1960 Volume 46 Issue 14 Pages 1744-1751
Macroscopic non-metallic inclusions are usually inspected by naked eyes on the surface of tubes cut by the lathe. Sometimes there are many small inclusions whose length is ranged from 0·1mm to 0·4mm, but whose width is quite thin. The accuracy of this inspection was discussed here.
At first, the accuracy caused by the individual inspector, the variance between the different inspector and the variance inspected at different times by the same inspector were tested. The results proved that the variance was large enough to cover the commercially permissible number.
The macroscopic non-metallic inclusions are compared with the number of non-metallic inclusions counted through a microscope. The former were proved to be about 10% of the latter. This means the uncertainty of this method of inspection. This should be paid attention from the commercial point of view.