Which type of discontinuities are best identified with liquid penetrant testing?

Liquid penetrant testing (LPT), also known as dye penetrant testing, is primarily utilized to detect surface-connected discontinuities in materials. The process involves applying a liquid penetrant to the surface of a material, allowing it to seep into any cracks or flaws present. After a specified dwell time, excess penetrant is removed, and a developer is applied, which draws the penetrant out of the discontinuities, making them visible under appropriate lighting conditions.

This method is particularly effective for identifying surface-breaking defects such as cracks, porosity, and inclusions, which are accessible at the surface of the material. Therefore, the best identification of discontinuities using liquid penetrant testing is limited to those that are directly connected to the surface.

Other discontinuities, such as internal or non-visible defects, are not adequately identified through this method since the penetrant cannot reach internal flaws that do not connect to the surface. Therefore, options that suggest either hidden or non-visible discontinuities do not align with the fundamental capabilities of liquid penetrant testing.