What test procedure could lead to false signals if the specimen is inadequately cleaned?

Penetrant testing relies on the application of a liquid penetrant that seeps into surface cracks and discontinuities of a material. For this method to be effective, the surface of the specimen must be thoroughly cleaned to eliminate any contaminants, coatings, or debris that could obstruct the penetrant from fully entering the defects. If the specimen is inadequately cleaned, contaminants may mask the actual flaws, leading to false indications of defects or, conversely, failing to reveal existing ones. This is crucial in ensuring the accuracy and reliability of the test results in penetrant testing.

In contrast, hardness testing, tensile testing, and ultrasonic testing have different principles that may not be as affected by surface cleanliness. For instance, hardness testing typically provides results based on the material's response to an applied load, and while surface preparation is important, it does not result in the same risk of false indication due to contaminants as seen in penetrant testing. Similarly, tensile testing evaluates the material's strength under force, and ultrasonic testing uses sound waves to detect internal flaws, making those processes less sensitive to surface cleanliness.