R stamp is required for repairs. This stamp is not required, but is good to have unless you plan on subbing the repairs out for warranty work and such. As for the requirements of any other stamp being needed, that is determined by the fabrication specification you are working to.

Kix

The only part it could possibly apply to is the code break. I.E. first weld out of a pre-existing vessel and or flange/valve vessel side.
Highly unlikely given your mention of new piping. Since there are more than one potential services and codes that could apply to that product form, and other variables not mentioned, it would be a good idea to look into the specifics. As Al mentioned, that's usually a insurance risk in the states at least, and likely some .gov regs and or laws involved.

Thanks for all the input. We have a Section IX program and work to B31.3 everyday...the question was asked of us by a client what more do we need to fabricate ammonia piping for their site....someone in the conversation suggested they "thought" a code stamp of some sort was required but I can't find any direct regulatory reference to support that statement. We simply want to know we are in compliance with the appropriate codes. B31.5 takes you back to Section IX as far as I can see.

The "R" Stamp is issued by the National Board and is separate from ASME. The scope of repairs is stated on the companies individual certificate (ie. Metallic repairs and/or alterations at the above (shop) location and field repairs and/or all repairs/alterations controlled by this shop.)

The ASME CODES cover NEW Construction.

B31.x - These Codes prescribes requirements for the
design, materials, fabrication, erection, test, inspection,
operation, and maintenance of piping systems.

The National Board Inspection Code (NBIC) comes in 3 parts and covers;
Part 1(Installation),
Part 2(Inspection) and
Part 3(Repairs and Alterations)

For Fabrication and Welding of NEW piping, the customer specification should call out the Code of Construction (ie B31.3, B31.5) which invoke ASME Section II(Materials), Section V(Nondestructive Examination), and Section IX(Welding).

Soooooo...
Based on your question "Is an ASME R Stamp (or any other) required for fabricating and welding new piping that will carry anhydrous ammonia? If yes, where can I find something in writing?"

My answer would be check your customer Specification first.

I would expect that it would call out ASME B31.3(Process Piping) and/or B31.5(Refrigeration Piping)
As such, no stamp is required for the work however WPS's, PQR's, and Welders must be qualified by the fabricator to ASME Section IX to the satisfaction of the Inspectior (meaning Authorized Inspector, with which the fabricator has a formal agreement with.) The Authorized Inspector will hold a National Board commission, which means that the fabricator will hold an ASME stamp of some sort.

Now, as to the "R" Stamp, if you will be Installing or repairing (returning the existing pipe to "as new" condition), and ASME or NBIC is called out in the customer specification, than yes, you will also need an "R" stamp.

I hope this helps