A new type of subsea-repairable pipeline Branch Barrier Valve, invented by Total and Statoil, has been developed by CAMERON, based on the ram-type blow-out preventer principle. This valve can be serviced by diverless techniques without interrupting the production of the pipeline. Extensive testing has proved the Branch Barrier Valve to be reliable and to provide increased safety for the operator. The need for a reliable subsea pipeline valve has long been of particular concern to the offshore petroleum industry The trend towards deepwater development has promoted an increasing need for such equipment. This subsea valve design is based on the proven technology of the subsea ram-type blow-out preventer (B.O.P.). The new valve has design features which use hydraulically actuated closing mechanisms and remote control functions. Testing, maintenance and repair may be performed subsea without interruption of the production flow and without seawater flooding of the pipeline, using a diverless workover tool This chapter explains the concept, reports test results and tries to emphasize potential applications.

GENERAL DESCRIPTION OF THE CONCEPT

The new subsea valve concept is composed of three main components:

  • The branch barrier valve,

  • The remote control system of the valve; and

  • The diverless workover tool for maintenance and repair

Branch Barrier Valve

The branch barrier valve is based on the proven technology of the subsea ram type B.O.P. The general design features and criteria of the branch barrier valve are summarized overleaf.

Development of the Branch Barrier

For development testing, a 16-in., 150 bar (2175 psi) working pressure subsea valve was used to study the feasibility of construction of valves ranging from 7 in. to 36 In bore with working pressures up to 2175 psi The valve test programme Included a significant number of cycles at pressures varying from full working pressure of the valve, to low-pressure gas test The valve Itself has three types of components: one body, two bonnets and two rams. The valve (8700 kg total weight) consists of a body with a frame to locate the workover tool (3650 kg) and two bonnets with rams (2525 kg each). A remote control system is also assembled onto the valve.

Table (available in full paper)

Operation of Valve

The body has no moving parts or pipe bore sealing surfaces and is installed in the pipeline with flanged connections or by welding. Once installed in the field, the body remains on the seabed for life, including periods required for maintenance. The frame, which locates the workover tool, is assembled to the body Each bonnet contains the hydraulic operating system for actuation of the rams and 1s equipped with a telescopic operated piston to position the rams during the production and maintenance mode (Fig 1).

Fig. 1 Bore open fully open and piggable, passive actuating system, rams and seals not loaded.(available in full paper)

The bonnet is attached to the body by means of four bonnet studs. During installation or removal of the bonnet, guide pins in the body locate the bonnet The studs are hydraulically stretched; subsequently the nuts are tightened.

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