RTS - ROV operated Tie-in System for Low Cost Subsea Developments
Authors: Halle Per Olav 
Published: October 2008

A new type pull-in and connection system is developed for very deep waters. The system is called ROV-operated Tie-in System (RTS). Main objectives during the development phase was to make a tool system more or less independent of waterdepth, use of simple lowcost intsallation vessels, minimum equipment left subsea, minimum support structure sizes, simple control system, various launching methods possible and use of field proven clamp hub and seal assemblies. The result has been a very cost effective tie-in system which is a key factor for reduction of total field development costs. The capacity for the tool is 10" 3000 psi flexible flowlines or alternatively 9?5000 psi.

The RTS replaces divers during tie-in operations and can be used down to at least 1500 m waterdepth. A full scale prototype has been built. Land testing and shallow water testing shows that the RTS concept is functioning.

The RTS represent a considerable cost saving for future subsea field developments.

Basis for new development

With experience from several diverless subsea developments in the North Sea an analysis of the different requirements were performed to find out what requirements that created cost.

Several changes were discussed to simplify the existing tie-in tools used for Troll Oil project (ref. 1). Most of the requirements listed below are certainly not absolute and can be discussed.

Following requirements were questioned:Requirement for no damage to clamp connection in case of 60 tonn snag force in the flowlines and umbilicals in any direction. Removal of this requirement can be done if adequat protection 'of the lines are done. Snag catcher structures will be removed and tie-in porches can be reduced in size.Remove requirement for fixed position of unconnected line. This possibility opens up for a radical shortening and simplification of the porches. The termination may be laid down on the seabed if connection is not made up. A protection cap should be mounted on in such cases.Remove requirement for pull-head with central pull-in wire. The tilting of the funnel during removal of the pullhead is avoided and pullhead reciever system can be removed from the tool.Use of multiple mating seals. During testing, the existing metal to metal seals used at Troll Oil (Ref. 1) are used up to 10 to 15 times. Use of the same seals 2-3 times offshore should be considered to avoid replacement of the clamp connector each time.Position of clamp connector permanently subsea. Recovery to be contingency operation only. The elevator system inside the tool is avoided.Use of the ROV to transfer signals and create power to operate the tool. Aseparate conrtol system with control container and separate umbilical are avoided.Remove requirement for 1.st end tie-in direct from laying vessel. The pull-in rope is then reduced to 30-40 meters on a subsea winch instead of pull-in wire going to surface and a subsea linear winch.

New additional requirements for a new generation tool system were as follows:Extended waterdepth range down to 1500 metersUse of guidelineless deployment