Before applying penetrant, the surface must be free of which contaminants to prevent false indications?

Before applying penetrant, the surface must be free of which contaminants to prevent false indications?

• A. Oil or grease
• B. Water
• C. All of the above
• D. Chromates

Answer: (C)

Before applying penetrant, the surface must be clean and dry because penetrant relies on proper wetting to enter defects. Oil or grease leaves a barrier film that prevents good wetting, so cracks may not fill with penetrant. Water on the surface can hinder wetting or interact with the penetrant/developer, leading to false indications or washed-away penetrant. Chromates or other surface residues can also cause background staining or interfere with development, producing misleading results. Since any of these contaminants can cause false indications or mask real defects, all of these must be removed.

Before applying penetrant, the surface must be clean and dry because penetrant relies on proper wetting to enter defects. Oil or grease leaves a barrier film that prevents good wetting, so cracks may not fill with penetrant. Water on the surface can hinder wetting or interact with the penetrant/developer, leading to false indications or washed-away penetrant. Chromates or other surface residues can also cause background staining or interfere with development, producing misleading results. Since any of these contaminants can cause false indications or mask real defects, all of these must be removed.