Which of the following techniques has been found to be effective for aiding penetration in certain instances in commercial application?

Heating the part is an effective technique for aiding penetration in liquid penetrant testing, particularly in scenarios where the material may have surface tension or viscosity issues that inhibit the penetrant from properly entering defects. By increasing the temperature of the part, the viscosity of the penetrant decreases, allowing for better flow into cracks, porosities, or other discontinuities. This thermal enhancement can improve the overall sensitivity of the inspection, enabling the detection of smaller defects that might otherwise go unnoticed at ambient temperatures.

Heating can also help to evaporate any moisture or contaminants on the surface, ensuring that the penetrant can completely adhere to and infiltrate the desired areas. This technique becomes especially useful when working with materials that tend to trap penetrants or when inspecting components subjected to high levels of surface contaminants. While other techniques may also have merits in specific contexts, heating has been widely accepted in commercial applications for its effectiveness in improving penetrant access and enhancing detection capabilities during the testing process.