Free spans of pipelines develop due to various reasons, e.g. installation on uneven seabed or due to scouring effects. These spans are subject to fatigue damage caused by direct wave and Vortex-Induced Vibrations (VIVs).
Previously, free spans in routing, detailed design and operations integrity management have been addressed by manual processes; going from simple screening criteria through to advanced calculations for each critical span configuration.
Lower cost and increased confidence
DNV GL research related to the recommended practice DNVGL-RP-F105 Free spanning pipelines has now resulted in an automated model for free span assessments which allows assessment of fatigue damage for free spanning pipelines. Fatigue damage is modeled per KP location along the entire pipe, allowing increased accuracy in the assessments of pipelines with changing free span lengths and locations. Advancements in data storage and processing can now be used to automatically manage multi-span interactions and changes in free span configurations over time.
- Significantly reduce and avoid costly intervention work for pipelines on shifting or uneven seabed because of increased accuracy in accumulated damage for the entire pipeline
- Account for multiple surveys, variations in operational conditions and seabed mobility as they change over time
- Eliminate the process of doing manual calculations for each span - the model runs the calculation in one automated run.
This is possible by employing a purpose-built finite element solver to calculate the pipeline response throughout the entire length of the pipeline. The potential for multi-span response is also automatically taken into account. Once the response quantities and characteristics of the pipeline have been mapped, a fatigue assessment is performed for each KP location.