Liquid penetrant testing is probably the most widely used NDT method. The test object or material is coated with a visible or fluorescent dye solution. The excess dye is removed from the surface, and then a developer is applied. The developer acts like a blotter. It draws penetrant out of the imperfections which are open to the surface. With visible dyes, the vivid color contrast between the penetrant and the developer makes the bleed out easy to see. An ultraviolet lamp is used to make the bleed out fluoresce nce brightly, thus allowing the imperfection to be seen clearly.
Non-destructive testing allows us to examine structures, materials or components without damaging or destroying the object being tested, and provides a means to ensure product reliability and quality. There are an assortment of NDT techniques used throughout a broad cross-section of industries. The Four most widely used techniques being Radiography, Ultrasonic, Liquid penetrant and Magnetic particle testing.
Non-destructive testing is used for in-service inspection and for condition monitoring of operating plant. It is also used for measurement of components and for the measurement of physical properties such as hardness and internal stress.
Around the world, NDT technicians do thousands of inspections and tests every day to assess new product quality, equipment condition and reliability. By doing so, they help prevent failures in nuclear power, aviation, transportation, oil and gas, petrochemical plants and anywhere else where public safety or the environment could be significantly impacted. All without destroying or disassembling the item that is being inspected.
(as per ANSI/ASNT CP-105,ASNT Standard Topical Outlines for Qualification of Non-destructive Testing Personnel, latest edition)Download Liquid Penetrate testing Syllabus