ISO 19905-3-2021 pdf free download.Petroleum and natural gas industries – Site-specific assessment of mobile offshore units – Part 3: Floating units.
5.1 General
5.1.1 Competency
Assessments undertaken in accordance with this document shall only be performed by persons competent through education, training and experience in the relevant disciplines.
5.1.2 Planning
Planning shall be undertaken before a site-specific assessment is started.
Planning shall include the determination of all assessment situations relevant or the site under consideration.
The assessment criteria shall be in accordance with the general requirements for assessment of existing structures specified in Iso 19900, as far as relevant for mobile floating units.
5.1.3 Reporting
The assessor should prepare a report summarizing the inputs, assumptions and conclusions of the assessment. Previous site-specific assessments may be taken into consideration when preparing the report.
5.1.4 Regulations
Each country can have its own set of regulations concerning offshore operations. It is the responsibility of the operator and the owner of the mobile floating unit to comply with relevant rules and regulations, which can depend upon the site and type of activities to be conducted.
5.1.5 Classification of unit
This document is applicable only to mobile floating units that are structurally sound and adequately maintained. To achieve this, the unit shall either
— have been verified by an independent competent body to be structurally fit for purpose for afloat operations, and are subject to periodic inspection, both to the standards of an RCS.
Mobile floating units that do not conform with this requirement shall be assessed in accordance with the provisions of Iso 19904-1, supplemented by methodologies from this document, where applicable.
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 stationkeeping 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.