Non-destructive testing (NDT) is a

technique to evaluate the properties

of a material without causing any

damage to the component being

tested. It determine the external

(surface) and or internal defect.

It takes less time as compared to

destructive testing. Thus it saves

time and money. It is applicable to

all spheres of life. Some of the most

important are inspection of welded joint,

human x-rays and ultra-sound testing.

Non-destructive testing (NDT) is also

said as Nondestructive

examination (NDE) or Nondestructive

inspection (NDI) or Nondestructive

evaluation (NDE)


  1. Visual Testing Technique

  2. Dye Penetration Technique

  3. Magnetic –Particle Technique

  4. Ultrasonic Testing Technique

  5. Eddy Current Testing Technique

  6. Radiographic Testing Technique

Visual testing

It uses the followings:

  1. Visual inspection by the naked eye

  2. Mirrors

  3. Magnifying glasses

  4. Microscopes (optical and electron microscopes)

  5. Closed circuit television (CCTV)

Dye Penetration Technique

Most commonly used method. It detects the surface and internal cracks. This test uses three fluids. These are

  1. Cleaner to clean the surface

  2. Penetrating dye to penetrate in the crack

  3. Developer to pull out the penetrating dye

Magnetic –particle technique

Determines the  surface defects (discontinuity, crack or foreign material) in magnetic materials like iron and ferrite steel. Magnetize the component with the help of MPT equipment. Then spray finally divided iron particles over the surface. The portion not having iron particles is defective. This method tests welded joint and gas pipes.

Ultrasonic testing technique

Locate the internal defects. Introduce  high frequency sound waves in the component. These sound waves reflected back from the surface and the defective portion. Inspection of the photographic plate clearly points the defective portions.

Eddy current testing technique

It finds surface defects.  Produce Eddy currents by a coil carrying AC current by induction. It determines the crack, corroded surface, thin material thickness, thickness of thin coating and measurement of conductivity.

Radiographic Testing

Determines the internal defects. It uses high energy photons (short wavelength electro-magnetic radiations). It is same as X-ray in medical radiography. However the wavelength used here is different.


  1. Firstly it is easy and fast.

  2. Secondly it is economical.  There is no harm to the material.

  3. Thirdly it increases the safety and reliability of a product.

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