Non-destructive testing refers to the method of inspecting the internal structure of mechanical materials without causing any damage or affecting the performance of the object being tested, and without harming the internal organization of the object. It utilizes the changes in thermal, acoustic, optical, electrical, and magnetic reactions caused by abnormalities or defects in the material's internal structure. This is achieved through physical or chemical means, with the aid of modern technology and equipment. The method involves examining and testing the structure, condition, type, quantity, shape, properties, location, size, distribution, and changes of the internal and surface structures of the specimen.