Zero Leakage for Offshore Productions With Rotary Gate Valves

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With the rotary gate valve, the design of the profiled flow orifice and the length of the flow passage ensure a different pressure drop characteristic to any other type of valve commercially available. The graph 2 shows the pressure characteristic of the rotary gate valve with profiled inlet (blue line), where no pressure recovery takes place. Trim designs were tested at the StatoilHydro test facility in Porsgrunn, Norway, using the same pressure drops through the valve, the increase in the flow rate can be seen on the graph. During tests the critical cavitation index for a profiled inlet was established as k = 0.3 (σ = 0.4) and for a square edged orifice k = 0.75 (σ= 1.7).

Rotary Gate Valve Seals and Testing

Due to its unique rotary design, the rotary gate valve offers superior sealing over more conventional control, choke or gate valves. The primary seal on the valve is across the gate – where the pressurised line fluid energises the seat rings, which in turn seal against the gate. This technology is based on existing design principles of the through conduit gate valve. Fundamentally, the energised seat rings ensure a leak proof seal to prevent fluid leakage between the seat and the gate. Additionally, for subsea applications a fully pressure compensated oil reservoir is located between the valve and actuator drive housing. This means that the valve is virtually leak proof.

The critical nature of the rotary gate valve means that the valve has undergone extensive testing to prove the integrity of the design. and ensure longevity of operation subsea. The conducted tests include:

Initial Development Tests

capacity tests with square edged orifice

capacity tests with profiled orifice

pressure distribution tests

cavitation tests

erosion tests

resistance to blockage test (sand at D100:700ƒÊ and deposition/corrosion product)

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