Heat zone cracks
Poor weld penetrations
Heat treatment cracks
An example of the process is shown below.
A bicycle crank arm was tested because the owner noticed a crack on the
square axle attachment point and suspected a crack at the pedal attachment
Stress corrosion cracks
The suspect areas were sprayed with a red dye penetrant and left to soak.
The dye was wiped off and the crank was sprayed with developer (chalk).
The crack at the axle attachment is clearly visible. The suspected
crack at the pedal attachment showed no red dye, indicating that it was a
scratch and not a crack.
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