Umbilicals

The definition of an umbilical in accordance with the Oxford Dictionary is as follows :- " ropelike structure passing from foetus to placenta ; central connected through the female line ".In simple terms it is the delicate life support connection that supplies nutrition, oxygen, blood, and removes waste product for keeping a baby alive whilst inside the mother's womb. Anyone using a diving umbilical or hose fed system for life support would be well advised to remember this definition before, during and after operating such systems.

For diving and life support work an umbilical would normally supply breathing gas (air or heliox mixture), communication between operative and supervisor, and strength member for emergency recovery.

In the case of surface demand diving (air dive) additional services would include a pneumofathometer hose (to record diving depth), in some cases hot water to warm the diver, and underwater video link.

In the case of saturation diving additional services to the diver would include those vital links as for surface demand diving plus a reclaim hose (to take breathing gases back to the surface for cleaning) and a tracking hose which regulates the reclaim system.

Other forms of umbilical include the following :

• Main Bell Umbilical, used for saturation diving to connect a diving bell to a surface support vessel and providing all services to keep the diving team alive and the bell systems working.
• Wet Bell Umbilical, used for surface demand diving to keep air divers alive whilst being transported through the splash zone down to working depth (normally 50 metres maximum in British waters)
• Habitat Umbilical, used to connected life support services plus power supplies, hydraulic supplies and monitoring facilities to a box like structure placed on the sea bed to carry out repairs in a dry environment such as pipeline welding.
• - Welding & Burning Umbilical, used to supply power, earth return and oxygen to a diver engaged in underwater 'wet' welding or cutting of structures.
• - Underwater Tool Umbilical, used to supply hydraulic power and return lines for underwater tools such as drills, saws and scrubbing equipment.
• - Hydraulic Workover Umbilical, used by the drilling engineers to supply sub sea controls to various valves for Emergency shut down during drilling operations.
• - Electro-Hydraulic Control Umbilical, used to connect a sub sea system to a platform which in some cases could be a number of miles away. Here again the umbilical is used to lower and control valves and also monitor sub sea operations.
• - Remotely Operated Vehicle (ROV) Umbilical, used to connect and control a remotely operated vehicle from the surface.

All the above umbilicals have one thing in common, going back to our initial definition, if you wish to protect personnel and equipment from harm it is essential to treat UMBILICALS with CARE and RESPECT.

BE KIND TO YOUR UMBILICAL AND IT WILL KEEP YOU ALIVE AND OPERATING.

In the United Kingdom sector up until the early 1970's most diving umbilicals consisted of standard rubber hoses plus standard electrical cables laid out straight and taped together at intervals. Due to the harsh environment of the North Sea diving operations better products were required to be developed to meet the arduous treatment about to be experienced.

The writer was involved with the development of the TWISTED "ROPELIKE" Umbilical structures, ie back to our initial definition. The first requirement was for a non-kink 3/8" air hose which could be bent around a 5/8" diameter rod without restricting air flow. This challenge was achieved with the use of a thermoplastic liner (suitable for breathing purposes) plus the application of several layers of polyester fibre braiding.

The next requirement was for a communication cable that would withstand the continual flexing and tensioning experienced during diving operations. This problem was overcome with the development of a communication cable built using the TWISTED ROPELIKE" principle which contained two screen twisted pairs of conductors plus a braided strength member.

Hose end fittings were the next area of concern due to :

a) failures caused by the incorrect fitment of reusable brass hose end fittings, or in some cases over tightening of retaining nuts which resulted in broken fittings,

b) compatibility of materials with the breathing gases being used.

These problems were overcome with the development of staged phosphor bronze hose end fittings. A comparison of 'pull off' strengths was carried out between re-usable brass hose ends which could be pulled off hoses at tensions between 200 and 600 kgsf, and swaged phosphor bronze hose ends which could be pulled off hoses at tensions over 1,000 kgsf. Phosphor bronze was considered to be compatible with air, oxygen mixtures, sea water and hydraulic fluids thus was accepted as being a versatile material for diving operations.

The next challenge was to develop an umbilical which got away from the straight laid taped components principle. Here again we go back to our initial definition for an umbilical, ie "ROPELIKE" STRUCTURE.

Twisting or laying up components in a manner similar to rope construction offers the following advantages :

• Increased flexibility as the individual components can move relative to one another without producing 'loops' that could snag.
• Tensile forces applied to the umbilical could be spread over all the components thus avoiding concentrated loading on one particular item (which could be the case with straight laid umbilicals) causing premature failure.
• With the inclusion of a strength member within the communication cable, umbilicals could be built without separate strain relief ropes thus reducing bulk and cost.
• With the use of lighter weight components umbilicals could be designed to be floating or sinking as~ desired by the particular diving operation.
• Colour coding of components makes the umbilicals easier to see in water and also distinguishes between different services.

Having used the above developments to improve the design and operation of surface demand umbilicals and bell excursion umbilicals, the next area to be tackled in the mid 1970's was the question of wet bell umbilicals and main bell umbilicals.

A Main Bell Umbilical has to provide all services, with the exception of the main lift cable, to a Submersible Diving Chamber which could contain typically two, three and possibly four divers. This includes the following links :

• Diver Breathing Gas Supply
• Bell Blow Down Gas Supply
• Hot Water Supply
• Reclaim Return (for those systems with gas reclaim)
• Pneumofathometer connections for individually divers, bell depth, and bell atmosphere monitoring
• Power supplies for lights, battery packs and bell scrubber units
• Communication between individual divers to surface and bell to surface
• Video supplies for diver hat mounted or hand-held cameras and bell mounted cameras
• Monitoring links as appropriate

One of the first problems to overcome with the development of main bell umbilicals, was the fact that rubber hot water hoses tended to be supplied in short lengths thus requiring a number of couplings along the length of the umbilical with the possibility of failure. A hot water hose was developed along similar lines as the gas supply hose but with the use of a more suitable liner material that could be used up to 100 deg C temperatures.

The next problem with the development of main bell umbilicals was the fact that in an emergency the umbilical could be used to recover the diving bell to the surface but not used to pull the bell out of the water. This problem was solved by :

a) the generous use of polyester fibre reinforcement of each hose and b) the reinforcement of individual electrical cables.

The combined strength of such components far exceeded likely tensile forces to be placed on the umbilical. Even so should an emergency recovery become necessary THE UMBILICAL SHOULD BE THOROUGHLY CHECKED AND TESTED before further use.

With the expense and bulk of helium being used for saturation diving, gas reclaim systems were developed calling for the need of a hose which would not collapse when a negative pressure was applied to bring breathing gases back to the surface for cleaning and 'topping up' with oxygen before re-use. A reinforced hose was developed for the purpose and included into umbilical structures as and where required.

Finally it was determined that having manufactured a TWISTED "ROPELIKE" Main Bell Umbilical it should be protected using a close mesh polythene monofilament fibre braided jacket which offered the following advantages :

• Increased flexibility
• Ease of 'In field' repairs should these become necessary
• Ability to monitor individual components
• Ability to offer refurbishment service as and when required

Having developed these products suitable test procedures were discussed and devised by both Lloyd's Register of Shipping and Det Norske Veritas in conjunction with umbilical manufacturers to ensure that umbilicals were being designed and manufactured to a high standard suitable for life support.

At Fibron BX Ltd our products have been designed and developed along the lines described above and always remembering that in the case of diving and life support umbilicals A PERSONS LIFE is at the end of our product.

From the original development of The Diving Umbilical we now have umbilicals serving Sub Sea Completion Systems, Workover Systems, Remotely Operated Vehicles etc etc etc.

THINK OF THE DELICATE LINK BETWEEN MOTHER AND UNBORN CHILD ...THE UMBILICAL

Tim Chaplin. Fibron BX