At what temperature do liquid penetrants generally lose sensitivity?

Liquid penetrants are widely used in non-destructive testing (NDT) to detect surface defects in materials. Their sensitivity can be adversely affected by temperature because the physical properties of the penetrant can change.

Generally, liquid penetrants begin to lose their sensitivity at lower temperatures where the viscosity of the penetrant increases, making it less effective at filling in small cracks or defects. Under 10 degrees Celsius, the viscosity can become high enough that the penetrant is unable to properly penetrate into surface flaws, thus reducing the effectiveness of the testing method. This is why the lower threshold of 10 degrees Celsius is significant; at this point, the testing material’s performance drops below acceptable levels.

The other temperature options, while potentially having an effect, either maintain sufficient penetrant effectiveness above those thresholds or are not considered as critical as the 10 degrees Celsius mark. Therefore, understanding the behavior and characteristics of liquid penetrants at various temperatures is crucial for effective non-destructive testing.