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  Title Challenges formed by the contact between large-diameter gas pipelines in a tight pipeline corridor
  Author(s) Dr Ljiljana Djapic Oosterkamp, Per Richard Nystrøm, and Audun Schanche Kristoffersen  
  Abstract LARGE-DIAMETER GAS PIPELINES are of a strategic importance for securing energy supply. They have to be robust and reliable. Pipelines are designed and built to match the volumes available throughout the lifetime of a field and sometimes design allows for additional volumes from new discoveries. Quite often, there is a demand for increased volumes to be transported, which can be done by increasing the export from the inlet or by connecting new assets through tie-ins. This causes changes in operational conditions both at the inlet and along the pipeline, and the pipeline’s design needs to be upgraded, particularly for buckling. In some cases, as with the case that this paper addresses, the main challenge is not the capacity of the pipeline in question, but the proximity of another asset, another large-diameter gas pipeline.

In connection with an increased flow study on one of the large-diameter gas export pipelines in the North Sea, an evaluation of the survey revealed possible contact with an adjacent pipeline. The available route corridor in the contact area is narrow and the seabed has a steep slope. The expansion design specified that no lateral movement was expected in this area.

This paper presents the work performed in order to evaluate the criticality of this contact, both with the present and with an increased gas flow through one of the pipelines in the corridor. The contact evaluation is based on several available surveys of the pipelines and, in addition, a FE model simulating the contact between the two has also been performed. The survey evaluation is based on the so-called five-point data and DTM files and the corresponding operational data at the time of survey. Marintek’ SIMVIS software has been used to visualize the pipeline movement during the operational life. For the finite-element model, Marintek SIMLA software was used. In addition, the model includes a contact formulation between the two pipelines together with the post- lay rock installations.

The work is intended to provide a reference for any project dealing with an increase of flow through existing pipelines, especially in cases where increased lateral movement could affect neighbouring assets along the route.

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