Information sheet

Non destructive testing

The field of Non destructive Testing (NDT) is a very broad, interdisciplinary field that plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion.

NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of less visible, but equally troubling events.

These tests are performed in a manner that does not affect the future usefulness of the object or material. In other words, NDT allows parts and materials to be inspected and measured without damaging them.


Because it allows inspection without interfering with a product`s final use, NDT provides an excellent balance between quality control and cost-effectiveness.

Generally speaking, NDT applies to industrial inspections. While technologiesare used in NDT that are similar to those used in the medical industry, typically non living objects are the subjects of the inspections.​

​Non Destructive Evaluation

Nondestructive Evaluation (NDE) is a term that is often used interchangeably with NDT. However, technically, NDE is used to describe measurements that are more quantitative in nature.

For example, a NDE method would not only locate a defect, but it would also be used to measure something about that defect such as its size, shape, and orientation.

NDE may be used to determine material properties such as fracture toughness, formability, and other physical characteristics.​

NDT/NDE Methods

The number of NDT methods that can be used to inspect components and make measurements is large and continues to grow.

Researchers continue to find new ways of applying physics and other scientific disciplines to develop better NDT methods.

However, there are six NDT methods that are used most often. These methods are visual inspection, penetrant testing, magnetic particle testing, electromagnetic or eddy current testing, radiography, and ultrasonic testing. These methods and a few others are briefly described below.

Visual and Optical Inspection (VI)

Visual inspection involves using an inspector`s eyes to look for defects. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. Visual examiners follow procedures that range from simple to very complex.

Dye Penetrant Inspection (DPI)

Test objects are coated with visible or fluorescent dye solution. Excess dye is then removed from the surface, and a developer is applied. The developer acts as blotter, drawing trapped penetrant out of imperfections open to the surface. With visible dyes, vivid color contrasts between the penetrant and developer make "bleedout" easy to see. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be readily seen.

Magnetic Particle Testing (MPI)

This NDT method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles (either dry or suspended in liquid). Surface and near-surface imperfections distort the magnetic field and concentrate iron particles near imperfections, previewing a visual indication of the flaw.

Radiographic Testing (RT)

Radiography involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. An X-ray generator or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other imaging media.

The resulting shadowgraph shows the dimensional features of the part. Possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones.

​Ultrasonic Testing (UT)

Ultrasonics use transmission of high-frequency sound waves into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo, wherein sound is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections or from the part`s geometrical surfaces.

Phased Array Testing (PAUT)

Phased array is widely used for nondestructive testing (NDT) in several industrial sectors, pipelines. This method is an advanced NDT method that is used to detect discontinuities i.e. cracks or flaws and thereby determine component quality. Due to the possibility to control parameters such as beam angle and focal distance, this method is very efficient regarding the defect detection and speed of testing. Apart from detecting flaws in components, phased array can also be used for wall thickness measurements in conjunction with corrosion testing. Phased array can be used for the following industrial purposes:

  • ​Inspection of welds  
  • ​Thickness measurements
  • ​PAUT Validation / Demonstration Blocks
  • ​Rolling stock inspection (wheels and axles)
  • ​​PAUT & TOFD Standard Calibration Blocks

Leak Testing (LT)

Several techniques are used to detect and locate leaks in pressure containment parts, pressure vessels, and structures. Leaks can be detected by using electronic listening devices, pressure gauge measurements, liquid and gas penetrant techniques, and/or a simple soap-bubble test.

Electromagnetic Testing (ET) or Eddy Current Testing

Electrical currents are generated in a conductive material by an induced alternating magnetic field. The electrical currents are called eddy currents because they flow in circles at and just below the surface of the material. Interruptions in the flow of eddy currents, caused by imperfections, dimensional changes, or changes in the material`s conductive and permeability properties, can be detected with the proper equipment.

Postal address:

Box 86

SE - 132 23 Saltsjö-Boo

​Phone: +46 8 - 715 16 60

​Email: info@nordicndt.se

Address:

​Stenhuggarvägen 1

​SE - 132 38 Saltsjö-Boo

Find us