Inspection of an FSW weld joint can be difficult due to the complex nature of the process. Visual inspection is usually not sufficient to assess the quality of the weld since it cannot detect internal defects such as porosity, inclusions, or lack of fusion. Additionally, FSW produces high-temperature plastic deformation, which results in reduced hardness of the weld and can cause a decrease in strength. Therefore, non-destructive testing methods such as x-ray radiography or ultrasonic inspection must be used to examine the internal structure of the weld joint for any potential flaws. It is also important to use specialized tools designed for FSW when inspecting the weld joint in order to obtain accurate results. Therefore, inspecting an FSW weld joint requires specialized tools and techniques that can be labor-intensive and costly.