1、Designator: Meta Bold 24/26Revision Note: Meta Black 14/16STP-PT-025EXTENDED FATIGUE EXEMPTION RULES FORLOW CR ALLOYS INTO THETIME-DEPENDENT RANGEFOR SECTION VIII DIV 2STP-PT-025 EXTEND FATIGUE EXEMPTION RULES FOR LOW CR ALLOYS INTO THE TIME-DEPENDENT RANGE FOR SECTION VIII DIV 2 CONSTRUCTION Prepar
2、ed by: Charles Becht IV, PhD, PE Charles Becht V Becht Engineering Company Date of Issuance: January 29, 2009 This report was prepared as an account of work sponsored by ASME Pressure Technologies Codes and Standards and the ASME Standards Technology, LLC (ASME ST-LLC). Neither ASME, ASME ST-LLC, th
3、e authors, nor others involved in the preparation or review of this report, nor any of their respective employees, members, or persons acting on their behalf, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any
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9、electronic retrieval system or otherwise, without the prior written permission of the publisher. ASME Standards Technology, LLC Three Park Avenue, New York, NY 10016-5990 ISBN No. 978-0-7918-3190-8 Copyright 2009 by ASME Standards Technology, LLC All Rights Reserved Extend Fatigue Exemption Rules fo
10、r Low Cr Alloys into the Time-Dependent Range STP-PT-025 iii TABLE OF CONTENTS Foreword v Abstract . vi 1 BACKGROUND . 1 2 SHAKEDOWN CONCEPTS 4 3 STRAIN RANGE FOR SHAKEDOWN AND INITIAL STRESS 8 4 CREEP FATIGUE WITH SHAKEDOWN TO ELASTIC ACTION . 9 5 DEMONSTRATION OF SHAKEDOWN 11 6 INTERMEDIATE CYCLES
11、 . 12 7 LOW CYCLE EXEMPTION 14 8 CONCLUSION 16 References 17 Appendix A - Relaxation/Damage Accumulation Curves . 19 Appendix B - Cyclic Fatigue Data and Charts . 22 Appendix C - Gr 22 Data Tables 32 Appendix D - Gr 91 Data Points 43 Acknowledgments 57 LIST OF TABLES Table 1 - Relaxation/Damage Accu
12、mulation Data for Various Chrome Alloys 8 LIST OF FIGURES Figure 1 Strain Range vs. Cycles to Failure 2 Figure 2 Stress-Strain Behavior Illustrating Shakedown 5 Figure 3 Stress-Strain Behavior Illustrating Elevated Temperature Shakedown 5 Figure 4 Cyclic Stress History with Shakedown. 6 Figure 5 Cyc
13、lic Stress History Without Shakedown. 6 Figure 6 Stress-Strain Behavior with Reset to Allowable Stress 7 Figure 7 Cyclic Stress History with Reset to Allowable Stress 7 Figure 8 - Relaxation/Damage Accumulation Curves for 1.25Cr-0.5Mo-Class 1 Material. 9 Figure 9 - Creep-Fatigue Interaction Diagram
14、. 10 Figure 10 Stress Strain Behavior with Stress Reset Caused by Relaxation at Second Operating Condition 12 Figure 11 Stress-Time Behavior with Stress Reset Caused by Relaxation at Second Operating Condition 13 Figure 12 - Nozzle Subjected to Internal Pressure with High Peak Stress at the Acute Co
15、rner 10. 14 STP-PT-025 Extend Fatigue Exemption Rules for Low Cr Alloys into the Time-Dependent Range iv Figure 13 - Stress, Plastic and Creep Strain, Strain Limit Ratio and Damage After 10 Cycles with 2 Year Hold Time 1014 Figure 14 - 9Cr-1Mo-V 900F19 Figure 15 - 2.25Cr-1Mo-V 900F.19 Figure 16 - 2.
16、25Cr-1Mo Class 2 900F 20 Figure 17 - 2.25Cr-1Mo Class 1 900F 20 Figure 18 - 1.25Cr-0.5Mo-Si Class 2 900F.21 Figure 19 - 1.25Cr-0.5Mo-Si Class 1 900F.21 Figure 20 - 1.25Cr-0.5Mo-Si-Class 2 Data Point Plotted Versus SCMV 3 Material (45/75 grade bainitic) which has Exhibited Similar Behavior to 1.25Cr
17、Alloys.12 .23 Figure 21 - 1.25Cr-0.5Mo-Si-Class 2 Data Point Plotted Versus Various Alloys with Similar Behavior to 1.25Cr Alloys.13.23 Figure 22 - 2.25Cr-1Mo Class 1 Data Point Plotted Versus 2.25Cr-1Mo Steel Whose Heat Treatment was Normalization and Tempering Followed by Stress Relief Annealing.1
18、4 24 Figure 23 - 2.25Cr-1Mo Class 1 Data Point Plotted Versus Fatigue Data for Annealed 2.25Cr-1Mo Steel. Note that this data does not appear to match any of the other data compiled during this investigation.15 25 Figure 24 - 2.25Cr-1Mo Class 2 Data Point Plotted Versus Fatigue Data for PWHT and QT
19、(both bainitic) 2.25Cr-1Mo Steel.1525 Figure 25 - 2.25Cr-1Mo Class 2 Data Point Plotted Versus Fatigue Data for 2.25Cr-1Mo Steel Class 2.16 .26 Figure 26 - 2.25Cr-1Mo Class 2 Data Point Plotted Versus Fatigue Data for 2.25Cr-1Mo Steel Class 2, Note HAZ stands for heat affected zone.1626 Figure 27 -
20、2.25Cr-1Mo Class 2 Data Point Plotted Versus Fatigue Data for Normalized and Tempered 2.25Cr-1Mo Steel.17.27 Figure 28 - 2.25Cr-1Mo Class 2 Data Point Plotted Versus Fatigue Data for Normalized and Tempered 2.25Cr-1Mo Steel.18.27 Figure 29 - 2.25Cr-1Mo Class 2 Data Point Plotted Versus Fatigue Data
21、for Normalized and Tempered 2.25Cr-1Mo Steel.19.28 Figure 30 - 2.25Cr-1Mo-V Data Point Plotted Versus Fatigue Data for 2.25Cr-1Mo-V Steel.20.28 Figure 31 9Cr-1Mo-V Data Point Plotted Versus Fatigue Data for 9Cr-1Mo-V Steel. See App. D 29 Figure 32 - 9Cr-1Mo-V Data Point Plotted Versus Fatigue Data f
22、or 9Cr-1Mo-V Steel. See App. D 29 Figure 33 - 9Cr-1Mo-V Data Point Plotted Versus Fatigue Data for 9Cr-1Mo-V Steel.21.30 Figure 34 - 9Cr-1Mo-V Data Point Plotted Versus Fatigue Data for 9Cr-1Mo-V Steel.21.30 Figure 35 - 9Cr-1Mo-V Data Point Plotted Versus Fatigue Data for 9Cr-1Mo-V Steel. See App. D
23、 31 Extend Fatigue Exemption Rules for Low Cr Alloys into the Time-Dependent Range STP-PT-025 v FOREWORD This document was developed under a research and development project which resulted from ASME Pressure Technology Codes the design temperature is for pressure design. 2. In fatigue design per Sec
24、tion VIII, Div 2, operating conditions, not design conditions, are considered. 3. In primary plus secondary stress range limits in Section VIII, Div 2, operating conditions, not design conditions, are considered. While design conditions are used in pressure design, expected operating conditions shou
25、ld be used for shakedown and fatigue assessments. In considering rules for exemption from fatigue analysis, two regimes of behavior are considered. These are when the component shakes down to elastic action, and when plasticity occurs each cycle. The behavior in each of these regimes is illustrated
26、in the stress-strain and stress-time histories illustrated in Figures 2 through 5. As an introduction to the concept of shakedown, consider elastic plastic behavior without creep. This behavior is illustrated in Figure 2, which is based on the assumption of elastic, perfectly plastic material behavi
27、or. Consider, for example, a case where the elastically calculated displacement controlled (secondary) stress range is two times the yield strength of the material. Because it is a deformation-controlled condition, one must actually move along the strain axis to a value of stress divided by elastic
28、modulus. In material, assuming elastic, perfectly plastic behavior, the initial start-up cycle goes from point A to B (yield) to C (strain value of twice yield). When the system returns to its initial condition (shut down) temperature, the system returns to zero strain and the system will unload ela
29、stically until it reaches yield stress in the reverse direction. If the stress range is less than twice yield, there is no yielding on the return to the initial condition. On returning to the operating condition, the system returns from point D and C, which is elastic. The system has essentially sel
30、f-sprung and is under stress due to displacement conditions in both the ambient and the operating conditions. If twice the yield strength is exceeded, shakedown to elastic cycling does not occur. An example is if the elastically calculated stress range is three times the yield strength of the materi
31、al. In this case, again referring to Figure 2, the startup goes from point A to point B (yield) to point E. Shutdown results in yielding in the reverse direction, from point E to F to D. The subsequent startup then is from point D to C, where yielding again is initiated, to E. Thus, each operating c
32、ycle results in plastic deformation and the system has not shaken down to elastic behavior. Extend Fatigue Exemption Rules for Low Cr Alloys into the Time-Dependent Range STP-PT-025 5 Figure 2 Stress-Strain Behavior Illustrating Shakedown Figure 3 Stress-Strain Behavior Illustrating Elevated Tempera
33、ture Shakedown The condition for shakedown at elevated temperatures is shakedown to elastic cycling. There will continue to be creep deformation. Deformation controlled stresses relax to a stress value sufficiently low that no further creep occurs. This stress value is the hot relaxation strength, S
34、H. Stress-strain behavior under the condition of creep is illustrated in Figure 3. The initial start-up cycle, which can include some yielding, goes from point A to point B. During operation, the stresses relax to the hot relaxation strength, SH, at which point no further relaxation occurs, point C.
35、 When the system returns to the initial condition, the system returns to zero strain (for displacement controlled conditions) and the system will unload elastically until it reaches yield stress in the reverse direction. If the stress range is less than SHplus to cold yield strength, there is no yie
36、lding on the return to the shut down condition. This is illustrated by going from point C to point D. On returning to the operating condition, the system returns from point D to point C elastically. Thus, if the stress range is less than the cold yield strength plus the hot relaxation strength, shak
37、edown to elastic behavior also occurs at STP-PT-025 Extend Fatigue Exemption Rules for Low Cr Alloys into the Time-Dependent Range 6 elevated temperature. The anticipated behavior over time, with multiple shut downs, is illustrated in Figure 4. Figure 4 Cyclic Stress History with Shakedown Figure 3
38、also shows the behavior when the shakedown stress range is exceeded at elevated temperatures. In this case, the startup goes from A to E. Stresses relax to point F. When the system returns to the shut down condition, yielding in the reverse direction occurs, going from point F to G to D. Returning t
39、o operating condition again results in yielding, from point D to H to E. Since high stresses are re-established (reset), another relaxation cycle then must occur. The behavior of this system over time is illustrated in Figure 5. Figure 5 Cyclic Stress History Without Shakedown In the development of
40、the piping codes, SHwas taken as 1.25 times the allowable stress at temperature. This has a long and successful history, although, as shown later in this report, the stress can relax to below this level of stress, given sufficient time. As a practical matter, this report recommends that the basic al
41、lowable stress be used as the hot relaxation stress. Even if the stress relaxes to less than this value, the stress reset on startup is back to the allowable stress. This behavior is illustrated in Figures 6 and 7. Initial loading is from point A to point B in Figure 6. Assuming the stress relaxes t
42、o below the basic allowable stress, S, to a lower value of SH, point C, unloading may result in plasticity, C to D to E. Such plasticity can result in re-establishing a stress value of S on reloading, point F, which then relaxes again to point C. The rationale for accepting this is that even with so
43、me cyclic plasticity, the stress does not exceed the basic allowable while at the operating condition after the initial period of relaxation. Extend Fatigue Exemption Rules for Low Cr Alloys into the Time-Dependent Range STP-PT-025 7 Figure 6 Stress-Strain Behavior with Reset to Allowable Stress Obs
44、erving Figure 5, shakedown to elastic cycling, the component experiences a single relaxation cycle over its lifetime. In contrast, as exhibited in Figure 6, high stresses can be re-established each cycle if the component does not shakedown to elastic cycling. The case somewhat between, as shown in F
45、igures 6 and 7, is proposed as the limit. Figure 7 Cyclic Stress History with Reset to Allowable Stress STP-PT-025 Extend Fatigue Exemption Rules for Low Cr Alloys into the Time-Dependent Range 8 3 STRAIN RANGE FOR SHAKEDOWN AND INITIAL STRESS The strain range for shakedown was calculated for the al
46、loys in this study. This is the strain range associated with an elastically calculated stress range of cold yield plus hot allowable stress. The strain range is the cold yield stress divided by the elastic modulus at ambient temperature plus the hot allowable divided by the elastic modulus at the op
47、erating temperature (the temperature for which the allowable stress was taken). This gives the strain range that will satisfy the above described shakedown criteria. These calculations are summarized in Table 1. Table 1 - Relaxation/Damage Accumulation Data for Various Chrome Alloys Material T (F) S
48、a(Ksi T) Sy(Ksi) Sy(Ksi T) rangeGoverning Sstart(Ksi) EcEhtrelax(hr) DSaMult. D 1.25Cr-0.5Mo-Si-1 900 13.7 35 23.8 1.73E-03 Syhx1.15 27.4 29.6 24.8 1482 2.58E-03 5.7 1.20E-02 1.25Cr-0.5Mo-Si-2 900 13.7 45 30.6 2.07E-03 Syhx1.15 35.2 29.6 24.8 14252 1.66E-02 3.6 4.32E-02 2.25Cr-1Mo class 1 900 13.6 3
49、0 25.6 1.51E-03 Syhx1.15 29.4 30.6 25.6 957 1.11E-03 11.2 1.13E-02 2.25Cr-1Mo class 2 900 17 45 32.4 2.13E-03 Syhx1.15 37.3 30.6 25.6 1622 1.38E-03 12.3 1.56E-02 2.25Cr-1Mo-V 900 23.8 60 47.8 2.89E-03 Syhx1.15 55 30.6 25.6 610 1.23E-03 16.5 1.90E-02 9Cr-1Mo-V 900 30.8 60 46.1 3.11E-03 Syhx1.25 57.6 31.0 26.2 578 3.65E-03 8.7 2.81E-02 12Cr-Al 900 11.3 25 1.34E-03 29.2 23.2 Notes (1) Governing: refers to how the starting stress is determined. It is the greater of either materials multiplier times Yi
