F-Numbers are usually used in Welding Procedures and Welder’s Performance. Very few people knows what is F-Numbers. To give some idea, the QW-431 of ASME IX, states as follows;
The F-number grouping of electrode and welding rod in QW-432 is based essentially on their usability characteristics, which fundamentally determine the ability of welders to make satisfactory welds with a given filler metal. This grouping is made to reduce the number of welding procedure and performance qualifications, where this can logically be done. The grouping does not imply that base metals or filler metals within a group may be indiscriminately substituted for a metal which was used in the qualification test without consideration of the compatability of the base and filler metal from the standpoint of metallurgical properties, PWHT design and service requirements, and mechanical properties.
F-Numbers of filler metal can be found in QW-432 of ASME IX