API 6A wellhead welding to B31.3 piping on production pad

[engr2GW]

Hi,
I understnad that API christmas tree are welded/pre-fabbed and heat treated (per API 6A) before bring them to the field to bolt them. For the last API flange that welds to the production flow line where you have an API 500--20,000 psi flange being welded to an ANSI grade B or API 5L pressure piping, since that welding is that of two dis-similar materials and two dis-similar application/code/pressure rating
1. is the use of a double studded adaptor (DSA) better in such cases so that an easier welding can be done on the ANSI flange on the production end of the DSA to an ANSI piping
OR
2. Is the welding usually done specially by the manufacturer of the well head with a special procedure?

Thank you.

 

[ricklts]

in most cases, the wellhead system takes a pressure drop thru a choke, and downstream of the choke orifice is typically considered a code break from API to ANSI, pressure/temperature depending. In other words, if the downstream conditions are met by an ANSI pressure class, the welded joint, even including an API flange to mate with the downstream outlet of the choke, is considered as an ANSI connection.

In most cases, at least here in the US, the flange is typically an API material, and the weld procedures are qualified to the lower strength piping materials.

The fun starts when the flowlines are still above normal ANSI pressure ranges.