F- Numbers are given based on the usability characteristics (defined in ASME Section IIC, SFA 5.1 for example for carbon steel SMAW electrodes) and metallurgy of the welding filler metal in ASME Section IX and AWS D1.1. An F-Number is a standard designation given to a defined group of filler metals having similar characteristics by the ASME. ASME Section IX, Table QW-432 have classified the welding electrode/ filler metals into their F-Number grouping of all welding filler metal (Ferrous & non-ferrous types).
F-number is an essential variable for performance and procedure qualification. The grouping of welding consumables (electrodes & wires) is based on their usability characteristics, which affects the welder’s ability to produce a satisfactory weld joint. Also, this F-Number grouping, helps to minimize the number of WPS qualification and welder performance qualifications, as similar welding electrodes can be used without re-qualification.
F Number Alloy grouping
F Number for electrode and filler metals are grouped based on their metallurgy. The below tables gives the classification based on BPVC ASME Section IX.
Below is the full list of F-Number chart as specified in ASME Section IX.
Importance of F Number for Procedure Qualification (WPS)
Table QW-432 in ASME Code Section IX gives the list of F-numbers. A change from a qualified F-number in a welding procedure to the other F-number is an essential variable and requires requalification. ASME Section IX does permit changes for non-essential variables or some specified range (For example current, voltage, preheat temperature) but in the case of F-Numbers, no range is permitted, but instead must be the same value as was used on the PQR. For reference see ASME Section IX Tables QW-252 thru QW-267 and paragraph QW-404.4. Refer to the below table and you will notice that F-Number is an essential variable for procedure qualification. Although the change in electrode diameter is a non-essential variable.
Importance of F Number for Performance Qualification (WPQ)
The change from one F number to another F-number is allowed within a range for welder performance qualification in ASME section IX or AWS D1.1. The essential variable tables in welding performance qualification (clause QW-352 thru 357 in ASME Section IX) gives reference to clause QW-433 for the range of qualification, abstract given below from ASME Section IX.
E.g., a welder qualified with F number four, also will be qualified on the F numbers one, two, and three.
Some companies use the essential variable tables (QW-352 thru 357) to reduce qualification costs. consider, for example, using carbon steel pipe or plate material instead of using the costly stainless steel for welder qualification test coupon. ASME Section IX allows the qualification of P1 material (carbon steel) to qualify welder on P8 material (Stainless steel). This helps to save a lot of money. In this way, a welder can be qualified for stainless steel (P8) by using carbon steel (P1) but as F-Number is an essential variable, the welding electrode must be used of stainless steel only.