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What are non-destructive testing methods in metrology?

Measurement News from Q-Tech

Non-destructive testing methods, or NDT for short, are methods used to check the quality of components. The methods offer a number of advantages over other testing methods, but also pose challenges for the tester. 

What do experts understand by non-destructive testing methods? NDT is a collection of test methods that are used to examine materials or components for functionality without damaging them. If the manufactured part is OK, it can be used in the industrial process and does not end up as scrap.

At Q-Tech, we primarily use computed tomography in addition to optical methods. In this article you will learn about some measurement methods and which ones we use. 

Fields of application

Non-destructive testing methods are used in various fields. Well-known examples are the aviation, automotive and aerospace industries. Here, non-destructive methods play an important role in meeting the high safety standards

This can be, for example, the inspection of engines, brakes, materials and gearboxes. But NDT is also used in power generation at nuclear power plants and wind turbines. 

What non-destructive methods are available? 

In the following, you will learn about the individual procedures and get an overview of what happens during each process. 

Penetration test

In this method, a liquid with low viscosity is applied to the component to be tested. After some time, the liquid runs into the cracks of porous areas. A developer is then used, which ensures that the penetrating liquid seeps through to the top. This then provides an indication of the defects present. 

The liquids used can be washed out with water or removed with appropriate solvents

Basically, a distinction is made between dye penetrant testing and fluorescent penetrant testing

Microwave test

This method uses microwave frequencies. Here, one test probe emits the radiations, which are in turn received by another. 

The probe detects pores, cracks, voids or foreign material inclusions and visualizes the results as a B- or C-scan

Magnetic flux leakage

This process uses a strong magnet. This generates magnetic fields that can even penetrate entire steel structures such as pipelines and storage tanks. 

A sensor helps to detect changes in the magnetic flux density. These provide information on the extent to which the material is being reduced by pitting, erosion or corrosion

Leak test

Leak testing takes place using four different methods: Bubble test, pressure decay test, halogen diode test or a helium leak test.


Bladder test

Here, a water bath is used to determine whether air bubbles are escaping at certain points in the component. 

Pressure drop test

This method is only used for closed systems. A loss of pressure or vacuum over a period of time would mean that there is a leak in the system

Halogen diode test

Here, too, the tester uses pressure to find possible leaks. However, a halogen-based tracer gas and air mixture is used here. Subsequently, a halogen diode detector unit locates the leaks in the component. 

Helium leak test

The component to be tested, in most cases a container, is filled with helium or a helium-air mixture. Similar to the halogen diode test , a mass spectrometer in a surrounding housing examines the component for changes in the gas composition. If the test meter strikes, this may indicate a leak. Alternatively, a vacuum can also be used. 

Electromagnetic testing

Electromagnetic testing is one of the best known methods. It is divided into eddy current testing, alternating current field measurement and far field testing. In all tests, an electric current or a magnetic field is passed through an electrically conductive part. 

Eddy current testing

In eddy current testing , the tester induces an electromagnetic field with an AC coil into the test part. 

AC field measurement

The magnetic field is generated here with a probe. No coil is used. 

Far field test

This test is similar to the AC field measurement. However, the far-field test is more commonly used for testing pipes

Acoustic emission test

Another frequently used method is acoustic emission testing. This method is based on the detection of short ultrasonic pulses. The ultrasonic emissions are detected by sensors distributed on the surface of the structure. 

The method is often used in the detection testing of pressure vessels, but is also used for structural integrity monitoring - an important process for bridges. Leaks and corrosion can also be detected with this test. 


This optical measurement method uses X-rays and gamma rays. These beams are passed through the test part to reveal defects. 

The strength of the radiation provides information about tolerance deviations in the material. While X-rays are mainly used for thin or rather less dense materials, gamma rays are the first choice for thicker or denser objects. 

The measurement results play an important role in computed tomography, computed radiography or digital radiography

Non-destructive testing methods at Q-Tech

At Q-Tech, we pretty much always use a computer tomograph due to the technical possibilities. 

This offers a huge advantage, as this measuring device can detect porous areas inside the part, for example, without much effort. 

A so-called CT scan also works excellently for assemblies: after all, sometimes an analysis of the individual parts is not enough to find the cause of the fault. 


A complete screwed housing is examined inside with the CT. Only by assembling the individual components into a housing could the cause of the fault be found. This could be, for example, a deviating shape and position tolerance that impairs functionality. 

In the case of loosened screws and a disassembled housing, on the other hand, the CT scan would possibly not have identified the cause of the defect at all and the individual parts would have been assessed as functional, although they show clear defects in the overall picture of the assembly. 


Now that you have learned about some non-destructive testing methods, here are all the advantages of using them.

  • Materials and components are not damaged during testing 
  • Cost reduction
  • Early detection of rejects
  • Avoidance of accidents, environmental and property damage
  • Production and delivery times can be met more easily 
  • Only defective parts are considered rejects 

Challenges with non-destructive methods

Despite the advantages mentioned, there are also some hurdles in the procedures. One of the biggest challenges is that NDT usually has to be performed by specially trained personnel because the activities require a high level of expertise and experience

At Q-Tech, we have recognized this fact and therefore place great emphasis on qualified and high-quality training of our employees so that they are able to perform the test procedures accurately without any problems. 

As experts in the field of metrology and optical test methods , we at Q-Tech have created a comprehensive portfolio of services over the years that is tailored to the specific needs of our customers. 

Our skilled workers use the latest technology to ensure that the highest standards are met and the best results are achieved.

This means that our customers can be absolutely certain that the measurement processes used are of the highest quality. 

Keep in mind that non-destructive methods cannot always detect all types of damage in components. There are advantages and disadvantages to each individual method. Therefore, in case of ambiguity, it is sometimes worth combining several methods to provide a meaningful assessment of the quality condition of the component. 


Non-destructive testing methods form an important part of modern measurement technology and offer, among other things, the great advantage that tested components are not damaged during testing. 

Due to the high technical requirements, experience, expertise and qualification are crucial. Q-Tech is your personal, reliable and experienced partner in this. We offer optical measurement processes that easily meet your requirements.