Inspection of welded joints is carried out by non-destructive methods, such as radiography, ultrasonic, magnetic particle or liquid penetrant.
Radiographic testing (RT) and ultrasonic testing (UT) are used for detection of internal discontinuities. Generally, they supplement each other. RT is the most effective method in detecting three-dimensional discontinuities, such as porosity and slag, and is less effective for two-dimensional discontinuities, such as laminations or cracks. UT, on the other hand, is generally most effective for detecting laminations and cracks and is less effective for detecting porosity and slag. Magnetic particle or liquid penetrant inspection is used for surface inspection of welds.
Further reading: ABS Guide for “Nondestructive Inspection of Hull Welds” (2002), can be downloaded from www.eagle.org