Best? Monel. A bronze body with monel trim will net you the best life provide you are not using sodium hypochlorite injection and the salt water isn't heavily contaminated with sulfides.
Good news is that this combination is maintained as an on the shelf package as it is specified by MIL standards. This keeps the price more reasonable.
I'll second TBE's recommendation.
The NAB will be fairly erosion resistant, fouling resistant, and plenty corrosion resistant. The Monel trim will last nearly forever.
And as he says, as long as you are not chlorinating right before the valve and do not have sulfides/H2S issues it will be fine.
If this were heavily chlorinated or contaminated and high pressure or flow, I would lean to super duplex. But your QA would need to be very good to assure that you got a good valve.
How big is this beast ? ........ Like most internet/eng-tips newbies you give a minimum of information
(.... and you never seem to use the terms "please" or "thank you")
Pete, when you use the term "Sea Water" ..... you can mean very many things ..
Are you talking about the corrosive liquid horror commonly called the Dead Sea or the mild and pristine Baltic Sea (which can sometimes substitute as a clear and refreshing dinner drink) ?
Concerning to mentioned subject,I understand ,My question about the material selection is general.and may be my mistake to be raised here with such a incomplete information's.
Of course ,For the Evaluation of Correct Material Selection in details ,It needed ,fully project specification/PMS/P&ID to be sent ,which may out of scope of responsiveness here.
Guidance on Practice for Valves GP 62-01(BP GROUP)
Typical application of metallic trim materials is as below :
1)Duplex Stainless Steel (22% Cr.)===>Corrosive hydrocarbon service.
2)Super Duplex Stainless Steel (25% Cr.)====>Sea water service, very corrosive hydrocarbon service. Extreme sour service.
3)Nickel Aluminium Bronze===>Sea water, black sewage, brine, fire water. Good for high velocities. Unsuitable for sulfide polluted water.
Regarding to cost ,of course "Nickel Aluminium Bronze" cost is about 20%~25% more than "Duplex Stainless Steel (22% Cr.)"