Line boring on pipe laying vessel

Scope

We were approached by a leading subsea contractor with regard to the machining of an auxiliary reel onboard an offshore vessel used for subsea pipe laying. 

The auxiliary reel is used to provide pipe laying tension on smaller subsea pipes such as piggyback lines and umbilicals. 

The 13m diameter auxiliary reel uses a pair of 22” diameter trunnions located within the bore of the reel to provide mounting support and a pivoting point. 

On this application the trunnion locating bore had suffered considerable wear caused by weld failure resulting in the reel being placed out of action. 

Solution

 It was decided that the reel would be line bored to remove wear defects, machined to size and a replacement trunnion fitted to bring the reel back to service. 

The work had to be scheduled for a period when the vessel was in port in Norway. 

Due to the diameter and depth of machining required detailed pre engineering and machine adaption was required to ensure suitability. A 6” (150mm) diameter boring bar was required for this operation together with a hydraulic power pack to drive it and specially manufactured bearing mounts and support sections. 

Two teams of Moss technicians were mobilised together with a hydraulically-driven line boring set up to provide 24 hour machining cover. 

Results & Benefits

• As well as the line boring operation ICR technicians were able to support the trunnion removal operation and drilling of holes in and assembly of the trunnion support ring.