NON-DESTRUCTIVE TESTING

NDT is an inspection of an object or material without damaging it physically. In short, NDT is the process of inspecting, testing, or evaluating materials, components or assembling for discontinuities. We can also say after the testing is completed, the object is used.

There are various Non-destructive testing processes. They are of immense help to multiple industries too. First, we shall look at the different possible testing processes!

MAGNETIC TESTING

In this process, more than one magnetic field is created to locate discontinuities in ferromagnetic substances. The application of magnetic fields can be in many ways, like with the help of electromagnets or permanent magnets. If the magnetic field encounters a discontinuity is the magnetic field direction, the flux lines produce a leakage field of their own.  

The magnetic testing techniques are:

• Yokes
• Prods
• Coils
• Heads
• Central Conductor

LIQUID PENETRATING TEST

The use of a low viscous liquid is the main principle for this test. When this liquid is applied to the surface, it will penetrate discontinuities. When the excess liquid is removed, the penetrant trapped in those voids will flow back out, creating an indication. It can be done on both magnetic and non-magnetic materials. But won’t work well on porous materials.

Some of the liquid penetrating test techniques are:

• Solvent Removable
• Water-Washable
• Post-Emulsifiable

RADIOGRAPHIC TESTING

Industrial Radiography involves exposing an object to penetrating radiation so that the radiation passes through the object. It is inspected and recorded against the opposite side of that object.  For thin materials such as aluminium, electrically generated x-radiation (X-rays), it is commonly used, and for thicker materials, usually, gamma radiation is used. 

The radiographic techniques are:

• Film Radiography
• Computed Radiography
• Computed Tomography
• Digital Radiography

ULTRASONIC TESTING

High-frequency sound waves are sent through the material being tested. If there is any part with different acoustic impedance, then some of the sent sound waves will return as signals. Ultrasound will not travel through the air, a liquid or gel called “couplant”. It is used between the face of the transducer and the surface of the part so that sound can be transmitted. 

The Ultrasonic testing techniques are:

• Straight Beam
• Angle Beam
• Immersion testing
• Through transmission
• Phased array
• Time of flight diffraction

ELECTROMAGNETIC TESTING

Electromagnetic is a general test category which is also known as a stand-alone test method. 

The electromagnetic testing techniques are:

Eddy Current testing

Alternating current field measurement

Remote field testing

VISUAL TESTING

The most commonly used testing method in the industry. It involves direct visual observation of the surface. Visual Testing inspections may be by Direct Viewing, using line-of-sight vision, or maybe enhanced with the use of various optical instruments such as magnifying glasses, mirrors, borescopes, Charge-Coupled Devices (CCDs) and Computer-Assisted viewing systems (Remote Viewing). 

LASER TESTING METHODS:

We all know laser. The Light Amplification by Stimulated Emission of Radiation is a definition in itself.

The laser testing techniques are:

• Holographic testing
• Laser Profilometry
• Laser Shearography

NEUTRON RADIOGRAPHIC TESTING:

Neutron radiography uses a high beam of neutrons which have low energy as a penetrating medium rather than gamma- or x-radiation which is used in conventional radiography.  It is generated by linear accelerators, betatrons and other sources. They are attenuated by most organic materials (including water, due to its high hydrogen content) which allow those materials to have an inspection. 

It is also used with conventional radiography, both the structural and internal components of a test piece can be viewed.

VIBRATIONAL ANALYSIS:

Vibration analysis is the process of analysing the vibration signatures specific to a piece of rotating machine and analysing that information to determine the condition of the equipment.  There are three types of sensors are commonly used: displacement sensors, velocity sensors and accelerometers.

Displacement sensors use eddy current to detect vertical and horizontal motion and are well suited to detect shaft motion and changes in clearance tolerances. 

The necessary velocity sensors use a spring-mounted magnet that moves through a wire coil, whereas the outer case attached is being inspected. The wire coil of wire runs through the magnetic field which generates an electrical signal which is sent back to the receiver. It is also recorded for analysis. The newer model vibration sensors use time-of-flight technology and improved analysis software. 

The above are only some of the testing methods and Growth of NDT in recent years. Now let us walk through the industries that require the help of NDT Inspection companies: –

• Aerospace
• Automotive
• Medical
• Consumer
• Commercial
• Construction
• Marine
• Military 

There are many more industries that use the non-destructive methods of testing to manufacture and learn the behaviour of various materials to determine their applications. NDT can be used without damaging a product as it allows inspection. Hence, NDT is an excellent balance of quality and cost-effectiveness.