Currently, there are three common non-destructive testing of weld, namely radiographic inspection, ultrasonic testing and magnetic flaw detection test.
The method of radiographic approach was used commonly in the past until the arrival of ultrasonic inspection technique. The major difference between the two is that ultrasonic testing detects very narrow flaws which can hardly be detected by radiographic method. Moreover, it is very sensitive to gross discontinuities. Tiny defects, which characterize welding problems, are normally not revealed by radiographic inspection.
Moreover, ultrasonic inspection possesses the advantages that it can accurately and precisely locate a defect as well as figure out its depth, location and angle of inclination.
In the past, it was expensive to adopt ultrasonic means for inspection. Nowadays, the rates for both inspection methods are comparable. Most importantly, the x-ray and gamma ray used in radiographs are radioactive and pose potential safety hazard to testing technicians on site. Reference is made to Paul G. Jonas and Dennis L. Scharosch
Magnetic flaw detection test can only be used for checking flaws in any metallic objects. This method is commonly used for inspecting surface cracks and slightly sub-surface cracks. However, surface and sub-surface cracks can be readily detected by radiographs and ultrasonic inspection.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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