Which penetrant method does not require a source of electricity?

The visible dye penetrant method is a non-destructive testing technique used for detecting surface defects in non-porous materials. This method involves applying a visible dye penetrant to the surface of the material, allowing it to seep into any cracks or voids present. After a specified dwell time, the excess dye is removed, and a developer is applied to draw the dye out of the defects, making them visible under normal light conditions.

This method does not require a source of electricity because it relies solely on the chemical properties of the dye and developer to highlight defects. The process can be performed without any electrically powered equipment, making it suitable for various environments, especially where electric sources might not be available or practical.

In contrast, fluorescent dye penetrant methods involve using ultraviolet light to illuminate the penetrated areas, which necessitates an electrical source. Water-soluble penetrants may require rinsing and cleaning agents that often rely on more advanced equipment. Ultrasonic testing additionally requires a device that uses electrical energy to send and receive sound waves, disqualifying it from being applicable without electricity. Therefore, the visible dye penetrant method stands out as the only method listed that operates independently of electrical power.