3. DEFINITION OF NDT
NDT has been defined as
comprising those test
methods used to examine an
object, material or system
without impairing its future
usefulness. The term is
generally applied to
nonmedical investigations of
material integrity
i.e. Inspect or measure without doing harm.
4. THREE TYPES OF
DEFECTS
Inherent defects :- exist in parent materials
Processing defects:- developed during processing
Service defects :- developed during service are
5. COMMON DEFECTS AND CAUSES
Description
The depth of the weld
is less than
specifications.
The weld metal is
not completely fused
to base metal or
passes are not
completely fused.
Weld material flows
over, but is not
fused with the base
metal.
Cause(s)
Excessive heat
Excessive speed.
Incorrect angle
Insufficient heat
Slow speed
5
6. COMMON DEFECTS AND CAUSES--CONT.
Description
Weld bead does not
extend to the
desired depth.
Small indentions in
the surface of the
weld
Small voids
throughout the
weld material.
Cause(s)
Low heat
Long arc
Incorrect joint design
Excessive gas in
the weld zone.
Moisture
Rust
Dirt
Accelerated cooling
6
7. COMMON DEFECTS AND CAUSES--CONT.
Description
Cause(s)
Usually visible cracks
on the surface or
through the weld
Accelerated
cooling
Small weld volume
Cracks in the
transition zone
between the weld
and base metal
Induced hydrogen
Incompatible
electrode or wire
Accelerated cooling
Irregular
shape and/or
uneven
ripples
Incorrect speed
Incorrect welder
settings
7
8. WHAT ARE SOME USES
OF NDT METHODS?
Flaw Detection and Evaluation
Leak Detection
Location Determination
Dimensional Measurements
Fluorescent penetrant indication
Structure and Microstructure Characterization
Estimation of Mechanical and Physical Properties
Stress (Strain) and Dynamic Response Measurements
9. SIX MOST COMMON NDT
METHODS
•
•
•
•
•
•
Visual
Liquid Penetrant
Magnetic
Ultrasonic
Eddy Current
X-ray
10. VISUAL TESTING
experienced inspector knows where are likely cracks ,
orientation of cracks relative to various zones in the weld,
surface porosity, weld penetration, potential weakness such as
sharp notches or misalignment
11. Most basic and common
inspection method.
Tools include
fiberscopes,
borescopes, magnifying
glasses and mirrors.
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.
13. INTRO•Penetrant Testing, or PT, is a
nondestructive
testing method that builds on the principle
of Visual Inspection.
•PT increases the
“seeability” of small
discontinuities that
the human eye might
not be able to detect
alone.
14. BASIC STEPS OF DYE
PENETRANT TESTING
clean the surface
apply penetrant
remove excess penetrant
apply developer
inspect / interpretation
penetrant seep
into flaw
developer draws
penetrant onto
surface
15.
16. A DVA NTA GES & LIMITA TIONS OF
LIQUID PENETRA NT METHOD
ADVANTAGES
LIMITATIONS
Simple & inexpensive
Detect surface flaws
Versatile & portable
Applicable to ferrous,
non-ferrous, nonmagnetic & complex
shaped materials which
are non-porous & of any
dimension
Detects cracks, seams,
lack of bonding, etc.
Non-porous surface of
material
Surface cleaning before
& after inspection
Deformed surfaces &
surface coatings prevent
detection
17. MAGNETIC PARTICLE
INSPECTION
The part is magnetized. Finely milled iron particles coated with a dye
pigment are then applied to the specimen. These particles are attracted to
magnetic flux leakage fields and will cluster to form an indication directly
over the discontinuity. This indication can be visually detected under
proper lighting conditions.
18.
19.
20. RADIOGRAPHY
The radiation used in radiography
testing is a higher energy (shorter
wavelength) version of the
electromagnetic waves that we
see as visible light. The radiation can
come from an X-ray generator or a
radioactive source.
High Electrical Potential
Electrons
+
-
X-ray Generator
or Radioactive
Source Creates
Radiation
Radiation
Penetrate
the Sample
Exposure Recording Device
21. FILM
RADIOGRAPHY
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.
X-ray film
Top view of developed film
The film darkness
(density) will vary with
the amount of radiation
reaching the film
through the test object.
23. MERITS & DEMERITS
Demerits
Merits
No need of washing and
developing films
Poor resolution
Low cost
Electronic image intensifier
required for increasing the
contrast
Image viewed immediately
on screen
Time consumption is less
Movement of defects
detected (real time images)
Permanent record can be
made
Low image contrast
26. Eddy current test
( a)
The alternating current flowing through the coil at a chosen frequency generates
a magnetic field around the coil.
( b)
When the coil is placed close to an electrically conductive material, eddy current
is included in the material.
(c)
If a flaw in the conductive material disturbs the eddy current circulation, the
magnetic coupling with the probe is changed and a defect signal can be read by
measuring the coil impedance variation.
27.
28. ULTRASONIC INSPECTION
(PULSE-ECHO) are introduced into a
High frequency sound waves
material and they are reflected back from surfaces or
flaws.
Reflected sound energy is displayed versus time, and
inspector can visualize a cross section of the specimen
f
showing the depth of features that reflect sound.
initial
pulse
crack
echo
back surface
echo
crack
0
2
4
6
8
Oscilloscope, or flaw
detector screen
10
plate
36. CRASH OF UNITED
FLIGHT 232
Sioux City, Iowa, July 19, 1989
A defect that went
undetected in an
engine disk was
responsible for
the crash of
United Flight 232.
38. BRIDGE INSPECTION
• The US has 578,000
highway bridges.
• Corrosion, cracking and
other damage can all
affect a bridge’s
performance.
• The collapse of the Silver
Bridge in 1967 resulted in
loss of 47 lives.
• Bridges get a visual
inspection about every 2
years.
• Some bridges are fitted
with acoustic emission
sensors that “listen” for
sounds of cracks
growing.
Hinweis der Redaktion
Eddy currents (also called Foucault currents are electric currents induced within conductors by a changing magnetic field in the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsion, attraction,[2] propulsion, drag, and heating effects.
Metal forging is a metal forming process that involves applying compressive forces to a work piece to deform it, and create a desired geometric change to the material
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section.
The heavy loads that trains place on the railroad tracks can result in the formation of cracks in the rail. If these cracks are not detected, they can lead to a derailment. Special rail cars equipped with NDT equipment are used to detect rail defects before they are big enough to cause serious problems.
