Lecture 5-6 Flashcards
Which examination tests are used for surface cracks? (5)
- Visual and optical
- Liquid penetrant
- Magnetic particle
- Leak
- Hydro Proof
Which examination test can be used on subsurface cracks?
Electromagnetic
Which examination methods fall under ‘volumetric methods’?
- Radiography
- Ultrasonic testing
- Acoustic emission testing
What is the aim of non-destructive examination?
To use non-invasive techniques to determine the integrity of materials, components or structures, or to quantitively measure some characteristics of an object
What are the uses of non-destructive examination techniques?
- Flaw detection/evaluation
- Location determination
- Leak determination
- Dimensional measurements
What is the general process of visual/optical testing?
Visual examiners follow procedures.
Some procedures compare workmanship samples with production parts.
What are the disadvantages to visual and optical testing?
- Not good for large areas with small cracks/defects
- Can become expensive when using lighting, microscopes, mirrors, boroscopes
How can visual and optical testing be improved?
- Take videos/photos for comparison
- Use image recognition
What is the general process of liquid penetrant testing?
Object is coated with dye
Excess dye is removed from the surface
Dry developer is applied, drawing penetrant out of imperfections
Why would visible dyes be used in liquid penetrant testing?
The vivid colour contrasts with the developer, so ‘bleedout’ is easy to see
Why would fluorescent dyes be used?
Ultraviolet light makes them fluoresce, so imperfections can be seen easily
What is liquid penetrant testing used on?
Microscopic cracks - dye gets into cracks by capillary action
What is an extra advantage of liquid penetrant testing?
It gives an indication of how deep the crack is - more dye will get into a deeper crack
What is the general process of magnetic particle testing?
Magnetic field is induced in a ferromagnetic material
Surface is dusted with iron particles
Surface imperfections distort the field and concentrate iron particles near imperfections
What must be taken into account with the magnetic field in magnetic particle testing?
It won’t pick up flaws parallel to the field. Therefore, use fields in at least 2 directions
What detecting methods are used in leak testing?
- Electronic listening devices
- Pressure gauge measurements
- Liquid and gas penetrant techniques
- Soap bubble test
What is leak testing in simple terms?
Listening or looking for escaping fluid
What is the general process of electromagnetic testing?
Electrical currents are generated in a conductive material by an induced alternating magnetic field
Eddy currents caused by imperfections/changes in conductive properties will cause changes in induced field
Why is electromagnetic testing more versatile than magnetic particle testing?
It works with any material that is electrically conductive, not just ferromagnetic
What is the general process of radiography?
Uses penetrating x-rays or gamma rays, directed through a part onto a film or other media
Imperfections are indicated as density changes in the film
What are the disadvantages of radiography?
- Expensive
- Requires skilled personnel
- Only sees flaws perpendicular to x-ray
- Dense targets need higher energy x-rays
What is the general process of ultrasonic testing?
Uses transmission of high-frequency sound waves to detect imperfections
What is the most common form of ultrasonic testing?
Pulse echo
How does pulse echo work?
Sound is introduced into an object and reflections are returned to a receiver from internal imperfections or geometrical surfaces
