Читать книгу Underwater Inspection and Repair for Offshore Structures - Gerhard Ersdal - Страница 35

Several recommended practices and standards address inspection and integrity management of mooring systems. API RP‐2I (API 2008) and API RP‐2SK (API 2005) have developed over many years and have been the industrial standards over this period. Recently, API issued a separate recommended practice (RP) for integrity management of mooring systems, API RP‐2MIM (API 2019b), which extends the guidance from these earlier RPs. NORSOK N‐005 (Standard Norge 2017b) and ISO 19901‐7 (ISO 2013) also address inspection of mooring systems.

Inspection intervals for chain mooring systems for floating structures are recommended in, for example API RP‐2I (API 2008) and NORSOK N‐005 (Standard Norge 2017b). The maximum interval between major inspections is linked to the age of the chain in years. For relatively new chains (i.e. 0–3 years) the recommended interval is 3 years; for slightly older chains (4–10 years) it is 2 years and for chains older than 10 years the interval is reduced to only 8 months. This short interval is very demanding and costly and hence chains are normally replaced before they reach the 10‐year criterion. Inspection of mooring systems can be undertaken visually by an ROV, but this has significant limitations. A more detailed inspection, e.g. by MPI, requires removal of the mooring and dockside inspection with significant cost and operational implications. More details of mooring line inspection are given in Section 4.9.

ISO 19901‐7 (ISO 2013) is accepted as the recommended code for offshore moorings in many parts of the world. HSE (HSE 2019) states that the following aspects of Annex B.2 of ISO 19901‐7 (ISO 2013) are considered important by HSE and should be met where this is reasonably practicable:

 increased wear and corrosion allowances in splash zone for permanent moorings;

 assessment of a simultaneous double failure (two‐line failure) for permanent moorings; and

 increased safety factors which take account of the operational state of the installation when connected to risers or when in proximity to other structures.

The Norwegian Maritime Directorate (NMD) has issued local regulations, including the Anchoring Regulations (NMD 2009), concerning positioning and anchoring systems on mobile offshore units. The 2013 version of Annex B.2 of the ISO 19901‐7 (ISO 2013) has been updated to reflect in part the NMD regulation (2009). A Canadian section is included in Annex B, which states the same technical requirements as for Norway.

The following codes and standards are now widely accepted in the offshore industry:

 API RP RP‐2SK (API 2005);

 DNVGL‐OS‐E301, which superseded POSMOOR ’96 (DNVGL 2018);

 Lloyds Register Rules for Classification Floating Units at Fixed location – Part 3 (Lloyds Register 2019).