11 Topsides Umbilical Termination Unit (TUTU)
11.1 Introduction
The Topsides Umbilical Termination Unit (TUTU), provides termination of the EHC umbilical tubes and cables and provides the interface between topside controls equipment i.e. HPU, chemical injection skids, EPU (or SPCU).
11.2 Description
The umbilical carrying hydraulic fluid, electrical power/signal, and chemicals, to the subsea system is usually located on the cellar deck of a FPSO or Platform, or at the edge of an anchored static FPU or the turret of a turret moored FPSO. This is usually a considerable distance from the HPU/EPU. The umbilical itself must be terminated close to its hang-off point, so some form of termination bulkhead and electrical junction box is required.
This usually takes the form of a Topsides Umbilical Termination Unit (TUTU).
The TUTU provides hose coupling points and an electrical junction box, but in addition houses block and bleed valves for each hydraulic function.
The hydraulic supplies from the HPU are usually carried by FPSO/Platform pipe work to the TUTU. The bleed valves allow this pipe work to be filled, flushed and bled after construction. Similarly, they also allow the umbilical to be bled down if required. The bleed valve outputs are usually routed back to the HPU to avoid local spillage of fluid.
The block valves allow a definite isolation point for the subsea umbilical. The block valves can be locked shut to prevent inadvertent pressurisation of the umbilical. This also allows the HPU outputs to be tested without having any subsea effect. Naturally, these valves must be open for normal operation and access to the TUTU is restricted by a lockable cabinet door. A drain port ensures that any build-up of pressure inside the unit caused by leakage cannot pressurise the unit.
The TUTU is usually constructed of stainless steel and is either safe area equipment or certified for operation in a Zone 1 or Zone 2 hazardous area as dictated by the specified hazardous area location.
The connections to the umbilical are usually arranged on the side of the unit, at an elevation that allows a generous radius for connection of the umbilical pigtails. This often requires that the TUTU itself be mounted at about 1 metre from deck level, so the unit may have a plinth.
If bottom entry is required, then a transition box is required to allow pull-in of the umbilical for hang-off and to then terminate the hoses in the bottom of the box.
Provision is usually made for enclosing the pigtails from the umbilical hang-off inside a length of protective conduit. Depending on the umbilical termination design, this may require one or two such conduits to house both the hydraulic hoses and electric cables, and the TUTU mechanical design must consider this. The electrical junction box is not usually located within the hydraulics enclosure and should preferably be kept isolated. It is usually mounted on the side of the unit.
11.3 Termination of Chemical Hoses
A similar item of equipment may also be provided for connection of the chemical hoses, although this is usually kept separate from the control system hoses and cables to avoid contamination. This "Chemical Umbilical Termination Unit" is placed adjacent to the TUTU at the umbilical hang-off point.
Again, precautions must be taken to avoid pressurisation of the box due to chemical leakage (particularly with the known phenomenon of migration of methanol through thermoplastic hoses, which can then travel to either extremity of the umbilical). It is usual for the termination box design to include a Methanol catcher when Thermoplastic hoses are used.
