The liquid penetrant method of nondestructive testing has been used since the 1940’s. But even after being used by generations of NDT professionals, there are still some common areas of confusion or misunderstanding.
Here we set the record straight on 10 misperceptions we’ve seen in the field in recent years.
1. The highest sensitivity penetrant is the best penetrant for my application
The best penetrant for an application is the one that finds the right indications with the least amount of money and time. Sometimes this means not using the highest sensitivity penetrant.
While it is true that a higher sensitivity penetrant will produce indications for very small discontinuities, a higher sensitivity penetrant will probably not give you the best inspection results if you only need to find medium discontinuities since you will see far more indications than are relevant to the inspection.
To start selecting a penetrant, review any governing specifications and work procedures for required sensitivity levels.
Take into consideration the surface finish and configuration of the part.
A high sensitivity level fluorescent penetrant is appropriate for smooth, highly machined surfaces. However, a high sensitivity level fluorescent penetrant may leave excessive fluorescent background on a rough cast part, making inspection difficult.
A lower sensitivity fluorescent penetrant is a better choice for rough surfaces.