ShipRight Notice 1 Design and Construction

Transcription

1 ShipRight Notice 1 Design and Construction Structural Design Assessment Primary Hull and Cargo Tank Structure of Type A Liquefied Gas Carriers, January 2017 The status of this Rule set is amended as shown and is now to be read in conjunction with this and prior Notices. Any corrigenda included in the Notice are effective immediately. Issue date: June 2018 Amendments to Approved date Chapter 1, Section 2 June 2018 Chapter 2, Section 4 June 2018 Chapter 2, Section 5 June 2018 Chapter 2, Section 6 June 2018 Working together for a safer world

2 Document History Date: November 2001 Notes: Preliminary release July 2002 Final release October 2002 Revisions as identified in History development up to January May 2004 March 2016 January 2017 June 2018 Notice 1 Revisions as identified in Notice Changes incorporated in May 2004 version. Consolidated version as incorporated in SDA Primary Hull and Cargo Tank Structure of Type A Tank Liquefied Gas Carriers, March 2016 version. Consolidated version to revise buckling acceptance criteria in Table and Corrigenda for January 2017 version. LLOYD S REGISTER 1

3 CHAPTER 1 Introduction Section 2 Symbols (Part only shown) 2.1 Definition P 0 = design vapour pressure, see Ch 4, Cargo Containment of the Rules for Ships for Liquefied Gases. P 0 is not to be taken as less than 0,25 bar. P hold+ = Cargo hold overpressure to be taken as the maximum positive pressure (above atmospheric) setting of the cargo hold pressure relief device. P hold- = Cargo hold underpressure (suction) to be taken as the minimum pressure (below atmospheric) setting of the cargo hold pressure relief device if fitted, or the lowest operating pressure of the dry-air/inert-gas circulation system for the hold. LLOYD S REGISTER 2

4 CHAPTER 2: Analysis of Primary Structures of Type A Liquified Gas Carriers Section 3 Boundary conditions 3.3 Symmetrical boundary conditions for locall local loads Section 4 Loading conditions Existing sub-sections 4.9 to 4.15 are to be renumbered 4.10 to Hold flooded load cases The objective of the load cases is to examine the yield and buckling capability of the transverse watertight bulkhead and double bottom structures to withstand the load in the event that the cargo hold is flooded as a result of collision or other accidental occurrence Each cargo hold is to be considered flooded separately. The hold flooded load cases to be analysed are specified in Table Special load cases All cargo tanks are to be fully loaded and the ship is to be at its deepest draught. The damaged loading condition is summarised in Table Summary of loading condition with one cargo hold flooded External and internal hydrostatic pressure due to flooded waterline in damaged heel condition is to be applied. The pressure described in Table Summary of loading condition with one cargo hold flooded is to be applied to the transverse bulkheads of the flooded cargo hold. Static load due to all deadweight and lightweight items is to be applied. The ship is to be balanced vertically on a trimmed waterline No additional vertical bending moment is required to be applied to the FE model, i.e. the vertical bending moment in the model is equal to the still water bending moment generated by the loads. LLOYD S REGISTER 3

5 Procedure for loading supports and chocks (Part only shown) Table Wave load cases Load case Still water bending moment Rule vertical wave bending moment External pressure Internal pressure Additional sub-load cases Tank loading pattern Boundary conditions M SW Hog M W Hog Balanced waterline g, P 0 (P hold+, P hold-) see Note 9 - (e) See Ch 2, 3.2 Symmetrical boundary conditions for global loads and Figure Boundary conditions for the application of symmetric global loads Alternate 1 S2.1, see Notes 5 and Wave crest (f) Tank loading pattern images See Ch 2, 3.3 Symmetrical boundary conditions for local locall loads and Figure Boundary conditions for the application of symmetric local load and loadsand Figure Alternative boundary conditions for the application of symmetric local loads (e) (f) M SW Hog M W Hog Balanced waterline g, P 0 (P hold+, P hold-) see Note 9 - (g) See Ch 2, 3.2 Symmetrical boundary conditions for global loads and Figure Boundary conditions for the application of symmetric global loads Alternate 2 S3.1, see Notes 6 and Wave crest (h) See Ch 2, 3.3 Symmetrical boundary conditions for local locall loads and Figure Boundary conditions for the application of symmetric local load and loadsand Figure Alternative boundary conditions for the application of symmetric local loads Tank loading pattern images LLOYD S REGISTER 4

6 (g) (h) Note 1. The Rule design vertical wave bending moment and the permissible vertical still water bending moment envelope, M sw, is to be applied to bending moment sub-load cases, see Ch 1, 2.1 Definition and Ch 2, 4.1 Introduction for definition of M sw. Note 2. All lightweight and deadweight items are to be applied in bending moment sub-load cases. Note 3. External pressure is applied to the wave crest and wave trough sub-load cases. No lightweight, deadweight and other load items are to be applied. See Ch 2, 4.2 Wave load cases and Ch 2, 4.13 Procedure to apply local wave crest or trough for the application of wave crest and wave trough. See Ch 2, 3.3 Symmetrical boundary conditions for local loads for the application of vertical ground springs and vertical balance forces. Note 4. Bending moment sub-load case and wave crest/trough sub-load case are run separately. The resultant stresses are to be combined by superposition. Note 5. Alternately loaded condition with odd number tanks full and odd number tanks empty. For illustration, figure shown is a ship with three cargo tanks. Note 6. Alternately loaded condition with even number tanks full and odd number tanks empty. For illustration, figure shown is a ship with three cargo tanks. Note 7. Full ballast tanks are shown in way of empty cargo tanks. If the ship s Loading Manual contains conditions in which ballast tanks in way of empty cargo tanks are empty or have reduced filling level, then these conditions are to be analysed. Note 8. A deep draught loading condition with most water ballast tanks filled. Note 9. Cargo hold overpressure (P hold+) is to be applied to the boundary of the holds with loaded cargo tanks. Cargo hold underpressure (P hold-) is to be applied to boundary of the holds with empty cargo tanks. These loads are applied for the assessment of the strength of the transverse bulkheads against build-up of pressure and suction in cargo holds. Cargo hold overpressure and underpressure are not to be applied to the cargo tank surface. LLOYD S REGISTER 5

7 (Part only shown) Table Special load cases Load case Still water bending moment Rule vertical wave bending moment External pressure Internal pressure Additional subload cases to apply Tank loading pattern Boundary conditions Flotation case (b) See Ch 2, 3.3 Symmetrical boundary conditions for local locall loads and Figure Boundary conditions for the application of symmetric local load and loadsand Figure Alternative boundary conditions for the application of symmetric local loads Tank loading pattern images Flotation case O5, see Notes 4, 5, 6 and 7 Deleted (b) Revised Reference plot (sample) of all holds flooded Hold Flooded case LLOYD S REGISTER 6

8 Actual due to flooded waterline in heel condition - Hydrostatic pressure due to flooded and heeled waterline Tank pressure Hydrostatic pressure due to flooded and heeled waterline - (c) An Inertia Relief solution is recommended. If the FE package being used does not provide this facility, then alternative boundary conditions given in Figure Boundary conditions for the application of symmetric global loads may be used. See Ch 2, 3.4 Asymmetric boundary conditions for transverse loads. Tank loading pattern images Case 1: Hold flooded cases O6, see Notes 2, 8 and 9 Case 2: (c) Case 3: LLOYD S REGISTER 7

9 Note 1. The tank test case(s) are to consider the ship in the actual loading conditions when the tank test procedures are undertaken. It may be necessary to analyse load cases for the testing of each cargo tank separately. The actual ship conditions proposed for the tests of cargo tanks 1 and 2 must be used together with the lightest draughts chosen for each condition as described in Ch 2, 4.7 Tank test condition Note 2. All still water load items are to be applied. Note 3. External hydrostatic pressures due to the still waterline are to be applied. Note 4. Cargo tanks are to be empty. External buoyancy, deadweight and lightweight items and all other loads are not to be applied. Note 5. This load case is not based on an actual loading condition. Note 6. Only the void space between the inside of the hold and the outside of the cargo tank boundaries is assumed to be flooded up to the scantling draught. Note 7. If damage stability calculations are available, then the depth of flooding from the damage stability calculations may be used in lieu of the scantling draught as described in Ch 2, 4.8 Flotation load cases Note 8. All cargo tanks are to be fully loaded. Each cargo hold is to be considered flooded in a separate load case. The heeled flooding condition is to be determined in accordance with Table Summary of loading condition with one cargo hold flooded. Damage stability calculation may be used to determine the flooded waterline and heel angle. See 4.9 Application of loads. Note 9. External and internal hydrostatic pressure due to flooded waterline in damaged heel condition is to be applied. The pressure described in Table Summary of loading condition with one cargo hold flooded is to be applied to the transverse bulkheads of the flooded cargo hold. Note 810. For illustration, figures shown are ships with three cargo tanks. LLOYD S REGISTER 8

10 Table Summary of loading condition with one cargo hold flooded Item Damage flooded condition Transverse bulkheads in flooded hold Cargo hold boundary, side and bottom shell Cargo tanks Loading condition All cargo tanks are to be fully loaded and the ship is at its deepest draught. Two separate flooding conditions resulting in the following scenarios are to be considered: Maximum draught at centreline of the forward and aft bulkheads of the flooded hold (T 1 ) Maximum draught at the outboard boundary of the forward and aft bulkheads of the flooded hold (T 2 ) The damaged heel waterline is to be determined based on the damage stability calculation. Where damage stability calculation is not available, T 1 and T 2 may be obtained as follows: T 1 = T ss + 1, 2 1, 000 V h +V b (in m) 111 TTT T 2 = T 1 + 0, 22 b where V h is the volume of the void space in the flooded cargo hold corresponding to the level of scantling draught (in m 3 ) V b is the volume of the double bottom and hopper tanks, on one side of the centre line, in way of the flooded cargo hold (in m 3 ) b is the width of the cargo hold TPC is the displacement (tonnes) immersion per centimetre as given in the ship s Loading Manual Hydrostatic pressure due to the flooded waterline and pressure head due to the ship s pitch motion. The pressure head due to the ship s pitch motion, h ppppp, is given by: h ppppp = 0, 33 l H ttt(ψ) l H ii ttt llllll oo ttt oloofff holf ψ is the pitch angle calculated in accordance with Pt 3, Ch 14, 1.6 Symbols and definitions of the Rules for Ships Pressure based on heeled waterline defined by T 1 and T 2 All cargo tanks fully loaded. Pressure differential due to cargo and flooded heeled waterline is to be applied to the tank boundary in the flooded hold.

11 Note 1. The pressure head to be applied to the external shell plating and longitudinal internal plating is different to that specified for the bulkhead. The purpose of these load cases is to impose flood water loads, including the effect of ship motions, onto the bulkhead structure; hence the increased pressure head applied to the bulkhead. Table Friction coefficient (reference values)

12 CHAPTER 2: ANALYSIS OF PRIMARY STRUCTURES OF TYPE A LIQUIFIED GAS CARRIERS Section 5 Permissible stresses 5.1 Permissible stresses Table Maximum permissible membrane stresses for collision (O1, O2 and O3) and flotation load cases (O5), flotation (O5) and hold flooded (O6) load cases Permissible stresses Structural item Load cases Combined stress, σ e Direct stress, σ Shear stress, τ Tank support systems and structure in way of Anti-pitching chock seating O1, O2 and O3 σ 0-0,55 σ 0 (see Note 3) Transverse bulkheads O1, O2 and O3 σ 0 0,95 σ 0 0,55 σ 0 (see Note 3) Anti-flotation chock seating O5 σ 0-0,55 σ 0 (see Note 3) Upper tank and topside transverse webs and flanges O5 0,75σ 0-0,35 σ 0 (see Note 4) Transverse bulkhead structure and immediate integration areas Transverse watertight bulkhead: Plating σ 0 0,95 σ 0 0,55 σ 0 (see Note 3) Vertical webs and horizontal stringers: (a) Web plating (b) Face plates O6 σ 0 _ 0,95 σ 0 σ 0 0,55 σ 0 (see Note 3) _ Double bottom girders, side shell, inner bottom, hopper, topside and deck integration with transverse bulkhead σ 0 0,95 σ 0 0,55 σ 0 (see Note 3) Note 1. Stress criteria are based on the coarse mesh described in Ch 2, 2.1 FE Modelling Note 2. If a finer mesh size is used, then stresses may be averaged over an area equal to the size of the coarse mesh element in way of the structure being considered. The averaging is to be based only on elements with their boundary located within the desired area. Stress average is not to be carried out across structural discontinuity or abutting structure. Note 3. Criteria relate to single FE element. Note 4. Criteria relate to mean stress over the depth of the member.

13 CHAPTER 2: ANALYSIS OF PRIMARY STRUCTURES OF TYPE A LIQUIFIED GAS CARRIERS Section 6 Buckling acceptance criteria 6.1 Buckling criteria Table Local plate panel required factor against buckling (collision and flotation, flotation and hold flooded load cases) Structural item Factor against buckling λ Tank support systems and structure in way of Anti-flotation chock seating Anti-rolling chock seating Supporting chock seating Topside transverse web 1,0 Bulkhead structure and immediate areas of integration Plating, vertical webs, stringers and girders 1,0 Structure in way of flotation chocks Topside tank plating and transverse web 1,0 Note 1. Immediate areas of integration are to include side, bottom and deck structure from one web frame aft of the bulkhead to one web frame forward of the bulkhead.