I was wondering if any of you could help me in getting the proper code for piping/vessel materials in use with water/salt solution (not necessarily NaCl). Is carbon steel fine or should we go to SS?
You state that you are interested in "getting the proper code for piping/vessel materials in use with water/salt solution " ....
As noted above, the selection of a piping code or standard does not depend on the fluid selected. The correct code will depend on where the system is installed and the ultimate purpose of the system.
If the piping system is aboard a ship or in a chemical plant or a part of a power plant, the codes would be different.
Material selection for seawater and brine systems is tricky ... a lot depends on the degree of salinity, temperature and pH.
Depending on many factors, carbon steels and austenitic stainless steels may be a very bad choices ......