Severn applies valve intelligence to solve Leman Delta challenge

Overcoming technical issues in North Sea platform simplification

Severn Unival, the advanced engineering services division of Severn Glocon Group, has designed and manufactured three highly-engineered choke valves for Shell’s Leman Delta platform. The rig is being transformed from Normally Attended to Normally Unattended Installation status as part of its ongoing decommissioning process. This raises new technical challenges, since it needs to perform consistently without the need for unplanned maintenance.

To reduce the velocity of the process medium and minimise erosion, some sections of pipework on the platform have been increased from a 10 ̋ to 12 ̋ diameter.

As the platform’s long-term valve maintenance partner, Severn Unival was commissioned to replace three 10 ̋ choke valves with 12 ̋ alternatives that could easily be installed in the new system. The valves also needed to meet new performance targets without requiring manual intervention between planned maintenance windows.

Severn’s solution was to switch from a 10 ̋ angle to a 12 ̋ 90 degree globe design, which meant the valves could be installed without the need to change the orientation of actuators. The valve trims have been manufactured from Tungsten Carbide to enhance their durability.

For added assurance, a Super Duplex trim guard has also been incorporated. This technique has previously been approved on valves Severn Unival devised for Statoil, and is proven to enhance the durability and lifespan of valves deployed in extreme environments.

A further challenge Severn Unival faced was reducing the risk of fugitive emissions. Traditionally, on a Normally Attended platform, manual adjustments can be made to tighten the valve stem and seal as necessary during routine management.

The new platform status meant measures needed to be taken to significantly reduce the likelihood of any stem/seal damage that could result in leakage. To achieve this, Severn Unival’s engineers initially planned to hard-face the valve stems with a Tungsten Carbide coating to reduce vulnerability to damage.

However, since this material is porous there was some doubt over whether the valves would pass the ISO 15848-2 type test for fugitive emissions, where helium is used as the test medium.

Instead, an advanced, non-porous surface coating from Hardide Coatings was used. Testing verified that the valves complied with the stringent ISO 15848-2 criteria.

The valves have now been dispatched, ready for the simplified Delta platform start up in March 2019.

Adam Eckersley, Technical Engineering Manager at Severn Unival, says a longstanding relationship and good collaboration with Delta’s maintenance and project teams was central to the success of this job.

Overcoming technical issues in North Sea platform simplification “We have more than a decade’s worth of repair intelligence data from failure analysis of OEM valves on the Delta platform,” he explains. “This meant that we were quickly able to predict the technical challenges that these valves would need to overcome, and develop robust solutions.

We have a strong partnership with Delta’s maintenance and project teams, so the whole process ran seamlessly and we’re all confident that the valves will perform reliably without the need for unplanned maintenance.”

Severn Unival is part of Severn Glocon Group,, +44 (0) 8456 070710

Tel: +44 (0)845 223 2040

Published in Valve User Magazine Issue 48

Winter 2019 // Issue 51
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