P-numbers, F-numbers and A-numbers

These three variables are commonly seen in welding specifications and some standards like ASME and API.

For example in this welding procedure specification following ASME IX, you can observe that these 3 parameters are seen.

What exactly do these 3 numbers denote and why are they important?

Almost all welding processes tag these variables as essential meaning they will have to be addressed when qualifying a weld, as seen below in the ASME IX tables.

P-numbers are assigned to base metals through alphanumeric designations to reduce the number of welding procedure qualifications required.

Simply put, P-numbers are assignments to a base metal. The material produced under ASTM specifications has the same P-number and minimum specified tensile strength value as that of the corresponding ASME specification.

Also, for a metal to be assigned a P-number, it shall be proven that it conforms to the material specifications of ASTM. For example, if a material coming from a location stated that it complies with ASTM A36 (that is P-1 material), it shall have documentation, i.e. material test reports that check out its mechanical and chemical properties complying with ASTM A36.

For example, if material A is P-1 and material B is P-1 and it passed the qualification test, then all the P-1 material can be welded to P-1 with those specifications. This is one of the reasons why a single PQR can support many WPS.

What about F-numbers?

F-number as defined in ASME IX is the grouping of electrodes and welding rods based essentially on their usability characteristics, which fundamentally determine the ability of welders to make satisfactory welds with a given filler metal. Just like the P-number, this grouping's intent is to reduce the number of welding procedures and performance qualifications.

So for example, if the specific filler number, say, F-1 is qualified, then all of the filler numbers under that classification will also be qualified.

But be cautious about qualifying an entire group of base metal or filler metal, ASME IX

QW-421.1 states this:

It only means that when qualifying for a metal, it shall be taken into account the suitability of the metal with the service, metallurgical properties, mechanical properties, and others.

This is similar to what is stated in QW-430 for the filler metals.

Lastly, the A-number is defined as the chemical composition of the deposited weld metal designated on the PQR and WPS.

But how do you determine the chemical composition of the deposited metal? ASME IX also defined it as the chemical analysis of an undiluted weld deposit such as that prepared according to filler metal specification as reported either in the filler metal specification or manufacturer's certificate of conformance.

If you want to know more about welding inspection and pass the CWI exam, I have a welding introductory course for the fundamentals part of the CWI just click the link here and it will take you to the course it's free! If you love more free stuff and want to know more, you can also check out my videos here regarding the fundamentals of WPS and PQR. This is where I discuss these variables as well.