This project was a world-first in subsea technology, involving the use of remotely-controlled hot tapping. This is the process of breaking into a live pipeline without interrupting the flow, in order to provide a pipeline branch for potential diversion of the flow in either direction or for connecting product compression systems to enhance flow in older wells. Prior to this project hot tapping was always done by divers and thus limited to diveable depths. Traditionally this process has been performed using pre-installed ‘tees’ before the pipe is laid, or by retrofitting once the pipe is in situ, requiring the pipeline to be shut down.
The Åsgard project was the first to use fully remote hot tap technology – the installation of retrofit Tee, fully remotely controlled welding and hot tap cutting operations – following on from the world’s deepest hot tap cutting operation, which was at the Ormen Lange field in the Norwegian Sea. This development, done without having to shut down pipeline flow, and using remotely-controlled hot tap equipment is the result of targeted research and development effort over many years.
CSS Isotek Ltd was chosen to supply the critical welding equipment and control system for the Remote Tee Welding Tool (RTWT), with our expert specialists involved in the specification, design, build and on-going qualification of the tool throughout the duration of the project. In addition to the machine concept and design, CSS Isotek Ltd was also tasked with the weld procedure development, setting the parameters and qualifying the welding procedures to the satisfaction of the client and obtaining third party approvals.
This highly challenging project required us to develop completely new solutions that would work reliably at depths in excess of 1000msw, performing tasks accurately without the assistance of divers. It presented a number of challenges, including installing and manipulating a welding-head and GMA welding torch, pre-heat coils, arc viewing and inspection cameras and lights inside a 12” branch pipe in order to perform a multiple-pass internal saddle weld at the pipe/branch interface. Additionally CSS Isotek Ltd’s world-leading welding expert Neil Woodward had to formulate new welding parameters and procedures that would cope with the untried depths and in a limited space.
The project required our electrical and electronic, mechanical, software and qualification experts to work closely with the client to design, test and refine the system. Testing was carried out both in-house and at the customer’s offshore integration site by CSS Isotek Ltd personnel. In addition to this testing we were involved in the operation itself – we carried out the welding; our software engineers were on the vessel in a support role, demonstrating our ability to operate our products operationally in the field.
This milestone project represents the world’s first application of diver-less dry hyperbaric GMA welding for subsea production applications. The benefits for the oil field operator are huge – the ability to utilise hot tap technology remotely is a step-change in approach, and gives us the ability to transfer this technology to other projects around the world. Furthermore, the procedure has helped our customer to reduce costs and downtime whilst making the pipeline more productive.
" Since we will be connecting a new compressor station on the seabed to an existing pipeline system on Åsgard, it is very beneficial to use the hot tap technology to avoid disrupting production. The savings are measured compared with what it would have cost to perform a similar operation, including shutting down production in the pipeline we were working on. This would also have taken much longer than the ten days we spent now – possibly as long as three months. "
- Torstein Vinterstø
- Portfolio Manager for Subsea Compression Projects, Statoil