Ultrasound based inspection techniques are used extensively throughout industry for detection of flaws in engineering materials. The range and variety of imperfections encountered is large and critical assessment of location, size, orientation and type is often difficult. The research presented in this paper has resulted in a knowledge-based engineering module, which was developed software for determining ultrasonic probe location precisely and detecting of the welded sections completely. The criteria for diagnosing these positions, which have been classified into different groups, included in type of material, thickness, geometry of welded section, couplant material, angle probes and etc. The expert system can display the limits that probe must be moved which caused an inspection welded section thoroughly. This study was conducted using three samples including different materials with V groove welded sections for verifying this expert system. Finally this module is very suitable in Q.C. labs and different industries for detection of flaws.