What is Group-Number in Welding & ASME?


What is P-NUMBER and GROUP-NUMBER in ASME?

The Group Number in ASME/ AWS Qualification is significant when toughness (CVN) requirements apply to materials used in WPS qualification. This is sub-division of the materials P-Number, considering similar mechanical properties but different toughness requirements. As given in ASME Section IX, a group number was added to the P-Number for materials to specify that toughness requirements are there for materials.

There are total four Group Numbers (G-Number) in ASME Section as ‘Group No. 1, No. 2, No. 3, and 4‘ while P-Number are From P-No. 1 to P No. 62. The above 4 groups under a P-Number are classified based on the tensile strength. Group-1 is for the lowest tensile strength materials while Group 4 is for the highest tensile strength material grades (In general, although you may notice some contradiction to this statement).

Group numbers in ASME Section IX, further classify P-Number into different groups that help WPS-PQR qualification for toughness requirements given by design code such as ASME Section VIII. Let’s assume for example- the designer designed a pressure vessel with material and stated that there are no toughness requirements applicable for this construction.

In this case, only the assigned material P-Number will be an essential variable and you can use any other grade of the same P-Number for your WPS/PQR qualification. but, in another case, the designer said that there are toughness requirements applicable. Then the WPS/PQR must be used with the same P Number in addition to the same Group-Number material.

Grouping number only applicable for welding qualification & brazing qualification when joining ferrous metals. For non-ferrous materials, only P-Number is applicable. If you refer the ASME Section IX, Table QB -422, you can find this information that for non-ferrous metals there are no Group Number.

ASME Material Group Numbers

The below table shows the example of ASME Section IX Table QW/QB-422 where we can find the materials P-Number and Group Number. Group Numbers are followed by P-Number in the table. This table is very useful to locate the basic metallurgy of the material grades used in the ASME constructions.

For each material specification (ferrous material specifications & Non-ferrous material specifications) & its grades, you can find their UNS Number, P-Number & Group Number, minimum Specified Tensile Strength (SMTS) in Ksi/ MPa, ISO 15608 material group number is also included in the latest 2019 edition of the ASME Section 9.

What is the Group Number in WPS & PQR and Welder Qualification?

As we can see in Table Qw-253, material Group Number is a Supplementary Essential Variable and therefore Group Number is related to toughness properties of materials. Group-Number being a supplementary essential welding variable attaches its importance for the weld toughness properties. So as long as there are no toughness requirements, a change in base metal group number will be a non-essential variable only.



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