Radio Graphic Film Inspection Question

This cannot be described in mere words. The ASME BPVC has pictures to illustrate various types of welding defects, but even that may not be sufficient. Much better would be to work for a time under the supervision of an experienced person.

Most people who read those films are certified and that has 3 levels of certification, the highest level takes more then 3 years to complete.

If you have some film that needs to be read, your best bet is to hire it out.