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CHAPTER 1: Introduction of Non-destructive Testing - Coggle Diagram
CHAPTER 1: Introduction of Non-destructive Testing
What is NDT
Inspection or testing (of materials and components): verify the structural integrity of material or component without compromising its ability to perform in service
NDT is a Quality Assurance Management tool which can give impressive results when used correctly
NDT plays an important role in everyday life and is necessary to assure safety and reliability
NDT requires understanding of the method available, their capabilities and limitations, knowledge of the relevant standards and specifications for performing the tests
NDT can be applied at any stage of a component manufacture and the components being tested by NDT are either accepted, rejected or repaired
Usage of NDT
Primary basis of assuring structural integrity, fitness for use and revalidation of structural integrity during maintenance overhaul operations
NDT is also used to monitor the integrity of the component throughout its design life
NDT can be used to find size and locate surface and subsurface (internal) flaws and defects
Aircraft, automotive, pipelines, bridges, trains, power stations, refineries and oil platforms
Advantages
Tested parts can be reused
More than one inspection method can be applied to a similar component
Inspection on a certain part may be repeated
Require minimum or no specimen preparation
Equipment are normally portable (suitable for field inspection)
Inspection may be performed while the components is in service
Limitations
Results are qualitative
Requires highly trained personnel
6 Most Common NDT Methods
Visual Inspection
Most basic and common inspection method
Tools include fiberscopes, borescopes, magnifying glasses and
mirror
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 area such as, air ducts, reactors, pipelines
Liquid Penetrant Inspection
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
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
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
Eddy Current Testing
Particularly well suited for detecting surface cracks but can also be used to make electrical conductivity and coating thickness measurements.
Ultrasonic Inspection (Pulse-Echo)
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
Common Application of NDT
Inspection of Raw Products
Forgings
Castings
Extrusions
Inspection Following Secondary Processing
Machining
Welding
Grinding
Heat Treating
Plating
Inspection For In-Service Damage
Cracking
Corrosion
Erosion/Wear
Heat Damage
The need for standard
(Variables : in NDT)
A method is said to have a good or high sensitivity of flaw detection when it can detect relatively smaller flaws and vice versa
The sensitivity of flaw detection for different NDT methods depends upon a number of variable factors
The objective of most non-destructive testing methods is to detect internal defects with respect their nature, size and location. This is done by different methods depending upon their inherent capability or sensitivity to flaw detection
Aims of standardization
Clear Communication
Written standards make it easy for the customer or user to communicate with the producer
Economy of Effort
The purchaser or designer may have a general idea of what is required (and what is available) for a desired level of inspection
Minimum Performance
Published codes and standards accepted by industry in general, provide the regulator or the purchaser with confidence that the product or service will at least perform to the level detailed in the standard
Historical Record
After the product has gone into service (sometimes years after) a life record of the standard use for production or inspection will likely be sufficient documentation of the process used to produce it
NDT
OBJECTIVES
Design stipulated standards (e.g. dimension, strength and stiffness) do not deviate beyond permissible limits and immediate action is initiated in case of such deviations
To establish reproducibility of the fabrication process for successive batches of production with minimum rejection and repair
To establish reliability of NDT methods so that potentially harmful defects, damages, material inhomogeneities or dimensions are noticed while minor defects or deviations do not lead to unnecessary rejection or repair
Factors Influencing
the reliability of NDE
Human factor
Testing factor
Test object
Nature of Defect or Discontinuity
Knowledge Based & Facilities
Risk Factors
The Science & Technology
of NDE involves:
Device that interacts with the test object which generates the information
Knowledge of materials & fabrication process
To understanding the mechanism of the interaction between the information which generate the device and also the test object itself
Educate tools which is hardware & software to capture & record the results of the interaction
To analyze generated information and its correlation
Presentation of the results
Evaluation of the test object (discussion)
To make a decision (accept, repair or reject)
Communication
Interaction between Design
Officers and NDT Officers
Structure & assembly inspectability using NDT methods
To ensure the damage tolerance concept of design
Incorporating the statistical approach in developing acceptance criteria for design stipulated properties