- Design review
- Evaluation (technical & commercial) and Support during fabrication stage
- Pre-engineering survey
- Jacket installation method development (lifting, floating, upending, launching)
- Static & Dynamic installation analysis (utilizing standard analytical softwares e.g. MOSES, SACS) to determine operational and weather criteria, including barge stability assessment, sensitivity study, launch analysis, lifting, pile driving refusal criteria etc.
- Installation vessel / barge & equipment (pile, hammer) selection – feasibility, capacity and availability
- Installation procedure development depending on field layout / constraints
- Interface with specialist subcontractors and fabricators
- Field engineering & operation support
- Pre- & Post-Installation survey support
- Cost benefits study and estimation, schedule
.. more on jacket and piling..
Jacket structures have been around since the early days of the offshore industry and more are getting installed each day, including the wind farms. Jacket is the foundation of fixed type platform and comes in various sizes and number of legs (from monopod, tripod, 4-legged to 8-legged). For deeper water, multi-section compliant towers have been installed in West Africa and Gulf of Mexico.
The weight and size of the jacket determines the installation method:
- Heavy lift using single block, float and upend (The lift and upending stages can vary depending on the use of diaphragms, buoyancy tanks, reach rods or ROV operated valves to flood and upend the jacket.)
- Heavy lift using dual block upending
- Heavy lift using dual crane or dual vessel
- Jacket launch (weight exceeds the lift capacity of installation vessel).
8-legged jacket can be designed for self-upending post-launching or via controlled flooding and crane upending. Detailed study and correct technical solutions can ensure successful delivery of projects.
These steps can be analysed using MOSES and SACS structural software to anticipate the dynamic load, allowable installation sea state and rigging design.
In order to secure the jacket post upending and set down, piles will be installed either through the legs of jacket or skirts depending on design. These piles will be stabbed to self penetration depth and driven using driving hammers (hydraulic is most common nowadays). The pile make up and stick up checks are done to suit the installation.
Handling long section and big diameter pile is a challenge. Optimized solution can be engineered to suit the crane capacity and hook height.
Available software such as GRL WEAP or OPILE will be used for piling driveability analyses and hammer selection. During this stage, tradeoffs between sizing of equipment, contingency and cost can be compared.
For installation of structure in area with rocky or calcareous soil, drill and grout method will be required (either pile top rig or with custom built caissons for skirt piles). Therefore early anticipation and preparation for such cases even at bid stage will determine the success of the project later on.