Most procedures and codes of good practice for the performance of industrial radiography base the choice of type of film for a specific application on the EN or ASTM classification systems. For weld inspection, when one is attempting to detect small cracks, a film of class C2 or C3 would be specified. For the examination of castings or general radiography a film of class C4 or C5 would normally be used. For small component inspection, where the image might be viewed under magnification to reveal small details, a film of class C2 or possibly even a single emulsion film of class C1 would be desirable.
In megavoltage radiography, because most equipment have a very high radiation output, class C3 films can be used for objects of great wall thickness. This has the advantage that a high film gradient can be achieved.