There is no Code requirement in B31.3 wrt FN of (S)DSS.
You typically see this as being a client requirement, however, I would strongly vote not to let the application depend on client requirements.
Get a copy of API TR 938-C, get familiar with it, and while reviewing, note down what you think is important to specify as a minimum to your own standard for (S)DSS.
FN in weldments is one.
The Code does not have provisions for some of the 'pitfalls' of this material. The Code specifies minimum requirement only.