In dye penetrant testing, what is used to reveal small cracks on the object's surface?

In dye penetrant testing, a UV reactive dye is utilized to reveal small cracks and surface defects on the object being inspected. The process involves applying the dye to the surface of the material, allowing it to seep into any cracks or voids. After a specified dwell time, excess dye is removed from the surface, and a developer is applied. This developer draws out the dye from the cracks to the surface, making the defects clearly visible under UV light.

The use of a UV reactive dye is particularly effective because it fluoresces under ultraviolet light, enhancing the visibility of the flaws against the background of the object. This increases the sensitivity of the inspection, allowing for the detection of very small surface-breaking cracks that may not be visible to the naked eye.

In contrast to other methods, such as using X-ray radiation or ultrasonic pulses, dye penetrant testing is a more straightforward and less complex technique suited specifically for surface inspection. Liquid nitrogen is not relevant in this context, as it is primarily used for other types of testing, like cryogenic treatment, rather than in revealing surface cracks.