THEORY EXAMINATION (SEM–VIII) 2016-17 NON-DESTRUCTIVE TESTING

Non-Destructive Testing (NDT) – Section Wise Explanation

Section A – Basic Concepts of NDT

Section A contains short questions that test the basic understanding of non-destructive testing methods and terminology. Students must attempt all questions in this section. 

Non-Destructive Testing (NDT) is a technique used to inspect materials, components, and structures without damaging them. It is widely used in industries such as aerospace, manufacturing, construction, and oil and gas to detect defects and ensure safety.

The main purpose of NDT is to identify flaws such as cracks, voids, corrosion, and internal defects without affecting the usability of the material. Unlike destructive testing, where a specimen is damaged during testing, NDT methods allow components to remain intact after inspection.

Some of the common NDT techniques include visual inspection, liquid penetrant testing, magnetic particle inspection, ultrasonic testing, radiographic testing, and eddy current testing. Each technique is used for detecting specific types of defects.

For example, visual inspection is the simplest method and involves examining the surface of a component using the naked eye or optical instruments. Fluorescent dyes are used in liquid penetrant testing to reveal surface cracks. Magnetic particle inspection is used for detecting defects in ferromagnetic materials.

Other important concepts include piezoelectricity, which is used in ultrasonic testing to convert electrical energy into mechanical vibrations. Similarly, acoustic emission refers to the sound waves generated when materials undergo stress or deformation.

Understanding these basic concepts helps students build a strong foundation for advanced NDT techniques.

Questions for Section A

What is Non-Destructive Testing (NDT)?

What equipment is commonly used in visual inspection?

What is fluorescent dye and how is it used in testing?

What are the advantages of magnetic particle inspection?

What is an emulsifier in liquid penetrant testing?

What is piezoelectricity?

What is acoustic emission?

What is the function of a transducer in ultrasonic testing?

What is eddy current?

What is dwell time in liquid penetrant testing?

Section B – Intermediate Concepts and Testing Techniques
 

Section B focuses on detailed explanations of different NDT methods and their applications. Students must attempt any five questions from this section. 

Liquid penetrant testing is one of the most commonly used NDT techniques. It works by applying a liquid penetrant to the surface of a material. The penetrant enters small cracks or defects, and after removing excess liquid, a developer is applied to make the defects visible. For this process to work effectively, the penetrant must have certain properties such as low viscosity, good wetting ability, and high visibility.

Radiographic inspection is another important NDT method that uses radiation such as X-rays or gamma rays to detect internal defects in materials. This method is widely used in welding inspection and aerospace industries because it can reveal hidden defects inside components.

Magnetic particle inspection is used to detect surface and near-surface defects in ferromagnetic materials. This method works by magnetizing the material and applying magnetic particles that gather around defect areas, making them visible.

Ultrasonic testing uses high-frequency sound waves to detect internal defects. A transducer generates ultrasonic waves that travel through the material and reflect back when they encounter defects. This method is widely used in medical diagnosis and industrial inspections.
 

Another important concept discussed in this section is the photoelectric effect, which is used in radiation detection systems. The limitations of radiographic inspection are also important because factors such as radiation hazards, equipment cost, and safety precautions must be considered.

Understanding these techniques helps engineers select the appropriate inspection method for different materials and situations.

Questions for Section B

What properties should penetrants have in liquid penetrant testing?

Classify the different types of penetrants used in inspection.

What are the sources of radiation used in radiographic testing?

How are magnetic fields generated in magnetic particle inspection?

Differentiate between ferromagnetic and non-ferromagnetic materials.

Explain how ultrasonic testing is used for medical diagnosis.

Describe how ultrasonic testing is used to inspect welded joints.

Explain the process of excess penetrant removal in liquid penetrant testing.

Explain the photoelectric effect and its role in radiographic inspection.

What are the advantages of gamma-ray radiography compared to X-ray radiography?

Section C – Advanced NDT Techniques

Section C contains advanced questions that require detailed explanations of NDT principles and testing methods. Students must attempt any two questions from this section. 

One of the important techniques discussed in this section is X-ray radiography. In this method, X-rays pass through a material and create an image on a film or detector. Defects such as cracks or voids appear as darker regions on the image because they absorb less radiation.

Another advanced technique is eddy current inspection, which is used to detect surface defects in conductive materials. In this method, an alternating magnetic field is applied to the material, which induces circulating electrical currents called eddy currents. If there is a defect in the material, it disturbs the flow of eddy currents, which can be detected by sensors.

Magnetic particle inspection is another technique used to detect cracks and surface defects in ferromagnetic materials. When the material is magnetized, magnetic particles accumulate at defect locations, making them visible. The direction of the magnetic field is important because defects are easier to detect when the magnetic field is perpendicular to the crack.

These advanced methods are widely used in industries such as aerospace, automotive manufacturing, pipelines, and power plants to ensure the structural integrity of components.

Questions for Section C

Explain the principle and working of X-ray radiographic testing with a diagram.

Describe the equipment used in radiographic inspection.

Explain the principle and working of eddy current inspection.

What are the main applications of eddy current testing?

What steps are followed during magnetic particle inspection?

Why is the direction of the magnetic field important in flaw detection?

Conclusion

The Non-Destructive Testing exam paper evaluates knowledge at three levels. Section A tests basic concepts and definitions related to NDT methods. Section B focuses on detailed explanations of inspection techniques such as ultrasonic testing, radiography, and magnetic particle inspection. Section C examines advanced applications and working principles of these techniques. 

Understanding these topics is important for engineers because NDT techniques help ensure the safety and reliability of industrial components without causing damage to the materials being tested.