API規格 2SK 4th Edition, 2024: Design and Analysis of Stationkeeping Systems for Floating Offshore Structures
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Description
This standard addresses the design and analysis of stationkeeping systems (mooring systems with or without thruster assistance) in conditions from survival to operational. Different design requirements for mobile and permanent moorings are provided.
The procedures for the design of permanent or site assessment of mobile mooring systems specified in this document are based on a deterministic approach where mooring system responses, such as line tensions, vessel offsets, and anchor loads, are evaluated for a design environment defined by an annual probability of occurrence or return period. Mooring system responses are then checked against acceptance criteria for mooring strength, offsets and orientation, clearances, anchor capacity, fatigue resistance, and so forth. The minimum acceptance criteria are either defined in this standard or are to be specified by the owner or the operator.
For moored vessels, system responses are calculated and compared to acceptance criteria for limit states describing acceptable extreme loads (line tensions), vessel offsets (translation and rotation), clearances (vessel, risers, water surface, seabed, anchors, field infrastructure, etc.), and fatigue (cumulative mooring component fatigue damage). Limit states associated with the extremes of the vessel’s first order wave-frequency motions (surge, sway, heave, roll, pitch, and yaw at a particular point on the vessel), such as serviceability of machinery, heave compensators, separators, tank sloshing, motion-sickness, etc., exist; however, they are not addressed by this standard.
The requirements of this standard mainly address spread and single-point mooring systems with mooring lines composed of chain, wire rope, fiber rope, or a combination of these. This standard is applicable to the following types of stationkeeping systems:
- spread moorings;
- single-point moorings, anchored by spread mooring arrangements;
- thruster-assisted moorings (TAMs).
NOTE Guidance on the design and operation of dynamically positioned vessels is contained in IMCA M103.
This standard is not applicable to the vertical tendons found on tension-leg platforms (TLPs), which are covered by API 2T. Parts of this standard may not be appropriate for stationkeeping systems that are normally unmanned and occasionally manned (such as wind farms) or normally unmanned floating facilities. API 2SM, API 2I, and API 2MIM provide more detailed guidance on fiber ropes, mooring inspection, and integrity management.