ISO 19905-3:2021 pdf free download.Petroleum and natural gas industries一Site-specific assessment of mobile offshore units – Part 3: Floating units.
5.2 Assessment
The objective of the assessment is to show that the acceptance criteria are met. Annex B provides a diagrammatic example of the process to be used in the site-specific assessment of a mobile floating unit. Other approaches may be applied; they shall be shown to give a level of reliability equivalent, or superior, to that implicit in this document.
In situations where hydrocarbons are being produced, the requirements of this document should be supplemented by those necessary to account for any additional risk.
5.3 Exposure levels
The exposure level for each site-specific assessment of a mobile floating unit shall be
a) determined by the unit owner and the operator,
b) where applicable, agreed by the regulator and the operator, and
c) where applicable, agreed by the regulator and operator(s) of adjacent facilities.
NOTE Adjacent facilities (workover platform, local platforms, transport lines, subsea facilities, etc.) are those that are sufficiently close to the unit for there to be a potential for impact if the unit drifts from location.
Exposure levels are defined in ISO 19900, with the following additional criteria:
— Li: The extreme storm event used in assessment of the hull, referenced in Clause 8, shall be the 50 year independent extremes or the classed return period, where it is known and more onerous.
— L2: The extreme storm event used in assessment of the hull, referenced in Clause 8 for exposure level L2 shall be the 50 year independent extremes that could be reached at the site prior to evacuation being effected (e.g. 50 year 48 hour notice sudden hurricane in tropical revolving storm areas). The unmanned post evacuation case shall be considered according to criteria to be agreed between the operator and the unit owner.
— L3: The assessment criteria shall be agreed between the unit owner and the operator. The station keeping system shall be assessed as per Clause 9.
5.4 Selection of limit states
ISO 19900 defines four limit state categories:
a) ultimate limit states (ULS);
b) serviceability limit states (SLS);
c) fatigue limit states (FLS);
d) abnormal/accidental limit states (ALS).ISO 19905-3 pdf download.