NDT Method.pdf

ndt

1. NDT methods
The most common NDT methods used are as
follows :
Ultrasonic Testing.
Magnetic Particle Testing.
Penetrant Testing.
Radiography Testing.
Eddy Current Testing.

2. Ultrasonic Testing
A typical UT inspection system consists of
several functional units, such as the
pulsar/receiver, transducer, and display devices.
A pulsar/receiver is an electronic device that can
produce high voltage electrical pulse. Driven by
the pulsar, the transducer generates high
frequency ultrasonic energy. The sound energy
is introduced and propagates through the
materials in the form of waves. When there is a
discontinuity (such as a crack) in the wave path,
part of the energy will be reflected back from the
flaw surface.

3. Ultrasonic Testing
The reflected wave signal is transformed into
electrical signal by the transducer and is
displayed on a screen. The reflected signal
strength is displayed versus the time from signal
generation to when a echo was received. Signal
travel time can be directly related to the distance
that the signal traveled. From the signal,
information about the reflector location, size,
orientation and other features can sometimes be
gained.

4. Ultrasonic Testing

5. In solids, molecules can support vibrations in other
directions so the number of different types (modes)
of sound waves are possible. On the basis of particle
displacement in the medium ultrasonic waves are
classified as longitudinal waves , transverse waves ,
surface waves and lamb waves . Velocity remains
the same in the given medium but differs when the
method of vibration changes.
Types Of Sound Waves & Propagation

6. •There are four types of sound waves :
•Longitudinal -Parallel to wave direction
•Transverse -Perpendicular to wave direction
•Surface (Rayleigh) -Elliptical orbit
symmetrical mode
•Plate Wave (Lamb) -Component
perpendicular to surface (extensional wave)
Types Of Sound Waves &
Propagation

7. Couplant
The couplant displaces the air and makes it
possible to get more sound energy into the test
specimen so that a usable ultrasonic signal can
be obtained. In contact ultrasonic testing a thin
film of oil, glycerin or water is generally used and
in immersion testing water is between the
transducer and the test surface.

8. Probe Placement for several weld
configuration

9. Probe Placement for several weld
configuration

10. Probe Placement for several weld
configuration

11. Probe Placement for several weld
configuration

12. Probe Placement for several weld
configuration

13. Magnetic Particle Testing
This NDT method is accomplished by inducing a magnetic
field in a ferromagnetic material and then dusting the
surface with iron particles (either dry or suspended in
liquid). Surface and near-surface flaws produce magnetic
poles or distort the magnetic field in such a way that the
iron particles are attracted and concentrated. This
produces a visible indication ofdefect on the surface of
the material.

14. Magnetization
There are basically two types of magnetic field:
1.Longitudinal Magnetic field.
2.Circular Magnetic Field.

16. Circular Magnetic Field for
Longitudinal Defects.
Longitudinal
Magnetic field for
Circular Defects.

17.  Before and after inspection pictures of cracks
emanating from a hole
Examples of Magnetic Particle Indication

18. Penetrant Testing
Penetrant solution is applied to the
surface of a precleaned component.
The liquid is pulled into surface-
breaking defects by capillary action.
Excess penetrant material is carefully
cleaned from the surface. A developer
is applied to pull the trapped
penetrant back to the surface where it
is spread out and forms an indication.
The indication is much easier to see
than the actual defect.

19. Steps of Penetrant Testing
1.Surface Preparation: One of the most critical
steps of a liquid penetrant inspection is the
surface preparation. The surface must be free of
oil, grease, water, or other contaminants that
may prevent penetrant from entering flaws. The
sample may also require etching if mechanical
operations such as machining, sanding, or grit
blasting have been performed. These and other
mechanical operations can smear the surface of
the sample, thus closing the defects.

20. Steps of Penetrant Testing
2. Penetrant Application: Once the surface has been
thoroughly cleaned and dried, the penetrant
material is applied by spraying, brushing, or
immersing the parts in a penetrant bath.

21. Steps of Penetrant Testing
3. Penetrant Dwell: The penetrant is left on the surface for a
sufficient time to allow as much penetrant as possible to be
drawn from or to seep into a defect. Penetrant dwell time is
the total time that the penetrant is in contact with the part
surface. Dwell times are usually recommended by the
penetrant producers or required by the specification being
followed. The times vary depending on the application,
penetrant materials used, the material, the form of the material
being inspected, and the type of defect being inspected.
Minimum dwell times typically range from 5 to 60 minutes.
Generally, there is no harm in using a longer penetrant dwell
time as long as the penetrant is not allowed to dry. The ideal
dwell time is often determined by experimentation and is often
very specific to a particular application.

22. Steps of Penetrant Testing
4. Excess Penetrant Removal: This is a most delicate
part of the inspection procedure because the
excess penetrant must be removed from the
surface of the sample while removing as little
penetrant as possible from defects. Depending on
the penetrant system used, this step may involve
cleaning with a solvent, direct rinsing with water, or
first treated with an emulsifier and then rinsing with
water .

23. Steps of Penetrant Testing

24. Steps of Penetrant Testing
5. Developer Application: A thin layer of developer is then
applied to the sample to draw penetrant trapped in flaws back
to the surface where it will be visible. Developers come in a
variety of forms that may be applied by dusting (dry
powdered), dipping, or spraying (wet developers).

25. Steps of Penetrant Testing
6. Indication Development: The developer is allowed to stand on
the part surface for a period of time sufficient to permit the
extraction of the trapped penetrant out of any surface flaws.
This development time is usually a minimum of 10 minutes
and significantly longer times may be necessary for tight
cracks.

26. Steps of Penetrant Testing
7. Inspection: Inspection is then performed under appropriate
lighting to detect indications from any flaws which may be
present.
8. Clean Surface: The final step in the process is to thoroughly
clean the part surface to remove the developer from the parts
that were found to be acceptable.

27. Used to locate cracks, porosity, and
other defects that break the surface of
a material and have enough volume to
trap and hold the penetrant material.
Liquid penetrant testing is used to
inspect large areas very efficiently
and will work on most nonporous
materials.

28. Radiography Testing
RT involves the use of penetrating gamma-or X-radiation to
examine material's and product's defects and internal features.
An X-ray machine or radioactive isotope is used as a source of
radiation. Radiation is directed through a part and onto film or
other media. The resulting shadowgraph shows the internal
features and soundness of the part. Material thickness and
density changes are indicated as lighter or darker areas on the
film.

29. This variation in radiation produces an image on the detector
that often shows internal features of the test object.
The part is placed between the radiation source and a piece of
film. The part will stop some of the radiation. Thicker and
more dense area will stop more of the radiation.
Used to inspect almost any material for surface and subsurface
defects. X-rays can also be used to locates and measures internal
features, confirm the location of hidden parts in an assembly

30. Advantages of RT
•Can be used to inspect virtually all materials
•Detects surface and subsurface defects
•Ability to inspect complex shapes and multi-
layered structures without disassembly.
•Minimum part preparation is required.

31. Disadvantages
•Extensive operator training and skill required.
•Access to both sides of the structure is usually
required.
•Orientation of the radiation beam to non-volumetric
defects is critical.
•Field inspection of thick section can be time
consuming.
•Relatively expensive equipment investment is
required.
•Possible radiation hazard for personnel.