The Drilling Riser Tensioner (DRT) is an active hydro-pneumatic type tensioner system that allows relative movement between the drilling riser and the Dry Tree Unit (DTU) and maintaining adequate tension at the top of the riser for the applicable riser system so each stroke of the DRT should allow initial wellhead offset in accordance with the worst wellhead offset distance and offset tolerance with the worst load case combination. This worst case offset should be considered in conjunction with all possible offset positions of the platform itself that may result in possible upstroke of the riser.
The DRT should be equipped with a tension control and have adequate stiffness so that the tension imparted to the riser at maximum upstroke or downstroke results in constant riser support tension. As, appropriate, worst-case minimum tension (maximum upstroke) should be considered in conjunction with a failed tensioner element with appropriate load case.
Twisting of the DRT should be considered according to the maximum yaw that can be developed and should accommodate the stroking of the riser due to thermal effects.
The DRT should be designed in such a way that one load support unit can be replaced in the operating condition, as appropriate.
Considerations when selecting the DRT:
- The DRT should be an independent, self-contained tensioning system designed to dynamically support a drilling riser and the surface BOP during the well drilling phase. The DRT design should satisfy all riser top tension requirements.
- The DRT should be sized to deliver designated system stiffness and a required stroke range for both the system intact and damaged conditions.
- Each tensioner element assembly should be a stand-alone system, where a failure of one compartment or element does not affect the other compartment/elements of the DRT. Means will be provided for removing and replacing one of the tensioner elements while the DRT is in service, or the DRT should be designed for a failed tensioner element if the element is not replaced in service.