What is coating inspection by VT, and when is it used?

• A. Ultrasonic thickness measurement used when high accuracy is required.
• B. Visually assessing coating integrity, adhesion, and surface defects; used when visual cues are sufficient or as a screening step before thickness tests.
• C. Coating color matching using spectrometry.
• D. A method to evaluate corrosion rate over time.

Answer: (B)

Coating inspection by VT is about what you can see on the surface. It focuses on visually evaluating the coating for integrity, adhesion, and surface defects such as holidays (voids), pinholes, cracks, blistering, delamination, runs, and uneven coverage. This approach relies on the inspector’s eyes (often with basic aids like a flashlight, magnifier, or UV light) to judge whether the coating looks acceptable on accessible areas.

It’s used when visual cues are enough to decide if the coating meets standards, or as a screening step before doing more quantitative tests. For example, after application or curing, you’d check for uniform color, proper edge coverage, absence of obvious defects, and good adhesion. If issues are found, you proceed to additional testing (like thickness measurements or holiday detection) as needed. This method is not about measuring thickness with ultrasonic devices, performing color analysis with spectrometry, or tracking corrosion rate over time.