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Blow Out Preventer

Part of the rig's well control equipment, the BOP allows the well to be shut-in/suspended in an emergency situation. The riser assembly will interface directly to the base of the BOP.

To see the full Claxton High Pressure (HP) Drilling Riser please click on the downward arrow at the top of the screen to progress to the next phase of operation.

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Drilling Adapter

Interfaces the rig's surface BOP with the upper riser assembly. Typically a high performance quick connector system rather than a flanged, to allow fast assembly and disassembly.



Gasket areas used within riser connections to provide the primary sealing mechanism.


Drilling Adapter

Interfaces the rig's surface BOP with the upper riser assembly. Typically a high performance quick connector system rather than a flanged, to allow fast assembly and disassembly.


Stud bolts

Stud bolts are utilised to assemble the riser flanges. The forces generated during assembly provide pressure sealing and mechanical strength within the flanged connection.


Riser handling tool

Allows handling of individual riser spools or the entire riser assembly during deployment. Locking segments are hydraulically activated to engage with internal lifting grooves within the riser spool flanges. Once engaged with the riser, all hydraulic lines are pressurised and disconnected from the tool.


Riser Spider

Allows the riser to be supported during assembly and deployment subsea. Interfaces directly with the rig’s rotary table. Can be hydraulic (activated open & closed), or a simple manual design.


Tension ring

A removable ring which acts as the load interface between the rig's tension system and the riser. Allows vertical tension to be applied to the riser assembly, countering the affects of environmental loading.


Tension joint

Typically a fully forged construction to provide high fatigue performance and to cater for the high bending moments and associated stresses. The Claxton proprietary tension ring would be installed anywhere along the pipe body providing infinite adjustment. This provides overall riser space out adjustment and works within the rigs tension system adjustment to maintain optimum cylinder stroke.


Multi-stud Tensioner

The flange connections will be assembled using a multi-stud tensioner (MST). This device enables all flange stud bolts to be tensioned in unison and thus greatly reducing make up time compared to standard 50% coverage tensioning or torqueing techniques. MST's are supplied with all the necessary pump units and hydraulic hoses.



Pup joints are typically of fully welded construction, though forged variants are available. These span the mid-section of the riser string, between the tension joint and stress joint, and allow the riser assembly stack up length to be tailored to specific client requirements.


Hydraulic power Unit (Hpu) & umbilical reel

The HPU powers and functions the wellhead connector from the surface. The umbilical reel houses the umbilical for storage and transit on a revolving drum. The drum is linked to a pneumatically driven motor which allows the umbilical to be deployed or retrieved subsea. The umbilical hydraulically connects the HPU at surface with the wellhead connector.


Umbilical sheave

Ensures the umbilical's minimum bend radius is exceeded during deployment and retrieval (ensures the inner hydraulic hoses are not damaged), while maintaining tension within the umbilical to avoid slump.


Intermediate Joints

Standard joints are typically fully welded constructions, though forged variants are available. These span the mid-section of the riser string, between the tension joint and stress joint.


Umbilical clamps

Umbilical clamps are utilised to tether/anchor the umbilical to a pod line or guideline during deployment subsea.


Gasket handling tool

Handling device to aid gasket installation or removal during the flange assembly/disassembly process. Removes the need for manual handling whilst fully enclosing the riser bore thus reducing dropped object potential.


Rov Panel

The ROV panel allows contingency control/functioning of wellhead connector, subsea via an ROV instead of the surface HPU. This can be used as primary or secondary contingency.


Wellhead connector guide Frame

Typically mounted on the wellhead connector's main body, the guide frame interfaces the permanent guide base's guide posts to ensure correct alignment with the subsea wellhead or subsea Christmas tree during riser deployment. The guide frame has funnels at either side which the guidelines and guideline latches pass through before they connect to the top of the permanent guide base's guide posts.


Wellhead connector

The wellhead connector enables the riser assembly to be interfaced and locked to the subsea wellhead or subsea Christmas tree. Hydraulically operated, the wellhead connector can be functioned from surface via the umbilical and HPU, or subsea through the ROV Panel. The connector can withstand the high bending loads imposed at the base of the riser by generating large pre-loads between itself and the subsea wellhead or subsea Christmas tree.


Wellhead Connector Transportation Frame

Dedicated transportation frame for the wellhead connector. Typically incorporates work platform to allow assembly of the stress joint to the connector before removal from the frame. Also permits the wellhead connector to be assembled with the guide frame and ROV panel.


Wellhead connector test Stump

Dedicated test stump to enable offline pressure and function testing of the wellhead connector. Housed within the wellhead connector transportation frame.



The permanent guide base sits just below the subsea wellhead and acts as a guiding mechanism during the installation of the wellhead connector during drilling and subsea Christmas tree when in the well completion phase.



The subsea wellhead is for a typical well construction and acts as the entry point. It supports the inner casing and tubing strings, whilst transferring the loads into the outer conductor (well foundation). The riser assembly will connect directly to the wellhead via the wellhead connector.

Download our Drilling Riser and Tensioning Systems Case Study Pack