Flowline Buoyancy
There is a growing requirement in deepwater applications for rigid flowlines to perform under high temperature/high pressure conditions. Large cyclic changes in temperature and pressure cause expansion of the flowline that can result in the occurence of lateral or upheaval buckling. Flowline system engineers therefore need to consider this potentially damaging phenomenon in their analysis and ways of mitigation.
An increasingly favourable mitigation solution is to establish spans of least resistance along the flowline to allow buckles to occur in known and controlled conditions. These sections of least resistance can be created via the addition of distributed buoyancy, designed to reduce the self weight of the flowline and friction against the seabed.
Our extensive buoyancy design experience encompasses the following:
Buoyancy can be applied to the flowline in various forms, for example as half shell modules or as a direct cast-on coating. The decision as to which solution is best suited will depend on thorough consideration of the design parameters as follows:
- Buoyancy requirement per metre and overall length of coverage
- Water depth
- Flowline characteristics - diameter MBR etc.
- Flowline coating characteristics - thickness, contraction, creep, frictional coefficients
- Installation method - J-Lay or S-Lay
- Installation and service loads acting upon the buoyancy
- Is the pipe reeled or jointed?
- Pipe installation speed
- Seabed conditions - what does the abrasion resistant coating need to withstand?
- Number of buckling cycles
- Allowable stiffness of flowline - buoyancy is designed to avoid adding unacceptable stiffness to riser
- Corrosion protection
- Design life
Installation Methods
All components are designed for rapid and straightforward installation. The quantity of components required is minimised and includes encapsulated fasteners and alignment dowels for rapid and accurate fit up with less likelihood of dropped objects.
A bespoke buoyancy solution is designed and provided in consideration with the client's pipe installation method, vessel space and handling restriction.