What is Group Number in Welding & ASME?

Understand the significance of group numbers in welding and ASME standards. Discover how group numbers classify materials based on their weldability and essential mechanical properties. Explore detailed explanations, practical examples, and expert insights to enhance your knowledge of group numbers in welding and ASME regulations.

Group Number in Welding are the material grouping given to base metals to signify their mechanical properties. Generally, higher the group number, higher the tensile strength of the material.

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

This is sub-division of the materials P-Number, considering similar mechanical properties but different toughness requirements. The Group Number in ASME/ AWS Qualification is significant when toughness (CVN) requirements apply to materials used in WPS qualification.

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.

P Number and Group Number in Welding

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 in welding.

ASME Material Groups Number

ASME Material Groups are given to divide same material specification by different grades based on their tensile & toughness properties. The most commonly used pressure vessel grade SA 516 has four grades listed below with their respective P Group Number.

SA 516 Gr 55: P1, Group 1
SA 516 Gr 60: P1, Group 1

SA 516 Gr 65: P1, Group 1
SA 516 Gr 70: P1, Group 2

The below table shows the example of ASME Section IX Table QW/QB-422 where we can find the ASME materials P-Number and Group Number.

ASME material Group Numbers are followed by P-Number in the table. This table is very useful to locate the basic metallurgy (type of main alloying, tensile strength) 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 in Welding 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.

ISO Material Groups

ISO Material groups for parent metal grouping are given by ISO 15608 to reduce the number of welding procedure qualifications similar to ASME Section IX. There are ISO material groups specified in ISO 15608 standard which help to classify different types of materials.

There are 11 base material groups, 1 through 11 in ISO 15708 standard. Each group has specific properties and applications.

Group 1 is for unalloyed and low-alloy steels. These steels have a carbon content of less than 0.25%.
Group 2 is for unalloyed and low-alloy steels with yield strength more than 360 N/mm².

Group 3 is for Quenched & Tempered Steel (Q & T).
Group 4 is for low alloy steel with added Vanadium.
Group 5 is for Cr-Mo Steel those are used for high temperature applications.

ISO Material Group chart

ISO 15608 is an international standard that classifies base materials according to their chemical composition. The standard is divided into 11 material groups, each of which is further divided into subgroups.

There are many benefits to using the ISO Material Groups chart. It provides a consistent way to classify materials across different types. The ISO Material Groups chart can be found online or in ISO 15608 Standard.

Click Here to Download ISO Material Group Chart.

AWS Material Groups & Base metal Grouping

AWS Material Groups and Base metal Grouping are given in AWS D1.1 for steel, in AWS D1.2 for Aluminum (Group M21 to M27 AWS Material groups) and in AWS D1.6 for Stainless steel AWS Material grouping.