What You Need to Know About Subsea Hydraulic Design

There are many factors involved in how much subsea hydraulic related applications are able to grow and increase in usefulness in the marine related industries. For example, key considerations are how long they can be kept in use without there needing to be maintenance performed or costly repairs and engineering undertaken. How safe are they for both the ocean and for people? How can the harsh environment be overcome for industries to achieve their goals?

Some maintenance for subsea work is of course something that cannot be avoided. For example, the high external water pressure, corrosion, powerful currents and operating machinery by remote control all come at a price. With clever design and careful planning, it’s possible to keep costs to a minimum.

Pressure compensation and seals

Something that can affect performance of any system is external pressure. Pressure compensation can be used to enable better underwater operation. Used as a means to keep pressure constant between the reservoir and the seawater, it helps to ensure that seals can still operate as they are usually designed to operate for flow travelling in just one direction, and to handle pressure drop for just one way.

The majority of components that are designed for hydraulic systems are land or surface based. They will have been built to cater for the environment without any specific issues such as high pressure. These components therefore cannot withstand the pressure found in deep water or even pressure drops that are severe.

One of the solutions to handling and supporting pressure-sensitive components in their operation is to seal them inside a protective chamber. However this can be difficult and costly to implement. The chamber would need to be of rigid construction with heavy-duty rugged seals installed that could handle the high external pressure. Pressure compensation is another method that is often seen as being more effective. It’s used by applying a pressure that is equal and opposite to that of the pressure found outside the component.

Piston rods and reservoirs

Plasma arc welding is used to apply high velocity oxygen fuel (HVOF) gun and cobalt-alloy  coatings to piston rods that will be used in subsea deep water conditions as part of a hydraulic cylinder.

When it comes to reservoirs, they will often be replaced by sealed reservoirs. They will contain a flexible medium separator to ensure that the pressure of the external environment will also be in the reservoir, just as can be found in normal surface systems. However, the difference being that the oil and the seawater do not mix as they are prevented from doing so.

This ingenious system then makes it possible to use any component that is used on the land, underwater, as long as any areas are filled with fluid as opposed to the air that would normally be in them if they were operating on the surface. They will then need to be connected to the reservoir to maintain the balance of pressure.

Corrosion is a subsea challenge

Another area of challenge is that of corrosion. The study of keeping seals and seawater working together is known as tribology. It’s essential for subsea hydraulic system designers to be familiar with the concepts involved – keeping seawater out and hydraulic fluid inside a system. For large hydraulic cylinders, keeping the integrity of the piston rod in full operation, even after being exposed to extreme environmental conditions is critical for securing a long-term operation of the system.

Another area of concern is ensuring that all subsea application machinery is designed to a level that does not hurt the ocean environment or people.

Overall, the challenges of designing subsea equipment are multiple due to the harsh environment of the ocean, the reliability required for operators in addition to safety. As industries opt to travel deeper into the ocean, we can only see the challenges increasing.