Non destructive testing

2. UNIT 3: INSPECTION
• LPT, MPT: Liquid penetrant testing – procedure; penetrant testing materials,
penetrant testing method – sensitivity; application and limitations; magnetic particle
testing; definition and principle; magnetizing technique, procedure, equipment
sensitivity and limitation; Application & Acceptance Standards
• RADIOGRAPHY: Basic principle, electromagnetic radiation in film, radiographic
imaging, inspection techniques, applications, limitations, real time radiography,
safety in Industrial radiography. Application & Acceptance Standards.
• ULTRASONIC TECHNIQUES: Ultrasonic transducers, inspection methods,
technique for normal beam inspection, flaw characterization technique, ultrasonic
flaw detection equipment modes of display, immersion testing, advantage,
limitations; Application & Acceptance Standards
2

3. LIQUID PENTRANTTESTING
• Also called as, Dye Penetrant Inspection (DPI) and penetrant testing (PT)
• Used to detect surface defects in casting, forging, welding and possible fatigue
failure areas. Can reveal cracks 2µm wide.
• Its popularity can be attributed to two main factors, which are its relative ease of
use and its flexibility. LPI can be used to inspect almost any material provided that
its surface is not extremely rough or porous.
• Standard:ASTM E165-80 Liquid Penetrant Inspection Method
3

4. • A liquid with high surface wetting characteristics is applied to the
surface of the part and allowed time to seep into surface breaking
defects.
• The excess liquid is removed from the surface of the part.
• A developer (powder) is applied to pull the trapped penetrant out
the defect and spread it on the surface where it can be seen.
• Visual inspection is the final step in the process. The penetrant
used is often loaded with a fluorescent dye and the inspection is
done under UV light to increase test sensitivity.
4

5. 5

6. 6

7. Penetrant testing materials
A penetrant must possess a number of important characteristics. A
penetrant must spread easily over the surface of the material being
inspected to provide complete and even coverage be drawn into surface
breaking defects by capillary action remain in the defect but remove easily
from the surface of the part remain fluid so it can be drawn back to the
surface of the part through the drying and developing steps be highly
visible or fluoresce brightly to produce easy to see indications must not be
harmful to the material being tested or the inspector.
7

8. Penetrant Types
Dye penetrants
• The liquids are coloured so that they
provide good contrast against the
developer
• Usually red liquid against white
developer
• Observation performed in ordinary
daylight or good indoor illumination
Fluorescent penetrants
• Liquid contain additives to give
fluorescence under UV
• Object should be shielded from
visible light during inspection
• Fluorescent indications are easy to
see in the dark
8

9. Cleaners and Emulsifiers
• A cleaning fluid must act as a solvent for the material to be removed.
• For water based penetrants, a simple water wash or rinse is suitable.
• For petroleum based penetrants, there are two methods
• The most direct approach is to use an oil or chlorine based solvent.
• Another method is to use an emulsifier
• It reacts with the oil based penetrant to form a water- soluble substance.
• Two types of Emulsifiers: Lipophilic and Hydrophilic.
9

10. Penetrants are then classified by the method used to remove the excess penetrant
from the part. The four methods are:
• Method A - Water Washable
• Method B - Post-Emulsifiable, Lipophilic
• Method C - Solvent Removable
• Method D - Post-Emulsifiable, Hydrophilic
10

11. Method A - Water Washable
• Penetrants can be removed from the part by rinsing with water
alone.
• These penetrants contain an emulsifying agent (detergent).
• This makes it possible to wash the penetrant from the part
surface with water alone.
• Sometimes referred to as self-emulsifying systems.
11

12. Advantages of method A
• High sensitivity
• Less cost
• Large surface discontinuities can be visualized.
• Easy removal of penetrant.
Limitations of method A
• Dark environment is required
• Insensitive to shallow discontinuities
• Quality of penetrant is degraded by contamination
12

13. Method B- Post-Emulsifiable, Lipophilic
• Lipophilic emulsifiers (Method B) were introduced in the late 1950's and work with both a
chemical and mechanical action.
• The penetrant is oil soluble and interacts with the oil-based emulsifier to make removal
possible.
• Lipophilic emulsifiers diffuse in to the penetrant, breaking down the structure so that the
penetrant may be rinsed away with water
• After the emulsifier has coated the surface of the object, mechanical action starts to remove
some of the excess penetrant as the mixture drains from the part. During the emulsification
time, the emulsifier diffuses into the remaining penetrant and the resulting mixture is easily
removed with a water spray. 13

14. Advantages of post emulsifiable penetrants
•Higher sensitivity to smaller defects
•Shows wide, shallow defects
•More controlled removal of penetrant from the part surface
Disadvantages of post emulsifiable penetrants
• Extra processing steps depending on Method B or Method D
• Emulsification time control is critical
• Penetrant removal is difficult in threaded parts, holes and slots
• Not good on rough surfaces 14

15. Method C - Solvent Removable
Method C, Solvent Removable, is used primarily for inspecting small localized areas. This method
requires hand wiping the surface with a cloth moistened with the solvent remover, and is, therefore,
too labor intensive for most production situations. Of the three production penetrant inspection
methods, Method A, Water-Washable, is the most economical to apply. Water-washable or self-
emulsifiable penetrants contain an emulsifier as an integral part of the formulation. The excess
penetrant may be removed from the object surface with a simple water rinse. These materials have the
property of forming relatively viscous gels upon contact with water, which results in the formation of
gel-like plugs in surface openings. While they are completely soluble in water, given enough contact
time, the plugs offer a brief period of protection against rapid wash removal. Thus, water-washable
penetrant systems provide ease of use and a high level of sensitivity. 15

16. Method D - Post-Emulsifiable, Hydrophilic
• Hydrophilic Emulsifiers are composed of materials similar to common detergents.
• It lifts the excess penetrant from the surface of the part with a water wash.
• Hydrophilic emulsifiers (Method D) also remove the excess penetrant with mechanical and
chemical action but the action is different because no diffusion takes place. Hydrophilic
emulsifiers are basically detergents that contain solvents and surfactants.
• The hydrophilic emulsifier breaks up the penetrant into small quantities and prevents these
pieces from recombining or reattaching to the surface of the part. The mechanical action of the
rinse water removes the displaced penetrant from the part and causes fresh remover to contact
and lift newly exposed penetrant from the surface.
16

17. Classification of penetrants based on sensitivity of
indication produced by flaws
Based on the strength or detectability of the indication that is produced for a number of
very small cracks.
The five sensitivity levels are:
Level ½ - Ultra Low Sensitivity
Level 1 - Low Sensitivity
Level 2 - Medium Sensitivity
Level 3 - High Sensitivity
Level 4 - Ultra-High Sensitivity
• The procedure for classifying penetrants into one of the five sensitivity levels uses
specimens with small surface fatigue cracks.
• The brightness of the indication produced is measured using a photometer.
17

18. Developer
• The role of the developer is to pull the trapped penetrant material out of
defects and to spread the developer out on the surface of the part so it
can be seen by an inspector.
• The fine developer particles both reflect and refract the incident
ultraviolet light, allowing more of it to interact with the penetrant,
causing more efficient fluorescence.
• Another function that some developers performs is to create a white
background so there is a greater degree of contrast between the
indication and the surrounding background.
18

19. Developer Types
• Dry powder developer –the least sensitive but inexpensive
• Water soluble – consist of a group of chemicals that are
dissolved in water and form a developer layer when the water is
evaporated away.
• Water suspendible – consist of insoluble developer particles
suspended in water.
• Nonaqueous – suspend the developer in a volatile solvent and
are typically applied with a spray gun.
Using dye and developer from different
manufacturers should be avoided.
19

20. Classification
• Developers are classified based on the method that the developer is
applied:
• The six standard forms of developers are:
• Form A - Dry Powder
• Form B - Water Soluble
• Form C- Water Suspendable
• Form D - Nonaqueous Type 1: Fluorescent (Solvent Based)
• Form E - Nonaqueous Type 2: Visible Dye (Solvent Based)
• Form F - Special Applications
20

21. Dry Powder
• Dry powder developers are generally considered to be the least sensitive but
they are inexpensive to use and easy to apply.
• Dry developers are white, fluffy powders can be applied to a thoroughly dry surface
in a number of ways.
a. by dipping parts in a container of developer
b. By using electrostatic powder spray guns
c. by using a puffer to dust parts with the developer powder
d. placing parts in a dust cabinet where the developer is blown around
21

22. Advantages and Limitations
Advantages
a. Inexpensive
b. Easy to apply
Limitations
a. Less sensitive to indications
b. Powder is only stuck to the area where penetrant is
present
22

23. Water soluble
• Consist of a group of chemicals that are dissolved in water, and form a
developer layer when the water is evaporated away.
• The best method for applying water soluble developers is by spraying it on the
part.
• Dipping, pouring, or brushing the solution on to the surface is sometimes used
but these methods are less desirable.
• Drying is achieved by placing the part in a warm air dryer with the temperature
21°C .
• Properly developed parts will have an even, pale white coating over the entire
surface.
23

24. Water Suspendable
• Consist of insoluble developer particles suspended in
water.
• They require frequent stirring or agitation to keep the
particles from settling out of suspension.
• They are applied to parts in the same manner as water soluble
developers.
• Then the parts are dried using warm air.
24

25. Nonaqueous
• Nonaqueous developers suspend the developer in a volatile
solvent, and are typically applied with a spray gun.
• These are commonly distributed in aerosol spray cans
for portability.
• The solvent tends to pull penetrant from the indications
by solvent action.
• Since the solvent is highly volatile, forced drying is not
required.
25

26. Special Applications
• Plastic or lacquer (a liquid made of shellac dissolved in
alcohol) developers are special developers
• Primarily used when a permanent record of the inspection
is required.
26

27. Advantages and disadvantages of the various
developer types.
27

28. Advantages and disadvantages of the various
developer types.
28

29. Advantages and disadvantages of the various
developer types.
29

30. Advantages and disadvantages of the various
developer types.
30

31. General characteristics of a good Developer
• High absorption to secure max blotting action.
• Easily spread to expose the defect.
• Provide a contrast background.
• Easily, evenly and readily applied.
• Form a thin uniform coating over the surface.
• Easily wet to allow penetrant to spread over the area.
• Non flourescent when used with flourescent penetrant.
• Easily removed after inspection.
• Inert to materials being inspected.
• Non toxic.
• Inexpensive.
31

32. Interpretation and Evaluation of indications
• Mechanical discontinuities at the surface will
be indicated by bleeding out of the penetrant.
• However, localized surface imperfections, may
produce similar indications which are non-
relevant to the detection of unacceptable
discontinuities.
• Any indication which is believed to be non-
relevant must be regarded as a defect and will
be further examined.
32

33. • Visual examination or another examination method may
be used for verification of non- relevant indications.
• Surface conditioning may precede the
reexamination.
• Inadequate cleaning may leave an excessive background,
making interpretation difficult.
• When using color-contrast penetrants, indications with a
light pink color may indicate excessive cleaning.
33

34. • Linear indications are indications in which the length is more
than three times the width.
• Round indications are indications which are circular or
elliptical with length less than three times the width.
• An indication of a defect may be larger than the defect that
caused it; however, the size of the indication and not the size
of the defect is the basis of acceptance or rejection.
• All indications will be evaluated in terms of the appropriate
acceptance standards
34

35. Health and Safety Precautions in LPI
• When proper health and safety precautions are followed, LPI
operations can be completed without harm to inspection personnel.
• There is a number of health and safety related issues that need to be
taken into consideration.
• Chemical Safety & Ultraviolet Light Safety
35

36. Chemical Safety
• Certain precautions must be taken, while handling chemicals.
• Material Safety Data Sheets (MSDS) for chemicals.
• Some of the penetrant materials are flammable and, therefore, should
be used and stored in small quantities.
• Should only be used in a well ventilated area and ignition sources
avoided.
• Eye protection should always be worn to prevent contact of the
chemicals with the eyes.
• Gloves and other protective clothing should be worn to limit contact
with the chemicals.
36

37. Ultraviolet Light Safety
• wavelengths ranging from 180 to 400 nanometers.
• These wavelengths place UV light in the invisible part of the
electromagnetic spectrum between visible light and X-
rays…Blacklight
• The most familiar source of UV radiation is the sun and is
necessary in small doses for human body.
• Too much exposure can be harmful to the skin and eyes.
37

38. • The individual is generally unaware that the damage is
occurring.
• There is usually no pain associated with the injury until
several hours after the exposure.
• Skin and eye damage occurs at wavelengths around 320 nm
and shorter,
• which is well below the 365 nm wavelength, where
penetrants are designed to fluoresce.
• UV lamps deliver UV light with more intensity.
• UV lamps used in LPI are always filtered to remove the
harmful UV wavelengths.
38

39. Air pollution
• Developing powders are considered non toxic, but
excessive inhalation must be avoided.
• Exhaust fans should be installed in confined areas.
39

40. ADVANTAGES
AND
DISADVANTAG
ES OF THE
VARIOUS
DEVELOPER
TYPES
40

41. RANKING OF DEVELOPER EFFECTIVENESS FOR
THREE DIFFERENT DEFECTS
41

42. SUMMARY OF FACTORS THAT
CAN AFFECT THE SENSITIVITY
OF A LIQUID PENETRANT
INSPECTION
42

43. SUMMARY OF
FACTORS THAT
CAN AFFECT THE
SENSITIVITY OF A
LIQUID
PENETRANT
INSPECTION
43

44. Alenia Aeronautics is a
company of the Finmeccanica
society. This company is one
of the major European players
in aerospace, it works with
full integration capability
through design, manufacture,
and support of advanced
military and commercial
aircrafts.
Main activities of the NDI area in Alenia Aeronautics
Reference: Caturano, Gennaro, et al. "Liquid penetrant testing: industrial
process." Comm. SIMAI Congress. Vol. 3. 2009.
44

45. Advantages of LPT
• The method has high sensitive to small surface discontinuities.
• The method has few material limitations, i.e. metallic and nonmetallic,
magnetic and nonmagnetic, and conductive and nonconductive
materials may be inspected.
• Large areas and large volumes of parts/materials can be inspected rapidly
and at low cost.
• Parts with complex geometric shapes are routinely inspected.
• Indications are produced directly on the surface of the part and constitute
a visual representation of the flaw.
• Aerosol spray cans make penetrant materials very portable.
• Penetrant materials and associated equipment are relatively
inexpensive.
45

46. Disadvantages of LPT
• Only surface breaking defects can be detected.
• Only materials with a relative nonporous surface can be inspected.
• Precleaning is critical as contaminants can mask defects.
• Metal smearing from machining, grinding, and grit or vapor blasting must be
removed prior to LPI.
• The inspector must have direct access to the surface being inspected.
• Surface finish and roughness can affect inspection sensitivity.
• Multiple process operations must be performed and controlled.
• Post cleaning of acceptable parts or materials is required.
• Chemical handling and proper disposal is required.
46

47. Liquid penetrant testing applications
Liquid Penetrant Testing or Dye Penetrant Testing is used for
performing the surface inspection for welded parts, machined parts,
casting and forging.
The main applications of Liquid Penetrant Testing or DPT are:
1.Surface NDT inspection of weldments in plates, pipes.
2.Penetrant testing to find defects in machined parts.
3.Surface inspection for highly critical aerospace components.
4.Inspection of welding repairs to ensure complete defects removal.
5.Surface inspection of in-service materials to verify presence of material
defects.
6.Inspection of components to check their integrity.
47

48. LPI test result – cracking in the
HAZ of an aluminum alloy weld
TWI Industries:
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supporting both individuals and companies
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best products possible.
48

49. Magnetic Particle Testing (MT) (also known as magnetic particle inspection – MPI) is a
non destructive test (NDT) method, used to detect surface or subsurface (near to surface)
discontinuities. This NDT method can be used on metals which can be easily magnetized
(ferromagnetic). Metals can be classified as ferromagnetic, paramagnetic, or diamagnetic.
•Ferromagnetic metals: Ferromagnetic metals are those, which are strongly attracted to a
magnet and can be easily magnetized. Examples ferromagnetic metals are iron, nickel, and
cobalt.
•Paramagnetic metals: Paramagnetic metals are those which are very weakly attracted by
magnetic forces of attraction and cannot be magnetized such as austenitic stainless steel.
•Diamagnetic metals: Diamagnetic metals are those which are slightly repelled by a
magnet and cannot be magnetized. Examples of diamagnetic metals are bismuth, gold, and
antimony.
Only ferromagnetic metals can be effectively inspected by Magnetic Particle Testing
Magnetic Particle Testing (MPT)
49

50. 50

51. • If there is any distinct change in
the continuity (such as surface
discontinuity) of magnet, then the
magnetic lines of force will get
distorted, this phenomenon is
known as flux leakage. During
flux leakage, additional North and
South poles will be created near
discontinuity (see, Figure), and
the magnetic lines of force will
redistribute themselves in the
material by bending around the
discontinuity.
51

52. How Magnetic Particle Test
works:
When fine Iron particle
(ferromagnetic particle) is
spread over a magnet, it gets
accumulated at the poles. But
in case of any discontinuity,
flux leakage would occur
and the Iron powder will
accumulate at the
discontinuity, due to the
creation of additional North
and South poles at the
discontinuity, as shown in Fig.
52

53. Particles used for Magnetic particle testing is similar to ferromagnetic particle and is called
as detection media. These particles may be applied in dry form or may be mixed with liquid
and spread over the area where Magnetic particle test has to be performed. Liquid like
kerosene or a similar petroleum distillate may be used. Water can also be used by using
suitable additives such as wetting agents and antifoam liquids. To provide better contrast
with the test objects and enhanced sensitivity, these particles are coated, there are two types
of coating;
1. Color contrast coating
2. Fluorescent coating
Color contrast coating: Color contrast coatings are available in several colors such as red,
blue, black and Gray etc. Color of particle are selected so as to provide a good contrast
with test object.
Fluorescent coating: Fluorescent particles can be seen under a ‘Black light illumination’.
These particles emit light when seen by a black light in a dark background. These particles
provide excellent contrast in dark background.
53

54. How to temporarily magnetize the test object:
To carry out Magnetic Particle Testing we need to temporarily
magnetize the test object. Magnetization should be temporary
in nature. To magnetize the test piece, common instruments
which are used are;
• Electromagnetic yoke
• Permanent Magnet
• Prod
• Coil
Electromagnetic Yokes, (see Figure)are also called as AC
yokes, it’s very portable and commonly used in Industries.
Yokes are connected with AC power source (Battery pack
version is also available). Many yokes come with adjusting
legs, to facilitate wide range of area profiles. These yokes
produce longitudinal magnetization. Hence, for complete
inspection, re-positioning of yokes in at least two
900 opposing direction is required.
54

55. Flux Direction Indicators:
Before inspection, the yoke shall be properly checked by the flux direction
indicators. The most common flux direction indicator used in the industries
is ‘A Pie Gauge’. Other flux direction indicators are Burmah Castrol strips
and Quantitative quality indicator (QQI).
A pie gauge is an octagonal flat plate which consists of eight low-carbon steel
segments. The octagonal flat plate is copper coated from the back side to hide
the joint lines. When particles are suspended, from back side, on the pie
gauge (under the influence of magnetic lines of force), particles get
accumulated at these joint lines revealing the eight segments.
55

56. Magnetic Particle Inspection (MPI)
• MPI uses magnetic fields and small magnetic particles, such as iron filings to
detect flaws in components.
• The only requirement from an inspectability standpoint is that the component
being inspected must be made of a ferromagnetic material such as iron, nickel,
cobalt, or some of their alloys
• The method is used to inspect a variety of product forms such as castings, forgings,
and weldments.
• Underwater inspection is another area where magnetic particle inspection may be
used to test such things as offshore structures and underwater pipelines.
56

57. Basic Principles
• In theory, magnetic particle inspection (MPI) is a relatively simple concept. It can be considered as a
combination of two nondestructive testing methods: magnetic flux leakage testing and visual testing.
• Consider a bar magnet. It has a magnetic field in and around the magnet. Any place that a magnetic line of
force exits or enters the magnet is called a pole. A pole where a magnetic line of force exits the magnet is
called a north pole and a pole where a line of force enters the magnet is called a south pole.
57

58. Interaction of materials with an external
magnetic field
• When a material is placed within a magnetic field, the magnetic forces of the material's electrons
will be affected. This effect is known as Faraday's Law of Magnetic Induction.
• This reaction is dependent on a number of factors such as the atomic and molecular structure of the
material, and the net magnetic field associated with the atoms.
• The magnetic moments associated with atoms have three origins. These are the electron orbital
motion, the change in orbital motion caused by an external magnetic field, and the spin of the
electrons.
58

59. Diamagnetic, Paramagnetic, and
Ferromagnetic Materials
Diamagnetic metals: very weak and negative susceptibility to magnetic fields.
Diamagnetic materials are slightly repelled by a magnetic field and the
material does not retain the magnetic properties when the external field is
removed.
Paramagnetic metals: small and positive susceptibility to magnetic fields.
These materials are slightly attracted by a magnetic field and the material does
not retain the magnetic properties when the external field is removed.
Ferromagnetic materials: large and positive susceptibility to an external
magnetic field. They exhibit a strong attraction to magnetic fields and are
able to retain their magnetic properties after the external field has been
removed.
59

60. General Properties of Magnetic Lines of Force
1. Follow the path of least resistance
between opposite magnetic poles.
2. Never cross one another.
3. All have the same strength.
4. Their density decreases (they spread
out) when they move from an area of
higher permeability to an area of lower
permeability.
5. Their density decreases with increasing
distance from the poles.
6. Flow from the south pole to the north
pole within the material and north pole
to south pole in air.
60

61. When a bar magnet is broken in the center of its length, two complete bar magnets with magnetic poles
on each end of each piece will result. If the magnet is just cracked but not broken completely in two, a
north and south pole will form at each edge of the crack.
The magnetic field exits the north pole and
reenters the at the south pole. The magnetic
field spreads out when it encounter the small
air gap created by the crack because the air
can not support as much magnetic field per
unit volume as the magnet can.
When the field spreads out, it appears to leak
out of the material and, thus, it is called a
flux leakage field.
61

62. If iron particles are sprinkled on a cracked magnet, the particles will be attracted to
and cluster not only at the poles at the ends of the magnet but also at the poles at the
edges of the crack. This cluster of particles is much easier to see than the actual crack
and this is the basis for magnetic particle inspection.
62

63. Cracks just below the
surface can also be
revealed
The magnetic particles form a
ridge many times wider than the
crack itself, thus making the
otherwise invisible crack visible
63

64. The effectiveness of MPI depends
strongly on the orientation of the
crack related to the flux lines
MPI is not sensitive to shallow
and smooth surface defects
64

65. Testing Procedure of MPI
• Cleaning
• Demagnetization
• Contrast dyes (e.g. white paint for dark particles)
• Magnetizing the object
• Addition of magnetic particles
• Illumination during inspection (e.g. UV lamp)
• Interpretation
• Demagnetization - prevent accumulation of iron particles or
influence to sensitive instruments
65

66. Magnetizing the object
There are a variety of methods that can be used to establish a
magnetic field in a component for evaluation using magnetic
particle inspection. It is common to classify the magnetizing
methods as either direct or indirect.
•Direct magnetization: current is passed directly through the
component.
Clamping the component between two electrical
contacts in a special piece of equipment Using clams or prods, which are attached or
placed in contact with the component 66

67. Indirect magnetization: using a strong external magnetic field to establish a
magnetic field within the component
(a) permanent magnets
(b) Electromagnets
(c) coil shot
67

68. •Longitudinal magnetization:
achieved by means of
permanent magnet or
electromagnet
•Circumferential
magnetization: achieved
by sending an
electric current through the
object
68

69. Demagnetization
After conducting a magnetic particle inspection, it is usually necessary to demagnetize the
component. Remanent magnetic fields can:
• affect machining by causing cuttings to cling to a component.
• interfere with electronic equipment such as a compass.
• can create a condition known as "ark blow" in the welding process. Arc blow may causes
the weld arc to wonder or filler metal to be repelled from the weld.
• cause abrasive particle to cling to bearing or faying surfaces and increase wear.
69

70. Magnetic particles
• Pulverized iron oxide (Fe3O4) or carbonyl iron
powder can be used
• Coloured or even fluorescent magnetic
powder can be used to increase visibility
• Powder can either be used dry or suspended in
liquid
70

71. Some Standards for MPI Procedure
• British Standards
• BS 4397: Methods for magnetic particle testing of welds
• ASTM Standards
• ASTM E 709-80: Standard Practice for Magnetic Particle Examination
• ASTM E 125-63: Standard reference photographs for magnetic particle indications
on ferrous castings
71

72. Advantages of MPI
• One of the most dependable and sensitive methods for surface
defects
• fast, simple and inexpensive
• direct, visible indication on surface
• unaffected by possible deposits, e.g. oil, grease or other metals chips,
in the cracks
• can be used on painted objects
• surface preparation not required
• results readily documented with photo or tape impression
72

73. Limitations of MPI
• Only good for ferromagnetic materials
• Sub-surface defects will not always be indicated
• Relative direction between the magnetic field and the defect line is important
objects must be demagnetized before and after the examination
• The current magnetization may cause burn scars on the item examined
73

74. Examples of visible dry magnetic particle indications
Indication of a crack in a saw blade Indication of cracks in a weldment
Before and after inspection pictures of cracks
emanating from a hole
Indication of cracks running between attachment holes
in a hinge 74

75. Examples of Fluorescent Wet Magnetic
Particle Indications
Magnetic particle wet fluorescent
indication of a cracks in a drive shaft
Magnetic particle wet
fluorescent indication
of a crack in a bearing
Magnetic particle wet fluorescent indication of a
cracks at a fastener hole
75

76. Norvic-Shoot—Magnetic-
Particle-Inspection
Norvic is one of the leading aircraft engine
overhaul companies. Our aviation customers know
from experience that the cheapest engine is not the
one that is overhauled or repaired for the least
money, but the one that provides the lowest cost
per flying hour. The engine that goes to TBO.
76

77. COMPANIES PROVIDING LPT & MPT SERVICES
Applied Technical Services – USA
• Leading NDT company in North America.
• Common services include LPT, MPT,
eddy currents, ultrasonic testings,
radiograph testing and visual inspection.
• Common inspections:
Tanks, pressure vessels, piping
systems, near drum, boiler, etc.
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77

78. DEKRA offers solutions to fully automate the visual inspection stage of the process. The inspection
can be performed by robotic handling of the specimen on a programmed procedure with inspection
camera viewing and pattern recognition to identify and recognize flaws. This method is increasingly
used in advanced mechanized applications.
DEKRA’s penetrant testing specialists are certified according to ISO 9712 and we meet the following
testing standards: ISO 3452-1:2013, PNAE G-7-018-89, GOST 18442-80.
DEKRA INDUSTRY – GERMANY
DEKRA’s magnetic particle testing experts also use a range of fluorescent methods, using fluorescent
particles which require UV-A illumination.
Liquid Penetrant Testing – a six-stage process:
1.Surface cleaning (degreasing etc.)
2.Application of a penetrant liquid (dipping, spray, brush)
3.Removal of excess penetrant (solvent, water)
4.Application of developer
5.Inspection of test surface (visual, television camera)
6.Post-inspection cleaning (anti-corrosion solutions)
78

79. TRINITY ENGINEERING QUALITY – INDIA
• Dye Penetrant Testing (DPT) Lab serving from Peenya Industrial
Area in Bangalore.
• Key highlights of the services provided
 Stationery penetrant inspection equipment's
 S2, S3 & S4 sensitivity
 UV lights
 Professionals are qualified and certified to PT Level I, II as per Written
Practice framed to the requirements of SNT-TC-1A, NAS410 & ISO9712
 Experienced in house ASNT NDT Level III consultants
 NDT Level III trainers for conducting NDT Level 1, 2 training and
certification courses on Liquid penetrant testing.
 Skilled NDT Level 2 certified inspectors
 Sales and Supply of Dye penetrant inspection (DPT), penetrants, cleaners,
solvents, developers
FPI Line Aerospace NDT
Labs In Bangalore India
79

80. Codes and specifications
Codes and specifications are similar types of standards that use the verbs "shall" or "will" to indicate the
mandatory use of certain materials or actions or both. Codes differ from specifications in that their use is
mandated with the force of law by governmental jurisdiction. The use of specifications becomes mandatory
only when they are referenced by codes or contractual documents. A prime example of codes is the ASME
boiler and pressure vessel code which is a set of standards that assures the safe design, construction and testing
of boilers and pressure vessels.
Standards
Standards are documents that govern and guide the various activities occurring during the production of an
industrial product. Standards describe the technical requirements for a material, process, product, system or
service. They also indicate, as appropriate, the procedures, methods, equipment or tests to determine that the
requirements have been met. There are different NDT standards available for respective methods issued by
different international standard-issuing organizations.
Codes and standards
80

81. Some of these organizations and their standards on magnetic particle testing are given below:
American National Standards Institute (ANSI)
(a) ANSI/ASTMA 275 Magnetic particle examination of steel forgings.
(b) ANSI/ASTMA 456 Magnetic particle inspection of crankshaft forging.
(c) ANSI/ASTME 125 Reference photographs for magnetic particle indications of ferrous castings.
(d) ANSI/ASTME 269 Definition of terms relating to magnetic particle inspection.
American Society for Testing and Materials (ASTM)
(a) A275 Magnetic particle examination of steel forging.
(b) A456 Magnetic particle inspection of large crankshaft forgings.
(c) E125 Standard reference photographs for magnetic particle indications on ferrous castings.
(d) E269 Definition of terms relating to magnetic particle inspection.
(e) E709 Standard recommended practice for magnetic particle examination.
(f) D56 Test methods for flash point by tag closed test.
(g) D93 Test methods for flash point by Pensky Martens closed tester.
(h) D96 Test methods for water and sediment in crude oils.
81

82. Radiography Testing
82

83. Radiography
• Radiography is used in a very wide range of applications including medicine,
engineering, forensics, security, etc.
• In NDT, radiography is one of the most important and widely used
methods.
• Radiographic testing (RT) offers a number of advantages over other NDT methods,
however, one of its major disadvantages is the health risk associated with the
radiation.
83

84. • RT is one of the most widely used NDT methods for the detection of internal defects such
as porosity and voids.
• With proper orientation of the X-ray beam, planar defects can also be detected with
radiography.
• It is also suitable for detecting changes in material composition, thickness measurements
and locating unwanted or defective components hidden from view in an assembled part.
84

85. 1. In general, RT is method of inspecting materials for hidden flaws by using the ability of
short wavelength electromagnetic radiation (high energy photons) to penetrate various
materials.
2. The intensity of the radiation that penetrates and passes through the material is either
captured by a radiation sensitive film (Film Radiography) or by a planer array of
radiation sensitive sensors (Real-time Radiography).
3. Film radiography is the oldest approach, yet it is still the most widely used in NDT.
85

86. Basic Principles
• In radiographic testing, the part to be inspected 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 radioactive source.
• The part will stop some of the radiation where thicker and more dense areas will stop
more of the radiation.
• The radiation that passes through the part will expose the film and forms a shadowgraph
of the part.
• The film darkness (density) will vary with the amount of radiation reaching the film
through the test object,
• where darker areas indicate more exposure (higher radiation intensity) and lighter areas
indicate less exposure (higher radiation intensity).
86

87. The variation in the image darkness can be used to determine thickness or composition of material and
would also reveal the presence of any flaws or discontinuities inside the material.
87

88. Advantages of RT
• Both surface and internal discontinuities can be detected.
• Significant variations in composition can be detected.
• It can be used on a variety of materials.
• 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.
88

89. Disadvantages
• 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.
• It requires a two-sided access to the component.
89

90. PHYSICS OF RADIATION
Nature of Penetrating Radiation
• Both X-rays and gamma rays are electromagnetic waves and on the electromagnetic
spectrum they occupy frequency ranges that are higher than ultraviolet radiation.
• In terms of frequency, gamma rays generally have higher
frequencies than X-rays.
• The major distinction between X-rays and gamma rays is the origin where X-rays are
usually artificially produced using an X-ray generator and gamma radiation is the product
of radioactive materials.
• Both X-rays and gamma rays are waveforms, as are light rays, microwaves, and radio
waves.
• X-rays and gamma rays cannot be 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.
90

91. 91

92. • Electromagentic radiation act somewhat like a particle at times in that they occur
as small “packets” of energy and are referred to as “photons”.
• Each photon contains a certain amount (or bundle) of energy, and all
electromagnetic radiation consists of these photons.
• The only difference between the various types of electromagnetic radiation is the
amount of energy found in the photons.
• Due to the short wavelength of X-rays and gamma rays, they have more energy
to pass through matter than do the other forms of energy in the electromagnetic
spectrum.
• As they pass through matter, they are scattered and absorbed and the degree of
penetration depends on the kind of matter and the energy of the rays.
92

93. Properties of X-Rays and Gamma Rays
• They are not detected by human senses (cannot be seen, heard, felt, etc.).
• They travel in straight lines at the speed of light.
• 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.
• Their degree of penetration depends on their energy and the matter they are traveling
through.
• They have enough energy to ionize matter and can damage or destroy living cells.
93

94. Electromagnetic Radiation sources
X ray source
• In the widely used conventional X radiography, the source of radiation is an X-ray
tube.
• It consists of a glass tube under vacuum, enclosing a positive electrode or ‘anode’
and a negative electrode or ‘cathode’.
• The cathode comprises a filament, which when brought to incandescence by a
current of a few amperes, emits electrons.
• Under the effect of electrical tension set up between the anode and the cathode,
these electrons are attracted to the anode.
94

95. 95

96. • The stream of electrons is concentrated in a beam by a cylinder or a focusing
cup.
• The anti-cathode is a slip of metal with high melting point recessed in to the
anode, where it is struck by the beam of electrons.
• It is by impinging on the anti-cathode that fast moving electrons give rise to X-
rays.
96

97. • The development of electronics has led to the availability of constant potential units
which give stable operating conditions.
• The replacement of glass tubes by metal ceramic ones has led to an extended tube life.
• X-ray machines are characterized by the operating voltage and current which
determine the penetrability and intensity of radiation produced.
• Modern X-ray generators are available up to 450 kV and 50 mA.
• Highly automated self propelled X-ray mini-crawlers which travel within pipelines
are used to take radiographs of pipelines and welds from inside.
97

98. • The area of the anti-cathode which is struck by the electron flux is
called the ‘focal spot’ or TARGET.
• It is essential that this area should be sufficiently large, in order to avoid local
heating which may damage the anti-cathode and to allow rapid dissipation of
heat.
• The projection of the focal spot on a surface perpendicular to the axis of
the beam of X-rays is termed as the ‘optical focus’ or ‘focus’.
• This focus has to be as small as possible in order to achieve maximum
sharpness in the radiographic image.
98

99. Production of X-rays
• X-rays are produced when fast moving electrons are suddenly brought to rest
by colliding with matter.
• Electrons may also lose energy by ionization and excitation of the target atoms.
• The accelerated electrons lose their kinetic energy (KE) very rapidly at the
surface of the metal plate, and energy conversion occurs.
99

100. Conversion in 3 different ways:
1. A very small fraction (< 1 %) is converted into X radiation.
2. The conversion factor f can be estimated using an empirical relation f = 1.1 x 10-9 ZV
Z = atomic number of the target, V = energy of electron in volts.
3. Approximately 99% of energy of electrons is converted into heat by increasing the
thermal vibration of the atoms of the target, the temperature of which may rise
considerably.
4. Some of the electrons have sufficient energy to eject orbital electrons from the atoms of
the target material that are ionized.
5. The secondary electrons produced in this way may escape from the surface of the target
and subsequently be recaptured by it producing further heat or secondary radiation.
100

101. • The two important distinguishing features of a beam of X rays are its
intensity and quality.
• The first term refers to how much radiation (quantity).
• The second term refers to the kind of radiation (how penetrating it is).
101

102. High energy X-ray source
• Inspection of thicker sections is carried out using high energy X-rays ( energy
value 1 MeV or more).
• Using high energy X-rays, possibilities of large distance to thickness ratios with
correspondingly low geometrical distortion, short exposure times and high
production rate can be achieved.
• Also, small focal spot size and reduced amount of high angle scattered X-rays
reaching the film result in radiographs with good contrast, excellent sensitivity and
good resolution.
• A number of machines are available: synchrotron, betatron, Van De Graff type
electrostatic generators, etc.
102

103. Gamma Radiation
• Radioactivity, is the process by which a nucleus of an unstable atom loses energy
by emitting ionizing radiation.
• Gamma radiation is one of the three types of natural radioactivity.
• The other two types of natural radioactivity are alpha and beta radiation, which are
in the form of particles.
• Gamma rays are electromagnetic radiation just like X- rays.
• Gamma rays are the most energetic form of electromagnetic radiation.
103

104. • Gamma radiation is the product of radioactive atoms.
• Depending upon the ratio of neutrons to protons within its nucleus, an isotope of a
particular element may be stable or unstable.
• When the binding energy is not strong enough to hold the nucleus of an atom
together, the atom is said to be unstable.
• Atoms with unstable nuclei are constantly changing as a result of the imbalance of
energy within the nucleus.
• Over time, the nuclei of unstable isotopes spontaneously disintegrate, or transform,
in a process known as “radioactive decay” and such material is called “radioactive
material”.
104

105. Gamma-rays
• A nucleus which is in an excited state (unstable nucleus) may emit
one or more photons of discrete energies.
• The emission of gamma rays does not alter the number of protons or
neutrons in the nucleus but instead has the effect of moving the
nucleus from a higher to a lower energy state (unstable to stable).
• Gamma ray emission frequently follows beta decay, alpha decay,
and other nuclear decay processes.
105

106. Basic terms
Isotopes
• The number of nucleons (both protons and neutrons) in the nucleus is the atoms mass
number, and each isotope of a given element has a different mass number.
For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element
carbon with mass numbers 12, 13 and 14 respectively.
Half life
• Half-life is the amount of time required for a quantity to fall to half its value as
measured at the beginning of the time period.
• It is the time required, for half of the unstable, radioactive atoms in a sample to
undergo radioactive decay.
106

107. Gamma ray sources
• Gamma rays are electromagnetic radiation emitted from an unstable nucleus.
• X-ray machines emit a broad band of wavelengths, but Gamma ray sources emit one
or a few discrete wavelengths.
• Radiography with gamma rays has the advantages of simplicity of the apparatus,
compactness of radiation source and independence from outside power.
• This facilitates examination of pipes, pressure vessels and other assemblies in which
the access to interior is difficult.
• Each isotope with unstable nucleus will have characteristic nuclear energy levels and
intensities for the emitted radiation.
• The gamma ray energy levels remain constant for a particular isotope but the intensity
decays with time as indicated by the half life.
107

108. • A variety of radioisotopes are produced in a nuclear reactor but a few have been
utilized for the purposes of radiography.
• Other isotopes are unsuitable for a variety of reasons such as shorter half life, low
intensity and high cost of production.
• The 4 most popular radiographic sources are Cobalt 60 (Co-60), Iridium 192 (Ir-
192), Caesium 137 (Cs-137) and Thulium 170 (Th-170).
108

109. • Manmade radioactive sources are produced by introducing an extra neutron to atoms of
the source material.
• As the material gets rid of the neutron, energy is released in the form of gamma rays.
• Two of the most common industrial gamma-ray sources for industrial radiography are
Iridium-192 and Cobalt-60.
• In comparison to an X-ray generator, Cobalt-60 produces energies comparable to a 1.25
MV X- ray system and Iridium-192 to a 460 kV X-ray system.
• These high energies make it possible to penetrate thick materials with a relatively short
exposure time.
109

110. Inspection techniques
• With the various techniques available, the choice of appropriate one is made on the
basis of geometry, size, sensitivity requirements, in-situ space availability etc.
• The techniques used for various engg. components for radiographic inspection are:
110
Double wall penetration technique
 Double wall single image
 Double wall double image
 Double wall superimposing image
Single wall single image technique

111. Single wall single image technique (SWSI)
• Used when both the sides of the specimen are accessible.
• The source is kept outside and the film inside or vice versa and the weld is
exposed part by part (a smaller length of weld).
• This is used for plates, cylinders, shells and large diameter pipes.
111

112. 112

113. 113

114. Panoramic technique
• The radiation source is kept in the centre of the pipe and
the film is fixed around the weld on the outer surface of the
pipe.
• The total circumferential weld length is exposed at a time.
• Reduces the examination time considerably.
• It can be effectively employed only when the source to
film distance is sufficient enough to ensure the proper
sensitivity.
114

115. 115

116. Double wall penetration technique
• Used where the inside surface of the pipe is not accessible.
• The source of radiation and the film are kept outside.
• The radiation penetrates both the walls of the pipe.
• This can be effectively adopted in 3 different methods.
 Double wall single image (DWSI)
 Double wall double image (DWDI)
 Double wall superimposing image
116

117. Double wall single image (DWSI)
117

118. • The radiation source is kept on the pipe or very near to the OD and just
near the weld.
• Used for pipes with diameter more than 90 mm OD.
• The image quality indicator (IQI) is placed on the film side.
• Here film side weld only can be interpreted.
• As the interpretable weld length is small, it requires a number of
exposures to cover the entire weld length, depending upon the pipe
diameter.
118

119. Double wall double image (DWDI)
119

120. • Specially suited for small diameter pipes up to 90 mm OD.
• The radiation source is kept at a distance SFD (Source-to-Film Distance)
with an offset from the axis of the weld,
• to avoid the super imposing of the source side weld over the film side weld
and to obtain an elliptical image on the film.
• Here both the source and film side welds can be interpreted from the image.
• Requires min. of two exposures, perpendicular to each other, to cover the
entire circumference.
120

121. Superimposing technique
• Used when the required offset to obtain double image could not be
possible due to site restrictions for the pipes with dia : 90mmOD.
• The source is kept at a distance without offset, thereby the source side
weld is superimposed on the film side weld on the film.
• Requires minimum of 3 exposures each at 120° apart, to cover the
entire length of the weld.
121

122. 122

123. Real time radiography
• Uses X or gamma radiation to produce a visible volumetric image of an object.
• In Film radiography, the image is viewed in a static mode; in Real time
radiography, the image is interpreted at the same time as the radiation passes
through the object (Dynamic mode).
• A positive image is normally presented in Real time radiography, whereas the
X-ray film gives a negative image.
123

124. • Basic equipment consists of a source of radiation, a
fluorescent screen, mirrors and a viewing port.
• Object is placed between the source and the screen.
• The fluorescent screen converts the transmitted radiation to
visible light.
• A specially coated mirror then reflects the visible image to a
viewing port.
• As low light levels are produced during conventional
fluoroscopy, an intensifier is used to provide brightness.
124

125. 125

126. • Real time radiography has the advantages of high speed and low cost of inspection.
• Real-time radiographic concept can be applied in the case of microfocal radiography.
(focal spot = 100 µm)
• In Real-time microfocal radiography the zooming is done by dynamically positioning
the object with the manipulators between X-ray tube and image receptor.
• Real-time radiography can be applied to the inspection of laser welds or electron beam
welds in thin pipes having thickness 1mm and porosities in the range of 0.025mm –
0.1mm can be detected in 1 second.
126

127. Films used in industrial radiography
• They are similar to photographic film in that there is a central carrier called film base
that is made of thin sheet of polyester type material.
• This is normally transparent and serves only as the carrier for the chemically reactive
material that forms the emulsion.
• Emulsion consisting of a silver halide recording medium with a binder (gelatin) is
applied to both sides of the base.
• The emulsion is usually coated on both sides of a flexible, transparent, blue-tinted
base in layers about 0.012 mm thick.
• The typical total thickness of the X-ray film is approximately 0.23 mm.
127

128. 128

129. • Though films are made to be sensitive for X-ray or gamma-ray, yet they are also
sensitive to visible light.
• 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.
129

130. • The film speed is another important film parameter.
• A film whose grains would begin reacting to the exposure considerably sooner
than other films – High speed film.
• For a constant intensity, the grains of a high speed film would produce the
required density before the grains of slow speed film.
• Grain size in a film affects quality and time of exposure.
• Faster speed films have larger grains and slow films have extra-fine or fine grains,
and give better quality even though the exposure time is longer.
130

131. Speed of film
• Speed is defined as the density recorded on the film resulting from a given
radiation input.
• It is measured in terms of inverse of exposure required to produce a radiograph of
a particular density, under specified conditions.
• A film requiring less exposure is called faster.
131

132. Film Selection
• Selecting the proper film and developing the optimal radiographic technique for a
particular component depends on a number of different factors;
• Composition, shape, and size of the part being examined and, in some cases, its
weight and location.
• Type of radiation used, whether X-rays from an X-ray generator or gamma rays from
a radioactive source.
• Kilovoltage available with the X-ray equipment or the intensity of the gamma
radiation.
• Relative importance of high radiographic detail or quick and economical results.
132

133. Film Packaging
• Radiographic film can be purchased in a number of different packaging options
and they are available in a variety of sizes.
• The most basic form is as individual sheets in a box. In preparation for use, each
sheet must be loaded into a cassette or film holder in a darkroom to protect it
from exposure to light.
133

134. • Industrial X-ray films are also available in a form in which each sheet is
enclosed in a light- tight envelope.
• The film can be exposed from either side without removing it from the
protective packaging.
• A rip strip makes it easy to remove the film in the darkroom for processing.
134

135. • Packaged film is also available in the form of rolls where that allows the
radiographer to cut the film to any length.
• The ends of the packaging are sealed with electrical tape in the darkroom.
• In applications such as the radiography of circumferential welds and the
examination of long joints on an aircraft fuselage, long lengths of film offer great
economic advantage.
135

136. Film Handling
• X-ray film should always be handled carefully to avoid physical strains, such as
pressure, creasing, buckling, friction, etc.
• Whenever films are loaded in semi-flexible holders and external clamping
devices are used, care should be taken to make sure pressure is uniform.
• Marks resulting from contact with fingers that are moist or contaminated with
processing chemicals, as well as crimp marks, are avoided if large films are
always grasped by the edges and allowed to hang free.
• Use of envelope-packed films avoids many of these problems until the envelope
is opened for processing.
136

137. Intensifying screens
• The radiographic image is formed by only approximately 1% of the amount of
radiation energy exposed at the film.
• The rest passes through the film and is consequently not used.
• To utilize more of the available radiation energy, the film is sandwiched between
two intensifying screens.
• The screens help to cut down the exposure time by utilizing more effectively the
radiations reaching the film.
• The intensification effect is primarily due to the liberation of photoelectrons from
the screen.
• Different types of materials are being used for this purpose.
 Lead screens
 Steel and copper screens
 Fluorescent screens
 Salt screens
 Fluorometallic screens 137

138. Lead screens
• Under the impact of X-rays and gamma-rays, lead screens emit
electrons to which the film is sensitive.
• In industrial radiography this effect is made use of: the film is
placed between two layers of lead to achieve the intensifying
effect and intensity improvement of approximately factor 4 can be
realized.
• This method of intensification is used within the energy range of
80 keV to 420 keV, and applies equally to X-ray or gamma-
radiation, such as produced by Iridium192.
138

139. • Intensifying screens are made up of two homogeneous sheets of lead foil (stuck on
to a thin base such as a sheet of paper or cardboard) between which the film is
placed: the so called front and back screens.
• The thickness of the front screen (source side) must match the hardness of the
radiation being used, so that it will pass the primary radiation while stopping as
much as possible of the secondary radiation (which has a longer wavelength and is
consequently less penetrating).
• The surface of lead screens is polished to allow as close a contact as possible with
the surface of the film.
• Flaws such as scratches or cracks on the surface of the metal will be visible in the
radiograph and must, therefore, be avoided.
139

140. Steel and copper screens
• For high-energy radiation, lead is not the best material for intensifying
screens.
• With Cobalt60 gamma-rays, copper or steel have been shown to
produce better quality radiographs than lead screens.
• With megavoltage X-rays in the energy range 5-8 MeV (linac) thick
copper screens produce better radiographs than lead screens of any
thickness.
140

141. Fluorescent screens
• The term fluorescence (often mistaken for phosphorescence) is used to indicate
the characteristic of a substance to instantly emit light under the influence of
electromagnetic radiation.
• The moment radiation stops, so does the lighting effect.
• This phenomenon is made good use of in film based radiography.
• Certain substances emit so much light when subjected to ionising radiation, that
they have considerably more effect on the light sensitive film than the direct
ionising radiation itself..
141

142. Salt screens
• These are fluorescent screens consisting of a thin, flexible base coated with a
fluorescent layer made up from micro- crystals of a suitable metallic salt (rare earth;
usually calcium tungstate) which fluoresce when subjected to radiation.
• The radiation makes the screen light up.
• The light intensity is in direct proportion to the radiation intensity.
• With these screens a very high intensification factor of 50 can be achieved, which
means a significant reduction in exposure time.
• The image quality, however, is poor because of increased image
unsharpness.
142

143. Fluorometallic screens
• Apart from fluorescent and lead intensifying screens, there are
fluorometallic screens which to a certain extent combine the advantages
of both.
• These screens are provided with a lead foil between the film base and
the fluorescent layer.
• This type of screen is intended to be used in combination with so-called
RCF-film (Rapid Cycle Film).
• The degree of intensification achieved largely depends on the spectral
sensitivity of the X-ray film for the light emitted by the screens.
143

144. Types of Films
(a) On the basis of photosensitive emulsion layer
i) Single coated
ii) Double coated
(b) On the basis of intensifying screens
i) Screen films
ii) Non-screen films
(c) On the basis of type of emulsion coating
i) Blue light sensitive films
ii) Green light sensitive films (Orthochromatic)
iii) Red light sensitive films (Panchromatic)
(d) On the basis of film speed
i) Standard speed films
ii) Fast speed films
iii) Ultra fast films
144

145. Types of films
Can be divided into 3 groups on the basis of radiography considerations.
• Films for use with salt screens, also known as salt screen films.
• Films for use with metal screens or without screens also called direct films. This
group covers a large range of film speeds.
• Films used for special purposes, such as single emulsion films.
145

146. i) Salt screen films
• These are used with salt screens.
• Salt screens are fluorescent screens consisting of a thin, flexible base coated with a
fluorescent layer made up from micro-crystals of a suitable metallic salt (usually
calcium tungstate) which fluoresce when subjected to radiation.
• The use of salt screens causes loss of definition and hence these films should be used
where their disadvantages are clearly understood and tolerable.
• For about 90% of the medical work, salt screen films are used.
146

147. ii) Direct films
• Generally used with metal screens.
• This group covers industrial films and some of the medical films.
• The contrast of industrial film increases as density increase, whereas that of a
medical film readily react as a maximum with increasing density.
• Industrial films have coating weights, which are usually between 2-2.5 times those
of normal screen type medical films.
147

148. iii) Special purpose films
• These find less frequent use in radiography and are discussed below.
• a) Fluorographic films
• These films are used for photographing a fluorescent screen on which X-ray image
has been projected.
• These films are usually sensitive to blue or blue-green glow emitted by the screen
in use.
• They differ from normal X-ray films in that they are coated on one side only.
148

149. b) X-ray paper
• Instant cycle X-ray papers are the latest addition to the family of X-ray films.
• When used in instant cycle processor units, these papers develop to completion
within seconds by the developing agents contained in the emulsion.
• Good for fast radiographic examinations.
• This paper is cheap compared to X-ray films and processing cost is very low.
149

150. Film Processing
• As mentioned previously, 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 X-rays, gamma rays or light rays strike the crystals or grains, some of the Br-
ions are liberated leaving the Ag+ ions.
• In this condition, the radiograph is said to contain a latent (hidden) image because the
change in the grains is virtually undetectable, but the exposed grains are now more
sensitive to reaction with the developer.
150

151. • 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.
151

152. 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.
4. Washing: The film is washed with water to remove all the processing chemicals.
5. Drying: The film is dried for viewing.
Film processing is a strict science governed by rigid rules of chemical concentration,
temperature, time, and physical movement.
Whether processing is done by hand or automatically by machine, excellent
radiographs require a high degree of consistency and quality control.
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153. Viewing Radiographs
• After the film processing, radiographs are viewed using a light-box (or they can be
digitized and viewed on a high resolution monitor) in order to be interpreted.
• In addition to providing diffused, adjustable white illumination of uniform
intensity, specialized industrial radiography light-boxes include magnifying and
masking aids.
• When handing the radiographs, thin cotton gloves should be worn to prevent
fingerprints on the radiographs.
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154. Interpretation and Evaluation of Test results
1. The common term for film interpretation is film viewing.
2. Film viewing in fact means the evaluation of the image quality of a radiograph for
compliance with the code requirements and the interpretation of details of any possible defect
visible on the film.
3. For this purpose, the film is placed in front of an illuminated screen of appropriate
brightness/luminance.
4. The edges of the film and areas of low density need to be masked to avoid glare.
5. The following conditions are important for good film interpretation:
• brightness of the illuminated screen (luminance)
• density of the radiograph
• diffusion and evenness of the illuminated screen
• ambient light in the viewing room
• film viewer’s eye-sight
6. Poor viewing conditions may cause important defect information on a radiograph to go
unseen. 154

155. • The light of the viewing box must be diffusive and preferably white.
• Radiographs should be viewed in a darkened room, although total darkness is not
necessary.
• Care must be taken that as little light as possible is reflected off the film surface
towards the film viewer.
• If the film viewer enters a viewing room from full daylight, some time must be
allowed for the eyes to adapt to the dark.
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156. • An yearly eye-test for general visual acuity is required while especially sight at close
range needs to be checked.
• The film viewer must be able to read a Jaeger number 1 letter at 300 mm distance
with one eye, with or without corrective aids.
• The trained eye is capable of discerning an abrupt density change/step of 1 %.
• While interpreting, a magnifying glass of power 3 to 4 can be advantageous.
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157. • The film-interpreter
• Apart from the requirements regarding “viewing conditions” and “viewing
equipment” the film- interpreter (film viewer) shall have thorough knowledge of the
manufacturing process of the object being examined and of any defects it may
contain.
• The type of defects that may occur in castings, obviously, differs from those in
welded constructions.
• Different welding processes have their own characteristic defects which the film
interpreter must know to be able to interpret the radiograph.
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158. • To become a qualified NDT operator, various training courses, course materials and
leaflets specifying the requirements they need to comply with, exist.
• The European NDT industry conforms to the qualification standards of the American
ASNT organization.
• So far, a training program for film-interpreter has not been established in similar
fashion.
• Textbooks for example are not uniform.
• Sometimes, the IIW-weld defect reference collection is used, beside which the
instructor usually has his own collection of typical examples, supplemented with
process-specific radiographs.
• ASTM has a reference set of defects in castings available.
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159. Radiograph Interpretation - Welds
• In addition to producing high quality radiographs, the radiographer must also be skilled
in radiographic interpretation.
• Interpretation of radiographs takes place in three basic steps: (1) detection, (2)
interpretation, and (3) evaluation.
• All of these steps make use of the radiographer's visual acuity.
• Visual acuity is the ability to resolve a spatial pattern in an image.
• The ability of an individual to detect discontinuities in radiography is also affected by
the lighting condition in the place of viewing, and the experience level for recognizing
various features in the image.
• The following material will help to develop an understanding of the types of defects
found in weldments and how they appear in a radiograph.
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160. Discontinuities
• Discontinuities are interruptions in the typical structure of a material.
• These interruptions may occur in the base metal, weld material or "heat
affected" zones.
• Discontinuities, which do not meet the requirements of the codes or
specifications used to invoke and control an inspection, are referred to as
defects.
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161. General Welding Discontinuities
The following discontinuities are typical of all types of welding.
Cold lap is a condition where the weld filler metal does not properly fuse with the base
metal or the previous weld pass material (interpass cold lap). The arc does not melt the
base metal sufficiently and causes the slightly molten puddle to flow into the base
material without bonding.
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162. 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.
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163. 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.
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164. 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.
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165. 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.
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166. Radiograph Interpretation - Castings
• The major objective of radiographic testing of castings is the disclosure of defects that adversely affect the
strength of the product.
• Castings are a product form that often receive radiographic inspection since many of the defects produced by
the casting process are volumetric in nature, and are thus relatively easy to detect with this method.
• These discontinuities of course, are related to casting process deficiencies, which, if properly understood, can
lead to accurate accept-reject decisions as well as to suitable corrective measures.
• Since different types and sizes of defects have different effects of the performance of the casting, it is
important that the radiographer is able to identify the type and size of the defects.
• ASTM E155, Standard for Radiographs of castings has been produced to help the radiographer make a
better assessment of the defects found in components.
• The castings used to produce the standard radiographs have been destructively analyzed to confirm the
size and type of discontinuities present.
• The following is a brief description of the most common discontinuity types included in existing
reference radiograph documents (in graded types or as single illustrations).
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167. Radiographic indications for castings
Gas porosity or blow holes are caused by accumulated gas or air which is trapped by the metal.
These discontinuities are usually smooth- walled rounded cavities of a spherical, elongated or
flattened shape. If the sprue is not high enough to provide the necessary heat transfer needed to force
the gas or air out of the mold, the gas or air will be trapped as the molten metal begins to solidify.
Blows can also be caused by sand that is too fine, too wet, or by sand that has a low permeability so
that gas cannot escape.
167

168. Sand inclusions and dross: are nonmetallic oxides, which appear on the radiograph as
irregular, dark blotches. These come from disintegrated portions of mold or core walls and/or
from oxides (formed in the melt) which have not been skimmed off prior to the introduction
of the metal into the mold gates. Careful control of the melt, proper holding time in the ladle
and skimming of the melt during pouring will minimize or obviate this source of trouble.
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169. Cracks are thin (straight or jagged) linearly disposed discontinuities that occur after the
melt has solidified. They generally appear singly and originate at casting surfaces.
Cold shuts generally appear on or near a surface of cast metal as a result of two streams of
liquid meeting and failing to unite.
They may appear on a radiograph as cracks or seams with smooth or rounded edges.
169

170. Inclusions are nonmetallic materials in an otherwise solid metallic matrix. They may be less
or more dense than the matrix alloy and will appear on the radiograph, respectively, as darker
or lighter indications. The latter type is more common in light metal castings.
170

171. Safety aspects required in Radiography
Radiation Health Risks
• The health risks associated with the radiation is considered to be
one of the major disadvantages of radiography.
• The amount of risk depends on the amount of radiation dose received, the time over
which the dose is received, and the body parts exposed.
• The fact that X-ray and gamma-ray radiation are not detectable
by the human senses complicates matters further.
• However, the risks can be minimized and controlled when the radiation is handled and
managed properly in accordance to the radiation safety rules.
• The active laws all over the world require that individuals working in the field of
radiography receive training on the safe handling and use of radioactive materials and
radiation producing devices.
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172. • The occurrence of particular health effects from exposure to
ionizing radiation is a complicated function of numerous factors.
Type of radiation involved.
• All kinds of ionizing radiation can produce health effects.
• The main difference in the ability of alpha and beta particles and
gamma and X-rays to cause health effects is the amount of energy
they have.
• Their energy determines how far they can penetrate into tissue and
how much energy they are able to transmit directly or indirectly to
tissues.
172

173. Size of dose received
• The higher the dose of radiation received, the higher
the likelihood of health effects.
Rate at which the dose is received
• Tissue can receive larger dosages over a period of time. If
the dosage occurs over a number of days or weeks, the
results are often not as serious if a similar dose was received
in a matter of minutes.
Part of the body exposed
• Extremities such as the hands or feet are able to receive a
greater amount of radiation with less resulting damage
than blood forming organs housed in the upper body.
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174. The age of the individual
• As a person ages, cell division slows and the body is less sensitive to
the effects of ionizing radiation. Once cell division has slowed, the
effects of radiation are somewhat less damaging than when cells
were rapidly dividing.
Biological differences
• Some individuals are more sensitive to radiation than others.
Studies have not been able to conclusively determine the cause of
such differences.
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175. Controlling Radiation Exposure
• When working with radiation, there is a concern for two types of
exposure: acute and chronic.
• An acute exposure is a single accidental exposure to a high dose
of radiation during a short period of time.
• Chronic exposure, which is also sometimes called “continuous
exposure”, is long-term, low level overexposure.
• Chronic exposure may result in health effects and is likely to be
the result of improper or inadequate protective measures.
175

176. The three basic ways of controlling exposure to harmful
radiation are:
• 1) limiting the time spent near a source of radiation,
• 2) increasing the distance away from the source,
• 3) and using shielding to stop or reduce the level of radiation.
176

177. 177

178. Applications of Radiographic Testing
• Used to inspect most types of solid materials, both ferrous and non-ferrous alloys as well
as non metallic materials and composites.
• Used to inspect the condition and proper placement of components, for liquid
level measurement of sealed components etc.
• Used extensively for castings, weldments and forgings when there is a critical need to
ensure that the object is free from internal flaws.
• Well suited to the inspection of semiconductor devices for detection of cracks, broken
wires, unsoldered connections, foreign material and misplaced components, whereas other
methods are limited in ability to inspect semiconductor devices
178