Petroleum and natural gas industries -- Site-specific assessment of mobile offshore units -- Part 3: Floating unit

: ISO 19905-3 specifies requirements and gives guidance for the site-specific assessment of mobile floating units for use in the petroleum and natural gas industries. It addresses the installed phase, at a specific site, of manned non-evacuated, manned evacuated and unmanned mobile floating units.

ISO 19905-3 addresses mobile floating units that are monohull (e.g. ship-shaped vessels or barges); column-stabilized, commonly referred to as semi-submersibles; or other hull forms (e.g. cylindrical/conical shaped). It is not applicable to tension leg platforms. Stationkeeping can be provided by a mooring system, a thruster assisted mooring system, or dynamic positioning. The function of the unit can be broad, including drilling, floatel, tender assist, etc. In situations where hydrocarbons are being produced, there can be additional requirements.

The requirements of ISO 19905-3 apply to the hull and stationkeeping system for all types of mobile units. The activity specific operating guideline document requirements can be modified to be appropriate to the situation being assessed.

ISO 19905-3 does not address all site considerations, and certain specific locations can require additional assessment.

ISO 19905-3 is applicable only to mobile floating units that are structurally sound and adequately maintained, which is normally demonstrated through holding a valid RCS classification certificate.

ISO 19905-3 does not address design, transportation to and from site, or installation and removal from site.

ISO 19905-3 sets out the requirements for site-specific assessments, but generally relies on other documents to supply the details of how the assessments are to be undertaken. In general:

- ISO 19901‑7 is referenced for the assessment of the stationkeeping system;

- ISO 19904‑1 is referenced to determine the metocean actions on the unit;

- ISO 19906 is referenced for arctic and cold regions;

- the hull structure and airgap are assessed by use of a comparison between the site-specific metocean conditions and its design conditions, as set out in the RCS approved operations manual;

- ISO 13624‑1 and ISO/TR 13624‑2[1] are referenced for the assessment of the marine drilling riser of mobile floating drilling units. Equivalent alternative methodologies can be used;

- IMCA M 220[5] is referenced for developing an activity specific operating guidelines. Agreed alternative methodologies can be used.

NOTE 1 The scope of ISO 19904‑1 specifically states that its requirements do not apply to mobile units, but the methodologies given for assessing metocean actions can be used.

NOTE 2 RCS rules and the IMO MODU code[4] provide guidance for design and general operation of mobile floating units. For more details on scope see: https://www.iso.org/standard/61143.html