What is Group Number in Welding? 

This article provides information about Group number in welding procedure specification based on the requirement of ASME Code Section IX.

The I4I Academy ASME Section IX Online Training course covers Group Number in ASME Section IX. 

The Group number in welding assigned additionally to the P number materials. These group numbers divide a P number to several group numbers for the purpose of welding procedure qualification when impact testing is a requirement by the construction code. This subject might be a little bit complicated, but I am going to give an example to comprehend better. 

You assume, you have pressure vessel under the design process, and your designer says to you that the impact testing is not a code requirement based on ASME Code Section VIII, which is your pressure vessel design code. The designer determines this through the requirement of ASME Code Section VIII Div 1 – UCS 66 (thickness and minimum design metal temperature combination identify the impact test requirement)

In this example, when you are preparing your welding procedure specification and procedure qualification record, you should not consider the group number. Consider, no group number exists. The entire supplementary essential variable will be nonessential variables in your WPS form. 

Group Number in Welding 

This time, consider that your designer says to you that the impact testing is the code requirement for you vessel (probably you have lower minimum design metal temperature and higher thickness material), now the group number matters. In one P number you might have several group numbers like:

P number 1 Group number 1

P number 1 Group number 2

P number 1 Group number 3 

Now you need your welding procedure, be qualified by impact testing as well. One set for weld metal and one set for heat affect zone. 

In this situation, if you have WPS that has been qualified for P number 1 and Group number 1 cannot be used for another job with P number 1 and group number 2. If you look at the tables QW-252 thru QW-269, you will see many supplementary essential variables which now are essential variables.  

Your all supplementary essential variables are essential variables now. 

The ASME Code Section IX is not determining of application of Group numbers; it is the construction code such as ASME Section VIII Div 1, or B31.3, etc. that is determining it. Please note the ASME Code Section IX is only a referencing code. The table QW-422 provides material P number and Group numbers. Consider it when impact test is a mandatory requirement by the construction code. 

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