JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech IV Year PRACTICAL NON-DESTRUCTIVE TESTING Previous Question Paper (September - 2022 - R18)

Non-destructive testing (NDT) is essential for identifying manufacturing defects without compromising the integrity of the component. The selection of an NDT method depends on the material type, defect geometry, and the location of the flaw.

Visual Testing (VT): The most fundamental method, involving direct or remote inspection to detect surface-breaking defects like cracks, porosity, or misalignment. It is cost-effective but limited to surface features.

Liquid Penetrant Testing (PT): Used for non-porous materials to detect surface-connected discontinuities. A penetrant is applied, drawn into the defect by capillary action, and then revealed using a developer. It is highly effective for detecting fine surface cracks.

Magnetic Particle Testing (MT): Applicable only to ferromagnetic materials. By inducing a magnetic field, surface and near-surface defects disrupt the flux lines, causing leakage fields that attract magnetic particles. It is superior to PT for detecting tight surface cracks and shallow subsurface defects.

Ultrasonic Testing (UT): Uses high-frequency sound waves to detect internal defects. Reflections (echoes) from internal boundaries or flaws are analyzed. It is highly sensitive for detecting volumetric defects like inclusions, voids, and deep-seated cracks in thick sections.

Radiographic Testing (RT): Utilizes X-rays or gamma rays to produce a shadowgraph of the internal structure. It is excellent for detecting volumetric defects such as gas porosity, slag inclusions, and lack of fusion. It provides a permanent record but requires strict radiation safety protocols.

Eddy Current Testing (ECT): Based on electromagnetic induction, this method is used for conductive materials. It detects surface and near-surface cracks and is also used for sorting materials or measuring coating thickness. It is fast and requires minimal surface preparation.

Selecting the appropriate method requires a critical balance between sensitivity, material properties, cost, and the specific manufacturing process (e.g., casting, welding, or forging) to ensure structural reliability.