Selection of duplex steel material for seawater pipelines

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Dear teachers, I’m working on a project involving overseas pipeline valves that are exposed to seawater; the salinity is high, with a chloride content of 84,000 mg/L, and the flow rate is 2,500 m3/hr (chloride level: 84,000 mg/L, total flowrate: 2,500 m3/hr). At first, we quoted based on the client’s request to use A995 4A duplex steel, but later they said there were high levels of chloride ions, so we had to quote again using A995 5A or 6A. I would like to ask the teachers for advice: 1-Is this salinity suitable for A995 5A duplex steel? Should we still use 6A? Is it true that the higher the salinity, the higher the grade of duplex steel that should be used? Is there any standard that specifies that a salinity level above a certain threshold requires the use of 5A or 6A? 3-Is the selection of duplex steel grades related to the flow velocity of the pipeline fluid? Thank you first.