The Prediction of Fatigue Endurance of Riser Tensioner Ropes for Floating Drilling Rigs as a Function of Location

Round Table The Application of Endurance Prediction for Wire Rope – Reading

lntroduction

Riser tensioners are used on floating drilling rigs to allow relative movement between the vessel and the riser as the vessel heaves up and down, whilst keeping the riser under constant tension. Typically, they consist of a hydraulic actuator connected to the top of the riser casing via a wire rope run through a series of sheaves. The actuator is connected to a pneumatic accumulator, which is used to maintain the pressure in the actuator. The system can be adjusted to keep the riser at the required constant tension, despite the vertical motions of the drilling vessel. A typical riser tensioner arrangement is shown in Figure 1. Heave compensation systems are also fitted to the drill string, to prevent the weight on the bit from fluctuating, which would adversely affect drilling operations. Like riser tensioners, these systems work on the principle of supporting the drill string on pneumatic springs. The heave compensating device is normally fitted to the crown block or the travelling block, and also consists of hydraulic actuators connected to a pneumatic accumulator. More information on riser tensioners and heave motion compensators can be found in work by Baker(1991), Hatleskog (1983) and Kozik et al (1990).

Author(s): J. E. Bradon and C.R. Chaplin