Section 8 Chains

8.1.1 Chains to be offshore Grades R3, R3S, R4, R4S or R5 (see Pt 3, Ch 10, 8.1 Chain grades 8.1.2) and are to comply with Ch 10, 3 Offshore Mooring chain cables and Ch 10, 4 Fittings for offshore mooring chain of the Rules for Materials, as applicable. Acceptance of other grades will be subject to special consideration.

8.1.2 Acceptability of chains of material grade R5 will be given special consideration and be subject to satisfactory qualification testing of the chain for validation of the API RP 2SK tension-tension fatigue curve by the manufacturer.

8.1.3 The maximum allowable tensile yield strength for the grade considered is to be agreed with the purchaser and documented for each project.

When the minimum tensile yield strength specified in Ch 10 Equipment for Mooring and Anchoring of the Rules for Materials is exceeded by more than 3 per cent of the specified minimum value for the grade considered, the purchaser is to be notified and the actual yield strength from tests to be reported.

8.2.1 A size margin over and above the minimum chain size required to satisfy Rule factor of safety requirements is to be included to allow for the corrosion and wear which can occur over the intended service life of the anchor chain or associated component. The minimum margins shown in Pt 3, Ch 10, 8.2 Corrosion and wear 8.2.1 are required.

Note: These rates are minimum requirements. The actual rate of corrosion should be monitored during successive periodical surveys to assess the necessity to replace the chains in case accelerated corrosion or excessive pitting is observed. It should be noted that in tropical and subtropical regions as well as some coastal areas much greater rates of corrosion (sometimes exceeding twice these rates through localised pitting) have been observed. The Owner is to specify their corrosion protection strategy and may specify a larger minimum rate of corrosion for specific projects, taking due account of the region of operation of the unit.

8.3.1 The purchaser is to specify the project specific material, manufacturing and testing requirements where these complement, exceed or are more onerous than those of Ch 10 Equipment for Mooring and Anchoring of the Rules for Materials (e.g. chain length and tolerances, maximum yield strength, coating, reference link identification).

These shall be reported and agreed with LR.

8.3.2 A datasheet is to summarise all characteristics of each chain segment as necessary to ensure satisfactory deployment of the chain within the Positional Mooring System and to support the in service inspection, repair and maintenance plan.