1、 GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES APRIL 2003 Guide to Color Coding Used in Online Version of the Rules The following summarizes the colors corresponding to Rule Changes, Corrigenda items and editorial changes in the Guide files which are available for download. Rule Changes: C
2、orrigenda: CORRIGENDA/EDITORIALS 1 November 2010 CORRIGENDA/EDITORIALS 1 February 2014 Editorials: Editorial Changes COMMENTARY ON THE GUIDE FOR FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES (APRIL 2003) JANUARY 2004 Guide to Color Coding Used in Online Version of the Commentary The following summarizes
3、 the colors corresponding to Rule Changes, Corrigenda items and editorial changes in the Commentary files which are available for download. Rule Changes: NOTICE NO. 1 February 2013 (effective 1 February 2013) Corrigenda: CORRIGENDA/EDITORIALS 11 June 2007 CORRIGENDA/EDITORIALS 6 April 2010 CORRIGEND
4、A/EDITORIALS 1 July 2014 Editorials: Editorial Changes Commentary on the Guide for the Fatigue Assessment of Offshore Structures (April 2003) COMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES (APRIL 2003) JANUARY 2004 (Updated July 2014 see next page) American Bureau of Shipp
5、ing Incorporated by Act of Legislature of the State of New York 1862 Copyright 2004 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Updates July 2014 consolidation includes: February 2013 version plus Corrigenda/Editorials February 2013 consolidation includes: Janu
6、ary 2004 version plus Notice No. 1 April 2010 consolidation includes: June 2007 version plus Corrigenda/Editorials June 2007 consolidation includes: June 2007 Corrigenda/Editorials ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 iii Foreword Foreword This Commentar
7、y provides background, including source and additional technical details, for the ABS Guide for the Fatigue Assessment of Offshore Structures, April 2003, which is referred to herein as “the Guide”. The criteria contained in the Guide are necessarily brief in order to give clear descriptions of the
8、fatigue assessment process. This Commentary allows the presentation of supplementary information to better explain the basis and intent of the criteria that are used in the fatigue assessment process. It should be understood that the Commentary is applicable only to the indicated version of the Guid
9、e. The order of presentation of the material in this Commentary generally follows that of the Guide. The major topics of the Sections in both the Guide and Commentary are the same, but the detailed contents of the individual Subsections and Paragraphs will not typically correspond between the Guide
10、and the Commentary. In case of a conflict between anything presented herein and the ABS Rules or the Guide, precedence is given to the Rules or the Guide. This Commentary shall not be considered as being more authoritative than the Guide to which it refers. ABS welcomes comments and suggestions for
11、improvement of this Commentary. Comments or suggestions can be sent electronically to rsdeagle.org. iv ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 Table of Contents COMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES (APRIL 2003) CONTENTS
12、SECTION 1 Introduction 1 1 General Comments . 1 2 Basic Terminology 1 3 The Deterministic Method and the Palmgren-Miner Rule to Define Fatigue Damage . 1 4 Application of the Palmgren-Miner (PM) Rule 2 5 Safety Checking with Respect to Fatigue . 3 TABLE 1 Deterministic Stress Spectra . 2 TABLE 2 Tub
13、ular Joints: Statistics on Damage at Failure, ( Lognormal Distribution Assumed) . 2 TABLE 3 Plated Joints: Statistics on Damage at Failure, ( Lognormal Distribution Assumed) . 3 SECTION 2 Fatigue Strength Based on S-N Curves General Concepts . 4 1 Preliminary Comments 4 2 Statistical Analysis of S-N
14、 Data 5 3 The Design Curve . 5 4 The Endurance Range 6 5 Stress Concentration Factors Tubular Intersections . 7 TABLE 1 Details of the Basic “In-Air” S-N Curves 6 FIGURE 1 An Example of S-N Fatigue Data Showing the Least Squares Line and the Design Line HSE(1995) . 4 FIGURE 2 The Design S-N Curve fo
15、r the ABS-(A) Class D Joint 7 FIGURE 3 Weld Toe Extrapolation Points for a Tubular Joint . 8 SECTION 3 S-N Curves 9 1 Introduction . 9 2 A Digest of the S-N Curves Used for the Structural Details of Offshore Structures . 9 3 General Comparison . 10 ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSME
16、NT OF OFFSHORE STRUCTURES .2004 v 4 Tubular Intersection Connections . 11 4.1 Without Weld Profile Control . 11 4.2 With Weld Improvement 12 5 Plated Connections . 13 6 Discussion of the Thickness Effect . 14 6.1 Introduction 14 6.2 Fatigue Test Data on Plated Joints . 15 6.3 Design F-Curves with Th
17、ickness Adjustment 15 6.4 Thickness Adjustments to Test Data and Their Regressed S-N Curves 15 6.5 Discussion . 16 6.6 Postscript . 16 7 Effects of Corrosion on Fatigue Strength 28 7.1 Preliminary Remarks . 28 7.2 A Summary of the Results . 28 7.3 The Summaries . 28 TABLE 1 Coverage of the Two Main
18、Sources of S-N Curves Used for Offshore Structures 11 TABLE 2 AWS-HSE/DEn Curves for Similar Detail Classes . 13 TABLE 3 Parameters of Plate Thickness Adjustment for Plated Joints . 14 TABLE 4 Parameters of Plate Thickness Adjustment for Tubular Joints . 15 TABLE 5 Parameters of F-curves 15 TABLE 6
19、Details of Basic Design S-N Curves HSE(1995) 29 TABLE 7 Life Reduction Factors to be Applied to the Lower Cycle Segment of the Design S-N HSE Curves . 29 TABLE 8 Life Reduction Factors to be Applied to the Lower Segment of the Design S-N DNV Curves . 30 FIGURE 1 API, DEn, and ABS S-N design Curves f
20、or Tubular Joints; Effective Cathodic Protection; No Profile Control Specified . 12 FIGURE 2 F-Curves with Thickness Adjustment and Test Data; 16 mm Plate 17 FIGURE 3 F-Curves with Thickness Adjustment and Test Data; 20 mm Plate 17 FIGURE 4 F-Curves with Thickness Adjustment and Test Data; 22 mm Pla
21、te 18 FIGURE 5 F-Curves with Thickness Adjustment and Test Data; 25 mm Plate 18 FIGURE 6 F-Curves with Thickness Adjustment and Test Data; 26 mm Plate 19 FIGURE 7 F-Curves with Thickness Adjustment and Test Data; 38 mm Plate 19 FIGURE 8 F-Curves with Thickness Adjustment and Test Data; 40 mm Plate 2
22、0 vi ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 FIGURE 9 F-Curves with Thickness Adjustment and Test Data; 50 mm Plate 20 FIGURE 10 F-Curves with Thickness Adjustment and Test Data; 52 mm Plate 21 FIGURE 11 F-Curves with Thickness Adjustment and Test Data; 70
23、mm Plate 21 FIGURE 12 F-Curves with Thickness Adjustment and Test Data; 75 mm Plate 22 FIGURE 13 F-Curves with Thickness Adjustment and Test Data; 78 mm Plate 22 FIGURE 14 F-Curves with Thickness Adjustment and Test Data; 80 mm Plate 23 FIGURE 15 F-Curves with Thickness Adjustment and Test Data; 100
24、 mm Plate 23 FIGURE 16 F-Curves with Thickness Adjustment and Test Data; 103 mm Plate 24 FIGURE 17 F-Curves with Thickness Adjustment and Test Data; 150 mm Plate 24 FIGURE 18 F-Curves with Thickness Adjustment and Test Data; 160 mm Plate 25 FIGURE 19 F-Curves with Thickness Adjustment and Test Data;
25、 200 mm Plate 25 FIGURE 20 Test data with DEn(1990) Thickness Adjustment and their Regressed S-N Curves (All Thicknesses) 26 FIGURE 21 Test Data with HSE(1995) Thickness Adjustment and their Regressed S-N Curves (All Thicknesses) 26 FIGURE 22 Test Data with DNV(2000) Thickness Adjustment and their R
26、egressed S-N Curves (All Thicknesses) 27 FIGURE 23 Regressed S-N Curves and Design F-curves . 27 SECTION 4 Fatigue Design Factors 31 1 Preliminary Remarks . 31 2 The Safety Check Expression . 31 3 Summaries of FDFs Specified by Others . 32 SECTION 5 The Simplified Fatigue Assessment Method . 34 1 In
27、troduction . 34 2 The Weibull Distribution for Long Term Stress Ranges . 34 2.1 Definition of the Weibull Distribution 34 2.2 A Modified Form of the Weibull Distribution for Offshore Structural Analysis . 35 3 Typical Values of the Weibull Shape Parameter for Stress . 35 3.1 Experience with Offshore
28、 Structures . 35 3.2 Experience with Ships . 36 4 Fatigue Damage: General . 36 4.1 Preliminary Remarks . 36 4.2 General Expression for Fatigue Damage . 36 ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 vii 5 Fatigue Damage for Single Segment S-N Curve 37 5.1 Expre
29、ssion for Damage at Life, NR37 5.2 Miners Stress 38 5.3 The Damage Expression for Weibull Distribution of Stress Ranges 38 6 Fatigue Damage for Bilinear S-N Curve . 38 7 Safety Check Using Allowable Stress Range . 40 8 The Simplified Method for Which Stress is a Function of Wave Height 40 8.1 The We
30、ibull Model for Stress Range; Stress as a Function of Wave Height 40 8.2 The Weibull Model for Stress Range; Stress as a Function of Wave Height; Considering Two Wave Climates 41 9 The Weibull Distribution; Statistical Considerations . 42 9.1 Preliminary Remarks . 42 9.2 Estimating the Parameters fr
31、om Long-Term Data; Method of Moment Estimators . 42 9.3 Estimating the Parameters from Long-Term Data; Probability Plotting 42 9.4 Another Representation of the Weibull Distribution Function 45 9.5 Fitting the Weibull to Deterministic Spectra . 46 9.6 Fitting the Weibull Distribution to the Spectral
32、 Method 47 TABLE 1 Data Analysis for Weibull Plot . 43 TABLE 2 Deterministic Spectra 46 FIGURE 1 A Short Term Realization of a Long-Term Stress Record 34 FIGURE 2 Probability Density Function of s . 36 FIGURE 3 Characteristic S-N curve . 37 FIGURE 4 Bilinear Characteristic S-N curve 39 FIGURE 5 Weib
33、ull Probability Plot . 44 FIGURE 6 Long Term Distribution of Fatigue Stress as a Function of the Weibull Shape Parameter . 45 FIGURE 7 Long-Term Stress Range Distribution of Large Tankers, Bulk Carriers, and Dry Cargo Vessels Compared with the Weibull 46 FIGURE 8 Probability Density Function of Stre
34、ss Ranges of the i-th Sea State 47 SECTION 6 The Spectral Based Fatigue Assessment Method 49 1 Preliminary Comments 49 2 Basic Assumptions 49 3 The Rayleigh Distribution for Short Term Stress Ranges . 50 4 Spectral Analysis; More Detail 51 5 Wave Data 51 6 Additional Detail on Fatigue Stress Analysi
35、s; Global Performance Analysis . 52 viii ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 7 The Safety Check Process . 53 7.1 General Considerations . 53 7.2 The Stress Process in Each Cell . 53 8 Fatigue Damage Expression for Wide Band Stress . 54 8.1 Preliminary C
36、omments 54 8.2 Definitions 55 8.3 The Equivalent Narrow Band Process . 56 8.4 The Rainflow Method . 56 8.5 A Closed Form Expression for Wide Band Damage 57 9 The Damage Calculation for Single Segment S-N Curve . 58 10 The Damage Calculation for Bi-Linear S-N Curve 59 TABLE 1 A Sample Wave Scatter Di
37、agram . 52 FIGURE 1 Fatigue Assessments by Spectral Analysis Method . 50 FIGURE 2 Realizations of a Narrow Band and Wide Band Process (Both Have the Same RMS and Rate of Zero Crossings) 55 FIGURE 3 Segment of Stress Process to Demonstrate Rainflow Method 56 SECTION 7 Deterministic Method of Fatigue
38、Assessment . 61 1 General . 61 2 Application to a Self-Elevating Unit . 61 TABLE 1 Deterministic Stress Spectra . 61 TABLE 2 Wave and Other Parameters to be Used in the Fatigue Assessment . 62 SECTION 8 Fracture Mechanics Fatigue Model . 63 1 Introduction . 63 2 Crack Growth Model (Fatigue Strength)
39、 . 63 2.1 Stress Intensity Factor Range . 63 2.2 The Paris Law 63 2.3 Determination of the Paris Parameters, C and m . 64 3 Life Prediction . 65 3.1 Relationship Between Cycles and Crack Depth 65 3.2 Determination of Initial Crack Size, ai65 3.3 Determination of the Failure (Critical) Crack Length,
40、ac. 66 TABLE 1 Paris Parameters for Structural Steel . 65 FIGURE 1 A Model of Crack Propagation Rate versus Stress Intensity Factor Range 64 SECTION 9 References 67 ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 1 Section 1: Introduction SECTION 1 Introduction 1 G
41、eneral Comments For over a half century, ABS has been involved in the development of fatigue technology, starting in 1946 with the formation of the Ship Structure Committee (SSC) for the specific goal of addressing avoidance of serious fracture in ships. The SSC, with strong financial support from A
42、BS, has executed several fatigue research projects. Over the years, ABS has also provided support to numerous joint industry/agency fatigue projects in addition to independent investigators for their own in-house projects. The current state of the art in fatigue technology represents worldwide contr
43、ibutions of a large numbers of investigators from government agencies, professional organizations, classification societies, universities and private industry, most notably petroleum companies. ABS has synthesized this body of knowledge to provide fatigue design criteria for marine structures. This
44、document provides a review of the most relevant literature, describes how ABS criteria were established and compares ABS criteria with those of other organizations. Because welded joints are subject to a variety of flaws, it is generally expected that fatigue cracks will start first at the joints. T
45、herefore, the focus of this document will be on the joints, but the general principles and some of the fatigue strength data will apply to the base material. 2 Basic Terminology NT(or T) = Design life; the intended service life of the structure in cycles (or time) Nf(or Tf) = Calculated fatigue life
46、; the computed life in cycles (or time) of the structure using the design S-N curve D = fatigue damage at the design life of the structure = maximum allowable fatigue damage at the design life of the structure FDF = fatigue design factor; FDF 1.0 The FDF accounts for: i) Uncertainty in the fatigue l
47、ife estimation process ii) Consequences of failure (i.e., criticality) iii) Difficulty of inspection 3 The Deterministic Method and the Palmgren-Miner Rule to Define Fatigue Damage Fatigue assessment in the Guide relies on the characteristic S-N curve to define fatigue strength under constant amplit
48、ude stress and a linear damage accumulation rule (Palmgren-Miner) to define fatigue strength under variable amplitude stress. Fatigue stress is a random process. Stress ranges in the long-term process form a sequence of dependent random variables, Si; i = 1, NT. For purposes of fatigue analysis and
49、design, it is assumed that Siare mutually independent. The set of Sican be decomposed and discretized into J blocks of constant amplitude stress, as illustrated in Section 1, Table 1. Section 1 Introduction 2 ABSCOMMENTARY ON THE GUIDE FOR THE FATIGUE ASSESSMENT OF OFFSHORE STRUCTURES .2004 TABLE 1 Deterministic Stress Spectra Stress Range SiNumber of Cycles niS1n1S2n2S3n3. . SJ-1nJ-1SJnJApplying the Palmgren-Miner linear cumulative damage hypothesis to the block loading of Section 1, Table 1, cumulative fatigue damage, D, is defined as: =JiiiNnD1.
