NDT Flashcards
Liquid penetrant
- enters flaw through capillary action
- area around flaw needs to be cleaned at least 1” around
- widely used in leak detection in welded thin walled vessels
Eddy current
- only one that needs A/C
- very good for checking surface and subsurface cracks beneath paint
- very fast & cheap
- pieces can be non-magnetic and conductive
- coil is the basic component
Solvent removable
-dye penetrant used for small area of a work piece
Fluorescent dye penetrant
- requires ultra violet light
- does not detect internal flaws
Magnetic particle inspection
- Sprinkle workpiece with dry iron powder or submerge in a liquid with suspended iron particles
- depth of 1/4”
- electric current is used to magnetize,but regular magnets can work as well
- 90 degrees or right angles to the defect
- portable equipment
Dwell time
-Time a penetrant or developer is in contact with a surface
Discontinuity
-interruption in normal structure such as crack, seam, porosity
Contrast in X-ray
-different degrees of darkening on the film
Definition in X-ray
-sharpness the image is projected on the film
Destructive testing
- tensile
- compressive
- torsion
- fatigue
- hardness
- impact
Non-destructive
- visual
- dye penetrant
- magnetic particle
- ultrasonic
- radiography
Radiography
- Electromagnetic energy
- Uses gamma & X-ray
- can be used for thick materials
Ultrasonic
- Up to 20ft
- High frequency sound waves between 20,000 cycles per second and 10,000,000
- for longitudinal & shear waveforms
Penetrameter
- Measures quality of radiography
- a plate with 3 holes in it 2% of the thickness of the specimen
Ultrasonic sound waves
- Electric pulses generated from the crystals and reflects back
- highly sensitive, but rough or small pieces are hard to test
Couplant
- gel, oil or water
- allows the sound beam to go from the transducer to the test piece
Retentivity
-easily loses its magnetism
Magnetic permeability
-easy to magnetize
Direct current
- penetrate the cross section of the part
- use single or three phase with a rectifier
Alternating current
- fields are confined to the metal at or near the surface of the part (skin effect)
- should not be used for subsurface discontinuities
- single phase only for magnification purposes
Magnetized bars
-magnetic lines of force flow through the bar south to north
X-ray
-best for checking engine or compressor cylinder heads
Gamma rays
- iridium 192 .25” to 3.5”
- cobalt 60 1” to 7”
- shielding container is the camera
- container holding the material is called the source
