What is a primary effect of heat on penetrant testing?

• A. Increases sensitivity and decreases viscosity
• B. Reduces sensitivity and may increase viscosity
• C. Has no effect on removal characteristics
• D. Improves rate of penetration without changing viscosity

Answer: (B)

Heat changes how the penetrant behaves on and in the surface. When you heat the part, solvents and carriers in the penetrant can evaporate more quickly, leaving behind a film that becomes more viscous. That thicker film doesn’t flow as readily into small cracks, so the penetrant may not reach the tiniest flaws as effectively, reducing the likelihood that tiny indications will stand out. In practice, this means sensitivity is reduced, and the penetrant’s film can appear more viscous after heating. The primary takeaway is that temperature tends to lower defect visibility and can make the penetrant film thicker, rather than improving penetration into small flaws.