Penetrant Testing (PT)
Penetrant testing (PT) is a non-destructive method that makes surface-breaking cracks and discontinuities visible to the eye. In aerospace and defence it is a standard part of series acceptance.
How the process works
The method relies on capillary action. Penetrant applied to the surface is drawn into the crack. After the excess on the surface has been carefully removed, the developer applied next draws the liquid back out of the crack, making the discontinuity visible as an enlarged indication.
The most sensitive step of the process is intermediate cleaning. Insufficient cleaning produces false positives; excessive cleaning removes the penetrant from the crack as well and hides the real defect. Cleaning parameters are therefore kept under strict control.
Where fluorescent penetrant is used, inspection takes place under UV light in a darkened booth. Booth illuminance and UV intensity are measured periodically.
Related topics
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