What factor can seriously impair the sensitivity of wet developers?

The sensitivity of wet developers in liquid penetrant testing can be severely impaired when the thickness of the coating becomes too heavy. This is because a thick layer of developer can hinder the movement of the penetrant fluid, preventing it from adequately drawing up into the surface discontinuities that are being inspected. A thick coating may not only mask small defects but also lead to uneven drying and development, ultimately resulting in inaccurate or false readings.

In contrast, a developer that is too thin may not adequately retain the penetrant, and environmental factors like humidity or sunlight can temporarily affect the application process, but they don’t have the same direct impact on the overall performance of the developer as excessive thickness does. Hence, controlling the thickness of the developer is crucial for achieving optimal sensitivity in detecting flaws during the inspection.