PART IIAnalysis and Design (continued)
Air Gap and Freeboard
51 (1) Subject to subsection (2), the air gap for an offshore installation, except for a surface platform, shall be determined in accordance with section 4.8 of Canadian Standards Association CAN/CSA-S471-92, General Requirements, Design Criteria, the Environment, and Loads.
(2) The air gap for a column-stabilized mobile offshore platform may be calculated assuming the platform is at survival draft and at its lowest position relative to sea level, as determined from its motion characteristics.
(3) Every surface mobile offshore platform shall have sufficient freeboard, taking into consideration the environmental criteria and loads at the drill or production site determined under section 45.
(4) Every fixed offshore production platform shall have sufficient freeboard to prevent ice rubble or waves from flowing over the side of the platform unless it is designed to withstand the loads due to water and ice without major damage, under the most severe conditions as determined pursuant to section 45.
Offshore Load Measuring System
52 Each leg on every self-elevating mobile offshore platform shall have a load measuring system that will permit
(a) registration of the load on the leg at any time during jacking operations; and
(b) measurement of the load on the leg periodically.
Gravity-Base, Fill, Fill-Retention and Self-elevating Platforms in the Offshore
53 Every gravity-base, fill, fill-retention and self-elevating platform shall be designed in accordance with sections 5, 6, 7 and 8, respectively, of Canadian Standards Association CAN/CSA-S472-92, Foundations, Offshore Structures, and section 5.2.2 of Canadian Standards Association Special Publication S472.1-1992, Commentary to CSA Standard CAN/CSA-S472-92, Foundations.
54 Pile foundations of every fixed offshore platform and, where applicable, subsea production system shall be designed in accordance with section 9 of Canadian Standards Association CAN/CSA-S472-92, Foundations, Offshore Structures, and section 5.2.2 of Canadian Standards Association Special Publication S472.1-1992, Commentary to CSA Standard CAN/CSA-S472-92, Foundations.
Structural Strength of Mobile Offshore Platforms
(a) withstand, without major damage, the ice loads to which it may be subjected when it is operating in accordance with the operations manual;
(b) stay on location in the ice concentration and under the ice forces to which it may be subjected, as stated in the operations manual; and
(c) be moved from the production site or drill site in the ice concentration to which it may be subjected, as stated in the operations manual.
(2) In an analysis undertaken in accordance with subsection 37(2) for the purpose of determining the resistance to overturning and the resistance to sliding of a self-elevating mobile offshore platform,
(a) a lattice type leg may be analysed using equivalent single- beam hydrodynamic coefficients as determined in accordance with Det norske Veritas Classification Notes, Note No. 31.5 — Strength Analysis of Main Structures of Self-Elevating Units, when determining
(i) the hydrodynamic loads to be used in calculating overturning forces and sliding forces, if a vertical load equal to 5 per cent of the horizontal load is applied at the centre of the leg, and
(ii) the hydrodynamic forces to be used in any detailed finite element analysis of the upper legs and hull;
(b) the overturning moments and sliding forces shall be assessed assuming no spudcan fixity and using the most critical combination and direction of environmental and functional loads;
(c) the reaction point for an independent leg platform shall be taken as the point located at a distance above the spudcan tip that is equal to the lesser of
(d) the reaction point for a mat-supported platform shall be determined considering the soil characteristics determined in the site investigation undertaken pursuant to section 46.
(3) Where any wave frequency or seismic ground motion predicted for the production site of a self-elevating mobile offshore production platform is close to the frequency of oscillation of the platform, a dynamic response calculation shall be performed as part of the analyses required by section 37 and the dynamic loads determined thereby shall be included in the relevant stress and fatigue analyses.
(4) The connection between each spudcan and each leg of a self-elevating mobile offshore platform shall be designed to withstand without failure the loads occurring at the full spudcan fixity condition.
(5) Each spudcan and each connection between each spudcan and each leg of a self-elevating mobile offshore platform shall be designed for all possible penetrations or conditions ranging from tip penetration to full spudcan penetration as determined by the site investigation undertaken pursuant to section 46, and the shape of the spudcan.
(6) Every spudcan of a self-elevating mobile offshore platform shall have sufficient strength to withstand storm-induced horizontal loads, vertical loads, and one half of the lower guide bending moment that is calculated assuming the leg is pinned.
(7) The secondary bending effects of the legs of a self-elevating mobile offshore platform shall be taken into account in the performance of an analysis pursuant to section 37.
(8) The analysis required pursuant to section 37 to verify whether a self-elevating mobile offshore platform is capable of withstanding the loads imposed during transportation shall be performed in accordance with Part 3, Chapter 2, Sections 3 C-100 and D-300 of Det norske Veritas Rules for Classification of Mobile Offshore Units.
(9) A self-elevating mobile offshore platform with independent footing support shall be designed to withstand the loads that may be imposed during preload operations, including where there is
(10) The legs, spudcans and mats of every self-elevating mobile offshore platform shall be designed for any impact load that might occur on setdown, in accordance with Part 3, Chapter 2, Section 3 E-400 of Det norske Veritas Rules for Classification of Mobile Offshore Units, using the maximum environmental and functional loading conditions for setdown operations, as specified in the operations manual.
(11) The legs of every self-elevating mobile offshore platform shall be preloaded to at least l.l times the reaction expected at the footing or mat at the extreme loading condition.
Motion Response Characteristics
56 The motion response characteristics of every floating platform shall be determined by analytical methods or by model tests for the six degrees of freedom for all relevant operational, transit and survival drafts.
Stability of Mobile Offshore Platforms
57 (1) For the purpose of this section, lightship, in relation to a mobile offshore platform, means a platform with all its permanently installed machinery, equipment and outfit, including permanent ballast, spare parts normally retained on board and liquids in machinery and piping at their normal working levels, but not including liquids in storage or in reserve supply tanks, items of consumable or variable loads, stores and crew and their effects.
(2) Subject to subsection (3), an inclining test shall be carried out to determine the lightship weight and the location of the centre of gravity on every mobile offshore platform.
(3) Detailed weight calculations showing the differences of weight and centres of gravity may be used in lieu of the inclining test required by subsection (2), in respect of a surface or self-elevating mobile offshore platform of a design that is identical with regard to hull form and arrangement to that of a platform for which an inclining test has been carried out, if the accuracy of the calculations is confirmed by a deadweight survey.
(4) Subject to subsection (6), during each five-year survey that is required and carried out by a classification society of a surface or self-elevating mobile offshore platform, a deadweight survey shall be carried out and, where there is a significant discrepancy between the measurement obtained from that survey and the weight change as calculated from weight records,
(a) in the case of a surface platform, an inclining test shall be carried out; and
(b) in the case of a self-elevating platform, the allowable variable load in the elevated condition shall be adjusted in accordance with the deadweight survey and the stability in the floating mode shall be calculated.
(5) Subject to subsection (6), an inclining test shall be carried out during each five-year survey that is required and carried out by a classification society for every column-stabilized mobile offshore platform, except that after the second inclining test, the subsequent tests need only be carried out during every alternate five-year survey if there was no significant discrepancy between the weight records and the results of the second test.
(6) An inclining test is not required pursuant to subsection (4) or (5) where the platform is equipped with instrumentation that is capable of accurately measuring or providing data that permit an accurate calculation of the centre of gravity.
(7) A comprehensive and up-to-date record shall be kept of every change to a mobile offshore platform that involves a change in weight or position of weight.
(8) Where the weight of a mobile offshore platform changes by more than 1 per cent of the lightship weight, a deadweight survey shall be carried out at the earliest opportunity and an up-to-date value of the lightship centre of gravity shall be recorded in the operations manual.
(9) Subject to subsections (10) to (13), the analysis of intact and damage stability of every mobile offshore platform undertaken for the purpose of paragraph 41(1)(e) shall include a verification as to whether the platform complies with Chapter 3 of International Maritime Organization Code for the Construction and Equipment of Mobile Offshore Drilling Units, 1989.
(10) Every mobile offshore platform shall be designed so that, in the intact condition, when subjected to the wind heeling moments described in the Code referred to in subsection (9), it has a static angle of heel of not more than 15 degrees in any direction.
(11) Every column-stabilized mobile offshore platform shall be designed so that, in the intact condition, it has a metacentric height of at least 1 m when it is in the operating and transit draft and a metacentric height of at least 0.3 m in all other draft conditions.
(12) Every surface and self-elevating mobile offshore platform shall be designed so that, in the intact condition, it has a metacentric height of at least 0.5 m.
(13) Every mobile offshore platform shall be designed so that, in the damaged condition or where any compartment is flooded, the final angle of heel does not exceed 15 degrees in any direction and the area under the righting moment curve is at least equal to the area under the heeling moment curve.
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