DNV RP-F105 – Pipeline Free Span Analysis Tool


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*****NOTE: The compact version which assesses VIV and fatigue check is launched! The full version which assesses stresses and moments too will be launched soon *****

Subsea Free spans can become a challenge in pipeline design and operation due to uneven seabed or seabed scouring effects. In many cases local scouring or erosion underneath the pipeline causes the free spans.
As a result of free-spans subjected to wave and current loading, not only the pipe may be subjected to ultimate load conditions, but also due to vortex induced vibrations (VIV)
the fatigue life may be significantly reduced. The costs related to seabed correction and span intervention is often considerable.

This sheet is created to automate the formulations used by DNVGL-RP-F105 for a pipeline free span assessment.
The sheet provides the assessments of Vortex Induced Vibration and Fatigue Check

Multiple tables and formulations are simultaneously solved to arrive at the conclusions in-line with DNVGL-RP-F105. The sheet maybe utilized at the Tender stage to identify the nature of free-spans resulting from pipe-lay and take into account mitigation measures for the free-span beforehand.

The current sheet is a COMPACT version. This means:

  • The sheet provides the assessments of Vortex Induced Vibration and Fatigue Check
  • The sheet takes into account the free-span frequency analysed by modal analysis performed in other tools like OrcaFlex, OFFpipe other other tools.

The conclusions can be utilized to preliminarily and quickly screen off the non-critical free-spans and identify the potentially critical ones.

In the FULL VERSION (NOT INCLUDED IN THIS VERSION) , apart from the compact analysis, the following are included:

  • Assess the natural frequency of the free-span if the information is not available to the user from other tool
  • Assess the stresses and moments generated from the highest vibration amplitude caused by the vibration.
  • Consider different material apart from high tensile steel.



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