PT Penetrant testing (PT)
Penetrant testing (PT) · Inspección y ensayos · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “PT level 2 ISO 3452 on weld area” states a penetrant testing (pt) requirement.
What controls
Non-destructive test that reveals surface-breaking discontinuities: a penetrant liquid is applied, enters the crack by capillary action, the excess is removed and a developer is applied that draws out the trapped penetrant and makes it visible as an indication. It detects only what is open to the surface: an internal crack, lack of fusion beneath the weld bead or closed porosity will not show up. It works on non-porous materials, whether magnetic or not.
How to verify
Cleaning, penetrant application, dwell time, excess removal, developer and development time, with evaluation under white light or ultraviolet light depending on the system used. Indications are sized and classified (linear, rounded, clustered) and compared against the drawing's acceptance criterion. Personnel must be qualified to the level required by the procedure, and the test is recorded with product, batch and conditions.
Common mistakes when interpreting it
- Expecting it to detect internal defects: it only sees what is open to the surface.
- Shot blasting or polishing before the test and mechanically closing the cracks you wanted to find.
- Shortening dwell and development times to go faster.
How to get it in the workshop / if it comes out of tolerance
The whole result depends on the pre-cleaning: paint, oil, rust or shot blasting that closes the crack edges defeats the test. That is why it is not done right after abrasive blasting, nor on surfaces finished by cold-working processes that may have closed the discontinuity. Respect the penetrant dwell and development times in the procedure: rushing them is the quickest way to see nothing.
Stained background that prevents interpretation: excess poorly removed or intermediate cleaning too aggressive. No indications at all on a part known to be defective: check the surface preparation, because it is the most common failure. Indications that reappear after grinding: the discontinuity is deeper than the material removed. And after the test the part must be cleaned thoroughly, especially if it is going to be welded or coated.
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