A technique for remote hot-tapping into subsea pipelines without the use of divers has been developed. The technique involve the installation of a valve module and hot-tapping equipment remotely operated from a support vessel, and provide a cost effective option for tie-in of new pipeline systems to existing infrastructure without turndown of production.
This paper describes the technique, the functionality of the equipment and the testing and operational characteristics of the system now available for commercial use. The development project has so far built and qualified the equipment required to hot-tapping into pre-installed hot-tap Tee's, while the ongoing development is concentrating on developing techniques for retro-fit hot-tap Tee's on unprepared pipelines. The equipment is designed to operate in water depths down to 2000 meters and for pipeline pressures of 250 bars.
Hot-tap technology has for many years been used onshore and in process plant applications in order to connect branch pipelines into production pipeline systems without stopping production. The majority of hot-taps are based on welding the branch pipe to the pipeline and then tapping by hydraulic operated drilling machines.
In the North Sea, so far less than ten hot-taps have been carried out on subsea pipelines, of which two were on the Statpipe system. These hot-taps have provided very cost effective solutions, but are based on an approach using divers and it is thus limited to water depths where diving may be applied. Typical layout of a hot-tap connection is shown in Figure 1.
Over the last few years, installed pipelines have been prepared for future connections by pre-installed Tee-assemblies of which some require hot-tapping to allow product flow. Some of these pre-installed Tees and future planned Tees are at water depths requiring diverless technology.
Statoil have therefore launched a development project to establish technology and tooling systems for remote hot-tapping such that the pre-investments done may be utilised within realistic time frames.
Figure 1: Typical subsea hot-tap connection (Available in full paper)
The development project is split in two main phases:
Phase 1 is to develop tooling systems required for remote controlled hot-tapping into prepared pipelines via pre-installed Tee's
Phase 2 is to develop technology and equipment for hot- tapping into unprepared pipelines.
The interface between phase 1 and 2 is defined such that equipment developed in phase 1 will be used together with the systems developed in phase 2.
All new tooling systems developed are incorporated as part of the Pipeline Repair System (PRS) operated by Statoil on behalf of a consortium of pipeline Operators in the North Sea to provide repair and construction support for oil and gas pipelines on and from the Norwegian Continental Shelf. The Pipeline Repair System (PRS) is a comprehensive suit of subsea pipeline construction and repair tools, from isolation plugs and cleaning tools to large manipulation and installation frames, and welding habitat enclosures.