If this is ASME Code work, then having the codes is a place to start to qualify the WPS. There are a few grades for the A-216 however you don't have to use the actual material for qualification of your procedure. SA/A216 is very widely used in steam and water lines. The code of construction that applies to the piping system should also be consulted before fabricating any components along with the design drawing and any customer provided specifications.

As far as welding goes, you would start with qualifying your procedure using the rules in ASME Sec IX for the process you are using. You can then write a WPS that covers exactly how you want to complete the weld. The ranges for the variables that can be used are all in ASME IX.

In addition to the WPS being qualified by testing, the welder must be also. If you follow the correct ranges as allowed by the code, you could qualify both a WPS and Welder at the same time.

With any code compliant work, it is suggested that more than what metal sticks what metal together be looked into. Both are just carbon steel and nothing special to weld but the statement "under ASME CODE" makes it something else.