There are many different types of non-destructive testing (NDT) methods, but some of the most common include: Ultrasonic testing: Uses high-frequency sound waves to detect and evaluate internal defects, such as cracks, inclusions, and laps, in metal and other materials. Radiographic testing: Uses X-ray or gamma-ray sources to create images of the internal structure of materials, which can reveal defects such as cracks, voids, and porosity. Visual inspection: Uses the naked eye or optical instruments to examine the surface of materials for defects such as cracks, corrosion, and other surface discontinuities. Magnetic particle inspection: Uses a magnetic field to detect surface and subsurface discontinuities, such as cracks, in ferromagnetic materials. Liquid penetrant inspection: Uses a liquid that is applied to the surface of a material, which is then drawn into any surface-breaking discontinuities, making them visible for inspection. These are some of the most common and widely used methods, but there are other methods such as eddy current testing, acoustic emission, thermal imaging and many others that are used in specific applications. Each method has its own advantages and disadvantages and is more suited to certain types of materials and conditions.