Another concern about material composition is Welder qualification.
As the WPS/PQR is governed by ASME IX, therefore the qualification of the welders will also be to ASME IX.
As you can see in QW-423, base metal used for welder qualification can be substituted for the metal specified in WPS.
However, as there are SS400 and SM400 materials involved in the fabrication of the storage tank, and as SM/SS 400 are not listed in table QW-422, they are therefore, categorized as “unassigned material”.
The qualification of welders, governed by ASME IX, has also, the provision for the “unassigned material” for welder’s qualification.
This provision is stated in QW-423, excerpted below.