Flexible pipeline is presently seen as an attractive alternative solution compared to rigid carbon steel pipeline for small internal diameter and short length pipeline in the offshore oil and gas industry. However, the complex multi-layered structure which provide high flexural compliance is not suitable for non-intrusive non-destructive inspection techniques, which makes structural integrity evaluation becomes a challenge.
This paper recount how PETRONAS as an operator evaluated and overcome the concerns, based on actual field incident (anchor dragged) of two number of flexible pipelines installed in shallow water ranging from 10m to 40m. It will described various activities being performed after the incident starting from desktop activities (e.g. planning, concept, strategizing and investigation) up to offshore field testing. All assessment and risk measures are discussed with correspondence action plans were presented.
Initial efforts concentrated on the search for a single technique which would ensure integrity of the damaged flexible pipeline, but thorough analyses have shown that the safest approach is to relocate the shifted/dragged pipelines to its close-initial positions and taking advantage of its flexibility and complex multi-layered structure whereby site integrity test to be performed. The work include measures taken for reinstating the shifted flexible pipelines to its initial positions, measures of controlling torsional angle, axial stresses and displacement were assessed during the detail pipeline shifting analyses.
As this happened during worldwide pandemic, offshore structural integrity test were performed with limited resources and thus implementing a good strategy to eliminate prolong stabilization hours. Finally, the two flexible pipelines were confirmed fit-for-purpose and able to resume operation.
The information shared in this paper would be an eye opening for assessing the consequence of major incident of flexible pipelines (caused by anchor dragged), concerning those complex multi-layered structure which is not suitable for inspection with most non-destructive inspection techniques and welding connection.