5. Introduction to NDT:
› An industrial product is designed to perform certain
function. It is basically designed to give trouble free
service without pre-mature failure.
› The trouble free service given by the product is called
reliability, and the product given trouble free service is
called reliabile product.
› The reliability of machine or structure further depends on
the reliability of the individual components.
› It is important that each individual component must be
reliable and perform its function smoothly for the pre-
assessed life.
6. › The quality of products components or structural parts
depends on many factors such as design , properties of
raw material used and fabrication techniques.
› Qualities is related to the defects , which reduce the
performance of the finish product.
› Knowledge of these defects with a view to detect and
evaluate them and then minimizing them in the product is
essential to achieve improved and acceptable level of
quality.
› Some common flaws found in metallic products are
seems sub-surface flaws and cracks resulting from
quenching and fatigue.
› There is a need to develop methods by which flaws in the
finished products can be detected or examined with out
affecting their performence.
7. › NDT is one such class of techniques widely used in
industry.
› Use of NDT of engineering materials , components and
structures has been gaining lot of interest to improving
the quality and the reliability of the product particularly
in the field of:
Atomic power
Aerospace
Defense
› The scope of NDT is very wide and includes the
measurement of properties and the detection of
defects which effects the performance of test
components.
8. Basic Objective of NDT:
Probability of survival.
Detection of defects and disorders.
Size , shapes and orientation of flaw.
Thickness measurement
Assessment of surface finish
Structure analysis.
11. Visual Inspection:
› Visual inspection of a component is the fastest and
the cheapest method of NDT.
› NDT should be used as the foremost method to
reveal gross surface flaws so that detection of any
flaw leads to immediate rejection of the component
under examination.
› Thus saving a lot of money and time which would
otherwise be spent on more complicated and
relatively time consuming methods.
› Visual Inspection can reveal surface defects or flaws
such as weld cracks, weld seams, weld undercutting
, surface porosity of weld and casting etc.
12. BASIC PRINCIPLES:
› Illuminating the test specimen with light invisible region.
› Specimen is examined with the aid of eye ,magnifying
glass and microscope or by light sensitive device such as
photo cell.
› Best result of a visual inspection is the contrast between
the defect and the background must be good.
› To achieve this contrast etching is to be done.
› IN many instances the area under examination should be
cleaned to reveal hair line flaws and to inspect the surface
with the aid of optical means such as magnifying glass or
optical microscope at low magnification.
13. Instruments for Visual Inspection:
Bore scope:
An instrument which is used to
inspect the inside of the narrow tube , bore or chamber.
Endoscope:
An instrument which is similier to
boroscope but much easier to use,and is used to detect
the internal flaws.
14. Applications:
General inspection of the component for the presence or
absence of corrosion or erosion product or cracking due
to them.
Inspection of thin walled tubular component for leakage.
Defects such as seams , tear cracks , porosity ,mismatch
, gross surface cracks etc.
Minute discontinuities in pumps , compressors , turbo
generators parts and instruments etc.
15. Liquid Penetrant Inspection(LPI):
Liquid penetrant testing is one of the oldest and
simplest NDT methods.
This method is used to reveal surface discontinuities by
bleed out of a colored or fluorescent dye from the flaw.
The advantage that a liquid penetrant inspection offers
over an unaided visual inspection is that it makes defects
easier to see for the inspector .
16. Steps Of Liquid Penetrant:
The exact procedure for liquid penetrant testing can vary
from case to case depending on several factors such as:
The penetrant system being used,
The size and material of the component being
inspected,
The type of discontinuities being expected in the
component and
The condition and environment under which the
inspection is performed.
18. Surface Preparation:
› One of the most critical steps of a liquid penetrant
testing 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 metal
over the flaw opening and prevent the penetrant from
entering.
19. Penetrant Application:
› Once the surface has been thoroughly cleaned and
dried, the penetrant material is applied by spraying,
brushing, or immersing the part in a penetrant bath.
20. 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 discontinuity being
inspected for.
21. › Minimum dwell times typically range from five 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 may be very specific to a particular
application.
22. Excess Penetrant Removal:
This is the 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.
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 powders), dipping, or spraying
(wet developers).
23. 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. Significantly longer times may be
necessary for tight cracks.
24. Inspection:
Inspection is then performed under appropriate
lighting to detect indications from any flaws
which may be present.
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.
26. Advantages:
› High sensitivity (small discontinuities can be detected).
› Rapid inspection of large areas and volumes.
› Suitable for parts with complex shapes.
› Indications are produced directly on the surface of the
part and constitute a visual representation of the flaw.
› Portable (materials are available in aerosol spray cans).
› Low cost (materials and associated equipment are
relatively inexpensive).
27. Disadvantages :
› Only surface breaking defects can be detected.
› Only materials with a relatively nonporous surface can be
inspected.
› The inspector must have direct access to the surface
being inspected.
› Surface finish and roughness can affect inspection
sensitivity.
› Post cleaning of acceptable parts or materials is
required.
› Chemical handling and proper disposal is required.
28. RADIOGRAPHIC INSPECTION:
Radiography inspection of NDT makes use of very short
wavelength electromagnetic radiations, namely, X-rays and
Gamma-rays.
These rays are generally penetrable through the solid
materials and are partially absorbed by the medium.
The amount of absorption that occurs will depend on the
density and thickness of the material through which the
radiation pass and also the characteristic of the radiation.
The radiation that passes through the material can be
detected and recorded on either a photographic film or
viewed on a fluorescent screen.
It can be detected and monitored by electronic sensing
equipment.
29. The term radiography can be defined as a process in
which an image is produced on a radiation sensitive film.
This technique is one of the most widely used NDT
methods for the detection of internal defects such as
porosity , inclusion and voids.
30. BASIC PRINCIPLE OF RADIOGRAPHIC
INSPECTION:
The object to be examined is placed on the path of the beam of
radiation of short wavelength (X-rays and gamma rays) source.
A photographic film is placed on the other side of the object.
Some of the radiations will be absorbed by the material ,but
some will travel through object and producing a latent image.
When the film is developed there will be a picture of dark and
light areas.
The dark areas represent the parts of the object having lower
density ,these parts may be the flaws such as pore or void in the
material.
31. › Figure:
Figure shows the principle of radiography in which the
specimen having the stepped shape block with thick and
thin steps and containing pore and an inclusion is exposed
to short wavelength radiations.
The developed radiograph shows a regions of variation in
darkness.
32. › The thin section of the object allowed more radiations to
pass through , and therefore, appear dark region on the
radiograph.
› The same effect is found in the area of porosity but this
region is darkest in the radiograph.
› On the other hand, the inclusion ,being denser than the
surrounding material ,absorbs more radiations therefore
produce light area on the photographic film.
› Basically, it is the contrast (density difference) on the film
that allows an observer to detect flaws in the specimen.
34. APPLICATIONS:
› Commonly employed to examine the welded products
such as:
Weld in pressure vessels
Bridge construction
Power projects
› Casting for blow holes and other flaw
› Radiography also used to measure the thickness of the
material.
