MOSS | Mechanical On Site Services

Christmas Tree Heavy Wall Cutting

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Moss were approached by a major North Sea operator with regard to machining assistance in the removal of a 5.1/8” lower master valve.


Previous attempts in the removal of the lower master valve had encountered considerable time delays due to the seized 2” diameter grub screws within the connector locking segment that required drilling out.

To alleviate the previous removal issues it was decided to cut through the connector body through the root diameter of the grub screw – this would allow the valve to be removed and reduce the clamping effort of the locking segment.


The connector body was 30” diameter and had a wall thickness of 90mm, therefore extra length cutting blades were required.

The pipe cutting machine had to be mounted upside down due to limited area to mount in the conventional position.


It was decided to carry out an onshore demonstration at Moss’s Aberdeen facility. This allowed the process to be filmed to confirm it’s suitability.

The machine was set up, operated by Moss competent technicians with the cutting operation complete and the machine removed within 6 hours.

This approach has been adopted on future lower master valve change outs with the machine mobilised as a contingency and technicians available at short notice if required.