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Rotary Gate Valves

Zero Leakage for Offshore Productions With Rotary Gate Valves

| Author / Editor: ROB TAYLOR / Dominik Stephan

(Picture: Weir)

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There are very few genuine new developments in the valve world, new ideas are mostly developed along a theme, however, one completely new concept in valve design is the Rotary Gate Valve (RGV) developed by Weir Valves & Controls UK – a part of the Weir Power & Industrial Division in the UK.

A rotary gate valve has been successfully supplied to FMC/StatoilHydro for the Ormen Lange project in Norway, where there was a particular problem in controlling regenerated Mono Ethylene Glycol (MEG) injection to prevent hydrate formation. Subsea equipment has been supplied for over 25 years, with more and more discoveries are being declared viable in deep and ultra-deep waters.

The Ormen Lange project situated off the north western coast of Norway was developed in water depths of 1,100 metres on the edge of the Arctic Circle and has an ambient sea temperature, which can reach -20C. Gas produced from the field contains entrained water, which if left untreated would form hydrate and potentially block up the process lines. Gas from the Ormen Lange project is piped to an onshore terminal, which is 120 kilometres from the subsea template.

In Australia, GE Oil & Gas has used the valve for Chevron’s Gorgon and Jansz fields, the most significant gas projects to date in the region. The valves were specified with the specific flow requirements for the fields and the physical layout of the choke module designed by GE Oil & Gas.

How Hydrocarbon Hydrates Form

Hydrates are an ice-like lattice structure of hydrocarbons, which form when the entrained liquids are taken below the hydrate formation curve. When these occur, equipment is usually required to be brought to the surface for removal or ‘melting’ of the hydrates.

Downtime is very costly to the producer, so it is important to prevent the formation of hydrates. MEG is used as a type of anti-freeze to inhibit the expected water content in the hydrocarbon at the given well head pressure, in order to eradicate hydrate formation in the gas production line. Even 5-10 per cent loss of MEG injection can lead to hydrate formation and it is critical to maintain injection, therefore, the valve used has to be totally reliable.

The Challenge: Valve Development

The valve was originally developed to isolate flow, with the ultimate advantage of not having a cavity (zero displaced volume during stroke). This is significant, because the valve will not drift on failure of the operator, and will not be detrimentally affected by a cavity, which could otherwise become pressure locked and/or blocked by hydrates of line debris.

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