The Development of Subsea Grouted TeeTM (SSGT) for Subsea Pipeline Live Intervention
Authors: Vu Dan , Booth Paul Allan 
Published: December 2009

The majority of subsea tie-in operations in the North Sea involve the installation of welded fittings, which are performed with assistance from highly skilled divers specialised in the execution of welding operations in hazardous subsea conditions for extended periods of time. Total diverless intervention has not been performed in the North Sea. The Grouted Tee™ technology was originally developed in the 1990's by Advantica, now GL Industrial Services UK Ltd, for use on cross country transmission pipelines for live interventions such as branch connections, bypass, damage repairs and removal of blockages. Grouted Tee™ is now a proven and accepted method of carrying out live intervention operations on onshore pipelines, without the need for hot tap welding. Compared to alternative methods, it is therefore a safer option with reduced risk and offers zero disruption to production throughout the installation process.

A joint industry project was commissioned in May 2006, with support from three major pipeline operating companies, to adapt Grouted Tee™ technology for subsea applications. The resulting technology is known as Subsea Grouted Tee™ (SSGT). The technique consists of a tee which incorporates a top half shell with a branch. SSGT branch consists of a high pressure double block and bleeds Hydrogenated Nitrile Butadiene Rubber (HNBR) elastomeric seal which is energised through spreader plates which activate when the Tee is clamped in position around the pipeline. The other lower half of the shell is split into two parts to create a door arrangement which is operated hydraulically once the Tee is positioned on the pipeline. The Tee deployed in an installation frame is sized to produce an annular gap between Tee and pipeline. The annular gap is injected with epoxy grout which once cured creates the mechanical bond between pipeline and Tee, allowing full transfer of load between tee and pipeline. The development of the DNV-verified SSGT™ conversion established critical design parameters suitable for offshore deployment and underwater installation, while addressing corrosion issues and environmental impacts. Methods for reliable mixing and injection of epoxy grout at the seabed were carefully assessed and tested during the development process. The resulting SSGT™ eliminates subsea welding and therefore the need to undertake extensive pre-qualification equipment testing and personnel training relating to subsea welding procedures. It removes any requirement for subsea welding habitat, subsequently reducing material, vessel time and overall project costs. SSGT™ can be installed by qualified mechanical construction divers, thereby achieving significant reductions in cost and time, while ultimately making operations safer.

This paper details the Subsea Grouted Tee™ conversion programme and design parameters, together with the anticipated client and industry benefits. It reveals some key design features which are adaptable to ROV deployment, making diverless live intervention in deepwater pipelines a closer reality.