Can you refine your description of the water. At this temperature water is innocuous, but 10, 100, or 1000ppm of chlorides makes a great deal of difference. 304 will SCC in water with 10ppm Cl at 100C in 1000 hours, in 100 hours at 100ppm. Pitting is a pre-cursor of SCC.
 So, we shouldn't recommend a material without pretty precise knowledge of the environment. If you prefer to search for yourself, Avestapolarit.com has some free on-line corrosion tables, but what you're looking for will probably require some deductions based on research papers.

Thanks for your reply

The water runs through the pipes quite slowley (I am waiting for the exact flow rate to be given to me).  The Cl level is 31ppm and the temperature is 85 degrees C.  There is also significant deposites of what I think is CaCO3 on taps and joins in pipes.  The SS 316 has failed after 5 years, they would like a material that would last longer and are aiming for 20 years - although I think this is a bit ambitious!

I am also considering the ferritics such as AISI 444, as these steels are reported to have better SCC resistance.  But I am concerned that other problems might occur, such as general corrosion and possibly pitting or crevice corrosion.  What do you think.

Thanks so much!!!
180

No, 20 years isn't too much to ask for. 444 won't have any better corrosion resistance than 316 although it won't SCC unless it is cold worked to a higher hardness as sometimes happens when securing tubes into a tube sheet.
 A better choice is a duplex, such as 2205, which won't SCC and has better corrosion resisatnce. For your twenty years, go with 2507, a more highly alloyed duplex than 2205. It is still much cheaper than nickel-base alloys.
 Incidentally, duplex stainlesses are much stronger than austenitics, if that matters in your system.