1、STP-PT-028IMPACT TESTING EXEMPTION CURVES FOR LOW TEMPERATURE OPERATION OF PRESSURE PIPINGSTP-PT-028 IMPACT TESTING EXEMPTION CURVES FOR LOW TEMPERATURE OPERATION OF PRESSURE PIPING Prepared by: Martin Prager Pressure Vessel Research Council Date of Issuance: January 29, 2009 This report was prepare
2、d 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, Pressure Vessel Research Council nor others involved in the preparation or review of this report, nor any of their respective employees
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9、nology, LLC Three Park Avenue, New York, NY 10016-5990 ISBN No. 978-0-7918-3204-2 Copyright 2009 by ASME Standards Technology, LLC All Rights Reserved Impact Testing Exemption Curves STP-PT-028 TABLE OF CONTENTS Foreword v Abstract . vi 1 INTRODUCTION . 1 2 BACKGROUND . 2 3 APPROACH 3 3.1 History an
10、d Concepts 3 4 NEW FRACTURE MECHANICS APPROACH TO REQUIRED TOUGHNESS 6 4.1 Description of FAD-Based Fracture Mechanics . 6 4.2 Reference Flaw Size 6 4.3 Required Material Fracture Toughness . 7 5 DERIVATION OF CHARPY V-NOTCH IMPACT TEST REQUIREMENTS 10 5.1 Required Fracture Toughness 10 5.2 Lower Sh
11、elf Vicinity CVN 10 5.3 Upper Shelf Region CVN 10 5.4 Transition Region CVN. 11 5.5 Final CVN Requirement 11 5.6 Derivation of Impact Test Exemption Curves for Thin Piping . 11 5.7 Derivation of Curves for Reduction in the MDMT Without Impact Testing 12 6 CONCLUSION 13 Figures 15 References 23 Ackno
12、wledgments 24 Abbreviations and Acronyms. 25 Nomenclature . 26 LIST OF FIGURES Figure 1 - UCS 66 Exemption Curves are Shown. Indicated Notes Define Covered Materials. 15 Figure 2 - Representative Hyperbolic Tangent Fracture Toughness Curve . 15 Figure 3 - Implied Dynamic Toughness Curves for Indicat
13、ed Various Specified Minimum Yield Strength Values 16 Figure 4 - Calculated Exemption Curves Based on Documented Initial Fracture Mechanics Assumptions as Compared with Published Curves 16 Figure 5 - Dependence of Charpy Energy Needed Meet the Toughness Requirement of the Exemption Curve for Indicat
14、ed Thicknesses as a Function of Loading Rates (Per Second) Shown in the Legend, Ranging from Impact to Static (1E+01/Sec) to Static (1E-05/Sec), for a Material with 38 KSI Specified Minimum Yield Strength. 17 Figure 6 - The FAD Approach Schematic 17 iii STP-PT-028 Impact Testing Exemption Curves Fig
15、ure 7 - Modified Hyperbolic Tangent Equation to Provide Uniform Lower Shelf Energy. The Relative Temperature is with Respect to To18 Figure 8 - Example of Charpy Toughness Requirement for As Welded Material for the Case that the Minimum is Set at 20 ft-lbs.18 Figure 9 - Pressure Vessel Exemption Cur
16、ves Calculated for Section VIII, Division 2 for Parts not Subject to PWHT 19 Figure 10 - Exemption Curves for Type A Assigned Materials of Various Possible Yield Strengths .19 Figure 11 - Exemption Curves for Type B Assigned Materials of Various Possible Yield Strengths .20 Figure 12 - Exemption Cur
17、ves for Type C Assigned Materials of Various Possible Yield Strengths .20 Figure 13 - Exemption Curves for Type D Assigned Materials of Various Possible Yield Strengths .21 Figure 14 - Exemption Curves for Type C Assigned Materials of Various Possible Yield Strengths Where PWHT has been Performed.21
18、 Figure 15 - Temperature Reduction Plots for Various Indicated Yield Strengths22 Figure 16 - Fracture Toughness Expectations Calculated from the Charpy Requirements in ASTM 333 for Steels for Low Temperature Service Using the Procedures Described Herein 22 iv Impact Testing Exemption Curves STP-PT-0
19、28 FOREWORD This document was developed under a research and development project which resulted from ASME Pressure Technology Codes however, it is anticipated that the results will show minor differences. 0.043587868exp 0.102270708 0.500090962 l nlnCylinderRFKtRt= + +(16) The plasticity interaction,
20、 , defined below, was derived by curve fitting the plots shown in Figure 9.19 of API 579-1/ASME FFS-1. (17) () ( ) ()( )() ( )()() ()()2233220.99402985 0.34259558 0.078495941.3153525 0.035075224 0.22229820.97610564 0.00413675920.0062624497 0.16970127PSRrrPSRPrrrPSR P SRrr r rLLLLLLL L L+ +=+ SRThe l
21、oad ratio parameters, PrL and SRrL , are defined by the equations below. In these equations, the parameter was derived using API 579-1/ASME FFS-1, Annex D using the RCSCLE2 Solution with a 1 ksi membrane stress and the reference flaw. The membrane stresses are set as noted above. The resulting equat
22、ions for the load ratio parameters are a function of the cylinder wall thickness and radius to thickness ratio. CylinderRFRPCylinderP mRFrysRL= (18) SR CylinderSR mRFrysRL= (19) ()()()()()()()232 3220.99829577 0.0071541778 1.3018206 0.00190471844.3132859 0.042484369 5.42846260.000114871580.12675001
23、0.0033013072CylinderRFcttRttRtRtRt RtttRtRt+ = + +(20) The above equation was developed based on API 579, 2000 Edition, Appendix D and is valid for a thickness range of 0.25 inch t 4 inches. Shown below is a new data fit developed for this project using the data in API 579-1/ASME FFS-1, Annex D and
24、is valid for a thickness range of 0.001 inch t 4inches. The difference in the data fits is typically less than 5% where they overlap. All fracture 8 Impact Testing Exemption Curves STP-PT-028 mechanics based results used to develop the toughness rules will be updated in future editions of VIII-2; ho
25、wever, it is anticipated that the results will show minor differences. 20.3656047958 0.5075585241.002550710 0.2401731622 expCylinderRFRRR tRtt=+ + (21) 9 STP-PT-028 Impact Testing Exemption Curves 5 DERIVATION OF CHARPY V-NOTCH IMPACT TEST REQUIREMENTS 5.1 Required Fracture Toughness The required ma
26、terial toughness, Kmat(t), as a function of thickness is based on the reference flaw and applied stress. When Kmat(t) was evaluated for ASME Section VIII, Division 2, the fracture toughness parameter and reference stress parameter given were evaluated at R = 100. To derive the required CVN for a mat
27、erial as a function of thickness and yield strength, the CVN transition curve is divided into three regions. 5.2 Lower Shelf Vicinity CVN In the vicinity of the lower shelf (near lower shelf, nls), the CVN requirement for the early part of the transition region is a function of thickness and is give
28、n, in U.S. customary units, by 2()() () 0.4515matnls nls ysKtCVN t for CVN t = (22) An extensive review of fracture toughness data by MPC indicates that the above relation applies for the indicated limitation based on the yield strength of the material. The fracture toughness for the near lower shel
29、f region is then simply given by (also see API 579-1/ASME FFS-1, Annex F, paragraph F.4.5.2) () 15 ()nls nlsKt CVNt= (23) 5.3 Upper Shelf Region CVN The dynamic fracture toughness for an ASME exemption curve material (A, B, C or D) with a group temperature, T0, for a specified yield strength, ys, at
30、 a temperature, T, may be estimated as shown below, see API 579-1/ASME FFS-1, Annex F, paragraph F.4.5.3. This equation provides more reasonable values for the dynamic fracture toughness than the simple equation of Corten in the important region approaching the lower shelf where Cortens equation giv
31、es unrealistically low numbers for steels with ordinary, low yield strengths (Figure 7). 012733 tanhdysysTTKC =+ (24) T0= 114F for ASME Exemption Curve A T0= 76F for ASME Exemption Curve B T0= 38F for ASME Exemption Curve C T0= 12F for ASME Exemption Curve D C = 66F For temperatures above the transi
32、tion region, i.e., upper shelf behavior, the equation below provides estimated required fracture toughness: 1(2 3 27)us d ysKK = (25) 10 Impact Testing Exemption Curves STP-PT-028 The Rolfe-Novak-Barsom correlation below, given in API 579-1/ASME FFS-1, Annex F, paragraph F.4.5.2, provides an estimat
33、e of the upper shelf CVN and the upper shelf fracture toughness and the yield strength. 252ysususysKCVN0=+(26) 5.4 Transition Region CVN The equation given below can be used to model the transition region. This equation maintains proportionality between the CVN and fracture toughness in terms of the
34、 fracture toughness and CVN . The parameters used are defined above. ()2() ()() () ()()mat nlstrans us nls nlsus nlsKtKtCVN t CVN CVN t CVN tKKt=+(27) 5.5 Final CVN Requirement The required CVN for a material can be calculated as a function of the yield strength and nominal thickness as shown for th
35、e new ASME Section VIII, Division 2 in Figure 8 for components not subject to PWHT. The energy requirement was established as follows. () max , (), (), ()min nls trans usCVN t CVN CVN t CVN t CVN t= (28) 5.6 Derivation of Impact Test Exemption Curves for Thin Piping For pressure vessels, the impact
36、test exemption curves in Figure 9 from ASME Section VIII, Division 2 gives exemption temperature based on a nominal component thickness for components not subject to PWHT. It is obtained by solving Kmat(t) equation above for the temperature directly, again noting that the exemption temperature is a
37、function of the thickness, or: 0() 3() Arctanh273mat ysysKtTt C T=+ (29) For all materials covered by the four exemption curves labeled A, B, C and D, the yield stress in the above equation was conservatively assumed to be 80 ksi, i.e., ys= 80 ksi. In addition, the cut-off limit for the lower bound
38、of the curve is taken as the temperature at which the thickness is equal to 0.4 inch as shown in Figure 9. This approach was modified for thin piping as described below. For piping components of interest in this study the equations for a thickness range of 0.001 inch t 4 inches cited above were used
39、 and evaluated at R=10 inches. A series of calculations showed that the effect of R on temperature was not strong. Exemption curves for various yield strengths are presented for piping in Figure 10 to Figure 13. The effect of yield strength is strong in thick sections. These plots allow the governin
40、g committees to make decisions regarding conservatism they wish to apply for piping applications based on relevant experience and operating practices with the materials in use. 11 STP-PT-028 Impact Testing Exemption Curves The effect on PWHT, of course, is to lower the exemption temperature as shown
41、 by comparing Figure 12 and Figure 14 for Type C materials at thicknesses greater than that at which the lower shelf cut off (truncation) is reached for the heat treated material. For materials that are not post weld heat treated, for a given yield strength the cut off temperature for the heat treat
42、ed material is acceptable but at a thinner wall and the corresponding assumed flaw size is proportionately smaller. The assumption of very small flaws permits achieving in principle the very low exemption temperatures indicated for material that is not post weld heat treated. For each yield strength
43、, the truncation of the exemption curve occurs just above the lower shelf energy. 5.7 Derivation of Curves for Reduction in the MDMT Without Impact Testing The permissible reduction in the MDMT without impact testing due to stress reduction is shown in Figure 15 for components not subject to PWHT. I
44、t is derived using the fracture mechanics concepts above with the important consideration regarding residual stresses. Residual stresses that comprise an important part of the crack driving force are not reduced when applied stresses are reduced. This was not properly accounted for in the calculatio
45、ns for stress reduction when done in the past for the ASME Code. The temperature reduction, TR(Rts), based on the stress reduction ratio, Rts, is: 0() 3()Arctanh273mat ts ysRtsysKRTR CT=+ (30) The reduced temperature, TR(Rts), is only a function of the stress reduction ratio, Rts, yield strength but
46、 not the wall thickness. The final equation for the temperature reduction, T(Rts), is simply given by: (31) () (1) ()ts R R tsTR T T R=In ASME Section VIII, Division 2, if the computed value of the Rtsratio is less than or equal to 0.24, then the MDMT may be set to 155F and impact testing is not req
47、uired unless a lower MDMT is desired. This requirement roughly stipulates that if the operating stresses are equal to, or less than, 10% of the specified ultimate tensile strength, operation for ferritic materials is permitted on the lower shelf. This rule is consistent with old ASME Section VIII, D
48、ivision 2 where the limit for the Rtsratio is 0.3. The purported justification for low-stress, lower shelf operation is that the stress is low enough that brittle fracture is not possible. The curves given in Figure 10 through Figure 14 are all truncated just above the lower shelf due to the tempera
49、ture sensitivity of the calculations. As the lower shelf is approached, the curves become nearly vertical and extremely low temperatures would be permitted. 12 Impact Testing Exemption Curves STP-PT-028 6 CONCLUSION Extension of exemption curves has been accomplished by consistent application of old and new ASME concepts intended for pressure vessel applications. It is recognized
