An F-Number is a numeric designation assigned to a group of filler metals. ASME Section IX Table QW-432 lists the assignment of filler metals into their F-Number grouping.
The grouping of filler metals is based on qualitatively defined 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.
With a fundamental understanding this system can be very useful in simplifying the determination of who is qualified to perform joining work within the ASME codes.
F-Numbers have been laid out in identifiable alloy patterns.
The following is the comprehensive list of F-Numbers, their general material description as well as some typical material specification examples.
When a procedure is qualified, a PQR or Procedure Qualification Record is created to document the applicable essential variables. For many of the variables on a WPS, there are permitted ranges that the author can specify based on the actual values of the PQR. 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.
Other essential variables related to filler metal such as classifications do permit some latitude based on rules set forth in ASME Section IX, all of this reinforces the importance of being familiar with the code book requirements for each variable.
When welders take a qualification test, the filler metal used during the test is recorded as an “Actual Value”. The filler metals specification, classification, and F-Number are recorded.
The Code then specifies a “Range Qualified” for the F-Numbers; it does not include a range for the specification or classification, as they are not a consideration for the Range Qualified. F-Number is one of many essential variables listed on the WPQ in the Range Qualified column; all must be observed to conform to Code requirements.