What is a key difference between nonwater-washable and water-washable penetrants?

The key difference highlighted in the correct answer involves the composition of water-washable penetrants, specifically their inclusion of emulsifiers. Water-washable penetrants are designed to be removed by water, and the presence of emulsifiers is what makes this possible. Emulsifiers help to disperse the penetrant in water, allowing for effective cleaning and removal after inspection processes. This property is particularly advantageous in non-destructive testing, as it simplifies the cleaning process and can enhance the reliability of defect detection.

In contrast, non-water-washable penetrants do not contain emulsifiers and must be removed using solvents or other means, which can complicate the inspection process and may take more time. Understanding this key distinction can aid professionals in selecting the appropriate penetrant for their testing needs, factoring in the ease of cleanup and the specific requirements of their inspection protocols.