Defects and NDT

Question 1

List the surface defects.

Answer 1

Cold shots
Bilster & Sinks
Joints & Vortexes
Mould defects

Question 2

List the bulk/sub-surface defects.

Answer 2

Gas porosity (micro & macro)
Shrinkage porosity
Inclusions
Hot tears/Hot cracks (from bot casting & welding)
Cold cracks

Question 3

Liquid penetrant testing

Answer 3

Surface
Fine and clean surface (not painted)
Non-porous

Question 4

X-ray inspection

Answer 4

Volume
Used to detect most defects
Not the best for thick /dense parts
A limited depth depending on the x-ray

Question 5

Magnetic & Electro-magnetic

Answer 5

Surface and sub surface
Find cracks
Must be a ferreous metal
Orentation sensitive
Easy geometry part!

Question 6

Eddy-current

Answer 6

Surface and small depth
Find any defect
Material must be:
Electrically conductive

Plastic deformation may interfere with the result
Have right frequency.
Operator trening is essential

Question 7

Ultrasound

Answer 7

Whole volume
depth depend on frequency. higher f -> smaller depth
Need coupling fluid
Detecteble defect is at least half the wavelength of the US beam
Hard with complex shape, because of positioning of the receiver

Question 8

Acustical Emission

Answer 8

Volume
Can only detect crack propagation, not. already present cracks
If multiple receivers we can detect the position of the crack.

Question 9

Infrared