E316L-15 is a good choice. I would suggest that you contact one of the specialty stainless manufacturers and tell them what you need and what it is for. 316L can easly be made to meet a max. of FN3. Put your requirements in your purchase order.
A couple of manufacturers:
Avesta - Sheffield: 800 441 7343
Sandvik: 800 781 9449
McKay: 800 424 1543
Lincoln:216 481 8100
Regards