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OverviewWith worldwide demand for oil, natural gas and minerals rising, and recent discoveries of sources located in the deep sea, new hydraulic subsea systems will be needed to harvest these resources from increasingly harsh environments.
With worldwide demand for oil, natural gas and minerals rising, and recent discoveries of sources located in the deep sea, new hydraulic subsea systems will be needed to harvest these resources from increasingly harsh environments.
With worldwide demand for oil, natural gas and minerals rising, and recent discoveries of sources located in the deep sea, new hydraulic subsea systems will be needed to harvest these resources from increasingly harsh environments.
Hydraulically driven systems that operate on the ocean floor, as well as remote operated vehicles (ROV), which can penetrate down to many thousand meters below sea level, place particularly high demands on the hydraulics. Rexroth is the first to adapt numerous standard hydraulic components, such as valves, cylinders, motors, hydraulic power units and manifolds, to fit the special requirements for subsea applications such as pressure compensation and corrosion protection to provide hydraulic subsea equipment with a longer maintenance-free life span and optimal performance.
In order to withstand the immense external pressure, encapsulated or pressure compensated subsea control plates and subsea hydraulic power units (HPU) have to be used. Subsea cylinders have to be built using special sealing systems and even individual subsea components, such as subsea valves and subsea motors, have to demonstrate specific features. Rexroth tested the subsea hydraulic equipment in a unique pressure chamber facility, was able to demonstrate suitability of its hydraulic components to a depth of 6,000 meters below sea level.
Standard solenoid operated hydraulic valves cannot operate submerged under water. The hydraulic subsea valves, or the complete manifolds, need to be placed in a fluid filled enclosure that is pressure compensated with the surrounding pressure. Due to the fact that the volume of the pressure compensator is limited, it is critically important that any captured air within cavities and chambers in the hydraulic valve and/or the manifold is vented completely. Rexroth has developed a special line of conventional and proportional hydraulic subsea valves which incorporate unique modifications to eliminate or bleed any captured air.
Complete subsea manifolds need to be placed in a fluid filled enclosure that is pressure compensated with the surrounding pressure. Due to the fact that the volume of the pressure compensator is limited, it is critically important that any captured air within cavities and chambers in the manifold is vented completely.
To ensure reliable functionality and performance of the new components and sub systems extensive tests up to 600 bar ambient pressure in a hyperbaric chamber have been carried out. A specially designed subsea hydraulic power unit (HPU) comprised a wide spectrum of different hydraulic components and sub systems. The final conclusion: every part of the subsea hydraulic power unit functioned correctly in the pressure chamber during the entire test cycle.
As a full liner Rexroth also offers a wide range of hydraulic cylinders, that can be modified to suit subsea applications. Depending on the customer‘s requirements, customized subsea cylinders are also possible, control manifolds can be mounted to cylinder directly. Rexroth has extensive experience with offshore cylinders used in riser tensioning, heave compensation, skidding, deck mating and jacking applications.
The surface technology for piston rods of hydraulic cylinders is one of the most essential parts of the hydraulic installation. The new Enduroq 3200, a dual layer, Ultimet based heavy-duty coating has been specially developed for offshore splash and subemerged applications and is the only coating in the market meeting the stringent DNV rules.
One special feature of Rexroth subsea hydraulic cylinder design is the pressure compensated cylinder head: In order to protect the wiper ring from the high ambient pressure, thechamber between wiper ring and main seal is pressure compensated. Secondly, the main seal is not in contact with salt water and well lubricated by the hydraulic fluid.