Normally, for austenitic stainless steel weldments you want to have a minimum ferrite number of FN 4 to avoid solidification cracking. Regarding base metals, the ferrite content should be as low as possible. I have seen ferrite numbers for austenitic stainless steel base metals vary from 1-4 depending on product form.

Acceptance criteria for corrosion tests and ferrite content should be based on service application. I would go back and discuss with the Purchaser what their needs are and service duty.

I presume as welded (no anneal), but with or without filler metal?

The base metal value should be low, limits of 0.5% are used in some process applications.  In some cases 1% would not be bad.

I would expect the weld to be what ever the weld was designed to be.  If the aim value was 4%, then 2-6% would be reasonable.
Why not measure magnetically?

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