Six billet inspection techniques have been listed in essays before. And today, we’d like to discuss the selection of inspection techniques for seamless steel pipe. As we know that not each of them has equal role during the whole inspection.

Actually, there are three of the methods would have more useful for the continuously cast billets than others. They are eddy currents techniques, optical techniques, and microwave techniques.

The optical system can resolve the smaller defective areas, for example, pinholes. Of course, it is also used for responding to other types of defects which show up in relief under the incident lighting conditions.

The microwave system has the benefit of reasonable operating clearances (of the order of 30 mm) and usually resolve large area defects and, both longitudinal and transverse cracks of the order of 10 mm or more in length.

The eddy current probe array on the other hand have to be positioned closer to the surface, at say 3 mm, but is capable of better resolution in the detection of transverse cracks, teeming arrests, reciprocation marks, etc. than the microwave technique.