eSubsea provide engineering, procurement and construction (EPC) including 3D modelling and drawings, structural analysis, piping analysis and FEA of subsea protection structures (SPS). The SPS for the subsea production system will be analysed for the installation lifting load case and relevant in-place loads such as dropped objects and fishing gear interaction according to NORSOK U-001.
Template and Manifold Protection
Subsea template structures and manifolds are foundations for well heads x-mas trees, manifold structures, control systems, etc. If there is fishing activities in the area there is most often a requirement that all equipment are protected with their own SPS including panels (often in GRP) to avoid hooking up with fishing gear and at the same time provide dropped object protection. This means that template and manifolds structures will be heavier and an alternative is to design and install a separate manifold protection structure which cover the subsea production system equipment.
Protection Structures for Subsea Modules and Units
In addition to subsea protection structures for template and manifold, we also design structures for the following units, modules and assemblies:
- Riser bases
- PLEM, PLET, FLET, Pipeline end modules
- SSIV, Subsea Safety Isolation Valve Modules
- HDU, Hydraulic Distribution Units
- UTA, Umbilical Termination Units
- SDU, Subsea Distribution Units
- EDU, EDA, Electrical Distribution Units or Assemblies
- HIPPS, High Integrity Pressure Protection System
- PLR, Pig launchers and receivers, Pig Traps
Dropped Object and Protection against Fishing Gear
The purpose of the subsea protection structure is to protect the subsea modules from damage due to impacts either from dropped objects or fishing activities. The integrated protection structures also use the protective structural framework as bearing members for lifting the subsea module.
Overtrawling and Fishing Friendly Design
The complexity of the structure is based on the local requirements for fishing protection and the Field Operators preferences. The most stringent fishing protection requirements (Norway North Sea) require full over-trawlable structures whilst others accept that fishing gear may impact the structure without damage to the subsea module internals, this is called “fishing-friendly” and is accepted in most parts of the world.
For deep water developments, or were fishing is not applicable (areas where there is no fishing or in fishing exclusion zones near the production facility), only dropped objects will be a requirement. Some fields have fishing exclusion zones in a 500 m radius from the structures and ensure these are known and clearly marked on fishing maps.
The SPS will need to with stand the horizontal loads from the trawling/fishing equipment which is typically 20 to 30 Tonn from trawl board impact or the trawl itself being dragged over the structure. The design of the SPS needs to be snag free and the corner protectors need to penetrate sufficiently into the seabed in order for the trawl ground not to snag.
If the protection structure is separate from the subsea structure, it will need to be fixed to the seabed using suction anchor, piles or ballast weights.
Protection Structure Concept Study
eSubsea with its engineering and geotechnical partners can carry out fast track concept and feasibility studies which include concept evaluation, preliminary foundation sizing based on input loads, dropped objects and trawling requirements, penetration resistance, bearing capacity and required suction or weight. The concept study is a cost effective way to quickly establish size, weight, budget cost and delivery schedule for your project.