Corrib Low Temperature Start-up

摘要

This paper presents the feasibility and concept selection study for the low temperature start-up of the Corrib Project. A number of diverse options were studied and their feasibility determined, but significant attention is given to the selected option which involved qualifying flexible flowlines to lower temperatures than previously were available, and to the second option, which involved the specification of a bespoke subsea warming spool pyramid structure. The Corrib project has been ongoing for a number of years and is, at present, in the execution phase with first gas estimated late 2014 / early 2015. A number of changes are required for the ability to start-up the production facilities outside the previous operating envelope of-20°C, which was constrained by the flexible flowlines that connect the subsea wells to the manifold. This was required as a result of a number of developments that occurred during 2009 to 2010. The most promising, (a) the low temperature testing and qualification of a flexible flowline, and (b) a low temperature rigid warming spool, were studied and the optimum was selected in the concept selection stage. The newly qualified low temperature flexible flowlines will be installed prior to initial start-up. Qualification testing of the end fitting design was performed based on the protocol presented in API RP 17B for low volatile content polymer pressure sheaths in order to demonstrate that the integrity of the end fitting sealing mechanism could withstand the potential temperature cycling predicted during service conditions. Mid scale flexible pipe and end fitting specimens were prepared and subjected to thermal cycling between the design temperatures, along with intermediate inspections and pressure tests to monitor for signs of failure initiation as the test progressed. The two specimens tested successfully and returned API RP 17B fully qualified low temperature results to-35°C with one specimen qualified to-45°C. With the increased use of more rigorous standards on asset integrity and reliability and longer subsea tie-backs, requiring wider pipeline operating envelopes, it is likely that this extended flexible pipe operating envelope will be used in many more future projects.