Nondestructive testing or Non-destructive testing (NDT) is a wide group of analysis techniques used in science and industry to reveal surface & some sub-surface defects within engineering materials, components and structural parts without causing damage, through their reactions to heat, sound, light, electricity, magnetism, etc. to judge and evaluate type, nature, number, shape, position, size, distribution and variation of flaws tested. Nondestructive testing is mainly used in industrial sectors closely linked with national economic development, such as steel, machinery and equipment manufacturing, petrochemicals, rail transport, shipbuilding, aerospace, and power.