Globe Valves for Marine & Offshore

For seawater cooling globe valves on marine vessels, the material specification depends on seawater temperature and flow velocity: Below 30°C, flow velocity < 3 m/s: Naval brass (C83600 / CC491K / G-CuSn7Pb) is the standard material — economical, widely available, type-approved by all major classification societies. Used universally on seawater cooling circuits of cargo ships, tankers, and container vessels. Above 30°C or flow velocity > 3 m/s: Standard naval brass suffers velocity-erosion and dezincification. Duplex stainless steel (UNS S31803, ASTM A276 / A351 CD4MCu cast) is preferred — excellent pitting and crevice corrosion resistance in warm seawater. Above 25 ppm chloride seawater at elevated temperature: Super Duplex 2507 (UNS S32750) for the most aggressive conditions — offshore platforms, tropical seawater desalination intakes. Offshore platforms with seawater injection: Super duplex or titanium grade 2 for highly aerated seawater at injection pressures above 200 bar. All materials must be type-approved by the relevant classification society (DNV GL, Lloyd's Register, BV, ABS, NK) for marine seawater cooling service.

A Screw-Down Non-Return (SDNR) valve is a globe valve that combines manual isolation (screw-down function — the handwheel can mechanically force the disc onto the seat to close it positively) with non-return function (when the handwheel is backed off, the disc acts as a check valve, allowing forward flow but preventing reverse flow by gravity or spring). The SDNR design provides two functions in one valve body. Marine SDNR globe valves are used at: (1) Sea water intakes (sea chests) — the SDNR prevents seawater back-flooding into the engine room if suction pressure falls while also allowing the operator to close the valve completely for maintenance; (2) Overboard discharge connections — the SDNR prevents sea water back-flooding through the overboard pipe and into machinery spaces; (3) Bilge pump discharges — prevents sea water re-entry through bilge discharge pipes; (4) Sanitary discharge (grey water, black water overboard) — SDNR or non-return valve required by MARPOL regulations to prevent sea water back-flooding. SOLAS (Safety of Life at Sea) Chapter II-2 and class rules require non-return devices at sea water connections — the SDNR globe valve is the most common way to meet this requirement on smaller connections (DN15–DN100).