Ex-proof hydraulics for offshore mooring systems

Mooring systems are a key equipment of offshore units deployed for petroleum and gas production, as they allow any floating platform to be safely held in position, avoiding risks or potential damages coming from rough sea waves.
Spread-mooring, tower systems and turret-type solutions: different executions are available on the market, but they all share the same key features, from the necessity to handle heavy equipment and strong forces – e.g. catenaries or winches –, to the strict requirements of the offshore oil&gas sector, such as the need for improved corrosion-resistance, the application of specific international norms and the mandatory use of explosion-proof certified products due to the presence of petroleum and gas.
Ex-proof hydraulic systems are thus the most widespread solution for the actuation of mooring systems, as they meet offshore requirements with long-term operative life, allowing also to perform high-performance motion controls.

A typical ex-proof electrohydraulic system for a mooring application comprises a central HPU for the Power Generation and various hydraulic manifolds directly mounted on the deck equipment, so that the control valves are as close as possible to the winches and the actuators.
Ex-proof solenoid valves are present in every actuation: on/off valves are used for simpler or auxiliary movements, while proportional valves or cartridges are generally applied whenever higher performances are required. A typical example is the Chain Jack System, where high-flow ex-proof proportional valves control the reciprocating movement of a big-bore cylinder used to haul-in and tension the mooring chain.
The hazardous area is typically classified according to the IEC 60079 directive as zone 1 for overdeck installation, requiring explosion-proof certification for hydraulic components and electrical equipment.
As for corrosion resistance, manifolds, valves and actuators are usually protected with dedicated marine painting cycles with thicknesses up to 300 μm, while piping and fittings are generally stainless steel made. Although, whenever the installation involves a particularly weathered location or very low temperatures, it is not uncommon to use ex-proof stainless steel valves.