T his article describes about the "A" number in welding procedure specification based on the requirement of ASME Code Sectio...
This article describes about the "A" number in welding procedure specification based on the requirement of ASME Code Section IX. "A" number gives a similar chemical composition in an “as weld” condition. The "A" number is an essential variable in most of the welding process as per ASME Boiler and Pressure Vessel Code Section IX. The Table QW-442 in ASME BPV Code Section IX provides the list of "A" numbers.
Please remember the "A" number in WPS does not refer to the filler wire or electrode chemical composition; it refers to the deposited weld metal chemical composition. The filler metal and deposited weld metal have different chemical compositions.
How do you determine the A number in Welding Procedure Specification?
It can be obtained from the procedure qualification coupon. The small piece of welding can be removed and a chemical analysis test to be performed. Then the obtained chemical composition must be compared against the table QW-422 and "A" number to be selected.
Alternatively, if your welding process is one of SMAW, GTAW, LBW and PAW processes you may use the filler metal specification or test report of filler metal manufacturer.
Similarly, you can do the same assessment for GMAW and EGW processes but the shielding gas should be the same as welding procedure specification.
Again, similarly you can do the same for SAW but the flux should be the same as welding procedure specification.
As mentioned above, the "A" number like "P" number and "F" number is an essential variable in most welding processes. It means if you have a WPS and you need to use that in other jobs with different A number (it means you are using different filler metal) then you need to re-qualify your WPS because it is an essential variable. The "A" number 1 and 2 are exceptions. You can consider it as nonessential variables.
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