LPI is best described as which of the following?

• A. A radiographic method for detecting internal flaws
• B. A physical chemical NDT procedure used to economically detect surface discontinuities in non-porous materials
• C. A magnetic method for surface defects
• D. A thermal method for continuous monitoring

Answer: (B)

Liquid Penetrant Inspection is a surface-detection nondestructive testing method. It uses a liquid penetrant that infiltrates only surface-breaking defects in non-porous materials through capillary action. After cleaning the surface, the penetrant is applied, allowed to dwell so it can seep into flaws, and then the excess penetrant is removed. A developer is added to draw the penetrant out of the flaw, creating a visible indication under proper lighting (colored or fluorescent). This approach is economical because it uses simple materials, straightforward steps, and is highly sensitive to surface discontinuities, making it ideal for finding cracks, laps, and porosity that meet the surface. It’s specifically for non-porous materials and targets surface defects, unlike radiography (internal defects), magnetic methods (magnetic particle focuses on magnetic leakage), or thermal methods (heat-based indications).