Non Destructive Testing | NDT Testing | Procedure Of NDT

What is Nondestructive testing (NDT)

Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system. In other words, when the inspection or test is completed the part can still be used.

In contrast to NDT, other tests are destructive in nature and are therefore done on a limited number of samples (“lot sampling”), rather than on the materials, components or assemblies actually being put into service.

These destructive tests are often used to determine the physical properties of materials such as impact resistance, ductility, yield and ultimate tensile strength, fracture toughness and fatigue strength, but discontinuities and differences in material characteristics are more effectively found by NDT.

Today modern nondestructive tests are used in manufacturing, fabrication and in-service inspections to ensure product integrity and reliability, to control manufacturing processes, lower production costs and to maintain a uniform quality level. During construction, NDT is used to ensure the quality of materials and joining processes during the fabrication and erection phases, and in-service NDT inspections are used to ensure that the products in use continue to have the integrity necessary to ensure their usefulness and the safety of the public.

It should be noted that while the medical field uses many of the same processes, the term “nondestructive testing” is generally not used to describe medical applications.

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.

Methods of NDT include , Types of NDT : 

  1. Magnetic Particle Testing (MT)
  2. Liquid Penetrant Testing (PT)
  3. Radiographic Testing (RT)
  4. Ultrasonic Testing (UT)
  5. Electromagnetic Testing (ET)
  6. Visual Testing (VT)
  7. Acoustic Emission Testing (AE)
  8. Guided Wave Testing (GW)
  9. Laser Testing Methods (LM)
  10. Leak Testing (LT)
  11. Magnetic Flux Leakage (MFL)
  12. Neutron Radiographic Testing (NR)
  13. Thermal/Infrared Testing (IR)
  14. Vibration Analysis (VA)

Procedure Of NDT 

Liquid penetrant method:
In this method the surfaces to be inspected should be free from any coatings, paint, grease. dirt, dust, etc., therefore, should be cleaned with an appropriate way. Special care should be taken not to give additional damage to the surface to be inspected during the cleaning process.
Otherwise, the original nature of surface could be disturbed and the results could be erroneous with the additional interferences of the surface features formed during the cleaning process.
Surface cleaning can be performed with alcohol. Special chemicals like cleaner-remover can also be applied if needed. In the experiment, only cleaner-remover will be sufficient. Subsequent to surface cleaning, the surface is let to dry for 2 minutes. Commercially available cans of liquid penetrant dyes with different colors are used to reveal the surface defects.

Steps used in the experiment:

1. Clean the surface with alcohol and let surface dry for 5 min.
2. Apply the liquid penetrant spray (red can) to the surface and brush for further penetration. Then, wait for 20 min.
3. Wipe the surface with a clean textile and subsequently apply remover spray (blue can) to remove excess residues on the surface and wait for a few min.
4. Apply the developer spray (yellow can) at a distance of about 30cm from the surface. The developer will absorb the penetrant that infiltrated to the surface features such as cracks, splits, etc., and then reacted with it to form a geometric shape which is the negative of the
geometry of the surface features from which the penetrant is sucked.
5. The polymerized material may be collected on a sticky paper for future evaluation and related documentation, if needed.

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