ANSI/AWWA C205 or C104

Plastics or glassfibre-reinforced-polyester are used successfully on seawater.

Both type of steel will rust. Go with plastic or reinforced plastic with graphite fiber works beutiful. Correct glass fiber filled plastic also does very good.

C205 and C104 are the AWWA standard numbers for Shop cement mortar lining (of steel and ductile iron piping, respectively). AWWA C205 also covers cement mortar coating of steel pipes when same is specified. I believe both types of piping have been used for many decades with general success for various seawater piping applications (see e.g. linings applications data sheet available for download at http://www.dipra.org/).

As far as I know AWWA Standards are not available free of cost on the web, although I suspect any notable vendor would probably provide you with any details you wish to know from same, or applicable to their pipes etc.

It is not steel which survived it is glass ceramic mix (cement). Early work has shown that steel corroded if exposed to sea water. I used to have copy of spec but no more since I changed and moved to electronic materials.

This is the reason current use is graphite or correct glass based composite.

If I have to revisit this area I will go steel with Nano glass coating of nano carbon fiber ink based coating.