MARINE: Hyflo Is Going Sub Sea
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Hyflo was approached by a world leading and well recognised producer of diving equipment to design and manufacture the hydraulic handling system for a SAT system. The hydraulic system was to be designed to comply with the American Bureau of Shipping (ABS) as well as Det Norske VERITAS (DNV) offshore standards for diving systems.
The SAT system was designed as a 12 man system; it would house 12 divers in the living chambers at any given time, however only three of the 12 divers would be in the water at a time.
The living chamber is a dry pressurised living space; the divers spend days, if not weeks, living in the chamber whilst they complete their required job. While the divers are in the chambers they live and work at a constant pressure. This eliminates the need to decompress the divers every time they surface once their shift has been completed.
The three divers are transported to and from the working depths, at a constant pressurized environment, in a smaller chamber known as the dive bell. The dive bell is connected to the living chamber when it is not being launched and is locked onto the chamber by means of a bell clamp.
The hydraulic handling system is responsible for launching the dive bell to the required depth and to retrieve it to the surface. Hyflo would have to design the hydraulic system for a bell weight of 10 tons and a maximum dive depth of 300m with a maximum breaking torque of 17 500Nm.
The dive handling system comprises three component groups, each satisfying a different role in the overall handling of the SAT System. These components are the hydraulic power unit, the drive and control systems for the winches and the hydraulic cylinders.
The dive bell is launched over board by means of an A-frame which is automated by two cylinders at either end. Due to the boom angle the cylinders were designed for a maximum extend force of 100.kN per cylinder.
While the A-frame is being boomed into the launching position, the dive bell is locked into the A-frame cursor by two cylinders at the top of the A-Frame, these cylinders are also required for lowering the dive bell into the mating position with the living chambers. A dampening cylinder was installed between the A-Frame and the cursor to prevent the dive bell from swinging uncontrolled as it is being launched and recovered during periods of large swell. Due to the extremely corrosive environment all the cylinders were designed with stainless steel shafts and were coated with a thick coating of marine grade paint to ensure their longevity.
The handling system was designed with three winches, one winch to launch the bell (bell winch) and a winch to launch a guide cable for the dive bell (guide wire winch). The role of the guide wire winch is to launch a guide cable, which is connected to guides on the bell to prevent it from rotating during the launch. The third winch on the system is the umbilical winch, which is responsible for paying out the umbilical, which is connected to the bell; the umbilical is the lifeline of the divers, and houses all the hoses which transports the breathing gases to the bell as well as all the communication and power cables.
As the dive bell is a means of transport for humans, the winches have to comply with the strict rules regarding man-rider winches set out by the classing societies. Various additional back-up handling systems are incorporated. The primary source of launching the dive bell is the bell winch; however the guide wire winch is designed as a secondary means of recovery of the bell in the event of a failure on the bell winch. Both winches are therefore designed as man riding winches.
Each winch has a main drive and a back-up drive in the event of failure of the main drive. Poclain hydraulic wheel motors were selected for this application.
The control system for the winches are complex as only one of the motors on the winch can power the winch at any given time. The standby motor will therefore just be free wheeling along while the main hydraulic motor is powered and visa versa.
The valves for the control of the winch braking systems, load holding and changeover from main to standby drive as well as the free wheeling process are all incorporated into the winch control block. This complex manifold block is designed and built in-house out of a solid piece of steel. It required more than 200 different drillings and almost 25 cavities for the different cartridge valves. The manifold block reduced the amount of piping required, reduced the space required and also the installation time required. These reductions ultimately resulted in a cost effective method of controlling the two hydraulic motors. The umbilical winch is not regarded as a man riding winch, which resulted in a single Poclain motor drive and a simple winch control block.
The hydraulic power unit consists of a main and an emergency hydraulic system, with two independent power units built into one frame. The main hydraulic system consists of two pressure compensated variable displacement piston pumps which are driven by two 45kW electric motors and deliver 200l/min at 320 bar, and one fix displacement pump which delivers 65l/min at 220 bar. The emergency system was designed to operate the system at half speed and consists of one pressure compensated variable displacement piston pump which is driven by one 45kW electric motors. It delivers 100 l/min at 320 bar, and one fix displacement pump delivering 35l/min at 220bar.
These pump and electric motor combinations supply oil to a set of proportional manually and remotely operated directional control valves that ultimately redirect and control the appropriate hydraulic end users. The directional control valves can be remotely operated from a maximum distance of 30 metres by means of a portable remote control unit. This gives the operator much greater mobility so that he has an excellent view of the entire launching and recovering procedure as it happens. The main and emergency hydraulic systems can also be operated manually from a control station on the power unit, if required.
Currently Hyflo has more than five such hydraulic systems in operation across the world’s seas with multiple new projects ongoing. Each system is custom built to individual clients requirements and operating conditions whilst maintaining the basic operating principles outlined above.
Hyflo has a dedicated hydraulic systems design team for SAT handling systems, and in conjunction with its client strives to produce quality, user friendly and cost efficient hydraulic systems, says project engineer at Hyflo, Cape Town.
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