T.D. Williamson performs subsea hot tap

T.D. WILLIAMSON S.A., a leading supplier of pipeline services and equipment, has performed a complex subsea hot tap operation on the Temsah Concession gas pipeline network for operator Petrobel on behalf of Eni S.p.A. The Temsah Concession network is located in the Nile Delta, Egypt.
Complex by-pass scenario reduces Platform Shutdown

Situated in deep water, the 140-tonne Temsah pipeline end manifold (PLEM) is connected to four 900-class pipelines, ranging from 14-inches to 32-inches in diameter. In 2007, Petrobel began working on several replacement scenarios in order to formulate the optimum approach to replacing the gas PLEM. The decision was made to employ a scenario using the Folding STOPPLE technique. The by-pass approach involved creating an alternative export pipeline network that began at a platform by-passing the gas PLEM, which enabled gas to flow to a subsea isolation valve (SSIV) before connecting with the 32-inch export sealine to an onshore gas plant.

These operations were carried out in two phases. The first phase consisted of laying down an additional subsea line to connect the platform to the alternate network. This subsea line on the platform was connected by performing a hot tapping operation. With support from hot tap technicians and project managers at the T.D. Williamson (TDW) base in Sheffield, England, and equipment at its base in Nivelles, Belgium, TDW mobilized to the platform in early August 2008. The tie-in project included a “Finite Element and Critical Assessment Study” to demonstrate that post-weld heat treatment could be successfully avoided. Based on these results, TDW performed the live welding operations of the hot tap tee at a pipe operating pressure of 106 barg. The 16-inch hot tap was subsequently carried out in a horizontal position on 39 mm thick pipe through class 900 ball valve, at a pressure exceeding 100 barg. TDW used a subsea machine with “double-block and bleed” and internal pressure compensation capabilities.



Folding STOPPLE plug technology plays key role

In order to isolate and replace the PLEM, the second phase required TDW to plug all lines. After shutting down the platform, TDW used its special STOPPLE plug technology to isolate several lines, thereby sidestepping the need to flood the entire network with salt water during the PLEM replacement.

All lines were isolated. A 14-inch line was isolated with the traditional STOPPLE plugging method, while a 24-inch line and a 32-inch line were isolated with TDW’s folding STOPPLE plugging technology. This method was used for several reasons: the smaller size of the hot tapping equipment makes it faster to operate subsea, the equipment weighs less, and it reduces intervention time. Folding STOPPLE technology also provides a better seal performance at the considered delta pressure, between water pressure (8.5 barg) and pipe pressure (12 barg). Overall, TDW carried out three hot tap operations, ranging from 14-inch to 24-inch, and installed STOPPLE plugging heads ranging from a 14-inch to 24-inch x 32-inch.

During each of the subsea hot tap operations, TDW technicians were in continuous communication with the divers, who were monitored via live images broadcast to a computer monitor located on-board a dedicated remotely-operated vehicle (ROV).

As a result of the work that TDW carried out on the Temsah Concession pipeline network, Petrobel was able to resume production, and gas flowed once again through the new central PLEM. By retaining TDW to facilitate replacement of the PLEM, Petrobel selected the most effective method of performing one of the key operations required to revamp their subsea network.



Challenges faced

The Temsah operation was complex, demanding innovative engineering and thoughtful application of TDW’s state-of-the-art solutions. It required a great deal of communication between the teams to cover all work sequences, and very detailed subsea procedures. TDW also took care to limit the number of clamps required by using all available points of connection, and developing a clear sequence of intervention with contingency plans. The operation required diving rotation, workforce flexibility and additional on-site training to ensure that procedures were understood, and that all safety requirements were fulfilled. In addition to working subsea, all hot tapping was carried out on pipeline walls of very high thickness (class 900).

“Although we have carried out a number of subsea hot tap operations in similar conditions, it was a real challenge to facilitate the by-pass PLEM replacement scenario, especially in light of the high pipe wall thickness and adverse weather conditions,” said Danny Haykal, General Manager – Africa for T.D. Williamson S.A. “We are extremely pleased with the high level of success achieved in planning and executing the by-pass pipeline network. We feel very fortunate to have had the opportunity to contribute to its design and execution, as well as performing the subsea hot tap and isolation operations necessary to remove and replace the PLEM,” he added.

Alain Charles Publishing, University House, 11-13 Lower Grosvenor Place, London, SW1W 0EX, UK
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