30-08-2013, 03:37 PM
NON DESTRUCTIVE TESTING
DESTRUCTIVE TESTING.pptx (Size: 1.01 MB / Downloads: 66)
Nondestructive testing (NDT) has been defined as
comprising those test methods used to examine an
object, material or system without impairing its
future usefulness.
Used for 100% checking of material in a production
quality control system.
Characteristics of NDT
Applied directly to the product
Tested parts are not damaged
Various tests can be performed on the same product
Specimen preparation not required
Can be performed on parts that are in service
Low time consumption
Low labour cost
NDT Methods
Visual Inspection
Liquid penetrant method
Ultrasonic Inspection
Radiography methods
Eddy current testing
Magnetic particle testing
1 Visual Inspection
Most basic and common inspection method.
Tools include fiberscope, borescopes, magnifying glasses and mirrors.
Portable video inspection unit with zoom allows inspection of large tanks and vessels, railroad tank cars, sewer lines.
2. Liquid Penetrant Method
This method is frequently used for the detection of surface breaking flaws in non- ferromagnetic materials.
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.
Visual inspection is the final step in the process.
The penetrant used is often loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity.
3. Ultrasonic Flaw Detection
This technique is used for the detection of internal and surface defects in sound conducting materials.
High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.
Whenever there is a change in the medium, the ultrasonic waves are reflected. Thus, from the intensity of the reflected echoes, the flaws are detected without destroying the material.
4. X-Ray Radiography
X-rays are passed through the specimen under inspection and it is differentially absorbed by the specimen.
The transmitted x-rays are received by the photographic film and the film is developed.
The dark and light shadows reveal the defects present in the specimen and hence the defects are defected.
Uses of NDT
To detect internal or surface flaws
To measure the dimensions of materials
To determine the materials’ structure
To evaluate the physical and mechanical properties of materials
To avoid failures, prevent accidents and save human life;
To make a profit for the user
To ensure customer satisfaction and maintain the manufacturer's reputation
To aid in better product design
To control manufacturing processes
To lower manufacturing costs
To maintain uniform quality level