1、 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 1 GUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS JANUARY 2010 NOTICE NO. 1 June 2011 The following Rule Changes become EFFECTIVE AS OF 1 JUNE 2011. (See http:/www.eagle.org for the
2、consolidated version of the Guide for Building and Classing Liquefied Gas Carriers with Independent Tanks 2010, with all Notices and Corrigenda incorporated.) Notes - The date in the parentheses means the date that the Rule becomes effective for new construction based on the contract date for constr
3、uction. (See 1-1-4/3.3 of the ABS Rules for Conditions of Classification (Part 1).) FOREWORD (Revise Foreword, as follows.) Foreword (1 June 2011) (Preceding text remains unchanged.) The ABS Guide for Liquefied Petroleum Gas Carriers with Type-A Independent Tanks became effective 1 JANUARY 2006. In
4、May 2009, the criteria was extended to cover liquefied gas carriers with Type B and Type C independent tanks. This revision adds guidelines for hull girder ultimate strength assessment and has an effective date of 1 January 2010. The June 2011 revision includes fatigue, fracture, and thermal analysi
5、s for type-B independent tanks which is required by IGC code. Paragraph 6/9.7 and Appendix 5 are added to the Guide. SECTION 6 ACCEPTANCE CRITERIA (Add new Paragraph 6/9.7, as follows.) 9.7 Fatigue and Fracture Analysis for Type-B Independent Tanks (1 June 2011) IMO IGC requires advanced analyses fo
6、r type-B independent tanks. Additional analyses are to be conducted for type-B independent tank in accordance with Appendix 5 “Fatigue and Fracture Analysis for Type-B Independent Tanks”: Fatigue damage analysis Fracture mechanics analysis Leakage analysis Thermal stress analysis Notice No. 1 June 2
7、011 2 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 APPENDIX 5 FATIGUE AND FRACTURE ANALYSIS FOR TYPE-B INDEPENDENT TANKS (Add new Appendix 5, as follows.) APPENDIX 5 Fatigue and Fracture Analysis for Type-B Independent Tanks (1 June 2011) 1 General IMO requi
8、res additional fatigue and fracture mechanics based analysis for type B independent tank. Structural members in independent cargo tanks are affected by dynamic loads from internal pressure caused by ship motion. The strength and safety of type B independent cargo tank are to be verified against dyna
9、mic loads through fatigue and fracture mechanics based analysis. This appendix provides procedure and acceptance criteria for fatigue and fracture analysis of a cargo tank to verify compliance with IMO type B independent tank requirements. Fatigue and fracture analysis are to be carried out for a ta
10、nk to verify adequate fatigue and crack propagation characteristics. Integrity of the structural member of an independent tank against fatigue and fracture is to be verified by: Fatigue damage analysis for high cycle and low cycle fatigue load Fracture mechanics based analysis for an initial crack L
11、eakage of cargo analysis in case of a penetrating crack The general procedure for fatigue and fracture analysis is shown in Appendix 5, Figure 1. 1.1 Selection of a Tank for the Analysis The internal pressure on an independent tank due to the acceleration of the center of gravity of liquid cargo can
12、 be estimated following the procedure in Subsection 3/11. The tank under the most severe internal pressure is to be selected for the fatigue and fracture analysis. The forward most cargo tank is normally selected as a target cargo tank for the analysis if the shape and size is similar to other tanks
13、. 1.3 FEA Model The global FEA model including hull, cargo tank, and supporting structure is to be used for the fatigue and fracture analysis. Global finite element modeling is described in Appendix 1. In the FEA model the target cargo tank is to be located in the middle of the model as shown in App
14、endix 1, Figure 1. 1.5 Critical Locations Fatigue damage assessment and fracture mechanics analysis are to be carried out for areas of the tank with high stress concentrations. Critical locations with high stress include; Tank skin including bottom, top, side, front, and rear plates Bracket connecti
15、ons of transverse web frames Bracket connections of swash bulkheads Bracket connections of horizontal stringers Brackets attached to tank at vertical supports and chocks Notice No. 1 June 2011 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 3 FIGURE 1 Analysis
16、Procedure (1 June 2011) 3D Global FEA Model(Hull and Tank)FE Analysis forCargo LoadingFE Analysis forFatigue Load PairsThermal Analysis(Section 9)High Cycle FatigueAnalysis (Section 3)Low Cycle FatigueAnalysis (Section 3)Cumulative FatigueDamage (Section 3)Leakage Analysis(Section 7)Crack Propagatio
17、n Analysisfor Leakage (Section 7)Fracture MechanicsAnalysis (Section 5)1.7 Hot Spot Stress with Global Course Mesh Generally, it is recommended to use hot spot stress as a local stress for fatigue and fracture analysis in this appendix. For an initial screening purpose of critical areas, global coar
18、se FEA model is to be used. When the stress result from global coarse FEA model is used for the analysis, hot spot stress can be estimated from nominal stress with appropriate stress concentration factors for stiffener attachments and skin plates with fillet welds. The bending stress of a plate betw
19、een stiffeners from internal pressure is to be considered for fatigue and fracture analysis of tank skin plates. The total stress amplitude is the sum of the membrane stresses from FEA results and local stresses caused by panel bending. Bending stress of a panel between stiffeners is to be calculate
20、d from 5C-1-5/3.5 of the Steel Vessel Rules. 1.9 Hot Spot Stress with a Local Fine Mesh For a critical areas identified from the global course mesh, additional fatigue and fracture analysis are to be carried out with local fine mesh FEA models. The hot spot stress is to be calculated from the FEA re
21、sults with a refined mesh. The mesh size of local area is to be small enough to detect the stress concentration and the element size at the critical location is to be equal to the plate thickness. The procedure to estimate the hot spot stress at a weld toe with refined mesh is specified in A3/11.5.
22、1.11 Plate Thickness Effect For the welded connections with thickness greater than 22 mm, stress range is to be adjusted by a factor (t/22)0.25as described in A3/5.7. Notice No. 1 June 2011 4 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 3 Fatigue Damage Asse
23、ssment Accumulated fatigue damage is to be assessed for high cycle and low cycle fatigue loading. High cycle fatigue damage is due to the internal pressure caused by the motion of a ship. For long term prediction of wave loads, wave spectra covering North Atlantic Ocean and a probability level of 10
24、-8are to be employed. Low cycle fatigue damage is caused by loading and unloading of a liquid cargo to the tank. Fatigue damage is to be calculated based on the appropriate S-N curve with the assumption of linear cumulative damage (Palmgren-Miner rule). Highly stressed areas are to be selected from
25、FEA results considering all fatigue loading cases. The hot spot stress can be calculated as described in A5/1.7 and A5/1.9. Fatigue damage estimation procedure is shown in Appendix 5, Figure 2. FIGURE 2 Fatigue Damage Assessment Procedure (1 June 2011) 3D Global FEA Model(Hull and Tank)FE Analysis f
26、orCargo LoadingFE Analysis forFatigue Load PairsPrimary StressBending StressPrimary StressBending StressHot Spot Stress Hot Spot StressLow CycleFatigue DamageHigh CycleFatigue DamageTotal Fatigue DamageDamage = CWCompleteFatigue AnalysisLocal Fine MeshYesNoNotice No. 1 June 2011 ABSGUIDE FOR BUILDIN
27、G AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 5 3.1 S-N Curves Stress results from the global FEA model are to be used for high cycle and low cycle fatigue damage estimation. The maximum principal stress range is to be used for the analysis. Appropriate S-N curves are to be used
28、 for the fatigue damage analysis. The selection of S-N curve depends on weld type, such as butt weld, transverse fillet weld, or longitudinal fillet weld. S-N curves for stainless steel are shown in Appendix 5, Figure 3. Formulation of S-N curve is given in Appendix 3, Figure 5. Application of each
29、S-N curve is to follow equivalent S-N curves for steel as shown in Appendix 3, Table 1. FIGURE 3 Design S-N Curves for Stainless Steel (1 June 2011) 1010010001.E+04 1.E+05 1.E+06 1.E+07Endurance (Cycles)StressRange (MPa)S1S2S3S4Details of S-N Curves Class m Log(K2) Equivalent S-N curve for steel S1
30、3.0 12.05 D S2 3.0 11.92 E S3 3.0 11.75 F S4 3.0 11.55 F2 Notice No. 1 June 2011 6 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 S-N curves for aluminum are shown in Appendix 5, Figure 4. Application of each S-N curve is to follow equivalent S-N curves for st
31、eel as shown in Appendix 3, Table 1. FIGURE 4 Design S-N Curves for Aluminum (1 June 2011) 1010010001.E+04 1.E+05 1.E+06 1.E+07Endurance (Cycles)StressRange (MPa)A1A2A3A4Details of S-N Curves Class m Log(K2) Equivalent S-N curve for steel A1 3.0 10.78 D A2 3.0 10.69 E A3 3.0 10.59 F A4 3.0 10.46 F2
32、Notice No. 1 June 2011 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 7 S-N curves for 9% Ni are shown in Appendix 5, Figure 5. Application of each S-N curve is to follow equivalent S-N curves for steel as shown in Appendix 3, Table 1. FIGURE 5 Design S-N Curv
33、es for 9% Ni (1 June 2011) 1010010001.E+04 1.E+05 1.E+06 1.E+07Endurance (Cycles)StressRange(MPa)N1N2N3N4Details of S-N Curves Class m Log(K2) Equivalent S-N curve for steel N1 3.0 12.37 D N2 3.0 12.18 E N3 3.0 12.03 F N4 3.0 11.89 F2 3.3 High Cycle Fatigue Damage High cycle fatigue damage is to be
34、calculated for the critical areas from the wave loading by the ship motion. The stress result form integrated hull and tank FEA model is to be used for the analysis. Standard design load cases for fatigue strength assessment is shown in Section 4, Tables 3 and 4. Four load case pairs for full load a
35、nd ballast conditions were considered in the tables. The stress amplitude is to be calculated from each load case pair. Each dynamic load case corresponds to a probability level of 10-4. Fatigue damage is to be calculated following the procedure in Subsection A3/5: Dfi= 61Dfi_12+ 61Dfi_34+ 31Dfi_56+
36、 31Dfi_78where Dfi_jk= fatigue damage due to the stress range from load case pairs jk The long term stress ranges can be characterized using a modified Weibull probability distribution parameter as described in A3/5.5. Design life of 20 years is to be used to assess the high cycle damage of the stru
37、cture. Notice No. 1 June 2011 8 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 3.5 Low Cycle Fatigue Damage Low cycle fatigue damage is due to the cyclic stress from loading and unloading of liquid cargo to the tank. Pressure levels for the tank are to be calc
38、ulated from the sum of liquid cargo and gas pressure. The densities of liquefied gas cargos are listed in Section 1, Table 2. The pressure envelope of the tank is to be applied to the global hull and tank FEA model to determine the stress at each critical location. The bending stress of a panel betw
39、een stiffeners is to be added to the membrane stress from the FEA model for skin plates. The total number of fatigue cycles from the loading and unloading of cargo is to be assumed as 1,000 for the lifetime of a vessel. 3.7 Total Fatigue Damage Total accumulated fatigue damage is to be assessed as t
40、he sum of high cycle and low cycle damage. Total cumulative fatigue damage factor is to be calculated by: DT= DF+ jN310where DT= total fatigue damage Df= high cycle fatigue damage calculated from Appendix 5/3.3 Nj= number of cycles to fracture for the fatigue loads due to loading and unloading of li
41、quid cargo 3.9 Acceptance Criteria The total fatigue damage is to be less than the allowable damage factor: DT CWwhere CW= maximum allowable cumulative fatigue damage ratio Cwis to be less than or equal to 0.5. 3.11 FEA with Refined Mesh A detailed fine mesh FEA is required for the critical areas th
42、at do not meet the acceptance criteria. The hot spot stress is to be calculated from the FEA model with a refined mesh for the critical areas as described in A5/1.9. 5 Fracture Mechanics Analysis A fracture mechanics based analysis is to be carried out for the critical locations of the tank structur
43、e with high dynamic stresses. A fracture mechanics approach assumes that an idealized crack propagates in relation to the stress intensity factor range. A fatigue crack propagation analysis is to be conducted for tank skin plates to verify the integrity of a cargo tank. Fatigue crack propagation is
44、to be assessed from the growth of an initial existing crack to a critical size. High stress concentration areas or large fatigue damage locations identified in Subsection A5/3 are to be selected for the crack propagation analysis. 5.1 Load Distribution The dynamic load spectrum is to be determined b
45、y long term distribution based on the design life of the ship corresponding to realistic wave spectra covering the North Atlantic and a probability level of 10-8. The long term stress ranges can be characterized using a modified Weibull probability distribution parameter. Simplified linear load spec
46、trum can be used for the load distribution. Notice No. 1 June 2011 ABSGUIDE FOR BUILDING AND CLASSING LIQUEFIED GAS CARRIERS WITH INDEPENDENT TANKS .2010 9 The total load spectrum is to be divided into more than 10 groups to remove the effect of loading sequence to crack propagation life as shown in
47、 Appendix 5, Figure 6. oin the figure is the most probable maximum stress range over the life of the ship. Two times of the FEA results from the high cycle fatigue analysis in A5/3.3 (based on 10-4probability level) can be used as the maximum stress range for fracture analysis. The hot spot stress c
48、an be calculated from the nominal stress obtained from the FEA results with geometric stress concentration factor as described in A5/1.7. FIGURE 6 Load Distribution for Crack Propagation Analysis (1 June 2011) 108o5.3 Initial Crack The size of an initial crack is one of the main parameters for the c
49、rack propagation analysis. An initial surface crack is to be assumed in a fillet or butt weld areas of the tank structure. The dimension of the surface crack is to be assumed as 0.5 mm depth and 5 mm length. 5.5 Stress Intensity Factor The stress intensity factor range is to be calculated from stress range, crack shape and size, and geometry. IIW or equivalent standard is to be used to assess the stress intensity factor for a surface crack. The stress range is to be based on the maximum principal stress. 5.7 Crack Propagation Analysis Crack propaga
