What is P Number and Group Number in Welding & ASME?

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.


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

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.

Related Reading: What is P-Number in Welding: In depth guide.

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.

group number in welding

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

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.

group number in ASME 1 What is P Number and Group Number in Welding & ASME?

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.

group number in ASME 1 1 What is P Number and Group Number in Welding & ASME?

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. 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%. T
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 D1.1 Base Metal Grouping

AWS D1.1 Base Metal Grouping is outlined in Table 5.3 of the AWS D1.1 Structural Welding Code – Steel. This Table covers the AWS Group Number in Welding.

There are total 4 Base Metal grouping in AWS D1.1. They are:

  • Group 1, E.g., ASTM A36 (upto 3/4 inch thk.), A53, A106, A516 (Gr. 55 & 60).
  • Group 2, E.g., A516 (Gr. 65 & 70), ASTM 572, ASTM A595
  • Group 3, E.g., ASTM A710, API 2W
  • Group 4, E.g., ASTM A709, ASTM A913.

This table provides the Engineers with information on different grades, their mechanical properties & correlate the grouping with qualified welding range for procedure and performance qualification..

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