TABLE OF CONTENTS On-bottom stability calculations are performed to establish requirements for pipeline submerged mass. The required pipeline submerged mass will have a direct impact on the required pipelay tensions, installation stresses and the pipe configuration on the seabottom. From the installation viewpoint, especially where spans are not a concern, the priority is to minimize the required pipeline submerged mass.
On-bottom stability calculations shall be performed for the operational phase and for the installation phase. For the operational phase, a combination of 100 year wave loading + 10 year current loading is to be checked, as well as 10 year wave loading + 100 year current loading. The pipeline is filled with content at the expected lowest density when considering the operational phase.
For the installation phase (temporary phase) the recurrence period may be taken as follows:
Duration less than 3 days:
The environmental parameters for determination of environmental loads may be established based on reliable weather forecasts.
Duration in excess of 3 days:
No danger of loss of human lives. A return period of 1 year for the relevant season may be applied.
Danger for loss of human lives: The parameters may be defined with a 100-year seasonal return period.
However, the relevant season may not be taken less than 2 months. If the empty pipeline is left unprotected on the seabed over the winter season, combinations of 10 year current + 1 year wave, and 1 year current + 10 year wave loading will be checked. The...
