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Nondestructive Testing

Publish Date 2010-11-01
Nondestructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research.
NDT methods may rely upon use of electromagnetic radiation, sound, and inherent properties of materials to examine samples. This includes some kinds of microscopy to examine external surfaces in detail, although sample preparation techniques for metallography, optical microscopy and electron microscopy are generally destructive as the surfaces must be made smooth through polishing or the sample must be electron transparent in thickness. The inside of a sample can be examined with penetrating electromagnetic radiation, such as X-rays, or with sound waves in the case of ultrasonic testing. Contrast between a defect and the bulk of the sample may be enhanced for visual examination by the unaided eye by using liquids to penetrate fatigue cracks. One method (liquid penetrant testing) involves using dyes, fluorescent or non-fluorescing, in fluids for non-magnetic materials, usually metals. Another commonly used method for magnetic materials involves using a liquid suspension of fine iron particles applied to a part while it is in an externally applied magnetic field (magnetic-particle testing).
NDT is used in a variety of settings that covers a wide range of industrial activity.
Engine parts
Aviation / Aerospace
Reciprocating Engines
Gas turbine engines
Maintenance, repair and operations
Machine parts
Castings and Forgings
Industrial plants such as Nuclear, Petrochemical, Power, Refineries, Pulp and Paper, Fabrication shops, Mine processing and their Risk Based Inspection programmes.
Pressure vessels
Storage tanks
Heat exchangers
Turbine bores
In-plant Piping
In-line Inspection using "pigs"
Pipeline integrity management
Leak Detection
Rail Inspection
Wheel Inspection
Tubular NDT, for Tubing material
Corrosion Under Insulation (CUI)
Amusement park rides
Submarines and other Naval warships
Medical imaging applications (see also Medical physics)

Methods and techniques
An example of a 3D replicating technique. The flexible high-resolution replicas allow surfaces to be examined and measured under laboratory conditions. A replica can be taken from all solid materials.
NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle. These methods may be further subdivided into various techniques. The various methods and techniques, due to their particular natures, may lend themselves especially well to certain applications and be of little or no value at all in other applications. Therefore choosing the right method and technique is an important part of the performance of NDT.
Acoustic emission testing (AE or AT)
Dye penetrant inspection Liquid penetrant testing (PT or LPI)
Electromagnetic testing (ET)
Alternating current field measurement (ACFM)
Alternating current potential drop measurement (ACPD)
Barkhausen testing
Direct current potential drop measurement (DCPD)
Eddy-current testing (ECT)
Magnetic flux leakage testing (MFL) for pipelines, tank floors, and wire rope
Magnetic-particle inspection (MT or MPI)
Remote field testing (RFT)
Hardness testing (Brinell) (HT)
Impulse excitation technique (IET)
Infrared and thermal testing (IR)
Thermographic inspection
Laser testing
Electronic speckle pattern interferometry
Holographic interferometry
Leak testing (LT) or Leak detection
Absolute pressure leak testing (pressure change)
Bubble testing
Halogen diode leak testing
Hydrogen leak testing
Mass spectrometer leak testing
Tracer-gas leak testing method Helium, Hydrogen and refrigerant gases
Magnetic resonance imaging (MRI) and NMR spectroscopy
Optical microscopy
Positive Material Identification (PMI)
Radiographic testing (RT) (see also Industrial radiography and Radiography)
Computed radiography
Digital radiography (real-time)
Neutron radiographic testing (NR)
SCAR (Small Controlled Area Radiography)
X-ray computed tomography (CT)
Scanning electron microscopy
Ultrasonic testing (UT)
Electro Magnetic Acoustic Transducer (EMAT) (non-contact)
Laser ultrasonics (LUT)
Internal rotary inspection system (IRIS) ultrasonics for tubes
Phased array ultrasonics
Time of flight diffraction ultrasonics (TOFD)
Time of Flight Ultrasonic Determination of 3D Elastic Constants (TOF)
Visual inspection (VT)
Pipeline video inspection

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