STAVANGER, Norway – TD Williamson (TDW) has completed a pipeline services program for a major offshore operator to assist with efforts to relieve increasing contact stress between a gas export riser and platform jacket offshore East Malaysia.
Due to changes in seabed conditions, the platform jacket had moved, producing stress on the gas export riser attached to the platform jacket. The stress was most acute at the contact point between the bracings (or riser clamps) that anchor the riser to the platform structure. Concerned that the amount of stress developing at the contact point could eventually damage the riser, the operator decided that the best solution was to cut out and remove a section of the jacket bracing. Removal of the brace would not affect the technical integrity of the structure.
To ensure that the bracing could be safely removed from the pipeline, the customer requested TDW to isolate the affected section of the subsea line by inserting and setting a remotely operated SmartPlug isolation tool in the line approximately 100 m (328 ft) from the platform. By doing so, only a short section of the pipeline had to be depressurized and isolated while the bracing was removed.
The only alternative would have been to depressurize the entire pipeline, which would have cost more time and money. Further complicating the situation was the fact that the line is tied in to another major pipeline that extends to a central riser complex. This line would have had to have been bled down as well, causing major disruption to overall production from the field.
Before the pipeline could be isolated, it became apparent that one of the topside motor-operated valves (MOVs) closest to the pig launcher would not open properly, so it would have to be replaced in order that the SmartPlug tool could reach the point of isolation.
To rectify this, TDW performed a hot tap and STOPPLE plug isolation on the line at a point located on the riser above the shutdown valve (SDV), thereby providing double-block isolation so that the operator could safely replace the malfunctioning MOV.
Once the MOV was replaced, the company launched the SmartPlug tool to the set location in order to isolate the line connected to the jacket bracing, which required a section to be removed. The line was isolated for five days, which allowed a diving contractor to safely remove the bracing without disrupting production. The SmartPlug tool was then unset and retrieved back to the launcher.
First, TDW manufactured a special custom fitting for the hot tap and STOPPLE plugging operation at its manufacturing plant in Tulsa, Oklahoma. It then managed the entire operation with its teams in Norway, Belgium, and Singapore, and collaborating with its network of specialists to provide welding, and nitrogen, and water pumping services. TDW completed the project in four months.