Zero Leakage for Offshore Productions With Rotary Gate Valves

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The turndown ratios far exceed those of more traditional controlling devices, and whereas conventional control and choke valves have an inherent leakage, the rotary gate valve gives zero leakage since the gate is based on conventional through-conduit gate valve technology.

Why Was a New Style of Valve Required?

MEG dosage is probably the most critical process on applications, where hydrates are present, so if the dosage valve was to fail then the operation would have to be shut down and the hydrates cleared. The Ormen Lange project was the first to use regenerated MEG, and therefore no other valve design had been tried in the application. As described below, several other valve types were considered, but the rotary gate valve was selected due to its superior design.

Screw and Piston Design

On screw and piston design applications pressure loss is achieved by the flow – as it passes along a course screw thread. This design has a low tolerance to impurities and can very quickly become damaged or stuck along the threaded area.

Needle and Piston Design

The needle and piston design valve relies on a two stage needle and seat to achieve a pressure drop. In industries, this type of design is not normally used on applications with high levels of impurities, as the impurities bridge across the flow orifice and erode the needle.

Spline Choke Valves

The spline choke valve has to distribute the pressure drop across a segmented plug. The plug clearances of this design means that the valve is often subject to blockages, and impurities in the flow mean that erosion can take place across the valve plug.

Design Features

The gate is designed with a series of profiled flow holes, which are selected according to the desired flow rate. Orifices can be combined to give additional profiles of up to 15 alternative low combinations. The valve has therefore got sufficient capacity (6-8 independent flow passages) to enable the valve to operate with a large range of differential pressures and flow rates. Debris, sand, deposition/corrosion products

have been found to pass through the valve.

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