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Overview of NDT
1. KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY
(AUTONOMOUS)
NAMAKKAL- TRICHY MAIN ROAD, THOTTIAM
DEPARTMENT OF MECHANICAL ENGINEERING
NON DESTRUCTIVE TESTING AND EVALUATION
SEVENTH SEMESTER
2. UNIT I OVERVIEW OF NDT
NDT Versus Mechanical testing, Overview of the
Non Destructive Testing Methods for the
detection of manufacturing defects as well as
material characterisation. Relative merits and
limitations, Various physical characteristics of
materials and their applications in NDT., Visual
inspection –Unaided and aided.
4. INTRODUCTION
What is NDT?
• NDT stands for Non-Destructive Testing.
• As its name implies, non-destructive testing
means testing of materials without destroying
them.
• A non-destructive test is an examination of an
object which will not produce any kind of
damage or destruction to the sample.
5. Definitions
(i)Non-destructive testing is the process of inspecting,
testing, or evaluating materials, components or assemblies
for discontinuities, or differences in characteristics
without destroying the serviceability the part or system.
In other words, when the inspection or test is completed,
the part can still be used.
(ii)NDT is an examination that is performed on an object
of any type, size, shape or material to determine the
presence or absence of discontinuities, or to evaluate other
material characteristics.
6. Definitions conti..
(iii)NDT is a procedure which covers the inspection and/or
testing of any material, component or assembly by means
which do not affect its ultimate serviceability
(iv) NDT is the examination of an object with the technology
that does not affect the object's future usefulness.
(v) NDT means the use of non-invasive techniques i) to
determine the integrity of a material, component or structure,
or ii) to characteristics of an object.
(vi) NDT refers to technology that allows a component to be
inspected for serviceability, without impairing its usefulness.
7.
8. Objectives of NDT
• Materials sorting;
• Materials characterization;
• Property monitoring (for process control);
• Thickness measurement;
• Defect detection/location; and
• Defect characterization.
However the major task of NDT is to detect and identify the
range of defects.
Defects can include production flaws such as heat treatment
cracks, grinding cracks, inclusions (of many types), voids
(pores), and fatigue cracks (generated during service).
9. What are Some Uses of NDE
Methods?
• Flaw Detection and Evaluation
• Leak Detection
• Location Determination
• Dimensional Measurements
• Structure and Microstructure Characterization
• Estimation of Mechanical and Physical Properties
• Stress (Strain) and Dynamic Response Measurements
• Material Sorting and Chemical Composition Determination
10. INTRODUCTION TO MATERIALS
TESTING
Purposes of Materials Testing(Why are Materials Tested?)
(i)To determine and evaluate various properties of materials both
quantitatively and qualitatively.
(ii) To detect and evaluate the surface or sub-surface defects in
raw materials or processed parts.
(iii) To check chemical composition.
(iv) To determine suitability of a material for a particular
application.
(v) To predict the strength and serviceability of the materials.
12. 1.Destructive tests
In this type of testing, the component or specimen to be tested
is destroyed and cannot be reused.
Definition:
As the name suggests, destructive testing (DT) includes
methods where the component or specimen is broken down
in order to determine physical and mechanical properties
such as strength, toughness and ductility.
Destructive testing is generally more suitable and
economical for mass produced objects, as the cost of
destroying a small number of pieces is negligible.
It is usually not economical to do destructive testing where
only one or very few items are to be produced.
13. Examples of destructive test
Tensile test
Compression test
Shear test
Hardness test
Impact test
Fatigue test
Creep test
Bending test
Torsion test
Chemical analysis, etc
19. Benefits of destructive testing
• To verify properties of a material.
• To determine quality of welds.
• To reduce failures, accidents and costs.
• To ensure compliance with regulations.
20. 2.Non-Destructive Tests
In this type of testing, the
component or specimen to be
tested is not destroyed and
can be reused after the test.
As its name implies,
non-destructive testing
means testing of components
or specimens without
destroying them.
21. Applications of NDT
• Nondestructive testing methods are routinely applied in industries where a
failure of a component would cause significant hazard or economic loss,
such as in transportation, pressure vessels, building structures, piping, and
hoisting equipment.
• To ensure product integrity and reliability.
• To control manufacturing processes.
• To lower production costs.
• To maintain a uniformity in quality level.
NDT tests can be performed on part:
(i) during manufacture, or
(ii) after manufacture, or
(iii) even on parts that are already in service
22. Features of NDT:
Using NDT, an entire production lot can be inspected, or selected
samples can be inspected.
Also different tests can be applied to the same item, either
simultaneous or sequentially, and the same test can be repeated on
the same specimen for additional verification.
It may be added that the NDT equipment is often portable. This
permits the use of NDT methods for on-site testing in most
locations.
Because NDT does not permanently alter the specimen being
inspected, it is a high valuable technique that can save both time and
money in product evaluation, trouble shooting, and research.
Non-destructive tests make components more reliable, safe and
economical
23. Objectives of NDT
(i) To detect internal or surface flaws
(ii) To measure the dimensions of the specimen.
(iii) To determine a material's structure or chemistry
(iv) To evaluate a material's physical or mechanical
properties.
24. Basic elements of Non-Destructive Testing
• Source or probing medium
• Detector
• Recorder
• Interpretation
25. (i)Source or probing medium
Source can be some probing medium that can be used
to inspect the specimen under test.
The source/probing medium can be liquid penetrant,
magnetic particle, ultrasonic wave, radiations, etc.
This probing medium must be changed or modified as a
result of which the discontinuities with the specimen can
be studied.
26. (ii)Detector
A sensitive detector or sensor which is capable of
detecting the changes in the probing medium.
(iii) Recorder
A recorder or indicator is used to indicate or
record the response from the detector,
(iv) Interpretation
Various means of interpreting the recorded results
through peaks, graphs, bar diagrams, etc.
27. Destructive tests Vs. Non-destructive
tests
Suitability:
• DT is generally performed when the
component or specimen can no longer be used
in service or is readily replaceable.
• NDT can be performed on component or
specimen which is in service.
28. Destructive tests Vs. Non-destructive
tests Conti….
Advantages of DT:
• Provides a direct and reliable measurements
• Provides quantitative measurements
• Result interpretation is easy.
• Can be performed without very high skilled
personnel
• Correlation between test measurements and
material properties is direct.
29. Destructive tests Vs. Non-destructive
tests Conti….
Advantages of NDT:
• Tests are done directly on the object.
• 100% testing (or representative samples) on
actual components can be performed.
• Different NDT methods can be applied on the
same component and hence many or all properties
of interest can be examined.
• Most NDT methods are quick and low labour
cost.
30. Destructive tests Vs. Non-destructive
tests Conti….
Disadvantages of DT:
• Tests are performed only to a sample and the
sample may not be a representative of the
group.
• Tested parts are destroyed during testing.
• Usually cannot repeat a test on the same
specimen
• Usually cannot use the same specimen for
multiple destructive testing
31. Destructive tests Vs. Non-destructive
tests Conti….
Disadvantages of NDT:
• Measurement are indirect
• Reliability is to be verified.
• Measurements are often qualitative or
comparative.
• Result interpretation is often difficult.
• Skilled personnel are required for testing and
result interpretation.
• Different observers may interpret the test results
differently
32. Methods of NDT
(i) Visual Inspection (VI)
(ii) Liquid Penetration Testing(LPT)
(iii) Magnetic Particle Testing (MPI)
(iv) Thermography
(v) Eddy current testing
(vi) Ultrasonic testing
(vii) Acoustic emission testing
(viii)Laser testing
(ix) Radiographic testing
(x) Leak testing
34. Introduction to Visual Testing
(VT)
• Visual testing is the most common, Simplest,
fastest and most widely used nondestructive
testing method.
• Visual testing can be done by looking at the
test piece directly (naked eye), or by using
optical instruments such as magnifying
glasses, mirrors, borescopes and computer-
assisted viewing systems.
• Visual examiners follow procedures that range
from simple to very complex.
35. Visual Inspection
• Portable video inspection unit with zoom
allows inspection of large tanks and vessels,
railroad tank cars, sewer lines.
• Robotic crawlers permit observation in
hazardous or tight areas, such as air ducts,
reactors, pipelines.
36. Characteristics detected in VT
• To detect surface characteristics such as finish,
scratches, cracks or color
• To check the strain in transparent materials
• To inspect corrosion
37. VT Applications
• VT can be applied to inspect castings,
forgings, machined components and welds and
is used in all branches of industry.
• Examining the surface condition of a
component
• Examining alignment of mating surfaces
• Checking presence of leaks
38. VT Advantages
• Simple method to perform
• Examination can be performed quickly
• Low-cost method
• Minimal training
• Minimal equipment
• Test speed is high
39. VT Disadvantages
• Inspector training necessary
• Good eyesight required or eyesight corrected
to 20/40
• Limited to detection of surface flaws
• Can miss internal defects
• Report must be recorded by inspector
• Open to human error
41. Introduction to Liquid Penetrant Inspection
• The principle of liquid penetrant tests is that the liquid
penetrants are drawn into surface flaws such as cracks
or porosities by capillary action. Then the developer
material in conjunction with visual inspection reveals
the surface flaw.
• The penetrant used is often loaded with a fluorescent
dye and the inspection is done under UV light to
increase test sensitivity.
42. Characteristics detected in LPI
• To locate cracks, porosity and other defects
that breaks the surface as a material and has
enough volume to trap and hold the penetrant
material.
• To inspect large areas very effectively and will
work on most non-porous materials.
43. Liquid Penetrant Inspection
1. Surface Preparation
2. Penetrant Application
3. Penetrant Dwell
4. Excess Penetrant Removal
5. Developer Application
6. Indication Development
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.
44.
45. Applications of (LPT)
Inspection of tools and dies
Inspection of tank, piping, and pumps
in the chemical, petrochemical, food,
paper and processing industries
Inspection of diesel locomotive,
trucks and automobile parts
Inspection of aircraft engine parts,
propellers, wing fittings and castings
Comments
Messy; need good ventilation.
46. Advantages & Limitations of (LPT)
Advantages
Inexpensive; easy to apply; more sensitive than
visual alone; use on most materials; rapid;
portable; applicable to complex shapes
Limitations
Surface only; not useful on hot, dirty, painted, or
very rough surfaces; Cleaning of material after
testing
47. Introduction to Magnetic Particle
(MPT)
Magnetic particle Test (MPT) is used
for the testing of material which can
be easily magnetized.
This method is capable of detecting
surface and subsurface flaws such as
cracks and inclusions.
Steps:
i) Magnetizing the test specimen
ii) Applying magnetic particles on
the test specimen
iii) Locating the defects
48. Basic Principles of Magnetic Particle
(MPT)
• When a bar magnet is broken in the center of its length,
two complete bar magnets 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.
49. Basic Principles cont’
• If iron particles are sprinkled on a cracked
magnet, the particles will be attracted to the
poles at the edges of the crack.
50. 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
51. Applications of (MPT)
• Inspection of fans and blowers
in thermal power plant
• Inspection of weld cracks
• Inspection of connecting rods
• Underwater inspections such as
offshore structural welds,
pipeline inspection and ship
sturucture.
• Comments
Messy. Can cause defects.
52. Advantages& Limitations
of (MPT)
• Advantages
Low cost; fast; more sensitive to tight
cracks than LPT; can do near
subsurface; portable.
• Limitations
Material must be ferromagnetic;
surface must be clean; part may be
demagnetized; alignment of field is
important; High current source
required
53. Ultrasonic Testing (UT)
• Ultrasonic Testing (UT) uses
piezoelectric Crystals to
produce high frequency sound
energy to conduct examinations
and make measurements.
• Ultrasonic inspection can be
used for:
– flaw detection/evaluation,
– dimensional measurements,
– material characterization, and more.
54. Applications of (UT)
• Applications
Surface and deep subsurface
discontinuities: Cracks,
laminations, porosity, lack of
fusion, inclusions, thickness.
• Comments
Need good standards.
Frequently used method.
55. Advantages& Limitations
of (UT)
• Advantages
Rapid if automated but manual is slow;
applicable to very thick specimens; can
give location and size of discontinuity;
good sensitivity; inspect from one side;
portable.
• Limitations
Couplant required; thin complex shapes
are difficult; orientation of discontinuity
important; very operator-dependent.
56. Introduction to
Radiographic Testing (RT)
• This method uses X or Gamma radiation using a radiographic Film as a
recording medium.
• In order to get maximum sensitivity the defect must be imparallel to the
radiation beam.
57. Applications
of (RT)
• Applications
Subsurface discontinuities:
Cracks, voids, inclusions, thickness
variation, lack of fusion, incomplete
penetration, corrosion, missing
components.
• Comments
One of the most frequently used
methods.
Industrial X-Ray Tube
58. Advantages& Limitations
of (RT)
• Advantages
Easily understood permanent record;
usually moderate cost; can be
portable; applicable to a wide range
of materials.
• Limitations
Cannot detect laminations; radiation
hazard and regulations; access to
both sides can be high cost; requires
trained operators.
Radiation
Sample
Front screen
Film
Back screen
59. 59
Eddy Current Inspection (ECT)
Eddy current inspection
is one of several NDT
methods that use the
principal of
“electromagnetism” as
the basis for conducting
examinations.
60. Applications
of ECT
• Eddy currents can be
used for:
– Crack detection
– Material thickness
measurements
– Coating thickness
measurements
– Thin tube inspection
61. Prepared byDr. Hassan
Shaaban
Applications of (ECT)
Cont’
• Applications
Surface and near surface discontinuities:
Seams, composition, thickness,
eccentricity, surface condition.
• Comments
Requires good standards.
62. Advantages& Limitations
of (ECT)
• Advantages
Extremely rapid; can be automated;
very sensitive; surface contact not
necessary; permanent record.
• Limitations
Conductive materials only; difficult
interpretation sometimes, may
require special equipment; sensitive
to geometry.
63. Acoustic Emission Testing
(AET)
Acoustic Emission differs
than other techniques in
two regards.
1.AET simply listens for the
energy released by the
object.
2.AET deals with dynamic
processes (Leaks), or
changes (Phase Change),
in a material.
64. Applications of AET
• Applications
Surface and subsurface discontinuities:
– Crack initiation and growth,
leaks, phase changes.
– detecting and locating faults in
pressure vessels or leakage in
storage tanks or pipe systems,
– monitoring welding
applications
65. Advantages& Limitations of (AET)
• Advantages:
Remote and continuous surveillance,
location, severity, permanent
record. Tests an entire vessel or
system.
• Limitations:
Contact with system; may need many
contact points; complex
interpretation; system must be
stressed; usually expensive; some
systems are too complex.
66. Introduction to Leak Testing
• Leakage occurs through a leak
(passage) when there is a pressure
differential between two sides of
a leak.
• Leaks can be detected by using
electronic listening devices,
pressure gauge measurements,
liquid and gas Penetrant
techniques.
67. Applications
of (LT)
• Applications
– Leaks in systems or
subassemblies.
– It includes hydraulic and
hydrostatic tests
– Hydrostatic tests can produce
damage.
• Comments
Usually the last testing
done, Thin Film Bubble Leak Testing
68. DISCONTINUITIES
Whenever there is a change in the homogeneity
of properties within a material, it can invariably
be attributed to the presence of discontinuities or
imperfection with in the material.
Example:
Voids; Inclusions; Laps; Folds; Cracks; Porosity
69. TYPES OF DISCONTINUTIES
• INHERENT DISCONTINUITIES
• PROCESSING DISCONTINUITIES
• SERVICE INDUCED DISCONTINUITIES
72. Inherent discontinuities are two further sub classifications:
Inherent wrought discontinuities related to the melting and
solidification of the original ingot before it is formed into slabs,
blooms and billets.
Inherent cast discontinuities related to the melting, casting
and solidification of a cast article.
81. SERVICE INDUCED DISCONTINUITIES
• The discontinuities that are created during the
use of a component are called “Service
Induced Discontinuities”
• Service discontinuities are related to the
various service conditions such as stress,
corrosion, fatigue and erosion
