1、 Guidance Notes on Topside Structure Fatigue Assessment for Ship-Type Floating Production Installations GUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FLOATING PRODUCTION INSTALLATIONS MARCH 2016 American Bureau of Shipping Incorporated by Act of Legislature of the State of New
2、 York 1862 Copyright 2016 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Foreword Foreword The purpose of these Guidance Notes is to supplement the topside structure fatigue assessment of ship-type floating production installations in accordance with the ABS Rules
3、 for Building and Classing Floating Production Installations (FPI Rules). These Guidance Notes provide recommended procedures for performing fatigue assessment of topside structures. Guidance Notes are not mandatory requirements. These Guidance Notes become effective on the first day of the month of
4、 publication. Users are advised to check periodically on the ABS website www.eagle.org to verify that this version of these Guidance Notes is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to rsdeagle.org. ii ABSGUIDANCE NOTES ON TOPSIDE STRUC
5、TURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 Table of Contents GUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FLOATING PRODUCTION INSTALLATIONS CONTENTS SECTION 1 Introduction 1 1 General . 1 3 Features 1 5 Application 2 SECTION 2 Topside Structures 3 1 General . 3 3 Topsid
6、e Design Principles 3 3.1 Hull Interface Structures 3 3.3 Fatigue Assessment Procedures . 5 FIGURE 1 Plated Support Structure . 4 FIGURE 2 Portal Frame Structure 4 FIGURE 3 Sliding Support Structure 5 FIGURE 4 Schematic Representation of Topside Structure Fatigue Analysis Procedure . 6 SECTION 3 Loa
7、ds . 7 1 General . 7 3 Operating Weights 7 5 Hull Girder Deformation Loads . 7 7 Inertia Loads due to Unit Motions . 7 9 Wind Loads . 7 11 Live Loads . 8 SECTION 4 Loading Conditions for Topside Structural Fatigue Analysis 9 1 General . 9 3 Design Operational Loading Condition . 9 5 Transit Conditio
8、ns . 9 7 Loading/Offloading Condition . 10 ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 iii SECTION 5 Structural Modeling and Analysis . 11 1 General . 11 3 Areas for Fatigue Strength Assessment . 11 5 Structural Modeling . 11 SECTION 6 Fatigue Damage Calculatio
9、n and Acceptance Criteria 13 1 General . 13 3 Methodology 13 3.1 Simplified Fatigue Method . 13 3.3 Spectral-Based Fatigue Method 14 3.5 Time Domain Analysis Method 14 5 S-N Data . 14 7 Nominal Stress Approach and Stress Concentration Factor (SCF) . 15 9 Hot Spot Stress Determination . 15 11 Accepta
10、nce Criteria . 16 FIGURE 1 Illustration of Stresses on the Throat Section of a Fillet Weld 15 APPENDIX 1 References 17 iv ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 Section 1: Introduction SECTION 1 Introduction 1 General The ABS Rules for Building and Classin
11、g Floating Production Installations (FPI Rules) require strength and fatigue assessment of the topside module/hull interface on the ship-type installations. The hull interface structure specified in the ABS FPI Rules is the interface structure between the main hull and topside structures, including
12、associated stools and elastomeric bearings, as fitted. Topside modules are the discrete structural units that support production facilities and supporting systems, and fatigue analysis of these structures is not required by the FPI Rules. For ship-type floating production installations such as FPSOs
13、, topside modules installed on deck of an installation may include but are not limited to oil/gas processing modules, gas compression modules, power generation modules, flare tower, vent stack, helideck, pipe rack, and laydown areas. Newer generations of topside structures are large in size and heav
14、y in weight. They are important parts of the installation structures that are critical to the operation and structural integrity of ship-type installations. Thus there may be a need to perform the fatigue assessment in addition to strength evaluation of the topside structures. As a supplement to the
15、 fatigue assessment of the topside interfaces on ship-type installations, these Guidance Notes provide the recommended procedures for performing fatigue assessment of the topside structures on ship-type installations. In general, Guidance Notes are not mandatory requirements. Note that Installation,
16、 Ship-type installation or Unit, as used in these Guidance Notes, refers to ship-type floating production installation. 3 Features The topside structure fatigue assessment involves the evaluation of the following areas: Environment wave conditions Metocean data, sea state scatter diagram Design load
17、 conditions Finite element model local boundary conditions Structural geometry Structural stress range and stress concentration factor Fatigue analysis methodology Accumulated fatigue damage, fatigue acceptance criteria and design fatigue life The primary features of these Guidance Notes include: De
18、sign principle of hull interface structure and topside structures Design loads for fatigue strength assessment Loading conditions for topside structure fatigue analysis Accumulated fatigue damage prediction Fatigue acceptance criteria for topside structures ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FAT
19、IGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 1 Section 1 Introduction 5 Application These Guidance Notes describe procedures to perform fatigue assessments of topside structures on ship-type floating production installations. The procedures can be used for Topside structure fatigue life prediction. Assi
20、stance in topside structure design and survey. These Guidance Notes should be used in association with ABS Rules and Guides for fatigue assessment, such as the ABS Guide for the Fatigue Assessment of Offshore Structures and the ABS Rules for Building and Classing Floating Production Installations (F
21、PI Rules). 2 ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 Section 2: Topside Structures SECTION 2 Topside Structures 1 General Topside structures are the modular structures including all types of equipment above the main deck, typically the processing modules on
22、 ship-type installations. The topside structures and the interface structures are designed to carry the weight of the equipment and topside structures, and to have structural adequacy for the inertia loads induced by the wave loads and the flexibility to minimize the stresses induced by the hull gir
23、der deformation in design environmental conditions and sea states. The stress distribution in the topside structure is governed by the structural design of the topside, local loads and ship-type installations accelerations and deformations. The design and analysis criteria to be applied to the topsi
24、de structures and hull interface structures are specified in the FPI Rules. The structural strength design of the hull and hull interface structures on ship-type installations is to be in accordance with 5A-1-3/1 and Sections 5A-1-4 and 5A-3-2 of the FPI Rules, regarding how load components can be a
25、djusted. A detailed fatigue assessment may be performed for topside structures combined with hull interface structures. Rational fatigue analysis methods are acceptable if the forces and member stresses can be properly represented. The dynamic effects should be taken into consideration if they are s
26、ignificant to the structural response. For the frame members of the topside structures, the S-N curves specified in the ABS Guide for Fatigue Assessment of Offshore Structures and API RP 2A (WSD -21stor later Edition) are recommended. The stress concentration factors (SCFs) for unstiffened tubular j
27、oints may be calculated based on applicable empirical formulas with validity limitations. The SCFs should capture the geometrical discontinuities inherent to the design as well as the effect of fabrication tolerances, when deemed necessary (e.g. mismatch between abutting plates). In this regard, for
28、 complex critical connections, the hot spot stress approach should be used in line with the mesh recommendations defined in ABS Guide for the Fatigue Assessment of Offshore Structures. 3 Topside Design Principles 3.1 Hull Interface Structures The various functions of the topside modules give rise to
29、 many disciplines in the topside design. The hull interface structures, which transmit loads between the main hull structure and topside structure, have impact on fatigue capacities of topside structures. Based on various deck stool design types, three typical designs of hull interface structures ar
30、e illustrated. 3.1.1 Plated Support Structure The connection between the deck and the stool or gusset is assumed to be welded. The actual connection design to the deck is typically comprised of welding along transverse frames and longitudinal stiffeners. Section 2, Figure 1 shows the typical hull we
31、lded connection in the longitudinal direction and shear plates in the transverse direction. The plated support structure, shear panels, decks including the hull backup structures and the reinforcements for the hull due to the transferred acceleration loads are to be designed in accordance with the F
32、PI Rules. Fatigue calculations are to be performed for all vital components. ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 3 Section 2 Topside Structures FIGURE 1 Plated Support Structure HullHull InterfaceTopside3.1.2 Portal Frame Support Structure In a portal f
33、rame design, the main girder/column joints are assumed to be welded on the longitudinal bulkheads or large longitudinal deck stringer underneath the girder/column in addition to a web frame. An example of a portal frame structure is shown in Section 2, Figure 2. The deck plating inserts and under de
34、ck reinforcement may be required for the frame bending moment. FIGURE 2 Portal Frame Structure HullHull InterfaceTopside4 ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 Section 2 Topside Structures 3.1.3 Sliding or Elastomeric Bearing Support Structure The sliding
35、 connection design provides the bearing supports for the topside structure except the locations that are fixed to the deck. This reduces the effect of the topside module supporting structure on the hull girder by allowing movement when the connection friction is overcome by the horizontal force. The
36、 uplift forces and friction forces on the bearings thus create the complication in the design and fabrication. Including the friction forces in the fatigue analysis may be difficult due to the non-linear behavior. The sliding connections evaluated with an all fixed analysis model might be conservati
37、ve for the main deck longitudinals. If an all fixed connection analysis produces unrealistic stresses in the main deck longitudinals, an advanced iterative analysis procedure should be employed to evaluate of the sliding connections. 6 The elastomeric bearing/pads design provides the supports of top
38、side structures with no sliding effect but large deformations of the pads in shear. The large deformation of the elastomeric bearings may reduce the force transfer of the hull girder deformation loads to the topside structures. The non-constant stiffness of the elastomeric pads may be employed to ev
39、aluate the loads transferring between the elastomeric bearings and topside structures. A sketch of sliding or elastomeric bearing supports is shown in Section 2, Figure 3. The sliding or elastomeric bearing support structure and decks including the hull interface structures are to be designed in acc
40、ordance with the FPI Rules. The effect of loads transferred through the sliding connections or elastomeric bearings onto the topside structures should be included in the topside structure fatigue analysis. FIGURE 3 Sliding Support Structure HullHull InterfaceTopsideSliding ElastomericSliding Elastom
41、eric3.3 Fatigue Assessment Procedures The procedure for topside support structure fatigue assessment in these Guidance Notes includes the following components: Identify the hull girder deformation loads and inertial loads due to the vessel motion and wave induced loads. Establish the topside environ
42、mental conditions. ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 5 Section 2 Topside Structures Assemble load cases for topside structure fatigue analysis. Perform topside structure response analysis. Calculate SCFs with a local model or refined mesh in the globa
43、l model if nominal stress method applied. Calculate fatigue damage for each load case. Calculate combined fatigue damage and determine the fatigue strength. If fatigue criteria are not met, modify the topside structural design and repeat the above analyses. The schematic representation of the topsid
44、e structure fatigue analysis procedures is shown in Section 2, Figure 4. FIGURE 4 Schematic Representation of Topside Structure Fatigue Analysis Procedure Global vessel wave analysisPerform global analysis of vessel motion and wave induced loadsConsider topside structure environmental conditions (Se
45、ction 3)Apply hull girder deformation loads and inertia loads due to installation motions(Section 3)Assemble load cases for topside structure analysis(Section 4)Perform topside structure response analysis, Calculate relevant SCFs(Section 5)Calculate fatigue damage for each load case(Section 6)Determ
46、ine fatigue strength(Section 6)Meets fatigue criteria?EndModify topside structural designYesNo6 ABSGUIDANCE NOTES ON TOPSIDE STRUCTURE FATIGUE ASSESSMENT FOR SHIP-TYPE FPIs .2016 Section 3: Loads SECTION 3 Loads 1 General Loads for the topside structure fatigue analysis relate to the probable variat
47、ions that the hull structures and the topside modules will experience during its on-site operation and in transit and installation process. The major loads considered in the analysis of topside structures on the ship-type installation are operating weights, hull girder deformation loads, inertia loa
48、ds due to unit motions, wind loads and live loads. 3 Operating Weights Operating weights in topside structures consist of self-weight of structural members such as columns, beams, plates, grating, etc., and static weight of the equipment, piping, electrical, instrumentation, and miscellaneous member
49、s. Dry weights of structural members and equipment, piping, etc., are considered in the transit loading conditions. Wet weights, that is, the dry weight plus fluid weights in the equipment, piping and instrumentation are considered in design environmental and operating conditions. 5 Hull Girder Deformation Loads Topside structures may be subject to the hull girder deformations of the ship-type installation as a result of still water bending and wave induced bending moments. In addition, the local mass distribution of the topside modules als
