Statoil has since 1985 installed and commissioned approximately 8000 kilometers of subsea pipelines in the North Sea area. Among these pipelines are several of the worlds largest offshore gas trunklines, and some of the most complex subsea developments. Commissioning and pigging these pipelines, represented several challenges, and the accumulated experience gained through successfully commissioning these pipelines have brought Statoil to the forefront within the pipeline industry. The paper will discuss several topics within pipeline commissioning, and relevant field experience will be presented
The topics above will be explored and field experience from relevant projects will be presented. The paper will give recommendations for future projects as well as elaborating on Statoils commissioning concept for the next huge pipeline, the Langeled-project, the 1200 km pipeline from Norway to UK that will be commissioned in 2006/7. Figure 1 shows the main pipelines in the North Sea.
Each pipeline project is unique and poses its own constraints and challenges regarding precomissioning and commissioning. Selection of an optimum concept for these operations is therefore not a straight forward task.
Initially, the constraints and possibilities must be reviewed in order to establish the preferred pigging direction. For the initial flooding operation, availability of water of sufficient quality and quantity is normally the most important issue. For the dewatering and later drying, there are two important issues that decide the pigging direction; one is the preferred discharge location for the linefill water. The second is what media that is available for propelling the pigtrain. The linefill water is normally treated with chemicals in order to minimize the risk of internal corrosion in the pipeline, and the environmental issues regarding discharge of the chemically treated water is a very common constraint, that will dictate the direction of the pigging and dewatering operation.
