Why must surfaces be clean before VT?

• A. Dirt, oil, grease, or coatings can mask defects; cleaning reveals true surface conditions.
• B. Cleaning is optional and not necessary.
• C. Surface condition is unaffected by contaminants.
• D. VT works best on dirty surfaces.

Answer: (B)

Before visual testing, surfaces need to be clean so defects can be seen clearly. Dirt, oil, grease, or coatings create a layer that can hide cracks, porosity, corrosion, or other surface flaws. This masking not only makes defects harder to detect, it can also distort how light reflects from the surface, causing glare or misleading indications. Cleaning removes that obscurity, allowing the true surface condition to be observed and enabling accurate, reliable defect detection.