Tension deck enables platform drilling

Read on to discover who Claxton’s fast-track design and supply enabled drilling on ConocoPhillips’s Judy platform, Central North Sea.

ConocoPhillips was in the planning phase of drilling three additional wells for the Judy platform in the Central North Sea; P20 being the first.

The Judy platform was initially built to accept skid-off drilling packages from the then, latest drilling rigs. However, improvements in jackup technology meant the Maersk Inspirer jackup rig with its extended-reach cantilever could access all the wells conventionally on the Judy platform.

Well P20 was more than 30 m from the Maersk Inspirer’s hull/barge, so the rig’s hook load would be significantly lower if used in conjunction with its riser tension system.

ConocoPhillips instructed Claxton to design, analyse, fabricate, install and commission a riser tension system on a fast-track basis. The P20 tension deck would enable ConocoPhillips to tension the conductor and support the weight of the blowout preventer and the well control equipment to reduce any potential buckling loads.

Claxton-designed tension cartridges ready for transportation in a frame

Claxton-designed tension cartridges ready for transportation in a frame.

The original plan was for a 300-t safe working load. However once project procurement and fabrication had commenced, a required safe working load of 400 t was requested. The structure’s final certified load capacity was 380 t.

ConocoPhillips’ design brief required a compact modular package. During the installation phase, there was to be no working under loads or around open deck hatches.

Bespoke tension deck designed and built by Claxton

A view across the system showing the riser connector and spreader beam support spools (left); A full view of the installed system and riser (right).


  • The modular design enabled three main lifts for ease of installation without needing to work under suspended loads.
  • The installation system enabled the deck hatch cover to be removed while always maintaining a substantial barrier around the opening.
  • The system included a work deck to offer ease of riser connection make up.
  • The tension deck offered full drift capability for large-diameter riser connections and wellheads to pass through.

Verification of the system before mobilisation was paramount:

  • Load testing of the four cylinders (pressure and pull testing to 150 t each, i.e., 1.5 times the safe working load (see left)
  • Load testing of the tension deck to 475 t
  • Function testing of the cylinders (see right)
  • Full non-destructive testing of all the load bearing areas.

Claxton also designed and supplied a self-contained hydraulic power unit able to be positioned within a 15m radius of the tensioning deck.

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