Ptccl,
Sainless steels can be braized with success using BAg alloys, these alloys require the use of a braizing flux. If the material is to be used for food service then a cadmuim free filler such as BAg 7 should be used this has a silver content of 55% -57%.
The braizing temp. of the alloys range from a low of 1150F to a high of 1550F. It is very important to make sure the metals are free of any oxides before braizing, and in the case of tubing a Nitrogen purge can keep the interior oxide build up during the braizing proccess to a minimum.
Certain stainless steels contain some chromium - nickle and at temps. between 900F and 1300F can experience carbide precipitation the trick is to complete the braizing proccess as soon as possible. I've also read that BCu and that BNiCr can also be used but don't know any more than that.
As far as operating temps. I coulnd'nt give you any recommendations the highest operating temps I've seen have been at the discharge line of a refrigeration compressor 250 - 300F tops.
Hope this helps, A.J. Gest