NAME 345
Welding Technology
Lecture
–
13
Non-Destructive Testing (NDT)
Md. Habibur Rahman
Lecturer
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology
Non-Destructive Testing (NDT)
NDT or Non-destructive Testing is
the testing of materials, for surface
or internal flaws or metallurgical
condition, without interfering in
any way with the integrity of the
material
or
its
suitability
for
service.
Non-Destructive Testing (NDT)
Destructive TestsAdvantages:
1. Measurements are direct and reliable 2. Usually quantitative measurements 3. Correlation between test measurements
and martial properties are direct.
Limitations:
1. Test are not made on the objects
directly. Hence correlations between the same.
2. A single test may measure only one or a few of the properties.
3. In-service testing is not possible. 4. Measurement of properties over a
cumulative period of time cannot readily be possible.
5. Preparation of the test specimen is costly.
6. Time requirements are generally high.
Non-Destructive Tests
Limitations:
1. Measurements are in direct and reliability is to be verified
2. Usually qualitative measurements 3. Skilled judgment and experience are
required to interpret indications.
Advantages:
1. Test are made directly on the objects. 100% testing on actual components is possible.
2. Many NDT methods can be applied on the same part and hence many or all properties of interest can be measured.
3. In-service testing is possible. 4. Measurement of properties over a
cumulative period of time is possible. 5. Preparation of the test specimen is not
costly.
Non-Destructive Testing (NDT)
Non-Destructive
Testing
Radiography- X And Gamma Ray
Eddy Current Testing Visual Inspection Ultrasonic Flaw Detection Dye/Liquid Penetrant Testing Magnetic Particle Inspection
Non-Destructive Testing (NDT)
Visual Testing
• Most widely used
• 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
• Generally considered to be the primary and oldest method of NDT
• Relies upon the detection of surface imperfections using the eye.
• Normally applied without the use of any additional equipment
• Can be improved by using aids such as a magnifying glass to improve its effectiveness and scope.
• Requires three basic conditions to be in place. These are: a) good vision, to be able to see what you are looking for b) good lighting, the correct type of light is important c) experience, to be able to recognize problems.
Non-Destructive Testing (NDT)
Most basic and common inspection method.
Tools include fiberscopes, borescopes, magnifying glasses and mirrors.
Robotic crawlers permit observation in hazardous or tight areas, such as air ducts, reactors, pipelines.
Portable video inspection unit with zoom allows inspection of large tanks and vessels, railroad tank cars, sewer lines.
Visual Testing (Contd.)
Advantages
• Simple
• Easy to Apply
• Quickly carried out
Non-Destructive Testing (NDT)
Radiography- X And Gamma Ray
• X-rays are generated electrically
• Gamma rays are emitted from radio-active isotopes
• 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
• The film darkness (density) will vary with the amount of radiation reaching the film through the test object
• If there is a crack/hole in the material, it will appear as a dark spot.
Non-Destructive Testing (NDT)
• This technique involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. 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 soundness of the part. Possible imperfections are indicated as density changes in the film in the same manner as an X-ray shows broken bones.
Non-Destructive Testing (NDT)
Film Radiography
Top view of developed film X-ray film
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.
= more exposure
= less exposure
The film darkness (density) will vary with the amount of radiation reaching the film through the test object.
Non-Destructive Testing (NDT)
Non-Destructive Testing (NDT)
Magnetic particle testing
• Magnetic particle inspection (MPI) is used for the detection of surface and near-surface flaws in ferromagnetic materials. A magnetic field is applied to the specimen, either locally or overall, using a permanent magnet, electromagnet, flexible cables or hand-held prods. If the material is sound, most of the magnetic flux is concentrated below the material's surface. However, if a flaw is present, such that it interacts with the magnetic field, the flux is distorted locally and 'leaks' from the surface of the specimen in the region of the flaw. Fine magnetic particles, applied to the surface of the specimen, are attracted to the area of flux leakage, creating a visible indication of the flaw.
• The materials commonly used for this purpose are black iron particles and red or yellow iron oxides. In some cases, the iron particles are coated with a fluorescent material enabling them to be viewed under a UV lamp in darkened conditions.
Non-Destructive Testing (NDT)
• For locating surface & subsurface discontinuities in ferromagnetic materials
• The part is magnetized.
• Finely milled iron particles coated with a substance, which fluoresces brilliantly under ultra-violet illumination 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
Non-Destructive Testing (NDT)
Non-Destructive Testing (NDT)
Penetrant
• extension of visual inspection • for detection of surface flaws
• two kinds ; dye penetrant and fluorescent penetrants
Non-Destructive Testing (NDT)
Dye/Liquid Penetrant Testing (PT)
• This method is frequently used for the detection of surface breaking flaws in non-ferromagnetic materials.
• A liquid (which is a very fine thin oil usually dyed bright red or ultra-violet fluorescent) 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 to form a visual, magnified in width, indication in good contrast to the background.
• In case of fluorescent penetrant the inspection is done under UV light to increase test sensitivity.
Non-Destructive Testing (NDT)
Dye/Liquid Penetrant Testing (Contd.)
•
Penetrant Testing, or PT, is a nondestructive testing method that builds on the principle of Visual Inspection.•
PT increases the “see-ability” of small discontinuities that the human eye might not be able to detect alone.Non-Destructive Testing (NDT)
Non-Destructive Testing (NDT)
Ultrasonic Flaw Detection
➢ This technique is used for the detection of internal and surface (particularly distant surface) defects in sound conducting materials.
➢ High frequency sound waves are introduced into a 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 showing the depth of features that reflect sound.
plate crack 0 2 4 6 8 10 initial pulse crack echo back surface echo
Non-Destructive Testing (NDT)
Ultrasonic Testing
• The use of ultrasonic waves to evaluate the condition of a material.
• Anomalies absorbs of deflects the sound waves, which are then detected as changes in the waves.
‒ Holes, delamination, voids
‒ Damage, debonds
Non-Destructive Testing (NDT)
Eddy Current Testing
• The eddy current technique can detect surface or subsurface flaws and measure conductivity and coating thickness
• A coil carrying an AC current is placed close to the specimen surface or around the specimen
• The current in the coil generates circulating eddy currents in the specimen close to the surface and these in turn affect the current in the coil by mutual induction.
• The presence of flaws is measured by electrical changes in the exciting coil.
Advantages Disadvantages
i. It gives instantaneous response ii. It can be easily automated
iii. It is versatile
iv. No contact between the probe and the test specimen is essential
v. Its equipment can be made portable.
i. It requires highly skilled operator ii. It is applicable to conductive
materials only.
iii. Depth of penetration is limited. iv. Its application to ferromagnetic
Non-Destructive Testing (NDT)
Non-Destructive Testing (NDT)
Summery
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