Leak Detection with Penetrant Testing Process

One of the many applications of liquid penetrant inspection is testing for leaks by using fluorescent or visible/color-contrast penetrant to enhance visual detection of leaks

By Cheri Stockhausen, Product Applications Manager









In non-destructive testing leak detection, “leak” refers to the physical hole and “leakage” refers to the flow of a fluid through a leak. Leak testing to detect and locate leaks is important to be able to repair unacceptable leaks in vessels or systems such as holding or process tanks, radiators, empty vessels, tanks, liquid containment systems, pipe systems or hydraulic systems. Penetrant inspection of leaks is generally subjective as compared to the quantitative leak inspection using tracer gas and pressure change techniques.

In liquid penetrant leak testing the penetrant is applied on one side of the enclosing wall or surface of the test object and then allowed to seep through any leaks. Both visible and fluorescent penetrants may be used here as liquid dye tracers. After the penetrant has dwelled, the opposite side of the wall is inspected to see if any penetrant seeped through.


Leak testing techniques when using penetrant testing method:

  • Observe all safety precautions when inspecting enclosed areas. Make sure there is enough ventilation when using chemicals. If not, use self-contained breathing apparatus for oxygen source.
  • Apply penetrant on the inside wall of the tank or area being inspected.
  • Depending on the thickness of the wall, let penetrant dwell on the surface between 10-30 minutes. Allow a dwell time of at least one hour if the wall thickness is greater than ¼ inch.
  • Apply developer on the other side of the wall.
  • Observe indications where the developer was applied.
    • When using SKL-4C, SKL-WP2 or SKL-SP1 (superseded by SKL-SP2) penetrant, use SKD-S2 non-aqueous developer and observe for red indications against the white developer background.
    • For fluorescent penetrant inspection with ZL-4C, ZL-19 or ZL-60D, apply ZP-4D dry powder developer and observe fluorescent green indications using a black light UV lamp in a darkened area.
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