Non destrictive technique advantage and limitation .ppt

NDT technique

1. WELCOME

2. NDT

3. •Non- destructive testing is a method of
quality control with out impairing their use.
•The material under inspection does not
under go any change in shape, size,
physical and chemical properties.

4. PRINCIPLE
•A beam of energy is admitted in to the specimen.
•The beam either transmitted, reflected or
scattered is detected, processed,analyzed and
evaluated to determine the soundness of the
material for acceptance / rejection.

5. SELECTION OF NDT
Depend up on
- Material
- Manufacturing process
- Type and origin of the defect
- Accessibility
- Cost

6. NDT TYPES
- Methods for detecting internal flaws,
UT & RT
-Methods for detecting surface and
subsurface defects
LPT & MPT

7. •
Radiography
Penetrating capacity of the X or gamma
rays is used to produce a shadow of internal
conditions of the job on a recording medium.
Exposing a film to X or Gamma rays that
have penetrated a specimen, processing the
exposed film and interpreting the results.

8. ADVANTAGES
- Can be used with most materials
- Provides a permanent visual image
- Reveals the internal nature of material
- Discloses fabrication errors
- Reveals structural discontinuities.

9. LIMITATIONS
- Impractical to test specimens of complex
geometry.
- Specimen should have two side accessibility.
- laminar type discontinuities are often
undetected by RT.
- Safety considerations
- Expensive.

10. SAFETY ASPECTS
- Radiation cannot be detected by any of
our five senses.
- Radiation can cause damage to or
destruction of the cells of living tissues.
- Trained / certified personnel are
compulsory.

11. REQUIREMENTS
- An enclosure or cordoned area
- X or gamma source
- Recording medium and its accessories.
- Processing accessories and chemicals
- Evaluating equipments
- Qualified persons.

12. RADIATION
- X or Gamma rays are family of
electromagnetic waves.
- Travel at the velocity of light (186000
Miles per second ).
- Travel in straight lines.
- Not affected by magnetic field
- will expose photographic film.
- Have penetrating power.

13. STUCTURE OF ATOM
Every atom has three particles
- Proton: has positive charge
- Neutron : has no electrical charge.
- Electron: has negative charge.

14. IDENTIFICATION OF ELEMENTS
-Atomic number: The no. of protons in the
nucleus. ( Z )
-Mass number: The no.of protons and
neutrons in the nucleus. ( A )
A = Z + N
- Where N is no. of neutrons in the nucleus.

15. – The no. of protons in the nucleus of an
atom determines the structure and
characteristics of the element.
General representation:
4 16 2
He O H
2 8 1

16. Radioactive Materials
•Elements with a common Z number and
different A number are called isotopes.
Common radioisotopes:
Radium 226 ( Ra – 226 )
Cesium 137 ( Ce – 137 )
Cobalt 60 ( Co – 60 )
Iridium 192 ( Ir- 192)
Thulium 170 ( Tm – 170 )

17. ISOTOPES

Artificial isotopes are created by bombarding
an element with an excess of neutrons by
fission process in a nuclear reactor .
This increases the A number of an element.

18. •These excess neutrons do up set the balance
of the nucleus.
•The isotope is unstable and disintegrate
continuously to become stable.
•Unstable atoms are radioactive.
•During disintegration tiny particles
traveling at high speed are emitted in the
wave form.

19. - Naturally occurring isotopes:
- Uranium & Radium
-Artificially produced:
- Co-60,
- Iridium – 192
- Cesium - 137

20. Measurement of radioactivity
• The basic unit of radioactive material is
CURIE
•37 Billion of its atoms disintegrate in one
second is called one curie.

21. HALF – LIFE PERIOD
•The half – life of an isotope is the time it
takes for half of the atoms to decay or
become stable .
•Every isotope has its own peculiar HLP
ranging from microseconds to years .

22. HLP
•HLP of common isotopes
•Radium 226 : 1620 years
•Cesium 137: 30 years
•Cobalt 60: 5.3 years
•Thulium 170:130 days
•Iridium 190: 75 days

23. UNITS OF RADIATION
•One ROENTGEN is the quantity of
Ionizing radiation that produces 2,083
million ion pairs in one CU.CM of air.
•The MILLIROENTGEN is used in the
measurement of personnel exposure ( MR )

24. PERMISSIBLE DOSSAGE
•For users: 2R / year or 40 MR /week.
•For public: 100 MR / year or 2MR/week.

25. source
-Two kinds of radiation used in
Radiography are Gamma rays and X-rays.
- Except for their sources, Gamma and
X-rays are exactly the same kind of
radiation.

26. RADIATION DETECTORS
•Pocket Dosimeter
•Film Badge
•Survey Meter
•Gamma area Monitor

27. ADVANTAGES OF ISOTOPES
•The cost of the equipment and source is
lesser than X-ray machines.
•Can be transported easily.
•Source is small enough to pass through
small openings.
•No external power source is required.
•High penetrating power.
•Both panoramic and directional exposures
can be done.

28. DISADVANTAGES
•Radiation cannot be turned off.
•The shielding necessary.
•Radiography general less contrast
•Penetration ability cannot be changed.
•Highly hazardous.

29. X-RAY EQUIPMENT
•Having a source of electrons.
•X-rays are generated when free high speed
electron gives up some of its energy during
interaction with the orbital electrons.

30. TECHNIQUES
•Single wall single image.
•Double wall, double image
•Double wall single image.
•Panoramic exposure

31. RADIOGRAPHY FILM
•The recording medium is known as film.
•PROPERTIES;
•Transparent
•Flexible
•Light weight
•Inert
•Stable/firm

32. FILM CONSTRUCTION
•Central part of the film is bas e.
•Material:Polyesters,(0.175mm)
•Emulsion—Silver Bromide (Ag.Br)
•Thick ness; 0.01 to 0.02mm
•Protective layer: Gelatine (0.002mm)

33. EXPOSURE TIME
•Based on strength of the source.
•Thickness of the job.
•Source to film distance.
•Job material.

34. •Sensitivity: is the measure of accuracy of
the job.
•Contrast:Sharpness of the boundry of the
defect.
•DENSITY:Blackening of the film is
measured in terms of optical density.

35. IQI
•Used to judge the quality of radio-graph
•Made of same material
•It is a permanent evidence.
Dia of smallest wire X 100
% of sensitivity: --------------------------------
Thickness of the job

36. TECHNIQUES
•Selection of a technique is bassed on type
of the job.
•SWSI: For butt welds.
•DWSI: Pipes of dia more than 80 MM
off set source by 10 degrees.

37. •DWDI: -Pipe of diameter 80 MM
-Source off set is required
-Minimum two exposures are required
taken with 90 degree shift.
PANORAMIC: More than one film is exposed at
time. Films are placed around the job.
-Source is placed at the middle of the job.
-All films are exposed at a time.

38. FILM LOADING
•Cutting the film to the required size .
•Film in to be kept in between two lead
screens of same size.
•Film and lead screens are to be inserted in
to two plastic envelopes.
•The whole process is to be done in dark
room.

39. FILM PROCESSING
•To transform the invisible latent image.to a
visible and permanent image.
•There are four stages involved in the film
processing.
»Development
»Fixing
»Washing
»Drying

40. DEVELOPMENT
•Chemical used: Hydroquinone & Metol
•Time duration: 5min
•The exposed silver halide got reduced to
Metallic silver and latent image is formed.
- To be processed at 20deg

41. •Stop bath: Running water for 2min
•Fixing bath: The fixer reacts with
undeveloped silverbromide and transform
into water soluble compound.
•Agent: Sodium thio sulphate &
Ammonium thio sulphate
- Duration: 10min

42. DRYING
•The excess water is removed by drying.
•Hot air of temp. 38 – 40* C is used.
•Film is very convenient to handle.

43. VIEWING
•By using illuminator industrial radiography
films can be inspected.
-Magnifying glass (3X) can also be used.
-Defects are to be located and interperated
with the standards.

44. DEFECTS
•Gas inclusions
•Slag inclusions
•Lack of penetration
•Cracks
•Lack of fusion
•Tungsten inclusions
•Grooves

45. •Concavity
•Excessive Reinforcement
•Overlap
•Excessive penetration
•Undercutting
•Mismatch

46. THANK YOU