How does marine riser tensioner work?
A hydraulic riser tensioner consists of a hydraulic cylinder with sheaves at both sides. The cylinder is connected to a number of high-pressure gas bottles via a medium separator. A wire rope is rigged in the cylinder; one end is connected to the fixed part of the tensioner, the other end is connected to the riser.
What is the capacity range for a riser tensioner system?
Typically, the system is designed for a maximum static vertical load of up to 4,800 kips at well center, and sliding with 1,600 kips. The tensioners are attached to sliding plates which ride on composite bearing material.
In which tensioners tension is magnified?
Yarn tension during winding Thus, if coming tension varies from 10 units to 20 units (i.e. doubles), outgoing tension varies from 30 to 60, i.e. doubles. Thus in gate type of tensioners the incoming tension variations are magnified by a multiplying factor ‘eμθ’.
Why is it important to know the minimum top tension?
Minimum tension is established to prevent buckling of the riser through established design standards that provide guidance to prevent the minimum acceptable effective tension (at the lower flex joint) in the riser from going below zero, i.e., the riser’s effective tension remains positive over the entire riser length.
What is a riser platform?
These offshore riser systems are conduits (or collection of conduits) used for the safe transportation of material (primarily fluids and gases) between the seafloor and the host platform. These fluids may travel from the seabed to the platform or from the platform to the seabed.
How does a drill string compensator work?
By supporting the crown block with controlled tension the compensator becomes a motion nullification device by raising and lowering the crown block. This then raises and lowers the traveling block and hook to nullify motion or to isolate rig motion from the drill string.
What is chain tensioner for?
Chain tensioner – For fixies or conversion to single speed Fixie frames with horizontal dropout often require a chain tensioner to fix the rear wheel in a fixed position and to screw the axle securely and firmly to the frame. The chain can only be held in tension by mounting a special chain tensioner.
How does a riser work?
The risers are located inside the tower, spanning the distance from the seafloor to the top of the tower and the buoyancy tanks. The buoyancy of the tanks keeps the risers tensioned in place. Flexible risers are then connected to the vertical risers and ultimately to the facility above.
What are the types of riser?
Types of riser
- Dry riser: Used to supply water within buildings for fire-fighting purposes.
- Wet riser: Used to supply water within buildings for fire-fighting purposes.
- Stairs riser: The vertical face between the back of the tread of one stair and the front of the tread of the stair above.
How does active heave compensation work?
Active heave compensation (AHC) is a technique used on lifting equipment to reduce the influence of waves upon offshore operations. AHC differs from Passive Heave Compensation by having a control system that actively tries to compensate for any movement at a specific point, using power to gain accuracy.
Why must the drilling equipment incorporate a Travelling block heave compensator?
A drill string compensator decreases the influence of the heave of a drilling vessel on the drill bit. Drill string compensators are also known under the more general name: heave compensator. Drill string compensators are used onboard drill ships and semi-submersible drill rigs.
How is tension maintained in a steel riser?
Tolerances – 1% on the weight of steel in the riser and 1% on the net lift from the buoyancy material. Tensioners Down – Positive tension is maintained in the riser if one out of twelve tensioners goes down.
What are the issues at the lower end of the riser?
At the lower end of the riser the primary issues are riser angle and loads and stresses applied to the SSBOP stack and wellhead system. The primary and influential parameters that influence riser behavior to be analyzed are water depth, top tension, mud weight, environmental loads, riser properties, and vessel offset and dynamic motions.
How does the marine drilling riser provide stability?
All of the marine drilling riser structural integrity and stability is provided by resisting all axial and lateral loads through tension. Only a very small amount of the riser ability is to resist lateral environmental loads resulting from the riser’s structural dimensions.
How much weight can you put on a riser string?
Although this is within the API tolerance levels, when compared to the manufacturers’ values in 9000 ft of water, this can amount to 150 kips of additional weight for the entire riser string.
