A-Number Groupings per ASME Section IX

What is an A-Number?

An A-Number is a deposited weld metal composition grouping defined in ASME Section IX Table QW-442 & Paragraph 404.5. The grouping of A-numbers is based on the measured values of six elements, namely Carbon (C), Chromium (Cr), Molybdenum (Mo), Nickel (Ni), Manganese (Mn), and Silicon (Si). 

It is important to emphasize that the A-Number is the chemical composition of the weld metal in the “as-welded” state, not of the filler metal product in its raw form. This is an essential difference as dilution with the base metal, shielding gas, or flux will influence the as-welded chemical composition.

A-Number P-Number F-Number

Ferrous & Non-Ferrous

A-Numbers only apply to ferrous weld metals and it is incorrect to apply the governing requirements to non-ferrous materials. This can sometimes cause confusion for those creating or reviewing PQR & WPS documentation, as it is sometimes assumed all weld metal compositions have a corresponding A-Number.

Ferrous metals or alloys are those which contain iron (ferrite), such as carbon steel, chromium steel, and stainless steel. On the periodic table of elements, iron is represented with the abbreviation of “Fe” derived from the term Ferrous. The term ferrous is derived from the Latin word “Ferrum”, which is defined as “iron” or “containing iron.” Ferrous materials are those represented by a specification that begins with “SA”, such as SA-516, SA-335, and SA-240.

Non-Ferrous metals are metals or alloys that do not contain iron (ferrite) in appreciable amounts, such as aluminum, Inconel, Hastelloy, and titanium. Non-ferrous metals are those represented by a specification that begins with “SB”, such as SB-209, SB-444, SB-622, and SB-338.

Where A-Numbers Apply

A-Numbers do not apply to performance documentation such as WPQ (Welder Performance Qualification) or WOPQ (Welder Operator Performance Qualification) welder qualifications. This can be a stumbling block for some, but reference ASME Section IX paragraph QW-350 to reference the essential variables for welders. Remember that for welders or performance, the F-Number and P-Numbers are used as essential variables, not A-numbers. 

A-Numbers apply to procedure documentation such as PQR and WPS, where the mechanical properties are being controlled. Reference ASME Section IX paragraph QW-250 and associated tables to determine the essential, non-essential, and supplementary essential variables of each welding process for application on welding procedures.

Determination of the A-Number

If applicable the filler metal specification is used to determine the A-Number. When that does not apply a chemical analysis is performed on the actual weld metal, those results are then compared against Table QW-442 and the A-Number is selected that way. In lieu of an A-Number designation, the nominal chemical composition of the weld deposit shall be indicated on the WPS and on the PQR. 

Authors of PQR and WPS documentation shall always reference the code for official information, (see ASME Section IX paragraph QW-404.5 (a) thru (d)) but the following summary is provided for the typical methods or options in determining the A-Number of the ferrous weld metal composition.

1. All welding processes: by chemical analysis of the actual PQR sample 

2. SMAW, GTAW, LBW, & PAW processes: one of the following

-by chemical analysis of a sample (other than the PQR) per SFA 5.XX, or

-by chemistry reported in the filler metal specification, or

-Supplier Certificate of Compliance (CofC)

3. GMAW/FCAW & EGW processes: one of the following

-by chemical analysis of a sample (other than the PQR) per SFA 5.XX, or

-by supplier CofC when the shielding gas is the same for the CofC and PQR/WPS

4. SAW: one of the following

-by chemical analysis of a sample (other than the PQR) per SFA 5.XX, or

-by supplier CofC when the flux is the same for the CofC and PQR/WPS

A-Number Table

A-Number Reference Chart

Download A-Number Reference Chart pdf


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