During recent decades the world has seen a decrease in coal mining, and many nations have raised concerns about the environmental impact of other types of land-based fuel sources. This has resulted in a move toward farming the sea for its rich energy sources— tidal energy, ocean energy and the piping of deepsea liquefied gas and oil. All of these resources need to be gathered with the greatest of care for the sake of the precarious oceanic environment and respect for the dangers that the oceans can pose for personnel working in these remote locations.
Fabrications placed on the seabed need to be durable and reliable to ensure the safety of personnel while avoiding any environmental disasters that could result from faulty machinery.
Highlighted below are six of the most challenging issues companies might face when producing hydraulics to be used within the subsea industry.
Many oil and gas wells are located off the coast of remote parts of Australia or South America, thousands of miles away from the cities where the hydraulic cylinders are manufactured. The main base is often an oil rig or floating LNG station many miles out in the sea. Beneath this base the fabrication being placed on the seabed can be hundreds of meters under water. The hydraulics used in these fabrications are among the most remote hydraulic systems in the world, and this means all hydraulic cylinders need to be precisely designed, manufactured and stringently tested to ensure they work the first time with no room for error. There is no scope for simply returning faulty machinery to the factory for repairs.
Long operating periods
Many subsea fabrications will be in place for decades. Hydraulics need to be able to work at the end of this time, sometimes having been immobile for the operation’s duration. For example, the locking mechanisms of subsea connectors use hydraulics to move locks into place. These can stay locked for up to 25 years and then need to be fully functional to be unlocked at the end of this period. Therefore, any machinery needs to be manufactured to last, with highly robust systems requiring very little and preferably no maintenance. This means that all coatings have to be of the utmost quality. Hydraulic cylinder manufacturers might make use of a special Everslik coating that has a solid lubricant in the top layer, giving a top-quality resistance to abrasion from the friction of moving parts. This can be used both on the outside and on interior valves to make the system remain in good working order for long periods.
Marine growth and corrosion
Long operating times present another challenge—corrosion from sea salts as well as natural marine growth, which can overpower fabrications, rendering them immobile. There are several materials that can be used to prevent both of these problems. Ceramic hydraulic rods resist the growth of algae and other marine plants. Coatings such as Corex are twice as hard as standard hard chrome plating and up to five times less porous, making them far less susceptible to corrosion. They also offer a high resistance to cracking in the event of an impact such as a piece of debris dropping from above. Seals need to be tough and durable so that any marine growth that does occur can be scraped off by the seals as the rods retract without damaging the seals themselves.
Subsea hydraulic systems often are placed many hundreds of meters below the surface of the sea at depths that are impractical for a diver to reach. In these cases, the cylinders need to be operated remotely by an ROV. Cylinders with hot stab connections have been designed that allow an interface with an ROV, meaning the hydraulic system can be operated independently subsea.
Every 10 m (33 ft) under water exacts an additional 14.5 psi on a structure. This means the materials used need to be extremely strong. In most cases, cylinder mandrels are made using forged steel, so the mandrels are thick and strong with no weaknesses that might result from parts being welded together. Any water that enters the hydraulic system will contaminate the hydraulic fluid, causing system breakdowns, so it is vital that seals are particularly strong to resist the force of the water.
Future of subsea hydraulics
As the resources of the sea continue to be mined with a push toward harnessing renewable energies, there will be an influx of money, skills and time invested in finding new and innovative ways to overcome the challenges of installing high-quality hydraulics in fabrications used on the seabed. The industry is likely to see many new technologies and materials developed in the coming years.
For more information, visit apexhydraulics.co.uk.