18 June 2021
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What is NDT?
What is NDT? Minimize

Non-destructive testing is the branch of engineering concerned with all methods of detecting and evaluating flaws in materials. Flaws can affect the serviceability of the material or structure, so NDT is important in guaranteeing safe operation as well as in quality control and assessing plant life. The flaws may be cracks or inclusions in welds and castings, or variations in structural properties which can lead to loss of strength or failure in service.

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 spacings and for the measurement of physical properties such as hardness and internal stress.

The essential feature of NDT is that the test process itself produces no deleterious effects on the material or structure under test.

The subject of NDT has no clearly defined boundaries; it ranges from simple techniques such as visual examination of surfaces, through the well-established methods of radiography, ultrasonic testing, magnetic particle crack detection, to new and very specialised methods such as the measurement of Barkhausen noise and positron annihilation.

NDT methods can be adapted to automated production processes as well as to the inspection of localised problem areas.

Here are some of the most widely used NDT techniques:

* Acoustic methods
* Acoustic emission (AE)
* Resonant inspection
* Acoustic ranging
* Coating thickness measurement methods
* Electromagnetic methods
* Magnetic particle inspection (MPI)
* Magnetic flux leakage methods
* Eddy current testing
* ACFM technique
* Potential drop flaw detection and sizing
* Erosion corrosion
* Leak testing methods
* Liquid penetrant inspection
* Optical methods
* Visual inspection
* Optical metrology and holography
* Laser-based inspection
* Thermography
* Radiography
* Real-time radiography and radioscopy
* Neutron radiography
* Stress measurement
* Ultrasonic methods
* Ultrasonic flaw detection
* Ultrasonic thickness gauging
* Ultrasonic advanced methods

For further information on these visit:

For advice on choice of NDT method, visit:

In addition, The Japanese Society for Nondestructive Inspection (JSNDI) has produced a DVD: "An introduction to NDT" which is available to purchase via the JSNDI website at:

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