Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Fatigue Testing of Shrink-Fit Riser Connection for High Pressure Ultra Deepwater Risers
Subsea Riser Products Inc. (SRP)
The Shrink-Fit connection approach to riser fabrication has been successfully designed and de-veloped to enable the manufacture of riser systems from high strength thick walled pipe that are capable of operating with high internal pressures, beyond that which are typically available within the industry today. This technology has already been employed for manufacture of a shallow water drilling riser system in the North Sea.
The main design issue in such systems is the large diameter and high pressure combination which results in a requirement for thick walled pipe to resist burst. If weldable steel grades (<80ksi) are used, wall thicknesses are typically in the range of 40mm - 55mm. Such wall thicknesses result in heavy riser joints that are expensive to manufacture and the system has a complex structural response due to the practical tension limit that can be applied by available vessels and rig types.
The objective of this project is to conduct resonant fatigue testing of a Shrink-Fit connection which, as an alternative to welding, facilitates the fabrication of riser joints from high and ultra-high strength steel (80>130ksi) Through qualifying such a system, that can be manufactured from steel in excess of 80ksi, the wall thickness of the pipe can be significantly reduced, which in turn will reduce the weight, current loading, tensioner requirements and cost of manufacture of critical deepwater riser systems.
A full bore Shrink-Fit drilling riser will enable two key developments in deepwater drilling. Firstly, the full bore riser (19” +) will enable larger casing to be deployed, ensuring that the final well diameter is larger than would have been possible given the current technology available. This will have a large positive impact on hydrocarbon recovery rate, efficiency and ultimate quantity.
Secondly, by enabling drilling to be conducted from a production vessel avoiding the need for a Mobile Offshore Drilling Unit (MODU), a large cost saving could be made to the project making an increased number of current and future reservoirs commercially viable. This technology will not only enable cost savings to be made on existing operations, but it will enable the commercial viability of smaller reserves that have, until this point, been non-commercial, thus increasing available and efficiency of production. Additionally the technology can be applied to top ten-sioned (surface tree) production risers with the same benefits of vessel payload reduction, ten-sioner capacity reduction, production riser diameter improvement.
The Shrink-Fit system has already been qualified and manufactured for a shallow water applica-tion in the North Sea. To achieve the technical step-change and application from shallow water to deepwater, SRP will need to qualify the fatigue performance of the Shrink-Fit coupling. Whilst SRP have a high confidence in the fatigue performance, industry requirements to evidence this performance are stringent and can only be achieved through large scale testing which is costly.
To achieve this level of qualification SRP propose a fatigue qualification program that will be conducted on 6 large scale specimens, testing by Stress Engineering Services is proposed. The fatigue tests will be conducted using a proven resonant bending rig with 2 samples, each at 3 stress ranges (low, medium and high). BP has offered to contribute pipe for the testing. Fatigue tests are conducted using internal pressure to identify leakage of the test piece and thus define fatigue limits. The tests are continued until the target number of cycles is achieved or failure of the connection occurs, whichever is sooner. Failure is deemed to have occurred once loss of pressure containment is achieved.
While this technology is initially focused on large diameter steel pipe risers and connections, a further important application is the use of the process on titanium pipe and particularly the ability to connect steel couplings onto titanium pipe. Such a capability is unique and facilitates more economic manufacture of titanium joints for special application such as taper joints and touch down point of steel catenary risers to improve their structural performance. This is considered an important further development of this technology and is considered a second phase of this qualification work building on development work already initiated by SRP.
Principal Investigator: Paul Brett
Final Project Report [PDF-4.01MB]