How Leak Detectors Really Work

We’ve previously mentioned that the leak detector liquid’s penetration into fine weld cracks results from its low surface tension. But here’s a point worth digging into: why does capillary penetration get stronger as a crack gets narrower?

The Relationship Between Crack Width and Penetration Power

When a liquid with low surface tension reaches a very narrow gap, the adhesive force between the liquid and the crack walls overcomes the liquid’s internal cohesive force, drawing it into the gap without any need for external pressure, much like ink soaking into paper fibers. The narrower the gap, the stronger this pulling force becomes. This is precisely why microscopic cracks invisible to the naked eye are exactly where the leak detector liquid performs best at penetration.

The Formulation Challenge: A Delicate Balance

If surface tension isn’t low enough, fine defects, often the earliest signs of structural failure, go undetected. On the other hand, reducing this property too much can compromise the formula’s overall stability or its ability to carry the fluorescent compound. Striking this precise balance is one of the key technical challenges in designing a high-quality leak detector.