Pipelines might comprise short, small diameter flexible infield lines, or long, large diameter rigid trunklines which carry product to shore-based facilities.
Principal pipeline design considerations include:
- seabed stability
- spanning and fatigue
- seabed temperatures
Installation conditions are also an important consideration, as pipelines and cables may often lie ‘exposed’ to ocean forcing for some time before ‘stabilisation’ measures can be implemented (burial, rock dumping, gravity anchors, rock-bolting etc).
In deepwaters, estimates of extreme near-seabed currents and water temperatures are all that is required. In shallower waters (less than 200 m), the near-seabed influence of waves must also be assessed.
A very important part of this process is the estimation of the near-seabed vertical current profile, which can change dramatically depending on the nature of the current forcing.
Recent measurement studies have demonstrated that ‘steady’ currents must be considered over a range of timescales, down to the order of a few minutes in stratified waters.