The Evolution of Nondestructive Testing

Over the past 100 years, Nondestructive testing has made tremendous advances. New NDT methods have been introduced, while old “tried and true” methods continue to be improved. Although some NDT methods have drastically changed or “evolved” over time, the principle behind each method has remained the same; “To ensure the safety and integrity of manufactured items or goods.”

Liquid Penetrant Inspection (LPI)

One of the first methods of NDT was an early form of Liquid Penetrant Inspection called the “Oil and Whiting Method”. Primarily used in the Railway industry, early inspectors used this method to increase the “see ability” of defects not normally seen visually. Parts were typically pre-cleaned then immersed in either hot oil or waste oil, sometimes diluted in kerosene. Once thoroughly coated in oil, the parts were carefully wiped clean and dry. Parts were then coated with a white chalk. Often the chalk was mixed in suspension with alcohol. This would provide a contrasting white surface layer on the part once the alcohol had evaporated. The chalk would then act as not only a contrasting background, but a type of “blotter” as well. This blotting action would aid the oil that had crept into surface openings, be drawn back to the surface to reveal the presence of a flaw. Present day penetrants are very similar in their properties. They still use the same principle of “capillary action” to enter surface flaws, and produce indications that are visible to the inspector. Penetrants are now more portable, safer and easier to use and relatively inexpensive.