Definition of NDTThe use of noninvasivetechniques to determinethe integrity of a material,component or structure orquantitatively measuresome characteristic ofan object. i.e. Inspect or measure without doing harm.
What are Some Uses of NDE Methods?• Flaw Detection and Evaluation• Leak Detection• Location Determination• Dimensional Measurements Fluorescent penetrant indication• Structure and Microstructure Characterization• Estimation of Mechanical and Physical Properties• Stress (Strain) and Dynamic Response Measurements• Material Sorting and Chemical Composition Determination
Common Application of NDT• Inspection of Raw Products• Inspection Following Secondary Processing• In-Services Damage Inspection
Visual Inspection Most basic and common inspection method. Tools include fiberscopes, borescopes, magnifying glasses and mirrors. Portable video inspection unit with zoom allows inspection of large tanks and vessels, railroad tank cars, sewer lines. Robotic crawlers permit observation in hazardous or tight areas, such as air ducts, reactors, pipelines.
Liquid penetrant testing1. Section of material witha surface-breaking crackthat is not visible to thenaked eye.2. Penetrant is applied tothe surface.3. Excess penetrant isremoved.4. Developer is applied,rendering the crack visible 2
RadiographyThe radiation used in radiography testingis a higher energy (shorter wavelength) High Electrical Potentialversion of the electromagnetic waves thatwesee as visible light. The radiation can Electronscome from an X-ray generator or a + -radioactive source. X-ray Generator or Radioactive Source Creates Radiation Radiation Penetrate the Sample Exposure Recording Device
Film Radiography The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation. The film darkness (density) will vary with the amount of radiation X-ray film reaching the film through the test object. = less exposure = more exposureTop view of developed film
Ultrasonic Inspection (Pulse-Echo)High frequency sound waves are introduced into a materialand they are reflected back from surfaces or flaws.Reflected sound energy is displayed versus time, andinspector can visualize a cross section of the specimenshowing the depth of features that reflect sound. f initial pulse back surface echo crack echo crack 0 2 4 6 8 10 plate Oscilloscope, or flaw detector
Eddy Current Testing Coils Coil magnetic field Eddy currents magnetic fieldEddycurrents Conductive material
→Introduction of the Magnetic Field:1.Using a permanent magnet or anelectromagnet that contacts the test piece2.Flowing an electrical current through thespecimen3.Flowing an electrical current through a coilof wire around the part or through a centralconductor running near the part.
Power Plant Inspection Periodically, power plants are shutdown for inspection. Inspectors feed eddy current probes into heat exchanger tubes to check for corrosion damage. Pipe with damage Prob e Signals produced by various amounts of corrosion thinning.