But, as it is almost impossible to distinguish between the grades, look for the identification printed on the tube if it is new or an offcut. If it is second-hand, you will take pot luck.
The best you are likely to find (and I have luck in my scrap yard) is 316L( for Low carbon).
This grade isalso frequently used for the food induustry and some of mine is ex Whitbread!
I can buy from Durbin Metals at Yate (near Bristol) 2" OD X 10 gauge seamless 316L for £41.80 per metre, minimum 6m length, or in welded for £19.30 per metre.