Duplex can be tough. And what you have heard is half right. The actual welding of duplex is virtually the same as SS, through the eyes of the welder. Little less hot crack sensitive, little more hydrogen crack sensitive, but the puddle, fusion, wetting, etc, are virtually indistinguishable. Even with supers, you can readily weld them as standard SS's (though supers are more susceptible to embrittlement-the reason why Charpies are often imposed). They just won't do what they are designed to do and you will most likely fail your necessary tests.
The trouble is, as you have experienced, finding the parameter balance that will allow you you to pass the required tests-especially difficult with the supers. And it doesn't help that sometimes customers, in their ignorance and enthusiasm for a viable weldment, impose unreasonable requirements.
Supers can be most frustrating, witness the fact that many weld procedures for supers are actually patented and nobody is really aware of it because they are almost never enforced.
The higher the alloy content, the more stringent the testing regime, the narrower the window of allowable parameters. And if your new to supers you may need to run several tests, accumulating important data, to 'dial in' your allowables.
joe , i asked ross to create a section for the SA 200 it's up and runing now this may help others who post all over these sections to get their answers . also thanks for all the nice things that you do on the forum . if your travels bring you back up here let me know i'll buy dinner . good luck . willie