PIPESIN

PIPESIN is a three-dimensional numerical model which can be applied to simulate interactions between a pipeline/cable and dynamic seabed. It can be used to assess self-lowering as an alternative to traditional mechanical trench, to assess free span development and calculate the maximum potential free span length and related duration. PIPESIN is suitable to simulate interactions of a pipeline and migrating sandwaves. It is also possible to apply PIPESIN to an existing pipeline on seabed with arbitrary configuration. Further PIPESIN can be used to assess feasibility of use of a spoiler to increase self-lowering and improve pipeline stability.

Processes

The processes modelled by PIPESIN are shown in the box right. PIPESIN predicts initial lowering of a pipeline due to its weight and laying forces. Input wave and current field is transformed to the seabed and resulting sediment transport is calculated. Onset of scour is determined based on the wave and current conditions and pipeline embedment. PIPESIN includes generation and development of free spans, tunnel erosion, leeside erosion and upstream backfilling. Pipeline deflection is calculated dependent on the seabed configuration and pipeline mechanics. Geotechnical failure of pipeline support is calculated dependent on soil conditions and pipeline forces.
In summary:

• initial pipeline lowering;
• nearbed wave and current field;
• onset of scour;
• tunnel erosion;
• leeside erosion and upstream backfilling;
• generation and development of free spans;
• pipeline deflection;
• geotechnical failure of support.

Representation

PIPESIN simulates a section of pipeline with a length typically of 500 m to 1000 m. It accounts for tunnel erosion, leeside erosion and free span development along pipeline. It is time-dependent model. Initial seabed configuration can be arbitrary.
In summary:

• three dimensional;
• time dependent;
• dynamic seabed (e.g. migrating sand waves);
• pipeline mechanics.

Applications

Typical applications of the PIPESIN-model are:

• pipeline self-lowering potential;
• free span development, maximum free spans;
• pipeline stability assessment;
• interactions of pipeline and migrating sandwaves;
• benefit of spoiler.

PIPESIN was originally developed by Danish Hydraulic Institute and WL|Delft Hydraulics. The program has been further developed by Alkyon Hydraulic Consultancy & Research so that the model is applicable to irregular seabed (trenched seabed) and sandwave areas. Extensive calibration of the upgraded model was carried out by Alkyon using field data in the North Sea.

Further reading

Klomp, W.H.G., E. A. Hansen, Z. Chen, R. Bijker, M.B. Bryndum (1995), Pipeline Seabed Interaction, Free Span Development. ISOPE 1995, The Hage.

© 2001Alkyon Hydraulic Consultancy & Research, The Netherlands.