This part of 6520 serves as the basis for a precise classification and description of weld imperfections. In order to avoid any confusion, the types of imperfection are defined with explanations and illustrations where necessary. Metallurgical imperfections are not included. Another system for the designation of imperfections is possible, according to TS 17845. Annex B gives the correspondence between the existing classification of imperfections according to 6520-1 and the designation system according to ISO/TS 17845.