RK,
good hints coming from hogan and jon20013 - as ever.
Nonetheless I guess it's hard in the field of NDT finding somewhat, bringing reliable assessments in regard to your topic.
I would - if ever - recommend to try Ultrasonic Testing due to Ferritic and Austenitic Materials have different physical properties in regard to their sound propagation (as far as I know based on their different microstructures).
But as an expert has told me once, it is tough and needs lots of experience to test only austenitic welding-joints. Thus I suppose it's a power tougher to Ultrasonic Testing joints you have spoken of. Additionally there is surely a varying amount of dilution between the materials to detect, complicating the matter certainly.
However meanwhile there are - as I could find out - some improved technologies been developed. In particular for welding-joints on dissimilar materials.
See also:
http://www.ndt.net/article/v04n09/erhard/erhard.htmhttp://www.ndt.net/article/v05n08/elbern/elbern.htmPerhaps this helps a bit but I am sure there are real NDT-experts in the forum to "throw some light on the issue"...
Kind regards,
Stephan