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non destructive testing
Nondestructive testing (NDT) allows inspection or measurement of materials without causing damage. Common NDT methods include visual testing, liquid penetrant testing, magnetic particle testing, ultrasonic testing, eddy current testing, and radiography. These methods are used to detect inherent, processing, and service defects in raw materials and components, as well as to inspect for in-service damage in applications like aircraft engines, rails, and bridges in order to ensure safety and prevent failures.
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non destructive testing
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- 2. OUTLINE Introduction to NDT Overviewof Six Most Common NDT Methods Selected Applications
- 3. DEFINITION OF NDT NDThas been defined as comprising those test methods used to examine an object, material or system without impairing its future usefulness. The term is generally applied to nonmedical investigations of material integrity i.e. Inspect or measure without doing harm.
- 4. THREE TYPES OF DEFECTS Inherentdefects :- exist in parent materials Processing defects:- developed during processing Service defects :- developed during service are
- 5. COMMON DEFECTS ANDCAUSES Description The depth of the weld is less than specifications. The weld metal is not completely fused to base metal or passes are not completely fused. Weld material flows over, but is not fused with the base metal. Cause(s) Excessive heat Excessive speed. Incorrect angle Insufficient heat Slow speed 5
- 6. COMMON DEFECTS ANDCAUSES--CONT. Description Weld bead does not extend to the desired depth. Small indentions in the surface of the weld Small voids throughout the weld material. Cause(s) Low heat Long arc Incorrect joint design Excessive gas in the weld zone. Moisture Rust Dirt Accelerated cooling 6
- 7. COMMON DEFECTS ANDCAUSES--CONT. Description Cause(s) Usually visible cracks on the surface or through the weld Accelerated cooling Small weld volume Cracks in the transition zone between the weld and base metal Induced hydrogen Incompatible electrode or wire Accelerated cooling Irregular shape and/or uneven ripples Incorrect speed Incorrect welder settings 7
- 8. WHAT ARE SOMEUSES OF NDT 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
- 9. SIX MOST COMMONNDT METHODS • • • • • • Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current X-ray
- 10. VISUAL TESTING experienced inspectorknows where are likely cracks , orientation of cracks relative to various zones in the weld, surface porosity, weld penetration, potential weakness such as sharp notches or misalignment
- 11. Most basic andcommon 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.
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- 13. INTRO•Penetrant Testing, orPT, is a nondestructive testing method that builds on the principle of Visual Inspection. •PT increases the “seeability” of small discontinuities that the human eye might not be able to detect alone.
- 14. BASIC STEPS OFDYE PENETRANT TESTING clean the surface apply penetrant remove excess penetrant apply developer inspect / interpretation penetrant seep into flaw developer draws penetrant onto surface
- 16. A DVA NTAGES & LIMITA TIONS OF LIQUID PENETRA NT METHOD ADVANTAGES LIMITATIONS Simple & inexpensive Detect surface flaws Versatile & portable Applicable to ferrous, non-ferrous, nonmagnetic & complex shaped materials which are non-porous & of any dimension Detects cracks, seams, lack of bonding, etc. Non-porous surface of material Surface cleaning before & after inspection Deformed surfaces & surface coatings prevent detection
- 17. MAGNETIC PARTICLE INSPECTION The partis magnetized. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.
- 20. RADIOGRAPHY The radiation usedin radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see as visible light. The radiation can come from an X-ray generator or a radioactive source. High Electrical Potential Electrons + - X-ray Generator or Radioactive Source Creates Radiation Radiation Penetrate the Sample Exposure Recording Device
- 21. FILM RADIOGRAPHY The part isplaced 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. X-ray film Top view of developed film The film darkness (density) will vary with the amount of radiation reaching the film through the test object.
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- 23. MERITS & DEMERITS Demerits Merits Noneed of washing and developing films Poor resolution Low cost Electronic image intensifier required for increasing the contrast Image viewed immediately on screen Time consumption is less Movement of defects detected (real time images) Permanent record can be made Low image contrast
- 24. EDDY CURRENT TESTING Coil Coil's magneticfield Eddy current's magnetic field Eddy currents Conductive material
- 26. Eddy current test (a) The alternating current flowing through the coil at a chosen frequency generates a magnetic field around the coil. ( b) When the coil is placed close to an electrically conductive material, eddy current is included in the material. (c) If a flaw in the conductive material disturbs the eddy current circulation, the magnetic coupling with the probe is changed and a defect signal can be read by measuring the coil impedance variation.
- 28. ULTRASONIC INSPECTION (PULSE-ECHO) areintroduced into a High frequency sound waves material and they are reflected back from surfaces or flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen f showing the depth of features that reflect sound. initial pulse crack echo back surface echo crack 0 2 4 6 8 Oscilloscope, or flaw detector screen 10 plate
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- 30. ULTRA SONIC FLAW DETECTION
- 32. COMMON APPLICATION OF NDT Inspectionof Raw Products Inspection Following Secondary Processing In-Services Damage Inspection
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- 34. INSPECTION FOLLOWING SECONDARY PROCESSING Machining Welding Grinding Heattreating Plating etc.
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- 36. CRASH OF UNITED FLIGHT232 Sioux City, Iowa, July 19, 1989 A defect that went undetected in an engine disk was responsible for the crash of United Flight 232.
- 37. RAIL INSPECTION Special cars areused to inspect thousands of miles of rail to find cracks that could lead to a derailment.
- 38. BRIDGE INSPECTION • TheUS has 578,000 highway bridges. • Corrosion, cracking and other damage can all affect a bridge’s performance. • The collapse of the Silver Bridge in 1967 resulted in loss of 47 lives. • Bridges get a visual inspection about every 2 years. • Some bridges are fitted with acoustic emission sensors that “listen” for sounds of cracks growing.
Editor's Notes
- #25 Eddy currents (also called Foucault currents are electric currents induced within conductors by a changing magnetic field in the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsion, attraction,[2] propulsion, drag, and heating effects.
- #34 Metal forging is a metal forming process that involves applying compressive forces to a work piece to deform it, and create a desired geometric change to the material Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section.
- #38 The heavy loads that trains place on the railroad tracks can result in the formation of cracks in the rail. If these cracks are not detected, they can lead to a derailment. Special rail cars equipped with NDT equipment are used to detect rail defects before they are big enough to cause serious problems.