M ATERIALS AND W ELDING
3 C ORROSION A DDITIONS .1 General
3.3 Application of Corrosion Additions .1 General
3.3.1.1 The application of corrosion additions described in 3.3.2 to 3.3.7 is to be applied unless otherwise specified in the specific rule requirements.
3.3.1.2 Compliance with the Rules may be performed either by:
(a) comparison of the proposed gross scantling with the gross required, in which case the applicable corrosion addition is added to the net requirement of the Rules
(b) comparison of the proposed net scantling with the net required, in which case the applicable corrosion addition is deducted from the gross proposed.
Methods (a) and (b) are suitable for assessment of thickness. Method (b) is the most suitable for assessment of section properties, e.g. section modulus, area and moment of inertia.
3.3.1.3 The gross scantlings specified in 3.3.2 to 3.3.7 used to derive the net scantlings are to exclude any owner’s extra thicknesses, see also Section 2/4.3.4.3.
3.3.2 Application for hull girder longitudinal strength calculations
3.3.2.1 The calculation of hull girder stresses for the assessment of longitudinal strength as given in Section 8/1 is to be based on the net hull girder sectional properties calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the gross thickness of all structural elements comprising the hull girder cross-section.
3.3.2.2 The local buckling capacity of plates and stiffeners subject to hull girder stresses are to be calculated based on the net scantlings, as given in Section 8/1.4.2. The net scantling is calculated by deducting the full corrosion addition, i.e. -1.0tcorr, from the gross thickness.
3.3.3 Application for scantling assessment of plates and local support members
3.3.3.1 The required gross thickness for plates and local support members are calculated byadding the full corrosion addition, i.e. +1.0tcorr, to the net thickness required in accordance with the scantling requirements in Sections 4/3.4 and 8/2 to 8/7.
3.3.3.2 The net sectional properties of local support members are calculated by deducting the full corrosion addition, i.e. -1.0tcorr, from the web, flange and attached plate gross thicknesses as described in Section 4/2.4.1 and are to comply with required section modulus, moment of inertia and shear area as given in Sections 4/3.4 and 8/2 to 8/7.
3.3.3.3 The calculation of hull girder stresses for the strength assessment of members under combined local and global loading is to be based on the net hull girder sectional properties calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the gross thickness of all structural elements comprising the hull girder cross-section.
3.3.3.4 The required minimum gross thickness of plates and local support members is calculated by adding the full corrosion addition, i.e. +1.0tcorr, to the minimum net thickness requirements given in Section 8/2.1.5.
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JULY 2012 SECTION 6.3/PAGE 5
3.3.4 Application of corrosion additions for scantling strength assessment of primary support members
3.3.4.1 The required gross thickness of primary support members is calculated by adding half the corrosion addition, i.e. +0.5tcorr, to the net thickness required in accordance with the strength requirements in Section 8/2.6 and 8/3 to 8/7.
3.3.4.2 The net sectional properties of primary support members are to be calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the web and flange gross thicknesses, and are to comply with the required section modulus, moment of inertia and area as given in Section 8/2.6 and 8/3 to 8/7.
3.3.4.3 The required minimum gross thickness of primary support members is calculated by adding the full corrosion addition, i.e. +1.0tcorr, to the minimum net thickness requirement given in Section 8/2.1.6.1, 8/3.1.4.1, 8/4.1.5.1, 8/5.1.4.1, 8/6.3.7.5, 8/6.4.5.4 and 10/2.3.
RCN 2 to July 2008 version (effective from 1 July 2010)
3.3.5 Application of corrosion additions for hull girder ultimate strength analysis
3.3.5.1 The calculation of the hull girder ultimate capacity, Mu, as given in Section 9/1, is tobe based on the net hull girder sectional properties calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the gross thickness of all structural elements comprising the hull girder cross-section.
3.3.5.2 The buckling capacity of the structural elements used to derive the hull girder ultimate capacity is to be calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the gross thicknesses of the plates and stiffener webs and flanges.
3.3.6 Application of corrosion additions for strength assessment by finite element analysis
3.3.6.1 For the cargo tank structural strength analysis, as given in Section 9/2.2 and Appendix B/2, the finite element model is to be modelled with thicknesses calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the gross thickness of all structural elements.
3.3.6.2 The local buckling capacity of plates and stiffeners are to be calculated by deducting the full corrosion addition, i.e. -1.0tcorr, from the gross thickness.
3.3.6.3 The local fine mesh structural strength analysis models, as given in Section 9/2.3 and Appendix B/3, are to be modelled with thicknesses calculated by deducting half the corrosion addition, i.e. -0.5tcorr, from the gross thickness. The specified fine mesh areas are to be modelled by deduction of the full corrosion addition, i.e. -1.0tcorr, from the gross thickness.
3.3.7 Application of corrosion additions for fatigue strength assessment
3.3.7.1 The calculation of hull girder stresses for the fatigue strength assessment, as given in Section 9/3 and Appendix C/1, is to based on the net fatigue hull girder sectional properties, calculated by deducting a quarter of the corrosion addition, i.e. -0.25tcorr, from the gross thickness of all structural elements comprising the hull girder cross section.
3.3.7.2 The calculation of stresses in local support members from lateral load for the fatigue strength assessment, as given in Section 9/3 and Appendix C/1, are to be based on deducting half the corrosion addition, i.e. -0.5tcorr, from the stiffener web, flange and attached plate.
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JULY 2012 SECTION 6.3/PAGE 6
3.3.7.3 For hot spot stress (FE based) approach, as given in Section 9/3 and Appendix C/2, the FE model of the hopper knuckle is to be modelled with thickness calculated by deducting a quarter of the corrosion addition, i.e. -0.25tcorr, from the gross thicknesses. The very fine mesh areas are to be modelled by deduction of half the corrosion addition, i.e. -0.5tcorr, from the gross thickness.
3.3.7.4 As an alternative to 3.3.7.3, the hopper fatigue FE model may be made in accordance with requirements for FE strength model, i.e. all areas at -0.5tcorr, as described in 3.3.6.1. However the calculated stress range is then to be corrected by the factor fmodel as described in Appendix C/2.4.2.7.
SECTION 6-MATERIALS AND WELDING COMMON STRUCTURAL RULES FOR OIL TANKERS
JULY 2012 SECTION 6.4/PAGE 1