Introduction to Non-Destructive Test(NDT)

Introduction to Non-Destructive Test(NDT)

Non-Destructing Test(NDT) is an analysis technique used in science and manufacturing industries for the inspection, testing, evaluating properties of the material and the assemblies for discontinuities without causing damage.

it was a big challenge for manufacturing industries to ensure the performance and the service life of a component or system so, to fix this challenge NDT was introduced.state of art methodology is applied to assess the current condition, fitness for service and remaining life of the equipment. Non Destructive Test inspection provides basic data helping to develop strategic plans for extending plant life.

Non Destructive Test life assessment service include -

1. Fitness for service evaluation.
2. Predict fatigue damage
3. Predict creep damage 
4. Assembly integrity analysis.
5. Predict corrosion damage.

Non Destructive Test technologies are -

1. Ultrasonic Test
2. Thermography Test
3. Visual inspection
4. Liquid Penetration
5. Radiography
6. Magnetic particle test

1.Ultrasonic Test:

Ultrasonic Test is used to find the defect and the discontinuity when the component is made up of ferrous and non-ferrous material. in this test, transmission of a  high-frequency sound wave into a material to detect the discontinuity and to locate the change in the material properties.. any internal discontinuity interrupts the beam and reflects back to a portion of the sound energy. the amplitude of the reflected energy and the time required for return, indicate the presence and the location of the defect in the components.

Advantages

1. Capable of being automated.
2. Instant test result.
3. Access to only one side necessary.
4. It is not hazardous.

Disadvantage

1. Rough material, an irregular shape is difficult to inspect.
2. It requires a highly skilled and experienced operator.

2.Thermography Test

Thermography Test is used to obtain the thermal image of the components in order to detect surface or sub-surface defect in the components. this test is based on the fact that the internal structure of the test components and its flaws will have a different thermal behaviour.when the thermal wave reaches to the defect then the rate of propagation changes.

Advantages

• It shows a visual picture 
• Able to find deteriorating.
• Not require skilled monitoring.

Disadvantages

• Cost of the instrument is relatively high.
• Difficult to interpret

3.Visual inspection

It is one of the basic inspection methods for many applications. This inspection involves using an inspectors eyes to look for defects. It is the first step in the examination process to inspect the product including, forging, casting, and machined products

Advantages

• Economical
• Gives fast result
• Portability

Disadvantages

• should have good eyesight
• Suitable for visible surface
• Not suitable for small defects

4.Liquid penetration

This method is suitable for the components which are made up of ferrous and non-ferrous material.

A cloured liquid is applied on the surface of the body is allowed to penetrate into the flaw by capillary action and low surface tension. The developer acts like a blotter and draws the penetrant out of the flaw. the components are inspected under ultraviolet light to reveal the presence of the defect.

Advantages

• the very small discontinuity can be detected 
• suitable for complex shape also
• portable 
• low cost 

Disadvantages 

• Only surface breaking detect
• post cleaning is required 
• Multiple process operation must be performed 

5.Radiography

In this method, either X-ray or Gamma ray is used to inspect the body. Radiation is directed through a part and then onto a film. finally, the inspection result shows in the dimensional features of the part.

Advantages

• Applicable for all the material
• permanent record of inspection.
• Assemblies can also be inspected

Disadvantages 

• Expensive 
• High-intensity radiation
• slow result 

6.Magnetic particle test

This inspection method is used to the body which is made up of the ferromagnetic material such as steel and iron. the test body is magnetised by inducing an electric current into it. In case of any defect, the magnetic field lines get interrupted creating magnetic poles of attraction. 

Advantages 

• Economical
• portable
• Excellent for very shallow and fine surface cracks

Disadvantages 

• Difficult to find out the internal defect
• post demagnetization is require
• chances to burnt the material during magnetization.