Case Study: Flexi-Coil^® 24in Gas Export Pipeline Decommissioning North Sea

As a part of decommissioning scope, a 24” Gas export pipeline was required to be flushed with seawater to a cleanliness criterion of OIW (Oil in water) content <30ppm. The pipeline length was 1000m with an estimated volume 150m³ of condensate present in the line.

Due to the pipeline being tied into a producing export system and being liquid filled, this meant conventional options such as cleaning pigs were not suitable and would involve subsea hot taps into the pipeline. This approach would have involved extensive vessel time and coordination of multiple critical vendors to execute the hot tap, flushing, and isolation scopes. Additionally, the intervention would have necessitated a production shutdown of the downstream export pipeline connected to the manifold. Further to these challenges, the additional concern of weather which can impact the schedule was also considered. This method was then ruled out due to high cost, lead-time and the technical challenges associated.

Following an engineering assessment, Flexi-Coil® was selected for its unique capability to negotiate multiple short-radius pipe bends at both surface and within the export riser, enabling a fully platform-based decommissioning campaign. The modular Flexi-Coil® package was distributed across multiple platform decks and installed remotely from the riser tie-in point, demonstrating its adaptability to the production facility’s space, weight, and layout constraints.

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