Pipeline End Manifold Replaced Without Flooding Lines
T.D. Williamson S.A announced that it 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. Situated in deep water, the 140-t Temsah pipeline end manifold is connected to four 900-class pipelines, ranging from 14- 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 sea line 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 mobilised to the platform. 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.