure must effectively remove the penetrant from

thesurface of the part without removingan appreciable amount of entrapped

penetrant from the discontinuity

Excess penetrant removal methods

i. Water washable

ii. Penetrant removable

iii. Post-Emulsifiable

a. Lipophilic : The emulsifier is oil-based and interacts with the oil

soluble penetrant to make removable possible

b. Hydrophilic : The emulsifier is water soluble detergent which

lifts excess penetrant from surface of part with a water wash

5. Developer Application

The main function of the developer is to provide a contrast background for

indications and the developer must be bright

Commonly a white contrast developer is used

Types of developers are:

i. Dry developers

ii. Water soluble developers

iii. Water suspendable developers



iv. Non-aqueous developers

Non-aqueous developers are generally recognized as the most sensitive when

properly applied

6. Developing Time

It is defined as the time taken by developer to pull the penetrant out from the

defect to make an indication

Developing time is around 2-5 minutes

7. Result and Interpretation

Results:

i. False Indications : It can be caused by improper cleaning. It should be

eliminated by using proper lint-free clothes and air covers

ii. Non-Relevant Indications: These are caused due to geometrical

changes in the part

iii. Relevant Indications: These are produced by actual discontinuities in

the part

a. Acceptable: If the indications matches the codes and standards

b. Reject-able: If the indications does not matches the codes and

standards

Interpretations(Weld Discontinuities):

1. Tungsten Inclusions:

2. Offset or Mismatch

3. Internal Undercut

4. Lack of Fusion

5. Lack of Penetration

6. Slag Inclusions

7. Cluster Porosity

8. Porosity

9. Suck Back



Fig. 2.4 Various discontinuities obtained on a weld part

8. Post Cleaning

It is the method of cleaning the material after inspection

9. Final Report

The final report is obtained by providing the photo copy of the procedure or by

drawing

Emulsifier

The function of the emulsifier is to remove the excess of penetrant from the

surface of the material

Emulsifier is give enough time to react with penetrant, but not enough time to

diffuse into the penetrant trapped in the defect

When there is excess penetrant, Post-Emulsification method is used

In this method, emulsifier is applied on the part and given some time for

dwelling

Functions of Emulsifiers

Penetrant inside the defect should not be over-washed

Excess penetrant should be removed easily

Emulsifier should have good sensitivity

Types of Emulsifiers

Lipophilic Emulsifiers

Hydrophilic Emulsifiers



Basic Steps involved in Post-Emulsification Method

1. Pre-Cleaning

2. Penetrant Application

3. Penetrant Dwell Time

4. Application of Emulsifier

5. Emulsifier Dwell Time

6. Excess Penetrant Removal

7. Developer Application

8. Developing Time

9. Result and Interpretation

10. Post Cleaning

11. Final Report

Safety Precautions

Two types of problems may cause to the inspector

Skin Irritation

Precaution: Wearing gloves, hand crings

Breathing problem/Air pollution

Precaution: Wearing masks and install exhaust fans

Fig. 2.5 A Inspector carrying out LPT process with wearing safety equipments

Wetting Ability and Contact Angle



The ability of the liquid to wet the surface of material is called as wetting ability

Liquids having good wetting ability have very low contact angle

Contact angle is represented by ’’

Liquids having contact angle less than 90, have a good wetting ability

Fig. 2.6 Wetting ability and contact angle diagram

Advantages of Liquid Penetrant Testing

High sensitivityi.e., small discontinuities can be detected

Rapid inspection of large areas and volumes

Suitable for parts with complex shapes

Indications are produced directly on the surface of the part and constitute avisual

representation of the flaw

Low cost i.e., the materials and related equipment are relatively inexpensive

Dis-advantages of Liquid Penetrant Testing

Only surface defects can be detected

Pre-cleaning is critical since contaminants can mask defects

Only materials with a relatively non-porous surface can be inspected

Surface finish and roughness can affect inspection sensitivity

Applications of Liquid Penetrant Testing

This method is used in the inspection of grinding, casting, welding defects



3. RADIOGRAPHIC TESTING

Introduction:

Radiography is used in a very wide range of applications including medicine, engineering,

forensic etc. Radiographic Testing is the method of inspecting materials for hidden flaws by

using the ability of short wavelength electromagnetic radiations to penetrate various

materials. The intensity of the radiation that penetrates and passes through the material is

either captured by a radiation sensitive film or by a planar array of radiation sensitive sensors.

Radiographic Testing offers a number of advantages over other NDT methods, however, one

of its major disadvantages is the health risk associated with the radiation.

Basic Principle:

The Radiographic Testing works on the principle of differential absorption and shadow

formation.

Fig. 3.1 Basic principle of Radiographic Testing

In Radiographic Testing, the part to be tested is placed between the radiation source

and a piece of radiation sensitive film.

The radiation source can either be an X-Ray machine or a radio-active source.

The radiation that passes through the part will expose the film and forms a shadow

graph of the part.

The film density will vary with the amount of radiation reaching the film through the

test object.



The darker areas indicate more exposure i.e., high radiation intensity

The lighter areas indicate less exposure i.e., low radiation intensity

Properties of X-Rays and Gamma Rays:

They travel in straight lines at the speed of light

Their degree of penetration depends upon their energy and matter they are travelling

through

Their paths cannot be changed by electrical or magnetic fields

They can be diffracted, refracted to a small degree at interfaces between two different

materials, and in some cases be reflected

Isotopes:

The atoms having same number of protons and different number of neutrons are

known as isotopes

They are also known as Unstable atoms

Natural Isotopes and Artificial Isotopes are its two types

Half Life: It is defined as the time required for the activity of any radionuclide to

decrease to one-half of its initial value

Radiation Intensity: It is amount of energy passing through the given area, that is

perpendicular to the direction of radiation travel in a given unit of time

Exposure: It is the amount of ionization in the air. Its SI unit is Roentgen

Various Isotopes are:

i. Cobalt-60

This is hard grain magnetic material having melting point of 1480C

Density is 8.9 gm/cm3

It has a half-life of 5.3 years

It is used for the inspection of iron, copper and other medium weight

metals

ii. Iridium-192

This isotope belongs to Platinum family and has a density of 22.4

gm/cm3



It has a half-life of 74.3 days

It is used for radiography of steel up to 100mm

iii. Helium-170

It is generally in the form of Helium Oxide and has a density of 4

gm/cm3

It has a half-life of 129 days

It is used in the inspection of steel of 0.8mm and 30mm of aluminium

iv. Caesium-137

It is a man made isotope and it can be extracted from Sulphate or

Fluorite

It has a half-life of 33.1 years

It is used for the inspection of steel of thickness between 40-100mm

v. Selenium-75

This isotope provides radiation energies considerably lower than

Ir-192, which results in largely improved quality of weld radiographs

It has a half-life of 120 days

It is highly volatile and chemically reactive

Its mass is about 7kg

These isotopes are commonly used in mid-thickness gamma

radiography applications requiring high image quality

Its code is EN1435, ISO 5579

Attenuation:

When X-Rays or Gamma rays are directed into an object, some of the photons interact

with the particles of the matter and their energy can be absorbed or scattered. This

absorption and scattering is called as Attenuation

The number of photons transmitted through a material depends on the thickness,

density and atomic number of the material, and the energy of the individual photons

The Linear Attenuation Co-efficient() describes fraction of a beam of X-rays or

Gamma rays that is absorbed or scattered per unit thickness of the absorber



Linear Attenuation Co-efficient() can be normalized by dividing it by the density of

the element. This constant(/)is known as Mass Attenuation Co-efficient and its unit

is cm2/gm

Half Value Layer : The thickness of any given material where 50% of the incident

energy has been attenuated

HVL= 0.693/

Scattering processes:

i. Photo-electric Effect: The proton of low radiation energy transfers all its

energy to electron, at that time, it will impart kinetic energy and electrons will

be ejected by the atom

ii. Rayleigh’s(Coherent) Scattering: It occurs due to direct interaction between

proton and orbitory electron

iii. Compton Scattering: It occurs due to direct interaction between

proton(0.123meV) and obituary electron

iv. Pair Production: It occurs due to creation of two protons(0.51meV). It scatters

an energy of 1.02meV

Types of Radiography:

1. X-Ray Radiography

Fig. 3.2 Working Principle of X-ray Radiography



The tube cathode is heated with a low-voltage current of a few amps.

The filament heats up and the electrons in the wire become loosely held.

A large electrical potential is created between the cathode and the anode by the high-

voltage generator. Electrons that break free of the cathode are strongly attracted to the

anode target.

The stream of electrons between the cathode and the anode is the tube current. The

tube current is measured in milliamps and is controlled by regulating the low-voltage

heating current applied to the cathode.

The higher the temperature of the filament, the larger the number of electrons that

leave the cathode and travel to the anode. The milliamp or current setting on the

control console regulates the filament temperature, which relates to the intensity of

the X-ray output Fig 3.3 X-Ray

camera

A focusing cup is used to concentrate the stream of electrons to a small area of the

target called the focal spot

Cooling of the anode by active or passive means is necessary. Water or oil re-

circulating systems are often used to cool tubes

To prevent the cathode from burning up and to prevent arcing between the anode and

the cathode, all of the oxygen is removed from the tube by pulling a vacuum

X-ray generators usually have a filter along the

beam path (placed at or near the x-rayport).

Filters consist of a thin sheet of material (often

high atomic number materialssuch as

lead,copper, orbrass) placed in the useful beam

to modify the spatial distribution of the beam.

2. Gamma Radiography

Fig 3.4 Working principle of

Gamma Radiography



The source capsule and the pigtail are housed in a shielding device referred to

as a exposure device or camera.

Depleted uranium is often used as a shielding material for sources.

The exposure device for Iridium-192 and Cobalt-60 sources will contain 22

kgand 225 kgof shielding materials, respectively.

Cobalt cameras are often fixed to a trailer and transported to and from

inspection sites

To make a radiographic exposure, a crank-out mechanism and a guide tube are

attached to opposite ends of the exposure device.

The guide tube often has a collimator (usually made of tungsten) at the end to

shield the radiation except in the direction necessary to make the exposure.

The end of the guide tube is secured in the location where the radiation source

needs to be to produce the radiograph.

The crank-out cable is stretched as far as possible to put as much distance as

possible between the exposure device and the radiographer.

To make the exposure, the radiographer quickly cranks the source out of the

exposure device and into position in the collimator at the end of the guide

tube.

At the end of the exposure time, the source is cranked back into the exposure

device.

Physical size of isotope materials varies between manufacturers, but generally

an isotope material is a pellet that measures 1.5 mmx 1.5 mm

The disadvantage of a radioactive source is that it can never be turned off and

safely managing the source is a constant responsibility

In comparison to an X-ray generator, Cobalt-60 produces energies comparable

to a 1.25 MVX-ray system and Iridium-192 to a 460 kVX-ray system

Types of Gamma-Ray cameras:

1. Indian Cameras

They have a Radio-active Source Power of 35 Ci

The shielding of Lead is provide

They weigh about 37kg



The cost of these cameras is estimated around 3.5 to 4 lakhs

Various Indian cameras are:

i. Roli 1

ii. Roli 2

iii. Delta

The most commonly used camera is Delta

It uses Ir-192 isotope

Fig. 3.5 Delta Camera

2. Foreign Camera

They have a Radio-active Source Power of 100 Ci

The shielding of Depleted Uranium is provided

They weigh about 25kg

The cost of these cameras is estimated around 5 to 6 lakhs

The most commonly used camera is TechOps USA

It uses Ir-192 isotope

Radiographic Film:



X-ray films for general radiography basically consist of an emulsion-gelatine

containing radiation-sensitive silver halide crystals (such as silver bromide or

silverchloride).

The emulsion is usually coated on both sides of a flexible, transparent, blue-tinted

base in layers about 0.12 mmthick

The typical total thickness of the X-ray film is approximately 0.23 mm.

When X-rays, gamma-rays, or light strike the film, some of the halogen atoms are

liberated from the silver halide crystal and thus leaving the silver atoms alone. This

change is of such a small nature that it cannot be detected by ordinary physical

methods and is called a latent (hidden) image.

When the film is exposed to a chemical solution (developer) the reaction results in the

formation of black, metallic silver

Types of films

i. Agfa:

D7, D4, D5, D2

ii. Kodak:

AA400,MX125,MX200,DR50

D7 has high thickness and it is commonly used film

D7 is equivalent to AA400

Film Density

It is defined as the amount of degree of blackening

or darkening the film

This density can be measured with an instrument

called Densitometer

A good film density on a Densitometer will have a reading of 2.5

Radiographic density is the logarithm of two measurements: the intensity of light

incident on the film and the intensity of light transmitted through the film

Industrial codes and standards typically require a radiograph to have a density

between 2.0and 4.0for acceptable viewing with common film viewers. Fig. 3.6

Radiographic Film

Film density is measured with a densitometer which simply measures the amount of

light transmitted through a piece of film using a photovoltic sensor



Fig. 3.7 Densitometer

Film Factor:

It is the amount of radiation required to produce the desired density

Radiographic Contrast:

It is the density difference between two areas on a radiograph. It has two types

Subject Contrast

Contrast appearing in the film because of density or thickness of part

Film Contrast

It is the density difference on the film due to the type of film used. It depends upon

the exposure and type processing of the film

Types of Contrast:

Low contrast poor Definition

High contrast poor Definition

Low contrast goodDefinition

High contrast goodDefinition

Details to be included in the film before radiographic action:

Diameter of the work material

Line number

Piping class

Joint number

Welder number



Radiography or X-Ray number

Thickness of the work material

Date on which the operation is carried out

Fig. 3.8 Details on the film

Penetra-meters or Image Quality Indicators:

IQI is a device, whose image on a radiograph is used to determine radiographic

quality level

IQIs should be placed on the source side of the part over a section with a material

thickness equivalent to the region of interest.

Image quality indicators take many shapes and forms due to the various codes or

standards that invoke their use

The two most commonly used IQI types are:

Hole type IQI

Hole-type IQIs are classified in eight groups based on their radiation

absorption characteristics.

The numbers on the IQI indicate the sample thickness that the IQI

would typically be placed on.

ASTM Standard Of Hole type is E1025

Holes of different sizes are present where these holes should be visible

on the radiograph.



Fig. 3.9 Hole type IQI

Wire type IQI

Wire IQIs are grouped in four sets each having different range of wire

diameters

ASTM Standard of Wire type is E747

ASTM Wire types consists of 6 wires whereas, DIN Wire types

consists 0f 7 wires

Wire IQIs are grouped in four sets each having different range of wire

diameters. The set letter (A, B, C or D) is shown in the lower right

corner of the IQI

Fig. 3.10 Wire type IQI

Film Processing:

Radiographic film consists of a transparent, blue-tinted base coated on both sides with an

emulsion. The emulsion consists of gelatin containing microscopic, radiation sensitive silver



halide crystals, such as silver bromide and silver chloride. When the film is processed, it is

exposed to several different chemical solutions for controlled periods of time.

Film processing basically involves the following five steps:

1. Development :

The developing agent gives up electrons to convert the silver halide grains to

metallic silver.

Grains that have been exposed to the radiation develop more rapidly, but

given enough time the developer will convert all the silver ions into silver

metal.

Proper temperature control is needed to convert exposed grains to pure silver

while keeping unexposed grains as silver halide crystals

The developer consists of chemicals like Metol, Phenidoletc

A p.H value of 9.8 is maintained so as to keep the developer solution alkaline

2. Stopping the development :

The stop bath simply stops the development process by diluting and washing

the developer away with water

3. Fixing :

Unexposed silver halide crystals are removed by the fixing bath. The fixer

dissolves only silver halide crystals, leaving the silver metal behind

The Fixer consists of Sodium Thio-sulphate(NaH2O3)

A p.H value of 4.5 is maintained so as to keep the developer solution acidic

4. Washing : The film is washed with water to remove all the processing chemicals

5. Drying : The film is dried for viewing.



Fig. 3.11 Steps of Film Processing

Positive Material Identification (PMI):

It is the identification and analysis of various metal alloys by their chemical

composition through non-destructive methods

It can be conducted on-site or in the lab

Fig. 3.12 Positive Material Identification (PMI)

Benefits:

Highly specific and accurate results, essential for good quality control

Field testing with lab quality

Assurance for verification of special metal parts

Quick results for product verification and sorting of product that may have been

inadvertently mixed

Ferrite Tester:



It is used to measure the ferrite content in different applications of steel

It uses a method called magnetic induction to measure ferrite content in given sample

It is carried out to ensure that ferrite content is at correct levels specified for material

testing

A device called Feritoscope is used to determine the iron content in the material

Fig. 3.13 Feritoscope used to determine the iron content in the material

Advantages of Ferrite Tester:

Rapid and accurate analysis

Highly portable digital technology

Testing instruments meet all requirements of ANSI/AWS A4.2 and DIN EN ISO

8249

Calibration is trace-able to internationally approved IIW secondary calibration

standards

Limitations of Ferrite Tester:

Surface preparation is very important for result accuracy

Minimum material thickness and Minimum specimen size are required

Not recommended where material is at temperature greater than 125F

Film Interpretations:

Interpretations(Weld Discontinuities):

1. Tungsten Inclusions

2. Offset or Mismatch



3. Internal Undercut

4. Lack of Fusion

5. Lack of Penetration

6. Slag Inclusions

7. Cluster Porosity

8. Porosity

9. Suck Back

Fig. 3.14 Interpretations obtained on the film after processing

Radiographic Safety:

Radiographic Safety depends upon TIDS system i.e., Time Distance Shielding

Time: Less time spent near the source, less radiation received

Distance: More distance from source, less radiation received

Shielding: Behind the shielding from the source, less radiation received

General Safety Precautions:

1. Safety suit

2. Radiation Alarm

3. Radiation Badges

4. Radiation Barrier

5. Maintain a qualified technician inside the radiographic areas

6. Sign Boards



Fig. 3.15 various sign boards used in radiographic areas

Sign boards should be in English

The colour of the board must be Yellow whereas, the colour of the writings

must be Red

The size of sign boards must be 450X450mm

Fig. 3.16 Direct Read Pocket Dosimeter

Single Wall Single Image (SWSI):

In this method, the source is made to fall on single wall of work material

The film is placed behind the wall of the work material

Double Wall Single Image (DWSI):

In this method, the source is passed through two walls of the work material

Here the film is placed behind only one of the wall and thus single image

Double Wall Double Image (DWDI):

The source is kept at 1/4th of the SFD (Source to Film Distance) from weld

The image formed on the film is in the form of Ellipse

Two film are used in this method



Panoramic Method:

This method is used in the inspection of very large circular work materials

In this method, the source is kept at the centre and a number of films are placed

throughout the diameter of the work material

It works on the same principle as Single Wall Single Image

(SWSI)

Advantages of Radiographic Testing:

Both surface and internal discontinuities can be detected.

Significant variations in composition can be detected.

It has a very few material limitations.

Can be used for inspecting hidden areas (direct access to surface is not required)

Very minimal or no part preparation is required.

Permanent test record is obtained.

Good portability especially for gamma-ray sources

Dis-advantages of Radiographic Testing:

Hazardous to operators and other nearby personnel.

High degree of skill and experience is required for exposure and interpretation.

The equipment is relatively expensive (especially for x-ray sources).

The process is generally slow.

Highly directional (sensitive to flaw orientation).

Depth of discontinuity is not indicated.

4.ULTRASONIC TESTING (UT)

Introduction:

Ultrasonic testing uses high frequency sound waves to conduct examination and make

measurements. Besides its wide use in engineering applications (such as flaw detection and

evaluation, dimensional measurements, material characterization, etc), ultrasonic arealsoused

in medical field. In general, ultrasonic testing is on capture and quantification of either the



reflected waves. Each of the two types are in certain applications, but generally, pulse echo

systems are more useful since they require one sided access to the object being inspected

Fig, 4.1 Introduction to UT

Basic principle:

Fig, 4.2 Basic principle of UT

A typical pulse-echo UT inspection system consists of several functional units, such as the

pulser/receiver, transducer and display device. A pulser/receiver is an electrical device which

can produce high voltage electrical pulses. Driven by the pulser, the transducer produces high

frequency ultrasonic energy. The sound energy is introduced and propagates through the

materials in the form of waves. When there is an discontinuity in the wave path, path of

energy will be reflected back from the flaw surface . The reflected wave signal is transformed

into electrical signal by the transducer and explained on the screen. Knowing the velocity of

the signal, information about the reflector location, size, orientation and other features can be

gained

WAVE PROPAGATION:

Ultrasonic testing is based on the vibration in materials which is generally referred to as

acoustics. All material substances are comprised of atoms, which may be forced into

vibrational motion about their equilibrium positions. Many different patterns of vibrational

motion with at the atomic level; however, most are irrelevant to acoustics and ultrasonic

testing. Acoustics is focused on particles that contain many atoms that move in harmony to

produce a mechanical wave. When a material is not stressed in tension or compressionbeyond

its elastic limit, its individual particles perform their elastic oscillations. When the particles of

a medium are displaced from their equilibriumposition, internal restoration forces arise.



These elastic restoring between particles lead to the oscillatory motions of the medium. In

solids, sound waves can propagate in four principal modes that are based on the way the

particles oscillate. Sound can propagate as longitudinal waves, shear waves surface waves

and in thin materials as plate waves longitudinal and shear waves are the two modes of

propagation used in the ultrasonic

testing as shown in the figure

Fig, 4.3 Wave propagation

Snell’s law:

It describes the relationship between

the angles and the velocities of the

waves. Snell’s law equates the ratio of

material velocities to the ratio of the

sine’s of incident and refracted angles, as shown in the

following equation

Transducers:

There are two types of transducer

i. Contact type transducer

ii. Immersion transducer

Piezoelectric transducer (contact type):

The conversion of electrical pulses to mechanical vibrations and conversion of returned

mechanical vibration into electrical energy is the basis of UT .The conversion is done by the

transducer using piezoelectric material with electrodes attached to the two of the opposite



faces .When an electric field is applied across the material, the molecules will align

themselves with the electrical field causing the material to change dimensions. In addition, a

permanently polarized material such as quartz and barium titanate will produce an electric

field the material will change dimensions as a result of imposed mechanical force. The

phenomenon is known as piezoelectric effect

Immersion type:

These transducers are designed to operate in the liquid environment and all the connections

are water tight.Immersion transducers usually have an impedance matching layer helps to get

more sound energy into water and in into components being inspected. Immersion

transducers can be purchased with a planer focused or spherically focused lens. A focused

transducer can improve the sensitivity and axial resolution by concentrating the sound energy

to a smaller area. It is used inside a water tank or as part of a squitter or bubbler system in

scanning application

Fig, 4.5 Immersion type transducers

Ultrasonic Testing Techniques:

There are three types of techniques which are mainly used during inspection

i. A-scan technique:

It displays the amount of received ultrasonic energy as a function of time. The relative

amount of received energy is plotted along the vertical axis and the elapsed time is

displayed along the horizontal axis. Most instruments with a an A-scan display allow

the signal to be displayed allow the signal to be displayed in its natural radio

frequency form, as a fully rectified RF signal, or as either the positive or negative half

of the RF signal, or as the positive or negative half of the RF signal. In the A-scan



presentation, relative discontinuity size can be estimated by comparing the signal

amplitude obtained from unknown reflector. Reflector depth can be determined by the

signal on the horizontal time axis

Fig, 4.6 A, B & C-scan technique

ii. B-scan technique:

The B-scan presentation is a type of presentation that is possible for automated linear

scanning systems where it shows a profile of the test specimen. In the B-scan, the time

of flight of the sound waves is displayed along the vertical axis and the linear position of

the transducer is displayed along the horizontal axis. From the B-scan, the depth of the

reflector and its approximate linear dimensions in the scan direction can be determined.

The B-scan is typically produced by establishing a trigger gate on the A-scan. Whenever

the signal intensity is great enough to trigger the gate, appoint is produced on the B-

scan. The gate is triggered by the sound reflected from the back wall of the specimen

and by smaller reflector within the material. In the B-scan image shown previously, line

A is produced as the transducer moves to the right of this section, the back wall line BW

is product. When the transducer is over flaws B and C, lines that are similar to the length

of flaws and at similar depth of the material are drawn on the B-scan .It should be noted

that limitation to this display technique is that reflectors may be masked by large

reflector near surface

iii. C-scan technique:

The C-scan presentation is a type of presentation that is possible for automated for two-

dimensional scanning systems that provides a plan type view of the location and size of

test specimen features. The plane of the image is parallel to the scan pattern of the

transducer. C-scan presentations are typically produced with an automated data

acquisition system, such as computer controlled scanning system. Typically, a data

collection gate is established on the A-scan and the amplitude or the time-of-flight of the



signal is recorded at regular intervals as the transducer is scanned over the test piece. The

relative signal amplitude or the time-of-flight is displayed as a shade of grey or a colour

for each of the positions where data was recorded. The C-scan presentation provides an

image of the features that reflect and scatter the sound within and on the surfaces of the

test piece

Calibration method:

Calibration refers to the act of evaluating and adjusting the precision and accuracy of

measurement equipment. In UT, several forms of calibrations must occur. First, the

electronics of the equipment must be calibrated to ensure that they are performing as

designed. In UT reference standards are achieved a general level of consistency in

measurements and to help interpret and quantify the information contained in the receive

signal. The fig shows some of the commonly used to validate that the equipment and the

setup provide similar results from one day to the next and that similar results are

produced by different systems

Reference standards are mainly used for

Checking the performance of both angle beam and normal beam transducers

Determining the sound beam exit point of angle beam transducers

Determining the refracted angle produced

Evaluating instrument performance

IIW Type US-1 Calibration Block:

This block is a general purpose calibration block that can be used for calibrating angle; beam

transducers as well as normal beam transducers. The material from which IIW blocks are

prepared is specified as killed, open hearth or electric furnace, low carbon steel in the

normalized condition and with a grain size of McQuaid-Ehn No.8. Official IIW blocks are

dimensioned in the metric system of units. The block has several features that facilitate

checking and calibrating many of the parameters and functions of the transducer as well as

the instrument where that includes; angle beam exit, beam angle, beam speed spared, time

base, linearity, resolution, dead zone, sensitivity and range setting.T



Fig, 4.7 IIW Type US-1 Calibration Block

ASTM-Miniature Angle-Beam Calibration Block (V2):

The miniature angle-beam block is used in a somewhat similar

manner as the IIW block, but is smaller and lighter. The

miniature angle-beam block is primarily used in the field for

checking the characteristics of angle-beam transducers.

With the miniature block, beam angle and exit point can be checked for an angle-beam

transducer. Both the 25 and 50 mm radius surfaces provide ways for checking the

location of the exit point of the transducer for calibrating the time base of the instrument

in terms of the metal distance. The small hole provides a reflector for checking beam

angle and for setting the instrument gain.

Inspection Technique :

i. Normal Beam Inspection

Pulse-echo ultrasonic measurementscan determine location of a discontinuity in a

part of a structure by accurately measuring the time required for short ultrasonic

pulse generated by a transducer to travel through a thickness of a material reflect

from the back of a surface of a discontinuity and be returned to the transducer. In

most applications, this time interval is a few microseconds or less. The two way

transit time measured is divided by two to account down-and-back travel path and

multiplied by the velocity of sound in the test material. The result is expressed in

the well-known relationship



Where d is the distance from the distance to the discontinuity in the test piece, V

is the velocity of sound waves in the material, and t is the measured round-trip

transit time.

Precision ultrasonic thickness gages usually operate at frequencies between 500

kHz and 100 MHz, by means of piezoelectric transducers that generate bursts of

sound waves when excited by electrical pulses. Typically, lower frequencies are

used to optimize penetration when measuring thick, highly attenuating, non-

scattering materials. It is possible to measure most engineering materials

ultrasonically, including metals, plastic, ceramics, composites, epoxies, and glass

as well as liquid level and the thickness of certain biological specimens. On-line

or in-process measurement of extruded plastics or rolled metal often is possible, as

is measurements of single layers or coatings in multilayer materials.

ii. Angle Beam Inspection

Fig, 4.9 Angle Beam Inspection

Angle beam transducers and wedges are typically used to introduce a refracted

shear wave into the test material. An angled sound path allows the sound beam to

come in from the side, thereby improving detectability of flaws in and around

welded areas. Angle beam inspection is somehow different than normal beam

inspection. In normal beam inspection, the back wall echo is always present on the

scope display and when the transducer basses over a discontinuity a new echo will

appear between the initial pulse and the back wall echo. However, when scanning

a surface using an angle beam transducer there will be noreflected echo on the



scope display unless a properly oriented discontinuity or reflector comes into the

beam path.If a reflection occurs before the sound waves reach the back wall, the

reflection is usually referred to as “first leg reflection”.

Fig, 4.10 Second leg Reflection

If a reflector came across the sound beam after it has reached and reflected off the

back all, the reflection is usually referred to as “second leg reflection”. In this

case, the “Sound Path” (the total sound path for the two legs) and the “Surface

Distance” can be calculated using the same equations given above; however the

“Depth” of the reflector will be calculated as

Advantages and Disadvantages:

Advantages:

It is sensitive to both surface and sub-surface discontinuities.

The depth of penetration for flaw detection or measurement is superior to other NDT

methods

Only single-sided accurate in determining reflector position and estimating size and

shape

Minimal part preparation is required

It provides instantaneous results



Detail images can be produced with automated systems

It has other uses, such as thickness measurement, an addition to flaw detection

Its equipment can be highly portable or highly automated

Disadvantages:

Surface must be accessible to transmit ultrasound

Skill and training is more extensive than with some other method

It normally requires a coupling medium to promote the transfer of sound energy into

the test specimen

Cast iron and other coarse grains are difficult is difficult due to low sound

transmission and high signal noise

Linear defects oriented parallel to the sound beam may go undetected

Reference standards are required to both equipment calibration and the

characterization of flaws


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